Stairs, Balustrades and Handrails, Design Guide 8

Transcription

08
Stairs, Balustrades
and Handrails
Class 1 Buildings - Construction
Technical Design Guide issued by Forest and Wood Products Australia
01
04
09
Building with Timber
in Bushfire-prone Areas
BCA Compliant Design and Construction Guide
Timber-framed Construction
for Townhouse Buildings
Class 1a
Design and construction guide for BCA compliant
sound and fire-rated construction
Timbe
r Floo
ring
for inst
Desig
n guide
Technica
l Desi
gn Guid
e issu
ed by
Forest
allatio
n
and Woo
d Prod
ucts
Australia
TechnicalDesignGuides
A growing suite of information, technical and
training resources created to support the use of
wood in the design and construction of buildings.
Topics include:
#01 Timber-framed Construction for
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Multi-residential Buildings Class 2, 3 & 9c
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#04 Building with Timber in Bushfire-prone Areas
#05 Timber service life design Design Guide for Durability
#06 Timber-framed Construction Sacrificial Timber Construction Joint
#07 Plywood Box Beam Construction
for Detached Housing
#08 Stairs, Balustrades and Handrails
Class 1 Buildings - Construction
#09 Timber Flooring - Design Guide for Installation
#10 Timber Windows and Doors
#11 Noise Transport Corridor Design Guide
#12 Impact and Assessment of
Moisture-affected, Timber-framed Construction
#13 Finishing Timber Externally
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Australia(FWPA).ItisacollaborativeeffortbetweenFWPA
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ISBN978-1-921763-16-8
Preparedby:
ColinMacKenzie
TimberQueenslandLimited
Firstproduced:April2007
Revised:May2012
© 2012 Forest and Wood Products Australia Limited.
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Table of Contents
Introduction
5
1. TypesofStairConstruction
6
1.1 StraightStairs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.2 StraightStairswithIntermediateLanding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.3 NewelStairs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.4 OpenNewelStair. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.5 Dog-legStair. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.6 Winders. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.7 GeometricalStairs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2. BCARequirements
10
2.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
2.2 Stairs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
2.3 BalustradesandHandrails . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
3. MaterialsforExternalStairsWithoutRiserBoards(OpenStairs)
13
3.1 TimberDurabilityandSpecies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13
3.2 TimberGrade. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15
3.3 MoistureContent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15
3.4 JointPriming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15
3.5 CorrosionProtectionofFasteners. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15
3.6 TermiteProtection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16
3.7 SlipResistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
3.8 Sizes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
4. MaterialsforInternalStairs–WithandWithoutRiserBoards(OpenandClosedStairs)18
4.1 TimberDurabilityandSpecies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18
4.2 TimberGrade. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19
4.3 MoistureContent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20
4.4 TermiteProtection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20
4.5 SlipResistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20
4.6 SpanTables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20
5. StairConstructionProcedure
21
5.1 MarginTemplateandPitchBoard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21
5.2 MarkingOutStrings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23
5.3 HousingStrings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26
5.4 StringEndJoints. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
5.5 StepBolts(TieBolts) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29
5.6 Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30
#08 • Stairs, Balustrades and Handrails Class 1 Buildings – Construction
Page 3
6. BalustradesandHandrails
31
6.1 Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31
6.2 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31
6.3 MemberSizes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32
6.4 Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35
7. Weathering,FinishesandMaintenance
38
7.1 ExternalStairsandBalustrades . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38
7.2 InternalStairs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38
Appendices
40
AppendixA–Glossary
40
A1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40
A2 MembersinaStaircase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40
A3 MembersinaBalustrade. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41
A4 ConstructionTerms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41
AppendixB–StairCalculations
43
B1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43
B2 Example1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44
B3 Example2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .45
B4 Example3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .46
B5 HeadroomforStairs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .47
B6 PracticalMethodforCalculatingNumberofRisesandtheRise . . . . . . . . . . . . . . . . .49
B7 QuantityCalculations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49
AppendixC–TotalRiseCalculations–SlopingGround
51
C1 DeterminingTotalRiseonSlopingGround . . . . . . . . . . . . . . . . . . . . . . . . . . . .51
Page 4
Introduction
This guide covers
stairs with straight
flights, with or
without risers for
external and internal
use and balustrades.
Staircaseandbalustradeworkisconsideredtobeaspecialisedsectionofcarpentryand
joinery.Thisdocumentcoversstairswithstraight flights, with or without risers for external
and internal use and balustrades.
Internalstairsareoftenpreparedinaworkshopmakingfulluseofavailablemachinesandequipment.
Interiorstairsmaydifferconsiderablyindesign,fromsimplestraightflights,commonlyusedin
domesticwork,tomoreelaboratestairsconstructedpurposelyasanattractivefeatureinpublicand
commercialbuildingsandinelaboratehomes.
