Fortified Builders Guide - International Barrier Technology, Inc.

Transcription

Fortified Builders Guide
Welcome
January 2005
Page 1
Welcome
The Institute for Business & Home Safety (IBHS) is a nonprofit organization, supported by the
insurance industry. IBHS conducts studies, public and professional educational activities, and data
gathering to gain greater understanding of the effects of losses that occur as a result of natural disasters,
and determine how best to reduce them.
IBHS envisions a nation that positions and builds its businesses and homes to keep its citizens
and their property safe from natural disasters.
The mission of IBHS is to reduce the deaths, injuries, property damage, economic losses and
human suffering caused by natural disasters. IBHS and its members seek ways to demonstrate what
works to make homes and businesses safer. IBHS has targeted three areas in which it identifies ways to
meet its goals. They are:
1. Evaluate the merits of disaster-resistant building practices and materials and recommend
improvements.
2. Provide technical expertise in public policy and construction arenas on behalf of safe
residential and commercial practices.
3. Conduct communications to stimulate property loss reduction activity by home and business
owners.
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Welcome
Table of Contents
1.0 Welcome.......................................................................................................................................... 3
2.0 Definitions of Peril Regions by State.............................................................................................. 8
3.0 Hurricane/Tornado and Hail/High Wind Criteria ......................................................................... 15
4.0 Flood Region Criteria.................................................................................................................... 36
5.0 Wildfire Region Criteria................................................................................................................ 38
6.0 Hail Region Criteria ...................................................................................................................... 42
7.0 Severe Winter Weather Criteria ................................................................................................... 43
8.0 Seismic Criteria ............................................................................................................................. 45
9.0
Reference....................................................................................................................................... 63
10.0 Contact Information ...................................................................................................................... 65
1.0 WELCOME
Fortified...for Safer Living is a program designed to help bring deserved recognition to builders
who know the value of a practical, yet strongly built and disaster resistant home. It is well known that
the home-buying public prefers a home that is built by a “good” builder. But, every builder will tell a
prospective buyer that “my house is a strong house”. Finally, the Fortified…for safer living program
provides a marketing edge on this claim for participating builders and also backs it with the type of
practical construction features that are known to really make a difference at a time when it’s most
needed – before disaster strikes.
The Fortified program specifies construction, design and landscaping guidelines to enable homes
to increase their resistance to the following natural hazards that are most likely to occur in the area:
Hurricanes
Floods
Earthquake
Tornados
Wildfire
Severe Winter Weather
High Winds
Hail
The Fortified program heralds a new way for premier builders to build, remodel, renovate, and sell more
secure homes to all classes of homebuyers and homeowners in disaster-prone areas.
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Welcome
Why should you be Fortified…for safer living when disaster strikes?
This section briefly explains the types of perils or hazards addressed by participating builders in
the Fortified…for safer living Program.
Severe Wind – Practically every part of the United States is subject to some type of severe
wind hazard that can readily exceed minimum requirements of even the best building codes.
Types of severe winds include:
Hurricanes – Catastrophic hurricanes can produce winds in excess of 150 mph.
Hurricanes have resulted in thousands of deaths and injuries to residents in the Gulf and
Atlantic coastal areas. They are also responsible for a large portion of the $5 billion per
year damages to buildings due to wind. On the immediate coast, storm surge accounts for
much of the damage and loss of life. The Fortified…for safer living program offers
simple, yet effective solutions to reduce a building’s vulnerability to both catastrophic
and common hurricanes.
Tornadoes – Tornadoes can occur in nearly any part of the country but are most
common in areas of the country where design level wind speeds in the building code are
at the lowest levels (see Figure 2-1 – Wind Speed Map and compare to Figure 2-2 –
Tornado Activity Map). Over 1,000 people are injured or killed by tornadoes each year in
the United States and hundreds of buildings are either damaged or destroyed – many
would have survived with only moderate improvements as featured in the Fortified…for
safer living program.
Severe Thunderstorms – Thunderstorms not only spawn tornadoes, but can also
produce damaging winds of 110 mph gust or more. This level of wind is at least 20 mph
greater than the 50-yr design wind speeds used over most of the country where
thunderstorms are frequent events (See Figure 2-1 – Wind Speed Map). Downbursts,
which are also associated with thunderstorms, can produce tornado-like damage. Hail is
also a hazard associated with thunderstorms and causes significant damage to the
exteriors of thousands of buildings each year. The Fortified…for safer living program
provides improved resistance to these hazards associated with severe thunderstorms.
Earthquakes – Unlike wind, earthquakes come with no warning. There is little opportunity to
take cover or vacate an unsafe building. In places like California, design level earthquakes may
occur several times in a lifetime. In other parts of the country, big earthquakes occur with less
frequency, but have happened in the not so distant past in several regions. This type of
earthquake is often the cause of significant damage and injury because it is “unexpected.” In
other words, the threat is forgotten with the passing of a generation or two. Earthquake hazard in
these areas, as well as California, are reflected in the latest earthquake hazard maps (see
Appendix A – Fortified Seismic Zones). The Fortified…for safer living program addresses this
significant and sometimes uncertain hazard with easily implemented solutions.
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Welcome
Floods – Buildings built in the inland or coastal 100-yr flood plain are in serious jeopardy of
complete loss in the event of a flood. For this reason, significant measures are necessary to
protect buildings from this potential hazard. Therefore, the Fortified …for safer living program
only applies to buildings that comply with the strictest condition in the National Flood Insurance
Program for both coastal and inland flood plains, when building is permitted in these areas.
Wildfires – Every year, and even more so in recent years, wildfires have threatened and
destroyed hundreds of buildings and lives. While some wildfires are naturally ignited from
lightening or other causes, many are the result of carelessness or arson. Simple site design,
material usage and landscape features of the Fortified…for safer living program can protect a
home against this increasingly widespread hazard.
Severe Winter Weather – Not too infrequently in some regions of the country an extreme
weather pattern develops that causes severe damage to structure from heavy snow and cold.
Even parts of the Southern US can be at risk of certain freezing weather-related damage. The
Fortified…for safer living program provides practical protection for homes from the damaging
effects of this hazard.
1.1
Benefits to the Builder and Consumer
The Fortified…for safer living program offers important benefits to builders and their homebuyers. These benefits are briefly listed below.
Key Benefits to the Builder
•
•
•
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•
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Provides market differentiation through a nationally recognized program.
Gives solid evidence as a “quality” house builder and that qualifying houses are built
better and stronger than the competition.
Offers marketable benefits to homebuyers (see below) through use of the practical
optional construction features that are affordable.
The program addresses only those hazards or types of disasters that are most relevant
to local conditions and most recognized by the local market.
Assurance that your homes are the “best in the market” when it comes to the safety
and protection of your buyers and their investment.
Potential favorable personal and business liability and “low risk” status for contractor
liability insurance.
Key Benefits to the Home-Buyer
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Improved security and safety in your home
Potential for reduced insurance premiums and discounts
A peace of mind that you own a home that will not only be an upstanding investment, but
will also be standing up in the face of disaster.
Potential improved resale value
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Welcome
1.2
Building Code Requirements
Building codes set a baseline of performance for many features within the home. While the
Fortified…for safer living program requires many items above and beyond building code requirements
in terms of natural disaster resistance, it is still crucial that the home meet minimum requirements
regarding electrical, mechanical, plumbing, and interior fire protection measures. In order to ensure that
all Fortified homes receive an adequate minimum level of protection in these fields, homes built in
locales where the Building Code Effectiveness Grading Schedule (BCEGS) rating is greater than 5
(lower values reflect more effective code jurisdiction) must be inspected by a registered architect or
professional engineer to certify that the home meets all applicable requirements of a specific model
building code.
1.3
Program at a Glance
General
The process starts with a plan review. Based on compliance with the Fortified program, the
builder is permitted to advertise the house as a Fortified...for safer living home . Following satisfactory
completion of construction, inspection checklists, product verification and/or other documentation, final
designation as a Fortified…for safer living home is issued by IBHS.
Quality Criteria
Inspection – An IBHS Certified Inspector verifies that materials, installation, construction and
building techniques meet program criteria for the location.
“Fortified for Wind” Criteria
- Standard Fortified Home Criteria (applies to all wind conditions and house types): The house
is built in accordance with the WFCM or SSTD-10, or is specially engineered to resist design wind loads
according to ASCE 7-02 Minimum Design Loads for Buildings and Other Structures.
“Fortified for Earthquake” Criteria
In regions where there is sufficient seismic risk so as to be deemed a Fortified Seismic Zone, as
defined in Appendix A, the Fortified Seismic Criteria of Section 8.0 shall apply to the home’s
construction and building materials.
“Fortified for Flood” Criteria
Houses located in the coastal or inland 100-yr flood plain must be built on elevated foundations.
The bottom of the lowest horizontal structural member of the lowest livable floor must have a minimum
of 2 feet of “freeboard” above the base flood elevation (BFE). In addition, areas of the building below
the lowest floor shall not be enclosed by solid walls in V or Coastal A zones. In these zones, piles used
to elevate the building shall be driven to required depth of penetration and bearing as prescribed and
certified by a registered design professional.
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“Fortified for Wildfire” Criteria (applicable to homes at moderate (or higher) risk of wildfire)
Homes located in areas at moderate (or higher) risk of wildfire, as determined using the Wildfire
Assessment that can be found at www.ibhs.org, shall adhere to the criteria given in Section 5.0.
Landscape features and construction materials used in such homes are chosen such that their risk of
being adversely affected by wildfire is minimized.
“Fortified for Severe Winter Weather” Criteria
Homes located in areas within the freezing weather criteria boundary have additional moisture
barrier and heat source requirements for attics and roof.
Verification Process
Inspectors will meet with the builder prior to construction to discuss the appropriate criteria and
review the building plans. The intent of this step is to set the stage for most of the field inspections. The
Fortified inspector will review the drawings for all relevant criteria and communicate the requirements
of the program to the builder. In order to effectively complete the drawing review, the builder will need
to supply the following information:
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•
•
•
•
•
Architectural drawings showing floor plans and elevations
Window/Door Schedule
Structural drawings if applicable
Flood Elevation Certificate (if applicable)
Truss drawings from the truss manufacturer
Documentation on wall and roof sheathing, fastening schedules and roof
covering materials used
The inspector will visit the site approximately 4 times during the construction of the building to
verify compliance to the Fortified…for safer living standards. After the last inspection, the builder or
homebuyer will receive a certificate from IBHS designating compliance with the Fortified…for safer
living program. (Figure 1-1)
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Welcome
Figure 1-1: Sample of Fortified…for safer living Certificate
2.0 DEFINITIONS OF PERIL REGIONS BY STATE
The following are descriptions of the areas of the country where each of the Fortified perils
apply. Note that one of the three wind perils (Hurricane, Tornado, or High Wind) will apply, depending
upon the home’s geographic location within the US. The Fortified Wind Peril Map in Figure 3.1 defines
the regions where each of these three wind perils applies. This map is based on (1) the ASCE 7-02
design wind speed map for the Atlantic and Gulf Coasts, shown in Figure 2-1, and (2) the NOAA
tornado frequency map Figure 2-2.
2.1
Hurricane Prone Region
ASCE 7-02 defines hurricane prone regions for the United States as areas along “the U.S.
