MASONRY CONCEPT HOME (4" BRICK BEARING WALL) WALTER

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MASONRY CONCEPT HOME
( 4" BRICK BEARING WALL)
WALTER LASKA
STAFF ARCHITECT
MASONRY ADVISORY COUNCIL
1550 NORTHWEST HIGHWAY
PARK RIDGE, 1L USA
ABSTRACT
In the past 40 years, the housing industry in the
United States has been dominated by the wood producers,
replacing masonry as a primary elemento
Based upon a previous program, the Masonry Advisory
Council designed and constructed a 4", vertically
reinforced, brick bearing wall house, and made an
economical feasability comparisson to a similar tract
house built by a developer.
Contained within this pape r
are the proceedures and results of this project.
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INTRODUCTION:
In the past, one of man's primary form of structure
was brick.
Unfortunately, most designers of today utilize
brick solely for its aesthetic qualities often overlooking
this materiaIs inherent structural capabilities.
The compressive strength of an average brick is rarely
lower than 6000 p.s .i ., while brick with strengths in
excess of 14 ,000 p.s.i. can be manufactured.
It is this
quality that makes brick ideal for load bearing walls.
However, corresponding tensile strengths of an average
brick are approximately 90% less then compressive
strengths, and the tensile bond streng th of a standard
mortar joint rarely exceeds 50 p.s.i..
Due to these
factors, the height of alI unreinforced masonry walls are
limited by their relatively low flexural strength.
A
means of lateral support must be provided to assist the
wal1 in transfering alI horizontally imposed forces.
Floor systems , roof framing columns, piers, pla'sters and
cross walls are alI forms of lateral support.
When determining maximwn wall hei ght s, the architect
and/or engineer has the option of using with one of
several masonry codes.
One widely used code is The
American Standard Building Code Requirements For Masonry
(ANSI A41.1)
This code is based on Empirical Design and
established 18 x nominal wall thickness (of nonreinforced solid components only) as the limiting factor
for the distance between lateral supports.
Or simply
stated, the thicker the wall the higher it can be built.
About 50 years ago architects and engineers in the
United States began to develop engineered masonry wall
systems to resist dynamic lateral forces produced by
earthquakes.
This led to a "new school of thought" when
building masonry structures in seismic areas.
By
vertically and horizontally reinforcing masonry walls, a
substantial increase in lateral stability could be
achieved.
With the ultimate strength method of design becoming
more commonplace, and with the recent research reports
from the Uniform Building Code and the Boca
Basic / National Building Code, a reduction of wall
thickness can now be easily achieved with the use of
vertical reinforcing bars.
This method now allows
vertically reinforced masonry walls to span greater
heights while maintaining a narrower profile.
Unfortunately, most designers throughout the Midwestern
and Eastern United States are unaware or were neve r
educated in the area of engineered masonry.
Hence, they
are unfamiliar with this type of construction method.
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SCOPE:
Following the Second World War, a transition of
standard construction techniques took place in the housing
industry.
Briek homes, which were once built with double
or triple wythe brick bearing walls, were now being built
with a wooden struetural frame, and veneered with brick.
The use of wood frame construction in lieu of brick
bearing wall had substantially redueed the cost of
eonstruction, and the amount of masonry used in housing.
If desired, the brick finish could be eliminated entirely,
with some form of siding taking its plaee.
This now
provided the builder with an avenue to use briek as an
"extra" elemento Brick homes were no longer the norm .
Overnight, they've been transformed into an item on whieh
a premium must be paid.
In 1975, the Western States Clay Product Association
[1] embarked on a project with the objective of
constructing a more economical, eost competitive brick
house.
Since the association is located in a seismic
area, all masonry structures must be vertica ll y reinforced
with steel reinforeing bars.
Based on this provision, a
4", vertically reinforeed, brick bearing wall house was
designed and developed.
About 30 homes of this type were
built in the Seattle area.
Unfortunately, due to the fact
that Seattle is probably the "lumber capitol" of the
United States, this system was not embraeed by the local
industry.
Recently, The Masonry Advisory Couneil decided to
embark on a projeet and construct a home of this type in
the Chicagoland area, a Masonry Concept Home.
This
location provided no advantage to either the manufacturing
and transportating of wood or brick products.
It was the
intent of the Council to compare this home's cost and
economical feasability to that of a similar briek veneer
tract house, located nearby.
It was not the Council's
intent to eliminate the carpentry trade, but to provide a
means of constructing a cost competitive masonry home.
DESIGN:
Contemporary floor plans and elevations were
developed.