Exteriorstairsarecommonlybuiltfromtreatedsoftwoodanddurablehardwoodswhileinteriorstairs
arecommonlybuiltfromjoinery-qualitytimbercutandseasonedespeciallyforstairs.Thefinishfor
exteriorstairsisgenerallypaintandinteriorstairsisoftenclearpolish,lacquer,etc,thereforeboth
materialandworkmanshipshouldbeoftheveryhigheststandard.
Theconstructionproceduredescribedherewouldbemoreorlessgeneralforallstairsofeither
conventionalorcontemporaryconstruction.
Atanearlystageintheconstructionofabuildinghavingexteriorand/orinteriorstairs,adecisionwill
havetobemadeonthelengthofthestairstodeterminethelocationofanyfoundations,concrete
pads,etc,andtheopeningrequiredinthefloortoaccommodateinternalstairsandprovidesufficient
headroom.Also,beforethetimberforthestairscanbeordered,itwillbenecessarytoknowthelength
ofthestring,newels,landingtrimmers,joists,etc,andthenumberoftreadsandrisersrequired.Refer
toAppendixBforthecalculationsneededtodeterminethesefacts.
Scope
Thisguideisintendedtobeusedbythebuildingindustryforthedesign,practicesandconstruction
oftimberstairs,handrailsandbalustrades.Informationwithrespecttobothinternalandexternal
stairsisprovided.Also,bothopenstairs(norisers)andclosedstairs(withrisers)arecateredfor.
Recommendationsarealsoprovidedontimberspeciesselection,durabilityandfinishing,etc,and
examplestaircalculationsaregiveninAppendixBandC.
Disclaimer
Theinformation,opinions,adviceandrecommendationscontainedinthispublicationhavebeen
preparedwithduecare.Theyareofferedonlyforthepurposeofprovidingusefulinformationtoassist
thoseinterestedintechnicalmattersassociatedwiththespecificationanduseoftimberandtimber
products.Whilsteveryefforthasbeenmadetoensurethatthispublicationisinaccordancewith
currentpracticesandtechnology,itisnotintendedasanexhaustivestatementofallrelevantdata.
Assuccessfuldesignandconstructiondependsuponnumerousfactorsoutsidethescopeofthis
publication,theauthorsandpublishersacceptnoresponsibilityforerrorsin,oromissionsfrom,this
publication,norforspecificationsorworkdoneoromittedinrelianceonthispublication.
Regulatory Requirements
Although national,
some BCA provisions
differ by state.
It’s vital to know
key elements for
your area.
ThispublicationfocusesontraditionalpracticesandcurrentrelevantBuildingCodeofAustralia(BCA)
requirements.FromtimetotimetheBCAisamendedandstatesmayalsovaryrequirements.Users
ofthisGuideshouldmakethemselvesawareofanychangesordifferencesandshoulddevelopafull
understandingoftheresultingimplications.OnlyonthisbasisshouldthisGuidebeused.
Page 5
1
Types of Stair Construction
Thedesignandconfigurationofstairscandiffermarkedlydependinguponspace
availability,functionalityanddesiredappearance.Thissectiondescribesdifferenttypesof
stairconfigurationsandthevariouscomponentsofthese.
ThecommontypeofstairconstructionistohousetreadsintostringersasshowninFigure1.1.Flights
maybeconstructedwith‘opentreads’withoutrisersor‘closedtreads’withriserboards.
Figure 1.1: Common stair construction.
Open tread stairs are
recommended for
external use.
Closedtreadstairsandopentreadstairsaresuitableforbothexternalandinternaluse.However
opentreadstairsarerecommendedforexternalusebecausetheygivebetteraircirculationallowing
thetimbertodryoutmorequicklyandthereforeimprovedurability.Metalanglebracketsmayalsobe
usedratherthanhousinginthetreads.
Asanalternativetotimber,metalmaybeusedforstringers.Metalstringsareoftenusedinexternal
locations,butcanalsobeusedforinternalstairs.Theyareavailableinsomestateswitha‘stock’rise
andgoingorcanbeorderedwithaspecificriseandgoing.
Dependingontheapplication,flightscanbeconfiguredinvariousways.Thefollowingillustratessome
ofthese.
Page 6
1.1 Straight Stairs
Asingleflightofstairshavingalltreadsparalleltooneanother.Thisformofstair,whichiswidelyused
fordomesticconstruction,hasnolandingandmaybeenclosedbetweentwowallsorbuiltagainst
onewallandtheothersideopenwithnewelsandbalustrade(Figure1.2).
Figure 1.2: Straight stairs.