Atlantic Ocean and Gulf of Mexico coasts where the basic wind speed is greater than 90 mph…”. These
regions include the Atlantic and Gulf Coasts, Hawaii, and the US territories of Puerto Rico, Virgin
Islands, Guam, and American Samoa. The Fortified… for safer living program uses a slightly modified
version of the ASCE 7-02 definition to delineate areas where Fortified homes meet Hurricane
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Requirements as described in this manual. Simply put, the Fortified hurricane provisions are required in
all counties or parishes having areas where the ASCE 7-02 basic wind speed is 100 mph or greater. In
Florida, they are required in all counties, regardless of basic wind speed. In addition to these counties,
the Fortified hurricane provisions are required within one mile of “coastal mean high water” where the
basic wind speed is between 90 and 100 mph.
2.2
Tornado and Hail Region
From the eastern ranges of the Rocky Mountains to the Atlantic Coast, severe thunderstorms
have a known history of spawning around 1000 tornados each year. These are some of the most
destructive forces of nature, killing an average of about 60 people, injuring 1300, and resulting in
approximately $1.5 billion of damage annually (Cutter 2001). Since hailstorms are born under the same
weather conditions as tornados, Fortified…for safer living considers all Tornado regions to be HailProne regions as well. Generally speaking, the Fortified…for safer living program defines the Tornado
and Hail region as being between the Rocky Mountains and the Appalachian Mountains, in addition to
the coastal plains and piedmont of Georgia, the Carolinas, and Virginia. This roughly encompasses all
areas of the US where, according to the NOAA National Severe Storm Laboratory, tornados occur
within a 25 mile radius an average of 0.6 times per year or more. Although the previously described
region partially overlaps the Hurricane-Prone region along the Atlantic and Gulf Coasts, hurricane
provisions take precedence over tornado and hail provisions in all such areas. This is due to the fact that
such areas are more likely to be affected by hurricanes than by tornados, and is reflected in the Fortified
Wind Peril Map of Figure 3.1. Fortified…for safer living homes in the Tornado and Hail region must
meet the Fortified prescriptive requirements for tornados and hail, including structural reinforcement,
opening protection for large windows and doors, and impact-resistant roofing materials.
2.3
High Wind Regions
While not at eminent risk of hurricanes or tornados, areas 1) west of the Rockies, 2) in the
northern Great Lakes region, 3) in the Appalachian Mountains, and 4) in interior areas of New England
are nonetheless at risk of high winds from other causes, including mid-latitude cyclonic activity, severe
thunderstorms, and localized weather phenomena. Because of this, the Fortified…for safer living
program considers these to be High Wind Regions, and homes built within them must be built according
to the High Wind provisions of Section 3.0. Prescriptive requirements for Fortified…for safer living
homes in these regions include the structural elements necessary for wind loading, but do not require
wind-borne debris protection or impact resistant roofing materials.
2.4
Earthquake Regions
Homes designated as Fortified…for Safer Living are built to withstand the lateral loading
brought about by 130 mph winds regardless of geographic location. For the most part, they are therefore
capable of withstanding the lateral loading brought about by slight-to-moderate ground accelerations as
well (i.e., ground accelerations between 17% and 50% of the acceleration due to gravity). For this
reason, only Fortified homes built in regions of significant seismic risk are required to adhere to the
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seismic criteria. Figure 2.3 roughly illustrates the varying levels of seismic risk throughout the
contiguous US. In the Fortified program, regions of significant seismic risk are defined on a county and
state basis, as given in Table 2-1 and the map in Figure A - 1.
2.5
Wildfire
Wildfire criteria of the Fortified program may apply anywhere in the country where a home is
located in proximity to areas of natural vegetation. Figure 2-3 gives examples of what such areas might
look like. Applicability is determined by site-specific risk assessments of vegetation, topography, and
many other factors. Such assessments are conducted using the Wildfire Risk Assessment form found at
www.ibhs.org. If, by using this assessment form, it is determined that the home is at a “moderate”,
“high”, or “extreme” risk from wildfire, the home must be built, and the yard must be landscaped
according to the prescriptive requirements of Section 5.0.
2.6
Flood Zones
Homes in Special Flood Hazard Areas (A or V zones) as determined by the Flood Insurance Rate
Map (FIRM) from the National Flood Insurance Program (NFIP) must meet the Fortified…for safer
living Flood Criteria. Your community flood plain management official, mortgage lender, or
insurer/insurance agent can help you determine the applicable flood zone for your site. Homes not in a
Special Flood Hazard Area are exempt from the Fortified flood criteria.
2.7 Severe Winter Weather
Severe Winter Weather criteria specifically addresses the potential for damage from ice dams in
areas prone to snowfall accumulations greater than 12 inches. Areas where the Fortified criteria for
Severe Winter Weather are required are shown in Figure 7.1. The boundary of the so-called Severe
Winter Weather Region outlined on this map follows state and county boundaries, and is roughly based
on a combination of 1) the 20 degree isotherm of the 97½ % winter design temperature map in the IRC,
and 2) a 20 lb/sq. ft. ground snow load from the 2000 International Residential Code. The northern
boundaries of NC, TN, AK, OK, NM, and AZ roughly define a geographic line where the danger of ice
dams from snow accumulation and freezing weather are most likely to occur. In California, ice dams
are a factor in the northern and western mountain regions.
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Table 2-1: Fortified Perils by State
State
Alabama:
Applicable Perils
100 mph and greater - Hurricane
Other areas – Tornado and Hail
State
Missouri:
Alaska:
High Wind
Seismic
High Wind
Seismic (some western counties)
Tornado and Hail
Seismic (northeastern and central
counties)
High Wind
Severe Winter (Northern and Eastern
Region)
Seismic
Tornado and Hail
Seismic (some counties)
Hurricane (most counties)
Tornado and Hail (Litchfield County)
Hurricane (Sussex County)
High Wind (all other counties)
Montana:
Arizona:
Arkansas:
California:
Colorado:
Connecticut:
Delaware:
Nebraska:
Nevada:
New
Hampshire:
New Jersey:
New Mexico:
New York:
District of
Columbia:
High Wind
North
Carolina:
Florida:
Hurricane
Georgia:
100 mph and greater – Hurricane
Hurricane
Seismic
High Wind
Seismic (most counties)
Tornado and Hail
Seismic (some southern counties)
Tornado and Hail
Seismic (some southwestern
counties)
Tornado and Hail
North
Dakota:
Ohio:
Hawaii:
Idaho:
Illinois:
Indiana:
Iowa:
Oklahoma:
Oregon:
Pennsylvania:
Applicable Perils
Tornado and Hail
Seismic (some southeastern counties)
High Wind
Seismic (some western counties)
Tornado and Hail
Freezing Weather
High Wind
Severe Winter (most counties)
Seismic
Hurricane (Rockingham County)
Other areas – High Wind
Tornado and Hail
Severe Winter weather
Seismic (some northern counties)
Seismic (some southwestern counties)
Tornado and Hail
Tornado and Hail
Tornado and Hail
High Wind
High Wind
Rhode Island:
Hurricane
South
Carolina:
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Kansas:
Kentucky:
Louisiana:
Maine:
Maryland:
Massachuset
ts:
Michigan:
Minnesota:
Mississippi:
Tornado and Hail
Severe Winter weather
Tornado and Hail
Seismic (western counties)
Within 1 mile of Atlantic Coast –
Hurricane
Hurricane (some southeastern
counties)
Tornado and Hail
Tornado and Hail
Seismic (some northern counties)
South
Dakota:
Tennessee:
Texas:
Utah:
Tornado and Hail
Tornado and Hail
Seismic (some western and eastern
counties)
High Wind
Vermont:
High Wind
Virginia:
Other areas – Tornado and Hail –
High Wind
High Wind
Tornado and Hail
Washington:
West
Virginia:
Wisconsin:
Wyoming:
Tornado and Hail
Note: In states where both hurricane and tornado/other high wind regions exist, the dividing line
will be defined along county boundaries in the vicinity of the 100 mph wind contour on the ASCE 7-02
map. If any portion of a county has a basic wind speed of 100 mph or greater, the entire county is
considered to be within the Hurricane Prone region. One exception is in Maine, where areas within one
mile of the mean high water line of tidewater are considered Hurricane Prone regions, regardless of
basic wind speed.
•
Wildfire & Flood occur in all states and are determined by a risk assessment form and
flood maps, respectively.
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150 - 160
140 - 150
130 - 140
120 - 130
110 - 120
100 - 110
90 - 100
Design Peak Gust Hurricane Wind
Speeds (mph) In Open Terrain
Welcome
Figure 2-1: Design Wind Speed Map from ASCE 7-02
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Welcome
Figure 2-2: Tornado Activity in the United States
Figure 2-3: Seismic hazard map of the contiguous US (US Geological Survey map)
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Figure 2-3: Typical wildland/urban interface areas (adapted from Western Fire Chiefs Association).
3.0 HURRICANE/TORNADO AND HAIL/HIGH WIND CRITERIA
The following sections summarize the Hurricane, Tornado and Hail, and High Wind
requirements developed by IBHS for the Fortified…for safer living program. Collectively these will be
referred to as “wind requirements” throughout the guide. Regions where each of these sets of criteria
apply are identified using the map given in Figure 3.1.
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Figure 3-1: Hurricane, High Wind, and Tornado/Hail regions as defined by the Fortified…for safer living
program.
The underlying premise behind the Fortified wind requirements is to use hurricane resistant
building techniques to protect homes against damage from all three types of wind perils. With this in
mind, the prescriptive requirements were developed based on the 110 mph fastest mile wind (equivalent
to about 130 mph 3 second peak gust) provisions of the SSTD-10-99 Standard for Hurricane Resistant
Residential Construction. The prescriptive requirements listed for the Fortified Hurricane Program can
be applied if the following conditions are met:
Construction type is either wood frame, timber frame, cold-formed steel, reinforced masonry, or
reinforced concrete construction.
Horizontal building dimensions are between 18’ to 60’ in length and 18’ to 36’ in width.
The length-to width ratio of the home’s plan dimensions is less than or equal to 2
The distance from grade level to the eaves does not exceed 30 feet at any point around the perimeter
of the home
If the home is wood frame construction, the following requirements apply:
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•
Commercial species grouping of wood used in construction must be either 1) Southern Pine, 2)
Douglas Fir, 3) Douglas Fir-Larch, 4) Hem-Fir, or 5) Spruce-Pine-Fir, in order to meet
minimum density requirements, and shall not be less than grade No. 2
•
Maximum spacing of 2x4 studs in exterior wood frame walls is 16 inches on center. If 2x6
studs are used, the maximum allowable spacing is 24”.
•
Story heights are 10 feet or less
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Home is either 1 or 2 stories high
If the home is reinforced masonry construction, the following requirements apply:
•
Concrete masonry units must meet certain standards for composition and strength.
Additionally, certain types of mortar are not allowed.
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Story heights are 20 ft or less
•
Home is not more than 3 stories high
If these conditions are met, the Fortified Inspector will verify that the following prescriptive
requirements are in place. If any of these conditions are not met, then a registered Professional Engineer
or Architect must certify that the structure was designed for wind loads corresponding to at least
130 mph (3 second peak gust) for a home to be considered Fortified.