The house consisted of approximately 2400
square feet and was two stories high, with a variety of
brick features integrated into the designo Several
criticaI design details had to be developed to satisfy the
various structural cri teria while accommodating
appropriate construction connections.
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Based upon the Uniform Building Code Research Report
No. 3119 (2],
BOCA Research Report #86-51 (3]. and
previous design details utilized on the original homes
built in Seattle, a standard wall section was developed
(see figo 1). Wall heights built from this section varied
from 11'-0" to 23'-0" at the gabIe peak.
A #4 vertical
steel reinforcing bar was required to placed and grouted
into the cores of the 4" brick at 3'-0" intervals on the
first floor and at the 4'-0" intervals on the second
floor.
These intervals were reduced in some areas where
unbraced wall heights exceeded 8'-0",
AlI walls were
laterally braced by means of attachment to the fIoor
system (see figo 2) or to the roof system.
The unbraced
heights of bearing walla ranged from 8'-0" to 17'-0".
Special attention had to be given to wall openings
with vertical reinforcing bara being placed at alI jamb
locations.
Structural support over openings could be
accomplished in two ways, either with a standard steel
angle or by designing a reinforced brick lintel (see fig o
3).
Special concideration has to be given to openings in
bearing walls due to the fact that the lintels carry the
dead load of the brick above along with both floor and
roof loads.
Steel angles with suitable properties and
dimensions were specified on this project, due to economic
considerations.
Finally, window frame attachment had to
be detailed.
The thickness of the window frame profile as
well as the Manufacturer selected will determine how the
window frames are attached to the wall opening (see figo
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After alI design provisions were met on the exterior
of the wall system, an interior framing and insulating
system was devised.
Once again, there are two options
open to the designer (see figo 5).
Each of these systems
offer maximum energy efficiency with R values in excess of
16.
Both have their advantages and disadvantages.
Providing a continuous layer of double foiled backed rigid
insulation board with the dry wall channels
(DWC's
channel) placed on top, eliminates alI thermal breaks to
the outer wythe of brick.
Also, electrical outlets can be
fitted in the space provided between the drywall and
insulation.
Although the "2" channel system does not
provide the same degree of thermal performance, it was
later selected (during the construction phase) due to
it's initial savings because of an easier and faster
method of construction.
Before applying the finished
wall, alI butted joints should be taped to provide a
continuous vapor barrier.
Flashing at the wall base
should also be lifted into place and tapped to the foil
backed insulation.
4"
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2x4 SOLE PLATE WITH 1/2"
ANCHOR BOLT AT 36" O.C.
BOND BEAM WITH #2 REBAR - - - - /
~.I-----
HORIZONTAL JOINT REIN. AT
12" O. C. VERTICALLY
#4 REBAR SPACED AT 41l" O.C. ----../
I
2" THERMAX INSULATION
1 1/2" DRYI~ALL CHANNEL~-----1/2" DRYWALL
I
SEE FIG. 2 _ _--../
SEE FIG. 4
3x5x5/16 GALVANIZED ANGLE
WITH HORITONZAL JOINT
REINF. PLACED IN BOTH COURSES
DF BRICK IMMEDIATELY ABOVE
OR SEE FIG . 3 FOR OPTION
--~
2" THERMAX INSULATlON
1 1/2" DRYWALL CHANNEL
1/2" DRYl<ALL
SEE FIG.5 FOR OPTION
4" CONC. SLAB l<ITH 6"x6"10/10
W.l<.F. ON VAPOR BARRIER
OVER 4" GRAVEL FILL
8" BY 16" CONC. FOOTING
WITH 2- #4 REBAR AND A #4
DOl<EL ROD SET IN PLACE AT
48" O. C.
Figure 1. Typical Wall Section
#4 REINF. AT 36" O. C.
BOND BEAM WITH 2-'4 REINF.
BAR
#4 DOWEL ROD EXTENDED 18"
ABOVE FOUNDATION AND SPACED
AT 48" O.C.
8" CMU FOUNDATION l<ALL
VERTICALLY REINF. WITH #4
REBAR AT 48" O.C. AND DM1P
PROOFED WITH ASPHALT
ROOFING CEMENT
4" DRAIN TILE CONTINUOUS
AROUND FOOTING SET IN LOOSE
GRAVEL FILL
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METAL JOIST HANGER NAILED
AT LEDGER
2x10 JOIST
#2 REINFORCED BAR PLACED
IN A CONTINUOUS BOND BEAM
1/2" DIA. ANCHOR BOLT SPACEDI
AT 12" O.C. FOR BEARING
WALLS AND 36" O.C. FOR
NON-BEARING WALLS
Figure 2. Ledger Joist Detail
REINFORCED BRICK BOND BEAM
~4
~
STEEL REINF . BAR GROUTED
SOLID INTO BRICK CORES
- - --~ .