1.2 Straight Stairs with Intermediate Landing
Stairshavingmorethanoneflightrisinginthesamedirectionandalltreadsparallel(Figure1.3).
Figure 1.3: Straight stairs with landing.
1.3 Newel Stairs
All stairs which
include newel posts
in their construction
are referred to as
newel stairs.
Allstairswhichincludenewelpostsintheirconstructionarereferredtoasnewelstairs.Thenewels
supportthehandrailsand/orbalustradeandmayalsosupportthelandingsandstrings.Figures1.2
and1.3illustratestraightnewelstairs.Figures1.4,1.5and1.6showotherformsofnewelstairs.
Figure 1.4: Newel stairs.
#08 • Stairs, Balustrades and Handrails Class 1 Buildings - Construction
Page 7
Figure 1.5: Dog-leg newel stairs.
Figure 1.6: Newel stairs with wide landing.
1.4 Open Newel Stair
Anopennewelstairisalsoreferredtoasan‘openwellstair’oran‘openwellnewelstair’.Thisform
ofstairhastwoormoreflightswhichreturnoneachotherformingaverticalspacecalledthewell
(Figures1.4and1.5).
1.5 Dog-leg Stair
Anewelstairhavingtwoflightsbuiltat180°toeachotherfromahalf-spacelanding.Theouterstring
oftheupperflightistenonedplumbabovetheouterstringofthelowerflightandbothtoasingle
commonnewel(Figure1.5).Thistypeofstairisnotcommonlyusedinhousing.
1.6 Winders
Triangularshapedtreadsusedtogainheightandinplaceofaquarter-spacelandingina90°turnstair.
Amaximumofthreewindersarefittedper90°andthecentreoneisnameda‘kite’winderbecauseof
itsshape(Figure1.7).
00
Figure 1.7: Stairs with winders or isolated step.
Page 8
1.7 Geometrical Stairs
Astairwhichchangesdirectioninplanwithoutusingnewels.Thestringsandhandrailsarecontinuous
fromfloortofloor,thecurvedportionsbeingeithercutfromsolidtimber(sawkerfed),stavedor
laminated(Figure1.8).
Figure 1.8: Geometrical stairs.
Page 9
2
BCA Requirements
TheregulatoryrequirementsforstairsandbalustradesprescribedbytheBCAareprimarily
concernedwithaddressingthesafetyissuesassociatedwithslips,tripsandfalls.Thebasic
BCArequirementsrelatingtostairandbalustradegeometry,openingwidth,landingsizes,
handrailheights,etc,needtobestrictlyfollowedtoensureregulatorycompliance.
2.1 General
Stairs, handrails
and balustrades
must be designed
and constructed
to comply with the
loadings given in
AS 1170 Part 1.
ForallClassesofbuildings,stairs,handrailsandbalustradesarerequiredtocomplywiththeBuilding
CodeofAustralia(BCA).TheBCArequirementsincludedesignandconstructionprovisionsforthe
variouscomponentsincludingcompliancewiththeloadingprovisionsofAS1170.1‘Structuraldesign
actionsPart1:Permanent,imposedandotheractions’.
Forstairs,handrailsandbalustrades,theBCAisprimarilyconcernedwiththesafetyofbuildingusers
andoccupants.Designandconstructionmustthereforetakeintoconsiderationboththestrengthand
durabilityofmaterialsandcomponentsaswellasthe‘geometric’constraintsprescribedbytheBCA.
ThefollowingprovidesabriefsummaryofsomeoftheBCArequirements.Forfulldetailsrefertothe
BCA.
2.2 Stairs
AsummaryoftherequirementsoftheBCAforstraightflightsofstairsisgivenbelow.
Eachflightmusthavenotmorethan18norlessthan2risers.
• Thenominaldimensionofgoingsandrisersofastairmustbeconstantthroughouteachstairflight.
• Theriseropeningmustnotallowa125mmspheretopassthroughbetweenthetreads.
• Thegoing(G),riser(R)andsloperelationshipquantity(2R+G)mustbeinaccordancewith
Table2.1.
• Landingsmustbenotlessthan750mmlongandwherethisinvolvesachangeindirection,the
lengthismeasured500mmfromtheinsideedgeofthelanding(AppendixFigureA1).
• Landingsmustbeprovidedwherethesillofathresholdofadoorwayopensontoastairthatprovides
achangeinfloorlevelorfloortogroundlevelgreaterthan3risersor570mm(Figure2.2).
The BCA does not
prescribe a minimum
width for stairs.
Note:TheBCAdoesnotprescribeaminimumwidthforstairs.
Table 2.1: Riser and going dimensions.