3.1
Elements common to all Wind Perils
A continuous and adequate load path from the roof to the foundation of the home must exist. To
be considered Fortified, the building must have positive connections from the roof to foundation as a
means to transmit wind uplift and shear loads safely to the ground. This includes providing roof-to-wall
connection hardware (e.g. hurricane straps), inter-story connection hardware, anchorage to the
foundation, and exterior walls fully-sheathed with structural wood panels meeting the stiffness ratings
and minimum thickness specified in this guide. The required minimum allowable loads for all
connection hardware to be installed within the house shall be identified on the building plans and
checked during the plan review. Required minimum allowable loads for connections at specific
locations within the load path are given in this section. Metal hardware and fasteners used in
applications where they are either exposed to the exterior, or in contact with pressure treated wood must
be either stainless steel or galvanized with a rating of G185 or greater. In Coastal A and V flood zones
(discussed in Chapter 4), all exposed hardware and fasteners must be stainless steel. Dissimilar metals
shall not be used in contact with each other. Thus, if stainless steel hardware is used, the fasteners used
with it shall also be stainless steel.
In addition, the roof framing, sheathing and covering must all be constructed to resist wind loads
and wind effects. This includes thicker roof sheathing fastened with ring-shank nails, bracing of gable
ends, wind resistant roof covering materials (impact resistant roof coverings in Tornado/Hail Regions)
and thicker roofing underlayment.
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Anchor Bolts
All anchor bolts shall be minimum 5/8” in diameter, with 3”x3”x3/16” washers. Bolts having a
90 or 180-degree hook (i.e., “J” bolts) shall have a minimum 7” embedment into the concrete or grout.
Bolts without a hook shall have a minimum embedment of 18”
Sill plates shall have anchor bolts every four feet and within 6 to 12 inches of the end of each
plate.
EMBED
5/8” ANCHOR BOLTS
MIN. 7”
w/ 3”x3”x3/16” PLATES AT 4’o.c. MAX.
SILL
PLATE
BOND
BEAM
REINFORCING
FOOTING
WALL REINF. @ 4’o.c. MAX
W/ GROUTED CELL
STANDARD HOOK
Figure 3-1: Typical foundation details for wood wall construction. Fortified inspectors are only required
to check for proper anchor bolts size and spacing.
3.1.1 Wood Shear Walls
All exterior wood framed walls must be fully sheathed with minimum 15/32” thick 32/16 rated
wood structural panels. Either plywood or OSB may be used. Sheathing shall overlap both top and
bottom sill plates and be continuous from the plate for at least 2 feet into the wall (as shown in Figure
3-2). In two story homes, sheathing shall also overlap wall framing in both stories by no less than 2 feet
to provide sufficient inter-story connections. Nailing schedule shall be 10d nails at 6” spacing along the
8’ edges, 6” staggered double row along the 4’ edges, and 12” spacing in the field of each structural
panel.
In one story wood frame walls, blocking shall be provided at 48” on center in the first two
framing spaces of wood framed walls from all corners and at either end of garage door openings. In two
story wood frame walls, blocking shall be provided where needed in all framing spaces to allow nailing
around the perimeters of wall sheathing panels.
All exterior walls shall be constructed as “shear walls” for at least 50% of their length. Fully
sheathed wall segments wider than 48 inches without any openings larger than 144 square inches are
considered shear walls provided that they have hold downs at the end of each segment (Figure 3-4) with
minimum allowable load capacities as follows:
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Top story end wall
1st story (under 2nd)
3,100 lbf.
10,000 lbf.
Top story Sidewall
1st story (under 2nd)
2,600 lbf.
5,300 lbf.
Min 2 ft
Min 2 ft
Figure 3-2: Example of how sheathing should overlap inter-story connection by at least 24 inches.
Note that these values reflect only the hold-down capacities required to resist overturning.
Additional uplift resistance must be provided through separate stud-to-sill hardware having a minimum
capacity of 520 lbs on each full length wall stud, except in end walls supporting gabled roofs. Stud-tosill connections on studs supporting headers must have sufficient allowable loads to resist uplift not only
from the stud itself, but also from any additional roof framing members (i.e., rafters, truss ends, or gable
end wall studs) that are supported by the header. Since headers are assumed to be simply supported
beams, it is reasonable to evenly divide the cumulative uplift loads on the header among the studs
supporting the header. Table 3.1 gives required uplift resistances for studs supporting headers, which, in
turn, support one or more roof framing members. The uplift values given for “end walls” are for gable
end walls only. If the end wall supports a hip roof, use the values given for “sidewall.” For studs at the
ends of shear wall segments, stud-to-sill hardware may be replaced with hold-down connectors having
sufficient capacity to resist both overturning and uplift. Ideally, the shear wall segments, and therefore
the hold-down connectors, will be aligned vertically. However, there is no specific requirement for
vertical alignment in the Fortified program. Specific Simpson Strong-Tie connectors that will meet the
hold-down requirements for overturning resistance alone are shown in Figure 3-5 below. Depending
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upon the required uplift resistance, this hardware may also be sufficient for the combined hold-down
requirement. Note that a single hold-down may be used when two shear walls meet at a corner. This is
allowed as long as the hold-down is sized for the larger of the two required capacities, and connected to
studs used for both shear wall segments as detailed in Figure 3-6. When a single hold down is used at a
corner on the first of two stories, the 16d nail spacing must be reduced to 4”. See Section 305.7 of
SSTD 10-99 for more information on hold-down connectors. Also note that hold-down connectors for
second stories must extend across floor framing to connect first and second story walls (as shown in
Figure 3-7). Note that this figure shows three types of connectors, and does not reflect the required
spacing of the hold-down connectors.
Table 3.1: Required uplift resistance for stud-to-sill hardware on studs
supporting headers. Note: where end walls support a hipped roof,
use values given for “Sidewall.” (Values given in pounds)
No. of Roof Framing Members Over Adjacent Header
Roof Framing Spacing = 16"
Roof Framing Spacing = 24"
0
1
2
3
4
5
6
7
8
Sidewall
710
1160
1610
2060
2510
2960
3410
3860
4310
Endwall
0
0
50
110
170
230
290
350
410
Sidewall
1155
1828
2500
3173
3845
4518
5190
5863
6535
Endwall
0
80
170
260
350
440
530
620
710
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Ignore openings
smaller than or
equal to 144 sq in.
Holddown
on each
segment
Sheathing
full wall
height
Shear wall figure from APA
1x1 ft
a+b+c > 0.5 L
At least
50%
Minshear
width
Min.
48 in.
walloflength
of 48”
Figure 3-3: Illustration of Shear wall length criteria.
2600 lbf hold-down
3100 lbf hold-down
5300 lbf hold-down
10,000-lbf hold-down
Figure 3-4: Typical Locations of hold-down connectors on 2-story house (adapted from SSTD10-99 from
Southern Building Code Congress International. 1999)
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PHD2 = 3610 lb allowable load
One story and top story of 2 story sidewall
and end wall
PHD6 = 5860 lb allowable load
Lower story sidewall
HD14A = 11,080 lb allowable load
Lower story end wall
Figure 3-5: Examples of hold-down connectors from Simpson Strong-tie that will qualify for the Fortified
hold-down requirements. (Simpson Strong Tie, 2002).
Figure 3-6: Example of single hold-down
connection detail at corner. When
used on the first of two stories,
reduce 16d nail spacing to 4”.
(adapted from SSTD10-99 )
Figure 3-7: First to Second story hold-down
installation examples. (adapted from
SSTD10-99).
3.1.2 Inter-story connections
Inter-story (2nd story to 1st story) details must include metal strapping every 48 inches (every 3rd
stud) along exterior walls with an allowable load capacity of at least 1500 lb and be sheathed with
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continuous wood structural panels (either plywood or OSB), with a minimum span rating of 32/16, and a
minimum thickness of 15/32 inches. Figure 3-8 shows four types of acceptable strapping. Note that the
hold-down connectors for the 1st to 2nd story connections (Figure 3-7) required for the wood shear walls
can be counted as inter-story connections if they are sized for both uplift and overturning forces.
In addition to the straps the builder should install sheathing so that the horizontal joints between
the panels are at least 2 feet above/below the floor connection as shown in Figure 3-2. This essentially
mandates that sheathing be oriented vertically across the inter-story connection.
Figure 3-8: Metal Strapping used for inter-story
connections (adapted from SSTD10-99
from Southern Building Code Congress
International. 1999)
3.1.3 Flooring
All wood framed floors must have full depth
2x blocking in the first two spaces between the floor
joists at each end of the floor diaphragm. Blocking
shall be spaced no more than 4 feet on center, and
shall correspond with the joints between subflooring
panels for edge nailing purposes. Subflooring shall be nailed to floor framing using 10d common nails at
6”/12” spacing on the 1st floor and 4”/12” spacing on the 2nd floor for shear resistance. Where
subflooring overlaps the first two framing spaces at each end of the diaphragm, proper edge nailing must
be used to connect the subflooring to the blocking below.
Figure 3-9: Required blocking of floor joists for wood frame floors (SSTD 10-99).
3.1.4 Roof-Wall Connectors
Hardware connectors must be provided from all roof framing members to wall frames. All
connectors shall wrap over the top of the roof truss or rafter and be installed according to the
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manufacturer’s recommendations. The minimum allowable load for these straps is 1345 lb for roof
framing spaced at 24”, and 900 lb for roof framing spaced at 16”. (per SSTD 10-99) These uplift loads
are based upon the SSTD 10-99 110 mph fastest mile requirements for a building 36’ wide, having a
roof dead load of 7 psf.
Figure 3-10: Strap types used in wood construction. Note that the non-wrapping clip styles on the left and
right are not accepted by the Fortified program. (used with permission from Simpson
Strong-Tie, 1991).
3.1.5 Attached Structures
Securely anchor connections for exterior
attached structures such as carports and porches
that attach to the main structure of the house (as
shown in Figure 3-11 and Figure 3-12). Stainless
steel or hot dipped galvanized hardware with a
minimum rating of G185 shall be used for any
connections that will be exposed to weathering in
service. Fasteners used with such hardware shall
consist of a similar metal to prevent accelerated
corrosion. In Coastal A and V flood zones
(discussed in Chapter 4), all exposed hardware
and fasteners must be stainless steel. Stainless
steel hardware and fasteners must also be used
when applied to preservatively treated lumber.
Figure 3-11: Connection of column on porch to
foundation with post anchor.
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Figure 3-12: Strapping of top of porch column to supporting beam.
3.1.6 Roof Truss and Gable Bracing
Gable end bracing shall be provided at all gable end walls to resist lateral loading and uplift of
the gable truss. This shall include lateral bracing of the bottom chord, anchoring of the bottom chord,
cross-bracing, and lateral bracing of top chord.
The following specifications and guidelines apply only to gable end construction with flat
ceilings constructed with truss or rafters/joists. Other configurations such as cathedral ceilings may be
accepted, but may require review by the Fortified inspector or by a design engineer.
Note that for truss roofs, the truss manufacturer has designed the truss under the guidance of a
professional engineer. In such cases, roof trusses shall be designed to resist the wind loading brought
about by a basic wind speed of 130 mph (3-second gust). Documentation that the trusses have been
designed for said wind loads shall be provided by the truss manufacturer.