,...
REINFORCED SOLDIER COURSE
Figure 3. Lintel Option Details
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STUFF WITH BATTED INSULATION
AND CONTINUOUSLY CAULK
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-~~~tiE~tt,/lj,
HEAD
I
- --- 2-2x4 STUDS
~I'-'--WINDOW
MOLDING
-"'--___1 WINDOW
FRAf1E ANCHOR STRAP
TO BE NAILED INTO BRICK WALL
OR WOOD FRAMING
NAILING PLUG PLACED EVERY
SECOND COURSE AROUNG WINDOW
PER mETER TO SECURE
2x4 STUD
STUFF '11TH BATTED INSULATION AND CONTINUOUSLY CAULK
1 -' ',- WI NDOvJ
~,---
_.-./
FRAME ANCHOR STRAP
1,INDOH MOLDING
JAMB
WINDOW FRAME ANCHOR STRAP
- WINDOW MOLDING
LIr~ESTONE
_.- 1/2" DRYWALL
SILL WITH DRIP - -
1/2" DRYWALL SHIM AROUND
2-2x4 STUDS --- ---
PERIHETER OF WINDOW
SILL
Figure 4. 'IYPical \'lindow Details
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h
ATTACH 1/2" ORYWALL TO HAT --CHANNEL
48" x 96" SHEET OF 2" RIGIO - - - - - FOIL BACK INSULATION
TAPE ALL JOINTS WHERE - -.-_. -.
INSULATION BUTTS
"<l
OUTER WYTHE OF 4" BRICK - - -
ORYWALL CHANNEL PLACEO
OVER INSULATION ANO
MECHANICALLY ATTACHEO TO
WALL 2'-0" O.C .
- --l
-,
TURN FLASHING UP AT THE
BASE OF THE WALL ANO TAPE
TO THE BACK OF THE
INSULATION
HAT CHANNEL FRAtU NG SYSTEM
ATTACH 1/2" ORYWALL TO "l" - - - - - -- -- CHANNEL
SHEET OF 2" RIGID FOIL BACK---- - - - INSULATION 24" X 96"
TAPE ALL JOINTS AT "l" --CHANNELS ANO INSULATION
JOINTS
?~
'O
"l" CHANNELS I1ECHANICALLY
FASTENEO OIRECTLY TO WALL
WITH INSULATION SECUREO
BETWEEN EACH UNIT AT 2'-0" O.C.
~
/'
-----------ITURN FLASHING UP AT THE BASE
-'. - - - - --- OF WALL ANO TAPE TO THE
.-/
FRAMING SYSTEM
BACK DF THE INSULATIDN
Figure 5. Optional Details For Interior Framing and Insulation
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CONSTRUCTION:
As one might expect, the early phases of construction
were handled tentively, as questions were posed from alI
Trades involved.
A 8" concrete block foundation (uncommon
in the Chicago areal was constructed as opposed to a
poured-in-place concrete foundation.
Although the
selection of concrete block over poured concrete resulted
in a economic "white wash" , two other advantages resulted
from the concrete block system:
First, superior lateral
support against cracking caused by back filling was
obtained due to the fact that the wall was vertically
reinforced at 4'-0" intervals with #4 rebar, and tied into
a continuously reinforced bond beam located at the top of
the wall. Secondly, installing an attractive split face
architectural block (by turning the finished face inward)
provided the basement with an attractive, finished room.
Upon completion of the foundation, #4 doweling rods
were set into the bond beam, ultimately tieing the brick
walls back into the foundation.
A hollow, 4" brick
meeting ASTM Specifications C652, was used for alI the
necessary brick work.
The mortar specified was a
Portland/lime mix with a grout mixture of 2000 p.s.i.
being used to fill the brick cores.
The actual size of
the brick unit was 3 5/8" x 3 5/8" x 11 5/8".
The core
size was approximately I 3/4" wide by 3 1/2" longo When
laying the first course of brick alI cores of the brick
which required the placement of rebar were carefully
designated by the Architect. A set of rebar placement
drawings had been developed to assist in this procedure.
The reinforcing bars were cut into 4'-0" sections, with
the mason laying the brick over the rebar or threading the
brick.
AlI cores were filled solid as the coursing
progressed.
A 15" bar splice was provided as specified by
code,
One must note that a half bond coursing is required
to provide clear access in the bricks core for vertical
steel placement and appropriate mortar bond.