Installation instructions provided by the truss manufacturer should come with details for
properly bracing the gable end. If the Fortified requirements are different than the specifications from
the truss manufacturer, the truss manufacturer’s engineer shall review the bracing requirements specified
here prior to construction in the same way that any other modifications or repairs to the trusses must be
reviewed by the truss manufacturer’s engineer.
3.1.6.1
Lateral Bracing of Bottom Chord
Install horizontal braces, running perpendicular to the bottom chords of the roof trusses, at 4 feet
on center and extending back 8 feet from the gable end wall. The brace will consist of a 2x4 fastened
with 2 16d nails at each truss chord and 4 16d nails into the blocking in the first framing space, as shown
in Figure 3-13. These lateral braces must be aligned with studs in the end wall below so that it is
possible to connect the braces to wall studs using metal strapping. Such metal strapping, when properly
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installed, helps to resist both lateral forces, and uplift on the gable end wall. Proper application of this
strapping is discussed in the following section.
3.1.6.2
Bottom Chord Anchoring for Uplift
For the platform styles of wall construction (wood or masonry), it is important to transfer the
uplift loads from the gable truss/frame wall to the end wall below. In order to ensure complete load
paths at these points, metal straps rated for a minimum tensile load of 770 lb shall be installed at each
lateral brace as illustrated in Figure 3-13. In addition, for wood construction, the wall sheathing shall
overlap the connection between the end wall and gable truss/frame by at least 12 inches (Figure 3-15).
3.1.6.3
Cross Bracing
This type of bracing will transfer lateral loads from gable truss to the ceiling and roof sheathing
planes where loads can be effectively transferred into shear walls. The Fortified program requires cross
bracing to be installed at the same spacing as the lateral bottom chord braces described above (every 4
feet). This bracing is to be installed in all configurations with flat ceilings. Keep the orientation of the
X in the vertical plane, and make sure that the connection between the cross braces and trusses is done
into the side of the top chord and bottom chord of the trusses, as shown in the inset of Figure 3-16.
3.1.6.4 Top Chord Bracing
Install 2x4x8' blocking along the top chords of gable ends at all locations where cross bracing is
installed (i.e., with a horizontal projection of not more than 48” O.C.). This bracing shall be constructed
in a manner that is identical to the bottom chord bracing, with the exception that the metal strapping is
not required. Proper installation of top chord bracing is illustrated in Figure 3-13.
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@ 4’-0”o.c.
2-16d nails
each truss
2-16d nails
2-16d nails
2-16d nails @
Metal strap satisfies
uplift requirement of
gable truss
Figure 3-13:Horizontal Lateral Bracing Construction Details (adapted from SSTD10-99 from Southern
Building Code Congress International, Inc., 900 Montclair Rd., Birmingham, AL, 352131204).
Figure 3-14: Hurricane Gusset Angle is
designed to transfer uplift and
lateral loads from gable end
truss to the wall below
(Simpson Strong Tie, 2000).
This can be used as alternative
to metal strap in Figure 3-13.
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Note sheathing
overlapping the
gable-side wall
connection by
12 inches
Sheathing overlaps
bottom plate
Figure 3-15: Example of how wall sheathing should overlap the gable wall-side wall connection.
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Figure 3-16: Gable End Wall Cross Bracing. [Inset: Cross Bracing should connect to truss as close to the
sheathing as possible. In this case, a special metal connector was used to make installation
easier in existing attic] Top and bottom chord bracing not shown.
3.1.7 Roof Sheathing
Roof decks must be fully sheathed with 40/20 rated wood panels having a minimum thickness of
19/32”. Either plywood or OSB may be used. Sheathing shall be attached with 8d ring shank (2.5” long
by 0.120” diameter) nails at 4” on center on any panel adjacent to a gable end (those panels shown in
color in Figure 3-18). The same nails are required at a spacing of 6 inches on center everywhere else on
the roof deck. Roof sheathing must be nailed to roof trusses/rafters, as well as to the blocking formed by
the gable end brace of the top chord. A minimum withdrawal design value of 60 lb per fastener is
required of all nails used to attach roof decking. This requirement will be met or exceeded, provided
that the roof framing lumber (i.e., roof trusses or rafters) consists of either Mixed Southern pine or
Southern Pine. If required due to roof geometry, piecework (panels ripped lengthwise to a width less
than 4 ft) is to be located in a strip located at least 4’ away from the ridge or eaves. This is illustrated in
Figure 3-18.
Note that the nails must be a full 2.5-inch long to qualify. Shorter nails may be qualified by the
Fortified inspector through comparative analysis using information about the nail size and wood species
from NER 272. All nails shall be installed such that they do not protrude out the side of the framing
members as shown in Figure 3-17.
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Figure 3-17: Avoid sidesplitting nails in deck to rafter connections. Note frequency of misses in this case
causes roof deck to be very vulnerable to wind damage.
6” spacing
in nonshaded
panels
4” spacing
in shaded
panels
Figure 3-18: Nail Spacing requirements for plywood or OSB roof deck
3.1.8 Secondary Water Resistance
All roof panel joints shall be covered with a self-adhering polymer modified bitumen tape of at
least 4” width to provide secondary water resistance. Alternatively, a self-adhering polymer modified
bitumen membrane may be used in lieu of both the underlayment and self-adhering tape. Self-adhering
polymer modified bitumen tape and membranes must comply with ASTM D1970 “Standard
Specification for Self-Adhering Polymer Modified Bituminous Sheet Materials Used as Steep Roofing
Underlayment for Ice Dam Protection”.
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Figure 3-19: Installation of secondary water resistance using self-adhering strips.
3.1.9
Roof Underlayment
At a minimum, roofing underlayment shall consist of either a single layer of 30# felt with a
minimum 2” overlap or two layers of 15# felt with a 19” overlap. Both underlayment application
methods require a minimum 6” end lap. Alternatively, a self-adhering polymer modified bitumen
membrane meeting ASTM D1970 may be used in lieu of both the underlayment and self-adhering tape.
In cases where the manufacturer of the roof covering to be used specifies more stringent underlayment
requirements, the more stringent procedures shall be followed. Nail spacing shall be no greater than 6”
along the laps and 12” in the interior of each strip using low profile roofing nails with load distribution
disks or capped head nails. Roofs within 3000 feet of salt water require hot dipped galvanized fasteners
for attachments of all roof coverings, including the underlayment.
3.1.10
Roof Covering
Roofing systems on homes built under the Fortified program must be built to withstand a design
3-second gust wind speed of at least 130 mph. The most common residential roof types and their
respective Fortified requirements are given below. Provided that the roof covering is selected and
applied in accordance with the applicable criteria given within this section, the roofing system will be
deemed to comply with Fortified standards.
•
Asphalt shingle roof coverings shall meet one of the test standards listed below, and be
installed in accordance with the manufacturer’s recommendations for high-wind regions.
Additionally, each strip shall be attached to the roof deck with no less than 6 roofing
nails. The tabs of shingles adjacent to, or along the eaves, hips, and ridges must be
manually adhered to the underlying surface with at least three 1” diameter dabs of asphalt
roof cement per tab. Along rake edges, shingles shall be manually adhered to the
underlying surface with 1” diameter dabs of asphalt roof cement at spacings of 2” on
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center. Shingles – including hip and ridge materials – must meet one or more of the
following standards:
ASTM D3161. Note: If materials tested under this standard are used, it must be
verified that they were tested to a minimum wind velocity of 130 mph.
UL 2390 and ASTM D6381. Note: These standards must be used together in
order to determine whether or not the shingles will be able to withstand a design
wind speed of 130 mph.
•
Clay and concrete tile roof coverings shall be installed in accordance with the
manufacturer’s recommendations for high-wind applications of 130 mph or greater.
Except along the hips and ridges, each tile shall be attached using two (2) mechanical
fasteners consisting of either #8 screws or 10d ring-shank nails. Mortar-set attachment is
not permitted. Nailer boards shall be installed along all hips and ridges with 1.5” wide,
26 gage galvanized steel straps screwed to the roof deck with two (2) #8 wood screws at
a maximum spacing of 37”. Hip and ridge tiles shall be mechanically attached to the
nailer board using a minimum of one (1) #8 screw per tile.
•
Metal panel roofing systems shall be designed for a minimum of 130mph 3-second gust
basic wind speed at exposure C using ASCE 7 to determine applicable loads, and ASTM
E1592 to determine resistance.
For all other roof coverings, documentation showing confirmation that hurricane level wind
loads were used in determining the fastening requirements. Any documentation showing acceptance in
Miami-Dade county will be adequate. All roof coverings, regardless of type, must be installed in
accordance with the manufacturer’s recommendations for high wind regions.
3.1.11
Soffits and Fascias
All soffits and fascias shall have a minimum design pressure of +33/-43 psf, as determined by
the AAMA 1402-86 test standard. Unsupported soffit lengths shall not exceed the maximum
dimensions of the tested configuration, as reported by the manufacturer. Soffits shall be installed
according to the manufacturers recommendations for high wind regions.
3.1.12
All Openings: Flashing and Installation
Windows and doors are installed according to manufacturers specifications. The Fortified
program has specific requirements for flashing around all windows and doors in wood frame walls that
may exceed requirements from manufacturer. Confirm that flashing meets the following specifications.
Note that there is no requirement for flashing in masonry walls. The intent of these details is to prevent
moisture penetration into the wall cavities as well as the interior spaces. As a builder, you are
encouraged to obtain training and certification through the AAMA (American Architectural
Manufacturers Association) InstallationMastersTM Residential and Light Commercial Window and Door
Installation Program. Contact Larry Livermore at (540) 877-9957 to obtain more information.
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The steps presented below are consistent with Method “B” from the AAMA
InstallationMastersTM guide for windows with mounting flanges and weather resistant barriers applied
after installation of the windows. These recommended steps are presented in a step-by-step format as
well as in Figure 3-20. Other types of windows or installations methods are acceptable as long as the
AAMA InstallationMastersTM guide, or ASTM E 2112-01 – Standard Practice for Installation of
Exterior Windows, Doors, and Skylights, recommends them.
The following five sections give instructions for installing windows with mounting flanges.
3.1.11.1 Step 1: Sill Flashing
Install a 9” wide piece of flashing flush with the rough opening of the window allowing the
flashing material to overlap the sheathing below. Fasten with staples at the top edge and do not remove
release paper until weather resistant barrier is installed in Step 5. Extend the flashing 9” beyond the
rough opening at the side jambs.
3.1.11.2 Step 2: Jamb Flashing
Install 9” wide flashing on the side jambs of the windows opening letting the material extend
above the top opening 8.5” and extending below the sill for a minimum of 9”. Jamb flashing should
overlap the sill flashing. Attach entire length except for lowest 9” to allow weather resistant barrier to
be installed in Step 5.
3.1.11.3 Step 3: Install the window
Apply a continuous bead of sealant to back of perimeter of mounting flange in line with the prepunched holes. Install window in wall according to the manufacturers recommended schedule. Cover up
any pre-punched holes in nailing flange with sealant.
3.1.11.4 Step 4: Head Flashing
Apply a bead of sealant to outside of top mounting flange and then install 9” wide flashing
overlapping nailing flange. Head flashing must cover top edge of jamb flashing and should extend a
minimum of 9” past side jambs of window. .
3.1.11.5 Step 5: Weather Resistant Barrier
Install weather resistant barrier consisting of house wrap or building paper in weather board
fashion starting from base of the wall and working upward. The first course of weather resistant barrier
should be tucked up under the sill and loose ends of jamb flashing. Attach sill and jamb flashing to
barrier. Apply next courses of barrier to overlap the jamb flashing as shown in Figure 3-20.
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Step 2: Jamb Flashing - Install 9” wide
vertical strips of flashing at
either side. Extend 8.5” above
head of rough opening. Overlap
the sill flashing by 9”.
Step 1: Sill Flashing - Install 9”
wide strip of flashing
aligned with rough
opening. Fasten at top
with staples only. Extend
9” past side jambs. .
(Optional) For added
protection, first bed a 25-gauge
metal Z-flashing into the caulk,
then caulk again and add the
flashing.
Step 3a: Install Window - Apply a
bead of caulk on perimeter of
mounting flange (all 4 sides)
in-line with pre-punched
holes.
Step 3b: Install window frame while
the caulk is still wet. Drive
the nails in all the way; never
bend them over.
Step 4: Head Flashing - Apply a liberal bead of
caulk across the top of the window
flange, then run a strip of 9” flashing
across the top, pushing the flashing
into the caulk. Flashing must cover
top of jamb flashing and extend 9” past
window sides.
Step 5: Weather Resistant Barrier - Apply
barrier in weather-board fashion from
bottom to top. Tuck barrier under the
sill and loose ends of jamb flashing,
then attach flashing to barrier. Next
courses overlap jamb flashing.
Figure 3-20: Water Penetration Resistant Window Flashing Details (diagram provided by AAMA).
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3.2
Elements that Differ by Wind Peril
3.2.1 Hurricane Regions
All entry doors, windows, skylights, patio doors and garage doors must be tested and certified to
meet impact resistance and pressure standards. If the units themselves are not tested, then they must be
protected by a protection system (storm shutter or screen) that meets the impact resistance standards.
Systems must be compliant with at least one of the following:
ASTM E 1996
SSTD-12
Miami-Dade County Protocol A 201
Florida Building Code TAS 201
3.2.2 Tornado / Hail Region
3.2.2.1
Roof Covering
An approved impact resistant roof covering – UL 2218 class 4 or FM 4473 Class 4 is required.
(Note that UL test is designed for flexible roof covering products, and the FM test is designed for rigid
roof covering products). See Section 6.0 for details.
3.2.2.2
Openings: Doors, Windows, Skylights, and Garage Doors
In the tornado / hail region, all openings must be rated for a minimum design pressure of positive
or negative 50 pounds per square foot as specified by the North American Fenestration Standard, which
combines the AAMA/NWWDA 101/I.S.2 and AAMA/WDMA 1600/I.S.7 test standards. Either the
WDMA (Window and Door Manufacturers Association) “Hallmark Certification” or the AAMA “Gold
Label” Certification Program shall certify these openings with a minimum DP rating of 50psf.
Openings (including doors, garage doors, skylights
and windows) greater than 32 square feet in area must be
impact-resistant or protected by a passive protection system
that complies with one of the impact standards listed for the
Hurricane Region. Passive protection means that the
window or door can withstand wind-borne debris without
any external protection; i.e., shutters or screens. Window
units connected by mullions supplied by the window
manufacturer are considered to be separate units in the
determination of area for impact criteria. Two double hung
units side by side that are 4 ft by 5 ft each are considered to
be separate units with areas of 20 SF instead of a single
opening that is 40 SF. In this case the double hung windows
would need to meet a DP of 50, but not need impact
protection.
Figure 3-17: Metal Screen that provides
impact protection, and
allows sunlight into the
building.
When one examines a double door, or a double slider, the rough opening of the unit should be
considered. The support between the door slabs is not a fixed permanent one, and thus is considered to
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be different than the mullions in window systems. Thus the double door or slider will often exceed the
32 square foot limit and therefore will need to meet the impact criteria.
3.2.1 High Wind Region
All openings must be rated by WDMA Hallmark or AAMA Gold Standard certification for a
minimum design pressure of positive or negative 50 pounds per square foot. All openings must be
flashed or properly caulked if installed directly to masonry.
4.0 FLOOD REGION CRITERIA
The IBHS flood requirements are, in general, no different than the minimum requirements of the
National Flood Insurance Program (NFIP), except in two respects. First, the building must be at least 2
feet higher than the BFE, and second, the foundations in Coastal A zones must adhere to the same
requirements as those in V zones. That is, only open elevated foundations are allowed in the Coastal A
zone in the Fortified program.
4.1
Flood Zones
V Zone – Areas along coasts subject to inundation by one percent annual chance flood events
with the additional hazards associated with storm induced waves. Mandatory flood insurance purchase
requirements apply.
Coastal A zone – A zone landward of a V zone, or landward of an open coast without mapped V
zones (e.g., the shorelines of the Great Lakes), in which the principal sources of flooding are
astronomical tides, storm surges, seiches, or tsunamis - not riverine sources. An example an elevation
showing V and Coastal A zones is given in Figure 4-1.
A Zone – other areas subject to inundation by one percent annual chance flood event (e.g., along
inland rivers, lakes and lowlands).
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Figure 4-1: Typical shoreline elevation showing flood zones V, Coastal A and X (from Coastal
Construction Manual, 3rd edition FEMA 55. Federal Emergency Management Agency).
4.2
Building Requirements
4.2.1
Foundation
Homes in Non-Coastal A zones must be designed and constructed with the lowest habitable floor
(including basements) above the Base Flood Elevation (BFE) by at least 2 ft. Community records or a
licensed survey are required to determine the BFE. (Figure 4-2)
Homes in V or Coastal A zones must be constructed on open foundation (including elevatedenclosed with breakaway walls) with continuous piles in accordance with the FEMA Coastal
Construction recommendations. The bottom of the lowest horizontal support member must be above the
BFE by at least 2 ft. Note that the NFIP would normally allow other foundation types such as
crawlspaces with flood vents in the Coastal A zone. (Figure 4-2)
4.2.2
Utilities
Electrical, heating, ventilation, plumbing, air conditioning equipment and other service facilities
must be elevated above the BFE by at least 2 ft in Special Flood Hazard Areas.
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Toward River/Lake
100-Year Wave
Crest Elevation
(BFE)
Crawlspace
Foundation
Non-Coastal A
zone requirements
Top of
Lowest
Floor
2 ft FreeBoard
100-Year
Stillwater
Depth
Wave Trough
Flood Vents
Eroded Ground
Elevation
Wave Height < 3ft
Toward Ocean
100-Year Wave
Crest Elevation
(BFE)
Bottom of
Lowest Horizontal
Structural Member
Wave Height > 3ft
V zone and
Coastal A zone
100-Year
Stillwater
Depth
Wave Trough
2 ft FreeBoard
Eroded Ground
Elevation
Figure 4-2: Requirements for Fortified foundations (adapted from Coastal Construction Manual, 3rd
edition FEMA 55. Federal Emergency Management Agency).
5.0 WILDFIRE REGION CRITERIA
The Wildland/Urban Interface is an area where structures and other improved property meets or
intermingles with wild land or vegetative fuels.
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5.1
Site Evaluation
The Fortified Inspector will identify the wildfire hazard level for the site by examining the
following items:
Ingress and egress into subdivision
Road widths
Road condition
Road terminus
Surrounding vegetation (fuel)
Topography/slope of surrounding area
History of fire occurrence due to lightning, railroads, burning debris, arson, etc.
Building setback
Fire protection systems (fire hydrants)
Utilities: gas and electric
Each factor is assigned a point value and the cumulative value of the points determines whether
the site is in a low, moderate, high or extreme wildfire hazard setting. Note that if the hazard level is
determined to be Low, then none of the wildfire criteria are applicable. For a risk assessment checklist,
visit www.ibhs.org.
5.2
Wildfire Protection Criteria Common to Extreme, High and
Moderate Wildfire Hazard Levels
The following items are applicable to all extreme, high, and moderate Wildfire Hazard Areas.
These requirements must be augmented by the hazard specific requirements that follow this section.
A non-combustible street number at least four inches high, reflectorized, on a contrasting
background, at each driveway entrance, visible from both directions of travel.
Firewood storage and LP gas containers must be at least 50 feet away from any part of the home
structure, and have at least 15 feet of survivable space around them.
Non-combustible, corrosion-resistant screening with a mesh size no greater than ¼” covering the
attic and sub-floor vents. Vent openings shall not exceed 144 square inches at each vent.
Spark arrestors in all chimneys (Figure 5-1)
Figure 5-1: Spark Arrestor for chimney
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Eaves of noncombustible materials as defined in Table 5-1. For materials not listed in Table 5-1,
any material that has passed when tested in accordance with Section 8 of ASTM E 136 “Standard Test
Method for Behavior of Materials in a Vertical Tube Furnace at 750°C (1382°F)” are generally
considered to be non-combustible.
Table 5-1: Combustible and Non-combustible Soffit Materials
•
Combustible:
•
Noncombustible:
•
Vinyl
•
Aluminum
•
PVC
•
•
Wood boards or
panels less than
or equal to ½”
thick (including
plywood
and
OSB)
Wood boards or
panels
greater
than
½”
in
thickness
(including
plywood
and
OSB)
Gutters and downspouts of noncombustible materials. Typical aluminum gutters and downspouts
are considered to be acceptable
Driveways must be at least 12 feet wide with at least 13.5 feet of vertical clearance.
If gated, the gate must open inward,have an entrance at least two feet wider than the driveway,
and be at least 30 feet from the road. If secured, the gate must have a key box of a type approved by the
local fire department.
Individual Fire Extinguishers
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5.3
Wildfire Protection Criteria that Varies by Wildfire Hazard Level
5.3.1 Survivable Space Characteristics
The following characteristics shall be applied in the survivable space whose extent is defined by
the wildfire hazard level below.
Grass mowed below 6 inches
Provide regular irrigation
• For trees taller than 18 feet,
prune lower branches within 6 feet
of ground.
Trees are 10 feet apart from
each other
No tree limbs within 10 feet
of home
All plants or plant groups are
more than 20 feet apart.
No vegetation under decks
Remove
all
dead/dying
vegetation
50’
No fire wood
within 50 ft of
structure’
Figure 5-2: Survivable Space features (courtesy of
Western Fire Chiefs Association, 1996).
5.3.2 Extreme Hazard Areas
If your home is in a wild land/urban interface area and has an “Extreme” hazard rating, it must
have the following additional items:
A survivable space of 100 feet.
A roof covering assembly with a Class A fire rating according to UL 790. Other standards that
are also accepted include ASTM E 108 Class A, or UBC 15-2 ratings. Consult the product packaging or
other manufacturer literature to determine if the product meets this standard. There are also publications
available from the National Roofing Contractors Association that list fire ratings (and other information)
by manufacturer and product name [NRCA 1999a, 1999b]. Wood shakes and wood shingles do not
qualify regardless of rating.
Non-combustible material enclosing the undersides of aboveground decks and balconies.
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Exterior windows are double-paned glass with a tempered outside lite and non-combustible,
corrosion resistant screens OR have non-combustible shutters.
Exterior glass doors and skylights are double paned, tempered glass.
Exterior wall assemblies must have one-hour fire resistive rating with non-combustible exterior
surfaces. The following materials are considered to be Non-combustible exterior surfaces: brick veneer,
concrete block, concrete, stone.
Monitored smoke alarms.