Due to this
condition, corner units must be cut or a special corner
unit should be provided.
On this project, the masons cut
and skillfully located these units in recessed corners,
chimney corners etc.
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Once a height was reached at which lateral bracing was
required, the walls were connected to either the floor or
roof system.
A continuous connection was made to the
walls at the second floor by providing a 2 x 10 ledger
joist .
1 / 2" diameter ancho r bolts were set into a bond
beam at 12" horizontal intervals where bearing wall
conditions existed, with the spacing increasing to 36" on
center for non bearing walls . The spacing of anchor bolt
were determined thru structural calculations.
Once alI
the anchor bolts were embedded in the wall, and proper
setting times were allotted, the ledges were lifted and
bolted into place.
The floor joists were then attached to
metal hangers secured along the ledger and the plywood
deck was added, now providing the wall with continuous
lateral support.
The process of connecting the roof
system to the walls was pretty much a standard procedure.
2 x 4 plates were anchored continuously along the top of
the wall with 1 / 2" diameter anchor bolts, providing the
carpenters with a conventional means of framing the roof
to the wall structures.
Once the building shell had been completed,
attachments to the perimeter brick structure proceeded.
Windows were set into place with sealants and the
protruding flanges were nailed into the wall.
The window
sills were deleted at this point to provide the carpenter
with more flexability.
Special steel recepticals known as
"wall plugs" were set into the mortar beds to receive the
nails and secure the frame.
"Z" channels with a 2"
profile were pneumatically attached to the brick wall at
2'-0" intervals using 3 / 4" round head P-nails with barbed
shanks.
Rigid insulation was then cut into 2'-0" sections
and inserted in the channels.
AlI joints were tapped
before dry wall installation was to begin .
It should be noted , that the workmanship and
communication (between Architect and Mason Contractor) on
this project was excellent and that these are essential
requirements if this system is to be successful. As
familiarity with the system grows, confidence and broader
usages should also follow.
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CONCLUSION:
A two story home containig 2170 square feet was
selected as the "model unit" to which a direct cost
comparison would be made.
This unit is one of several
prototypes being offered for sale in a nearby subdivision.
Some of the major features included with purchase are : a
three or four bedroom option, basement, 2 1 / 2 baths with
bath and whirlpool in master bedroom, air conditioning, R
value of walls at 13, a connected garage and approximately
15% of the house veneered with brick while the majority of
the exterior is cedar siding . The lot size on which the
unit is located is 75 X 125.
Upon completion of the masonry work, a final cost
analysis had been made.
The price of the remaining
interior work was fixed, although allowances for cost
overruns had been factored in.
The Masonry Concept Home
included alI of the model units majority features with
many added features such as:
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10ft or fourth bedroom option
cathedrial ceiling
two story interior brick wall with a brick sculpture
partially finished basement
Wall's with an average R value of 18
200 square feet of additional living space
1800 square feet additional reet of property
and 75% more brick on the exterior of building.
The model units listed price was $176,900 . 00 .
Ir the
Masonry Concept Home was sold at that same price, a profit
margin of 21% could be realized.
There are still several more advantages afforded to
the model unit :
1.
Prices for both homes included the cost of land.
(It is obvious that the developer should have payed a
considerably lower premium for the land due to the
quantity of land he purchases).
2.
Tract housing affords the developer initial savings
due to quantity purchases of material, and
construction crews operating in production line
fashion .
3.
Due to the fact , that this particular method of
construction was new to this region, there were
several delays.
These delays can be avoided in
the ruture.
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4.
The homes built in Seattle employed a more
productive "high lift grouting" method of
construction. This technique , which is prominent
in the Western United States, was not used, due to
its relative unfamilarity in the Midwest.
At this point it should be evident that i f a builder
or developer utilizes this new system in tract house
construction, in lieu of conventional brick veneer
construction, larger profits could be obtained.
He would
also bee offering higher quality construction at a lower
cost than his competitor.
Brick could once again serve as
both structure and as an exterior finish, with brick homes
being offered to the public as a standard item, not as an
extra.
REFERENCES
[1] Western Clay Product Association in association with
Interpace Industries Inc., Engineering Guidelines For
Single Unit Brick Wall Construction, 1983.
[2] Uniform Building Code Research Report #3119, One and
Two-Story Residential Reinforced 4 - Inch Hollow Clav
Brick Construction, Recommendations IV., April 1976.
[3] BOCA Research Report #86-51, Design of Concrete and
Masonry Slender Walls, Description and Use of ProductIdentification, April 1987.
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