In-home sprinkler system that complies with NFPA 13-D-1999: Installation of sprinklers in 1
and 2 family dwellings.
5.3.3 High Hazard Area
If your home is in a wild land/urban interface area and has a “High” hazard rating, it must have
the following additional items:
A survivable space of 50 feet.
A roof assembly with a Class A fire rating. Wood shakes and wood shingles do not qualify
regardless of rating.
Non-combustible material enclosing the undersides of aboveground decks and balconies.
Exterior windows are double-paned glass and non-combustible, corrosion resistant screens OR
has non-combustible shutters.
Exterior glass doors and skylights are double-paned glass.
Exterior wall assemblies must have one-hour fire resistive rating with fire resistant exterior
surfaces. The following materials are considered to be fire-resistive: wood boards or panels greater
than ½” in thickness (including plywood and OSB), stucco, plaster, and brick or stone veneer.
Non-monitored smoke alarms.
5.3.4 Moderate Hazard Area
If your home is in a wild land/urban interface area and has a “Moderate” hazard rating, it must
have the following additional items:
• A survivable space of 30 feet.
A roof assembly with a class B fire rating.
Fire-resistive material enclosing the undersides of aboveground decks and balconies. .
Exterior windows and skylights are double-paned glass.
Exterior walls are fire resistant materials. The following materials are considered to be fireresistive: wood boards or panels greater than ½” in thickness (including plywood and OSB), stucco,
plaster, and brick or stone veneer.
Non-monitored smoke alarms.
6.0 HAIL REGION CRITERIA
Install an impact resistant roof covering – UL 2218 Class 4 or FM 4473 Class 4. (Note that UL
test is designed for flexible roof covering products, and the FM test is designed for rigid roof covering
products). This is the only criterion for Hail regions.
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UL 2218 is a test that is administered by Underwriters Laboratories and involves dropping steel
balls of varying sizes from heights designed to simulate the energy of falling hailstones. Class 4
indicates that the product was still functional after being struck twice in the same spot by 2 inch steel
balls. Examine the package of the roof cover product, or consult manufacturer documentation to
determine if the product has met the Class 4 designation of UL 2218. If difficultly is encountered
locating products that meet UL 2218 Class 4, contact the Fortified Program manager at IBHS for a list
of approved roof covering products. Note that this standard is appropriate for flexible roofing products
like asphalt shingles, and metal panels or shingles.
FM 4473 is administered by Factory Mutual Research and is a test that is similar to UL 2218, but
instead of using steel balls, frozen ice balls are used. The FM 4473 test standard is used on rigid roof
covering materials (like cement tiles) and involves firing the ice balls from a sling or air cannon at the
roof-covering product. Class 4 indicates that the product was still functional after being struck twice in
the same spot by a 2-inch ice ball.
7.0 SEVERE WINTER WEATHER CRITERIA
7.1
Overview
Severe Winter Weather criteria specifically addresses the potential for damage from ice dams in
areas prone to snowfall accumulations greater than 12 inches. Areas where the Fortified criteria for
Freezing Weather are required are shown in Figure 7-1. The boundary of the so-called Severe Winter
Weather Region outlined on this map follows state and county boundaries, and is roughly based on a
combination of 1) the 20 degree isotherm of the 97½ % winter design temperature map in the IRC, and
2) a 20 lb/sq. ft. ground snow load from the 2000 International Residential Code. The northern
boundaries of NC, TN, AK, OK, NM, and AZ roughly define a geographic line where the danger of ice
dams from snow accumulation and freezing weather are most likely to occur. In California, ice dams
are a factor in the northern and western mountain regions.
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Fortified . . .for safer living Severe Winter Weather requirements
Figure 7-1: Regions where Severe Winter Weather requirements apply under the Fortified…for safer
living program.
Fortified…for safer living homes located in areas within the freezing weather criteria boundary
shall include the following requirements in addition to those of other perils:
7.2
•
Roof Requirements
An additional moisture barrier shall be applied along the eaves of the roof to prevent
water intrusion caused by ice dams. This shall consist of a self-adhering polymer
modified bitumen membrane meeting ASTM D1970. The moisture barrier must extend
from the eave’s edge to at least 24” past the exterior wall line. Where roof valleys exist,
the additional moisture barrier shall extend up the entire length of the roof valley and be a
minimum of 36” in width. This additional ice dam protection is not necessary in cases
where a self-adhering polymer modified bitumen membrane is applied over the entire
surface of the roof deck.
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7.3
Attic Requirements
No heat sources shall be installed in unconditioned attic space (i.e., ductwork, etc).
No uninsulated recessed lights.
All attic access doors located in conditioned spaces shall be treated as exterior doors, properly
insulated, sealed and weather-stripped or gasketed.
All hidden attic penetrations (stack vents, partition walls, electrical chases, etc) shall be properly
sealed and insulated.
8.0 SEISMIC CRITERIA
8.1
Introduction
Fortified criteria have been developed for mitigation of damage brought about by earthquakes in
seismically active regions of the United States,. Structures built within these regions will likely
experience their most severe loadings during seismic events. Although it is impractical to build a home
such that it will withstand an intense earthquake unscathed, one may be built in such a manner that it
poses a minimal risk to the lives and safety of its occupants. Likewise, the severity of damage incurred
by homes built in this manner may be minimized as well. This paper details the seismic criteria that
have been developed for the Fortified…for Safer Living program.
Many of these criteria were developed using the International Residential Code’s (IRC) special
provisions for residential buildings in Seismic Design Category D2 as a basis. The IRC is a variation of
the International Building Code (IBC) intended specifically for one- and two-family dwellings. It is
used as a basis for Fortified seismic criteria because it, along with the IBC, is compatible with – and
designed to eventually replace – the other model building codes currently used in the United States. For
the Fortified seismic criteria that are based upon the IRC, special provisions established within the IRC
for Seismic Design Category D2 were used because they provide a practical level of protection from
earthquake damage in most seismically active regions of the United States. If the stringency of any
criterion herein prescribed is less than that which is mandated by building codes applicable to the site of
construction, code mandated provisions shall take precedence over the Fortified criterion in question.
All remaining Fortified criteria that are not directly nullified by a more stringent building code
provision, however, shall be adhered to.
The Fortified program requires wind peril criteria of one form or another throughout the entire
United States. Because of this, many of the features that would otherwise be required for prevention of
earthquake damage are already required for protection against high wind, tornado, or hurricane damage,
and are thus not included herein. It is therefore imperative that the seismic criteria specified in this
document be used in conjunction with the applicable wind peril criteria of the Fortified…for safer
living program. In some cases, the requirements for protection against earthquakes are more stringent
than the corresponding criteria for other perils. In such cases, the earthquake criteria take precedence.
One example of this is seen in the reinforcement required for stem walls and concrete masonry walls;
Fortified earthquake requirements mandate the use of No. 5 reinforcement bar for all concrete and
masonry, as opposed to the No. 4 bars that are required for the wind perils.
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8.2
Seismic Risk Zones
Homes designated as Fortified…for Safer Living are built to withstand the lateral loading
brought about by 130 mph winds regardless of geographic location. For the most part, they are therefore
capable of withstanding the lateral loading brought about by slight-to-moderate ground accelerations as
well (i.e., ground accelerations between 17% and 50% of the acceleration due to gravity). For this
reason, only Fortified homes built in regions of significant seismic risk are required to adhere to the
seismic criteria prescribed herein. The Fortified definition of an area having significant seismic risk is
based upon the US Geological Survey map of 0.2 second Design Spectral Response Acceleration (SDS),
given in Section 301.2 of the 2000 IRC. Contours of equivalent SDS shown on this map are the
maximum 5 Hz ground accelerations expected with a 2% probability of exceedance in 50 years. They
represent what the SDS contours would be throughout the contiguous United States for a uniform site
class of D.
Since the areas defined by these contours are not contained within easily identified political and
natural boundaries, it was necessary to develop a separate map defining areas in which the Fortified
seismic criteria apply. This map, in conjunction with its accompanying list, identifies all states and
counties in the United States where the Fortified seismic criteria must be in place before a home may be
designated as Fortified…for safer living. Both the Fortified Seismic map and the list of counties are
given in Appendix A. Counties identified therein are those containing areas with an SDS of at least 50%
of the acceleration of gravity (50% g) – corresponding to a Seismic Design Category of D1, D2, or E. If
any part of a county is within an area having an SDS of 50% g or more, the entire county is considered a
zone of significant seismic risk under the Fortified program. In some cases, every county in a given
state contains areas with an SDS of greater than or equal to 50%. In such cases, the state is listed rather
than its individual counties.
8.3
House Geometry
One of the biggest factors affecting a building’s susceptibility to earthquakes is its basic
geometry. The building’s height and shape – both in plan and in elevation – have major influences on
its response to seismic loading. All other factors being equal, the greater a building’s height, the higher
its center of gravity. A higher center of gravity results in greater overturning forces. The Fortified
program places a limit on building height in order to ensure that the overturning forces brought about by
seismic events do not exceed the allowable loads of the hardware designed to resist them. Homes with
light-frame wood (i.e., “wood-frame”) exterior walls shall have no more than 2 stories (not including a
basement), eave heights no greater than 25’ above grade, and a mean roof height no greater than 30’.
Homes with masonry exterior walls are limited to one story (not including a basement), with eave
heights no greater than 15’ above grade, and a mean roof height no greater than 20’. Allowable heights
for individual stories are discussed in Section 7.0.
Buildings with complex or irregular geometries have historically incurred more damage due to
seismic events than buildings with more traditional geometries. Because of their detrimental affect on a
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building’s response to seismic loading, features that cause a building to be irregular, as defined by the
IRC, are not permitted in Fortified homes. Such features include the following:
Where shear wall lines of the second story are offset, or not in the same vertical plane as shear
walls of the first story.
Where the floor or roof diaphragm – or a part of either – is not directly supported by shear walls
along all sides.
Where any part of a shear wall in the second story is not directly over a shear wall in the first
story.
Where an opening in the floor or roof diaphragm has a dimension greater than or equal to the
lesser of 12 feet or 50% of the least floor or roof dimension.
Where a floor diaphragm does not lie entirely within one horizontal plane, except when the entire
perimeter of the diaphragm is supported directly by a continuous foundation.
Where shear wall lines do not occur in two perpendicular directions.
Where the shear walls within a given story of a house are constructed of dissimilar bracing
systems such that they have differing stiffness, strength, or other mechanical properties.
8.4
Building Material Mass
Another factor having a major influence on a building’s susceptibility to earthquake damage is
the mass of building materials used within it. The magnitude of lateral loading imposed upon a structure
during a seismic event is directly proportional to the structure’s overall mass. For this reason, the
Fortified program places limits on the allowable masses of structural assemblies making up the home.
The following mass (weight) limitations shall apply to all Fortified homes in seismic regions:
Floor diaphragms dead loads shall not exceed 10 pounds per square foot (psf)
Exterior wood-frame walls shall have dead loads no greater than 15 psf
Interior wood-frame walls shall have dead loads no greater than 10 psf
Masonry walls shall have dead loads no greater than 80 psf
Masonry veneer shall have dead loads no greater than 30 psf
Roof and ceiling dead loads shall not exceed 10 psf
These limitations on dead loads are based upon the provisions of Section R301.2.2.4 of the IRC.
8.5
Site Specific Criteria
The Spectral Response Acceleration map that was used to develop the Fortified seismic map is
based upon Site Class D. Site Class D was chosen as a basis for this map because it corresponds to a
practical worst-case scenario for soil conditions. Although it is acceptable to assume Site Class D as a
default soil condition in most cases, building sites with exceedingly poor soil characteristics must be
more closely analyzed for seismic risk. If the site index is E or F, methods specified in the IBC shall be
followed to determine the SDC. In such cases, construction of homes under Seismic Design Categories
D1 and D2 mandate the utilization of Fortified seismic criteria, regardless of whether or not the building
site is within a seismic risk zone as defined by the Fortified Seismic map.
In states such as California, where designated fault zones have been established and mapped,
Fortified homes are not permitted to be built within the so-called “fault zones.” This requirement is
designed to prevent construction of Fortified homes in areas where surface rupture is a concern, and also
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keeps the homes out of the areas where the most intense ground shaking occurs during a seismic event.
Additionally, if the state has developed Seismic Hazard Zone maps (as has California), Fortified homes
that are to be built in an area designated as being at risk of either liquefaction or ground failure must
have their foundations designed by a licensed structural engineer.
8.5.1 Foundations
In seismically active regions, Fortified…for safer living homes constructed using these
prescriptive criteria must have foundations consisting of one of the following three types:
A monolithic slab-on-ground with integral footing,
A reinforced concrete foundation wall, or stem wall, on a continuous reinforced concrete strip
footing, or
A grouted, reinforced masonry block foundation wall, or stem wall, on a continuous reinforced
concrete strip footing.
Other foundation types, including piers if deemed necessary, must be designed by a licensed
professional engineer to resist the applicable seismic forces, as defined in ASCE 7-02. For foundations
of the three types previously mentioned, all concrete shall have a minimum compressive strength of
3000 pounds per square inch. All reinforcement for concrete and masonry walls shall consist of Grade
60 No. 5 rebar. In addition to these and the code requirements of the IRC, the following criteria must be
in place:
8.5.2 Footings
Foundations shall have a footing depth – both for perimeter and interior footings – of at least 18” below
exterior grade. Note that in many areas of the United States, the frost line mandates greater depth.
Footing widths must be sized as required for soil load bearing, but must not be less than 12” in
width.
8.5.2.1
Strip Footings
Strip footings shall be no less than 10” thick, and greater than the projection lengths beyond the
interior and exterior planes of the foundation wall.
Strip footings shall have horizontal reinforcement consisting of a minimum of one No. 5 bar in
the center of the footing width with 4” clear cover from the bottom of the footing. For footings with
widths greater than or equal to 16”, an additional two (2) No. 5 bars shall be added, one on either side of
the central bar.
Strip footings supporting concrete foundation walls shall have minimum vertical reinforcement
of No. 5 bars at 40” spacing. Vertical reinforcement shall hook around the horizontal reinforcement
with a 180-degree standard hook and shall have a minimum clear cover of 3” from the bottom of the
footing. Vertical reinforcement shall extend to a minimum of 28” above the top of the footing and into
the foundation wall.
The minimum requirement for vertical reinforcement of strip footings supporting masonry
foundation walls depends upon the type of above-grade shear walls that will be constructed. Strip
footings for homes that will have wood-frame shear walls shall have minimum vertical reinforcement of
No. 5 bars at 40” spacing. Strip footings for homes that will have reinforced, grouted masonry shear
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walls shall have minimum vertical reinforcement of No. 5 bars at 16” spacing. In either case, vertical
reinforcement shall hook around the horizontal reinforcement with a 180-degree standard hook and shall
have a minimum clear cover of 3” from the bottom of the footing. Vertical reinforcement shall extend
to a minimum of 28” above the top of the footing and into the foundation wall.
8.6
Slab-on-Ground Foundations
Footings cast monolithically with a slab-on-ground shall have minimum horizontal
reinforcement consisting of one No. 5 bar approximately 4” from the bottom of the footing, and one No.
5 bar approximately 3” from the top of the slab. Horizontal reinforcement in footings shall result in a
reinforcement ratio (by area) of at least 0.002.
Slab-on-ground foundations supporting masonry shear walls shall have minimum vertical
reinforcement consisting of No. 5 bars at 16” on center. Vertical reinforcement shall hook around the
horizontal footing reinforcement with a 180-degree standard hook, shall have a minimum of 3” clear
cover from the bottom of the footing, and shall extend a minimum of 28” into the shear wall to allow for
an effective lap splice.
Slab-on-ground foundations supporting cast-in-place concrete shear walls shall have minimum
vertical reinforcement consisting of No. 5 bars at 40” on center. Vertical reinforcement shall hook
around the horizontal footing reinforcement with a 180-degree standard hook, shall have a minimum of
3” clear cover from the bottom of the footing, and shall extend a minimum of 28” into the shear wall to
allow for an effective lap splice.
Slab-on-ground foundations supporting wood-frame shear walls shall have 5/8 “J” or “L” anchor
bolts embedded in the slab to a minimum depth of 7”. These bolts shall be spaced no greater than 48”
on center and shall also be embedded between 6” and 12” of the ends of each sill plate in the bottom of
the wood-frame wall.
8.7
Foundation Walls
Foundation walls shall have a minimum thickness of 8”.
Foundation wall height shall be limited to 8’.
The maximum allowable height of unbalanced backfill against the foundation wall is 4’.
8.7.1 Cast-in-Place Concrete Foundation Walls
Cast-in-place concrete foundation walls shall have minimum vertical reinforcement consisting of
No. 5 bars at 40” on center, in addition to placement within 8” of the edges of openings and corners.
This vertical reinforcement shall either be continuous from the bottom of the footing to the top of the
foundation wall, or shall be lap spliced with vertical reinforcement in the footing for a minimum of 28”.
Cast-in-place concrete foundation walls shall have minimum horizontal reinforcement consisting
of one No. 5 bar in the top 12” of the wall, in addition to one No. 5 bar at mid-height for foundation
walls greater than 4’ in height. Horizontal No. 5 bars shall also be placed within 8” of the tops and
bottoms of openings. Where vertical control joints are located, horizontal No. 5 bars shall be spaced no
more than 16” on center from the bottom to the top of the wall, and shall extend at least 28” on either
side of the control joint.
Cast-in-place concrete foundation walls supporting wood-frame shear walls shall have 5/8”
diameter “J” or “L” bolts embedded a minimum of 7” into the top of the foundation wall for sill plate
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anchorage. These bolts are required at spacing no greater than 48” on center, with additional placement
required between 6” and 12” from where each end of each sill plate will fall. Calculations are required
to determine the proper placement of these anchor bolts, as the location of each end of each sill plate
must be determined prior to construction of the foundation wall. Care must also be taken to ensure that
the bolts to not interfere with – or end up to close to – the bottoms of wall studs.
8.7.2 Masonry Foundation Walls
Masonry foundation walls shall have minimum vertical reinforcement consisting of No. 5 bars at
16” spacing, regardless of whether the shear walls being supported by the foundation are wood-frame or
masonry. For masonry shear walls, the vertical reinforcement shall either be continuous from the
foundation wall into the shear wall, or shall be lap spliced with the vertical reinforcement in the shear
wall a minimum of 28”. Regardless of the type of shear wall to be built, vertical reinforcement in
masonry foundation walls shall either be continuous with vertical reinforcement of the footing or shall
be lap spliced to it for a minimum length of 28”.
Masonry foundation walls shall have minimum horizontal reinforcement consisting of one No. 5
bar in the top 12” of the wall, in addition to No. 5 bars at spacing of no greater than 16” on center. Note
that the maximum allowable spacing corresponds to placement after every 2 rows of 8” masonry block.
Masonry foundation walls supporting wood-frame shear walls shall have 5/8” diameter “J” or
“L” bolts embedded a minimum of 15” into the top of the foundation wall for sill plate anchorage.
These bolts are required at spacing no greater than 48” on center, with additional placement required
between 6” and 12” from where each end of each sill plate will fall. Calculations are required to
determine the proper placement of these anchor bolts, as the location of each end of each sill plate must
be determined prior to construction of the foundation wall. Care must also be taken to ensure that the
bolts to not interfere with – or end up to close to – the bottoms of wall studs.
8.8
Floor Diaphragms
Due to the fact that floors (acting as diaphragms) play an integral role in the three-dimensional
response of a residential structure to ground accelerations, certain limitations and/or specifications are
necessary to ensure dynamic stability. All structural elements of floor diaphragms shall be installed in
such a manner that there are direct load paths – both for gravity loads, lateral loads, and uplift loads – to
adjacent floor diaphragm members, interior supports, and exterior supports. In addition to the code
requirements of the IRC, the Fortified seismic requirements for floor diaphragms are as follows:
•
Where a floor diaphragm is supported directly by the foundation, sill plates on which floor joists rest
shall be directly anchored to the foundation with the previously specified anchor bolts (see Sections
5.1.2, 5.2.1, and 5.2.2). Plate washers with minimum dimensions of 3”x 3”x ¼” must be placed
between the nut and the sill.
Full-depth blocking is required at all floor joist supports. Additionally, steel or wood diagonal
bridging shall be installed at a maximum spacing of 6’ for joists with depths of 12” or greater and 8’ for
joists with depths of less than 12”.
The greatest dimension of openings in the floor shall not exceed the lesser of 12’ or 50% of the
least floor dimension.
No split-levels shall be permitted unless each floor level is supported directly by the foundation
at the perimeter.
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Total dead loads of floor assemblies shall not exceed 10 psf, and shall be relatively uniformly
distributed.
8.9
Walls
Load-bearing walls acting as “shear walls” are not only responsible for transmitting vertical loads to
the foundation, but also for horizontal (lateral) loads. Since lateral ground accelerations during an
earthquake may approach – or in some cases even exceed – the acceleration of gravity, it is imperative
that a home has a sufficient percentage of its exterior wall length devoted to serving as shear walls.
Equally as important is each wall’s ability to transmit its base shear into the foundation. The Fortified
seismic requirements for walls are designed to address these concerns. They are as follows:
Where wood-frame shear walls are supported directly by the foundation, the bottom sills of the
walls shall be directly anchored to the foundation with the previously specified anchor bolts (see
Sections 5.1.2, 5.2.1, and 5.2.2). Plate washers with minimum dimensions of 3”x 3”x ¼” must be placed
between the nut and the sill.
At least 55% of the lengths of exterior walls on the first floor of a two-story building shall be
shear walls.
Story heights shall be no more than 10’ for wood-frame walls and 9’ for masonry block walls.
The height of the 2nd floor can be less than the 1st floor by no more than 12”. Reinforced masonry walls
shall be no more than one story high.
Masonry block walls shall have the same reinforcement as is specified for masonry block
foundation walls. Vertical reinforcement shall be continuous or effectively lap spliced with a minimum
lap length of 28” from the top of the wall to the foundation.
On wood frame walls, masonry veneer is permitted up to 10’ feet above grade, with an additional
8’ permitted on gable ends. Masonry veneer shall be attached to the wood frame wall with a minimum
of # 9 gage wire ties at a maximum spacing of 16” on center both vertically and horizontally. No. 9
gage wire reinforcement shall be continuous in veneer bed joints. Masonry veneer shall weigh no more
than 30 pounds per square foot. Perimeter nail spacing for connections between sheathing and wall
framing shall be reduced to 4” on center wherever brick veneer is present.
Steel straps shall be nailed or screwed to the corners of openings in non load-bearing walls prior
to application of gypsum wallboard.
8.10 Roofs
In general, the roof criteria specified for 130 mph winds, including fastenings for sheathing as well as
roof-to-wall connections, are more than sufficient for seismic loading. Some additional requirements
include the following.
The greatest horizontal projection of an opening in the roof shall not exceed the lesser of 12’ or
50% of the least roof dimension.
The combined dead load of the roof and ceiling shall average 15 psf or less and shall be
relatively uniformly distributed.
8.11 Nonstructural
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The following criteria, while not related to the structural integrity of the home, will help prevent other
seismic-related disasters such as personal property damage, flooding, and fire.
Water heaters shall be securely attached to structural members such as wall studs within a loadbearing wall.
All glazing shall either consist of tempered glass or shall have a safety film applied on the
interior side, even for windows that have protective shutters.
All natural gas lines shall have flexible connections, in addition to an automatic shutoff valve.
Masonry chimneys shall be connected to structural members of exterior walls in the same
manner as is required for masonry veneer. Chimneys shall not extend more than 24” above the rooftop.
8.12 Additional Criteria
The length of an exterior wall line beyond a re-entrant corner shall be less than or equal to 15%
of the total building dimension in that direction for at least one projection of said corner.
8.13 Recommendations
The following criteria, while not required by the Fortified…for safer living program, are strongly
recommended. For the most part, they are simple steps that can be taken to drastically decrease the
amount of damage done to the homeowners’ possessions within the home during an earthquake. See “A
Homeowner’s Guide to Earthquake Retrofit” for details on the best methods of accomplishing these.
Install L-brackets or Z-brackets to attach bookcases, file cabinets, entertainment centers, and
other furniture to the wall.
Secure picture frames and bulletin boards to the wall by using closed screw-eyes instead of
traditional picture hangers.
Secure ceiling lights to supports using safety cables.
Anchor large appliances such as refrigerators to the wall using safety cables or straps.
Install locking mechanisms on cabinet and cupboard doors to prevent them from opening and
letting the contents fall out during an earthquake.
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Appendix A – Fortified Seismic Zones
Figure A-1: Fortified Seismic Zones of the contiguous US (Alaska and Hawaii are also considered seismic zones)
The following states shall meet the seismic requirements of the Fortified…for Safer Living program:
Alaska
California
Hawaii
Nevada
In addition, the following counties within the states listed below shall meet the requirements
of the Fortified…for Safer Living Program:
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Arizona
Coconino
Pima
Yuma
Mohave
Arkansas
Arkansas
Clay
Cleburne
Craighead
Crittenden
Cross
Faulkner
Fulton
Greene
Independence
Izard
Jackson
Lawrence
Lee
Lonoke
Mississippi
Monroe
Phillips
Poinsett
Prairie
Pulaski
Randolph
Sharp
St. Francis
Stone
White
Woodruff
Jackson
Jasper
Jefferson
Johnson
Lawrence
Madison
Marion
Massac
Monroe
Perry
Pope
Pulaski
Randolph
Richland
Saline
St. Clair
Union
Wabash
Washington
Wayne
White
Williamson
Hickman
Hopkins
Livingston
Lyon
Marshall
McCracken
McLean
Muhlenberg
Todd
Trigg
Union
Webster
Illinois
Alexander
Bond
Clay
Clinton
Crawford
Edwards
Effingham
Fayette
Franklin
Gallatin
Hamilton
Hardin
Indiana
Gibson
Knox
Pike
Posey
Spencer
Vanderburgh
Warrick
Kentucky
Ballard
Caldwell
Calloway
Carlisle
Christian
Crittenden
Daviess
Fulton
Graves
Henderson
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Mississippi
Benton
Coahoma
Desoto
Lafayette
Marshall
Panola
Quitman
Tate
Tippah
Tunica
Missouri
Bollinger
Butler
Cape Girardeau
Carter
Dunklin
Iron
Jefferson
Madison
Mississippi
New Madrid
Oregon
Pemiscot
Perry
Reynolds
Ripley
Scott
Shannon
St. Francois
St. Louis
Ste. Genevieve
Stoddard
Washington
Wayne
Lewis and
Clark
Lincoln
Madison
Meagher
Missoula
Park
Pondera
Powell
Sanders
Silver Bow
Teton
Rio Arriba
Sandoval
Santa Fe
Socorro
Valencia
Cherokee
Graham
Swain
Oregon
Baker
Benton
Clackamas
Clatsop
Columbia
Curry
Coos
Deschutes
Douglas
Harney
Hood River
Jackson
Josephine
Klamath
Lake
Lane
Lincoln
Linn
Malheur
Marion
Multnomah
Montana
Beaverhead
Broadwater
Cascade
Deer Lodge
Flathead
Gallatin
Glacier
Granite
Jefferson
Lake
New Mexico
Bernalillo
Los Alamos
New York
Clinton
Franklin
St. Lawrence
North Carolina
Polk
Tillamook
Umatilla
Wasco
Washington
Yamhill
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Welcome
South Carolina
Aiken
Allendale
Bamberg
Barnwell
Beaufort
Berkeley
Calhoun
Charleston
Chesterfield
Clarendon
Colleton
Darlington
Dillon
Dorchester
Fairfield
Florence
Georgetown
Hampton
Horry
Jasper
Kershaw
Lee
Lexington
Marion
Marlboro
Orangeburg
Richland
Sumter
Williamsburg
Tennessee
Anderson
Benton
Blount
Bradley
Chester
Coclee
Carroll
Crockett
Decatur
Dyer
Fayette
Grainger
Gibson
Hamblen
Hamilton
Hardeman
Hardin
Haywood
Henderson
Henry
Houston
Humphreys
Lake
Lauderdale
Jefferson
Knox
Loudon
Montgomery
Obion
Garfield
Iron
Juab
Kane
Millard
Morgan
Piute
Rich
Salt Lake
Sanpete
Sevier
Summit
Tooele
Utah
Wasatch
Washington
Wayne
Weber
Jefferson
King
Kitsap
Kittitas
Klickitat
Lewis
Mason
Pacific
Pierce
San Juan
Skagit
Skamania
Snohomish
Thurston
Wahkiakum
Walla Walla
Whatcom
Yakima
Park
Sublette
Teton
Monroe
Madison
McNairy
Polk
Sevier
Perry
Shelby
Stewart
Tipton
Union
Weakley
Utah
Beaver
Box Elder
Cache
Carbon
Davis
Duchesne
Emery
Washington
Benton
Chelan
Clallam
Clark
Cowlitz
Grays Harbor
Island
Wyoming
Freemont
Lincoln
Uinta
Page 56
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Appendix B – Foundation Reinforcement Requirements for
Seismic Regions
This appendix contains five illustrations, each of a different commonly used foundation system.
The drawings and text contained therein show the minimum reinforcement requirements for foundations
of Fortified homes built in areas defined by the Fortified program as seismic risk zones. Note that each
illustration is preceded by a title that describes what type of system it is. An elevation (left) and a
profile (right) are shown for each system.
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NOTES
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Welcome
9.0 Reference
AAMA 1402-86 “Standard Specifications for Aluminum Siding Soffit and Fascia” American
Architectural Manufacturers Association. www.aamanet.org . 2003.
ANSI/AAMA/NWWDA 101/1.S.2-97. American National Standard. Voluntary Specifications
for Aluminum, Vinyl (PVC) and Wood Windows and Glass Doors. American Architectural
Manufacturers Association, Schaumburg, IL, 1997
ASCE 7-98: Minimum Design Loads for Buildings and Other Structures. American Society of
Civil Engineers. Reston, Virginia, 2000.
ASTM D3161-03b “Standard Test Method for Wind-Resistance of Asphalt Shingles” ASTM
International, West Conshohocken, PA, 2001.
ASTM D1970-01. “Standard Specification for Self-Adhering Polymer Modified Bituminous
Sheet Materials Used as Steep Roofing Underlayment for Ice Dam Protection.” ASTM International,
West Conshohocken, PA, 2001.
ASTM E136 “Standard Test Method for Behavior of Materials in a Vertical Tube Furnace at
750°C (1382°F),” ASTM International, West Conshohocken, PA.
ASTM E1592 “Standard Test Method for Structural Performance of Sheet Metal Roof and
Siding Systems by Uniform Static Air Pressure Difference” ASTM International, West Conshohocken,
PA
ASTM E2112-01 “Standard Practice for Installation of Exterior Windows, Doors, and Skylights”
ASTM International, West Conshohocken, PA, 2001.
ASTM D6381 “Standard Test Method for Measurement of Asphalt Shingle Mechanical Uplift
Resistance” ASTM International, West Conshohocken, PA.
Coastal Construction Manual, 3rd edition, FEMA 55. Federal Emergency Management Agency,
Mitigation Directorate, June 2000
FM 4473: Specification Test Protocol for Impact Resistance testing of Rigid Roofing Materials
by Impacting with Freezer Ice Balls. Class 4473. September 1999. Factory Mutual Research.
GA-600-2000 - Fire Resistance Design Manual, Gypsum Association, Washington, DC, 2000.
HIP-91 Commentary and Recommendations for Handling, Installing and Bracing Metal Plate
Connected Wood Trusses, Truss Plate Institute, Inc., Madison, WI, 1991.
“Installation Masters Training Manual”, American Architectural Manufacturers Association,
Schaumburg, IL, 2000.
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“Is your home protected from hail damage? A homeowner’s guide to roofing and hail.” The
Institute for Business and Home Safety. Tampa, FL 1999.
“Is your home protected from hurricane disaster? A homeowner’s guide to hurricane retrofit.”
The Institute for Business and Home Safety. Tampa, FL 1998.
“Is your home protected from wildfire disaster? A homeowner’s guide to wildfire retrofit.” The
Institute for Business and Home Safety. Tampa, FL 2001.
Low Slope Roofing Material Guide, 1999, National Roofing Contractors Association, Rosemont,
IL, 1999.
NER-272: Power-Driven Staples and Nails for use in all types of Building Construction.
National Evaluation Service, Inc. September 1997.
SSTD10-99 “Southern Standards Technical Document 10 - Standard for Hurricane Resistant
Residential Construction”. Southern Building Code Congress International, Birmingham, AL 1999.
Steep Slope Roofing Material Guide, 1999, National Roofing Contractors Association,
Rosemont, IL, 1999.
UL 2218 “Impact Resistance of Prepared Roof Covering Materials,” Underwriters Laboratories
Inc., Northbrook, Illinois, 1996. ISBN 0-7629-0033-4
UL 2390 “Test Method for Wind Resistant Asphalt Shingles with Sealed Tabs” Underwriters
Laboratories Inc., Northbrook, Illinois, 1996. ISBN 0-7629-0033-4
Page 64
Welcome
10.0 CONTACT INFORMATION
Institute for Business & Home Safety
4775 E. Fowler Avenue
Tampa, FL 33617
www.ibhs.org
Charles T. (Chuck) Vance
Fortified Program Administrator
813 675-1039
813 286-9960 (fax)
[email protected]
Page 65

Fortified Builders Guide - International Barrier Technology, Inc.

Transcription

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