StairRiserandGoingDimensions(mm)
Riser(R)Going(G)
(seefollowingFigure)
SlopeRelationship
(2R+G)
StairType
Max
Min
Max
Min
Max
Min
Stairs(otherthanspiral)
190
115
355
240
700
550
Spiral
220
140
370
210
680
590
Page 10
Figure 2.1: Landing length.
Figure 2.2: Threshold landings.
2.3 Balustrades and Handrails
Acontinuousbalustradeorotherbarriermustbeprovidedalongthesideofanyrooftowhichpublic
accessisprovided,anystairwayorramp,anyfloor,corridor,hallway,balcony,verandah,mezzanine,
accessbridgeorthelikeandalongthesideofanypathofaccesstoabuilding,ifitisnotboundedby
awall;andanylevelismorethan1mabovethesurfacebeneath(Figure2.3).
Theheightofabalustradeorotherbarriermustbenotlessthan1mabovethefloorofanyaccess
path,balcony,landing,etc,andnotbelessthan865mmabovethenosingsofthestairtreadsorthe
floorofaramp(Figure2.4).
Page 11
Openingsinbalustrades(includingdecorativebalustrades)orotherbarriersmustbeconstructed
sothatanyopeningdoesnotpermita125mmspheretopassthroughitandforstairs,thespaceis
testedabovethenosingline(Figure2.4).
Forfloorsmorethan4mabovethesurfacebeneath,anyhorizontalelementswithinthebalustradeor
otherbarrierbetween150mmand760mmabovethefloormustnotfacilitateclimbing.
Balustrades and
handrails are
required when stairs
are not bounded by a
wall and any level is
more than 1 m above
the surface beneath.
Figure 2.3: Balustrades – when required.
Figure 2.4: Minimum handrail height.
Page 12
3
Materials for External Stairs
Without Riser Boards (Open Stairs)
Theconstructionofstairsisverydemandingandrequiresahighlevelofworkmanshipand
accuracy.Opentreadstairsarerecommendedforexternalusesincehousedriserswilltrap
moistureandpreventgooddrainageanddryingout.Housedtreadscanalsotrapmoisture
sopre-primingbeforeassemblyishighlyrecommended.AspertheBCArequirements,the
riseandgoingmustbeuniformthroughouttheflight,howeverforexternalstairsthebottom
risemayvaryslightly.
3.1 Timber Durability and Species
Inweather-exposed,above-groundapplicationsorwheresubjectedtoothersourcesofmoisture,
stringers,treads,risers,handrails,posts,newels,balusters,andinfillshouldbe:
(i)Warm,humidtropicalnorthernclimates:eitherAboveGroundDurabilityClass1specieswithany
sapwoodpresenttreatedtoH3(orhigher)orH3(orhigher)treatedsoftwoodsuchasSlash,Hoop
orRadiataPine.PreservativetreatmenttocomplywithAS1604.
(ii)Temperate,coolsouthernclimates:eitherAboveGroundDurabilityClass2orbetterspecies
withanysapwoodpresenttreatedtoH3(orhigher)orH3(orhigher)treatedsoftwoodsuchas
Slash,HooporRadiataPine.PreservativetreatmentshallcomplywithAS1604.Lowerdurability
speciescanalsobeutilisedalthoughcarefuldetailingofjointswithapplicationandmaintenanceof
protectivecoatings(paints,stains)and/orinstallationofprotectiveshielding(e.g.malthoid)ontop
ofexposedtimberedgesneedstobeutilised.
SuitablespeciesaregiveninTable3.1.
Note:
1. Meranti,VictorianAsh,TasmanianOakandDouglasFirarenotsuitableforweatherexposed
structuralapplications.
2. Forharshclimatestimberwithasawnupperfaceprovidesgreaterlongtermweatheringabilitythan
adressedsurface.Steptreadsexposedtotheweathershouldthereforebesawnallroundorsized
ontwoedgesandoneface(underside)only.
3. InQueensland,timberspeciesusedinstructuralapplicationsincludingstairsandbalustrades
shallcomplywith‘ConstructionsTimbersinQueensland’asreferencedbytheBuildingCodeof
Australia.
Page 13
Table 3.1: Suitable species.
Species
Availability
Postsinground
contact
Postsnotin
ground,stringers,
treads,landing
framingand
decking
AboveGroundDurabilityClass1
PreservativeTreatedPine
(CaribbeanHoop,
Radiata,Slash)
Allstates
4H5Treatment
4H3Treatment
MixedOpenForest
Hardwoods(Qld,NthNSW)
Qld,NSW
SeeNote1
4
Blackbutt
Qld,NSW
SeeNote1
4
Cypress
Alleasternstates
SapwoodFree
4
GumForestRed
Qld
4
4
GumGrey
Qld,NSW
4
4
GumRiverRed
Vic,NSW
SeeNote1
4
GumSpotted
Qld,NSW,Vic
SeeNote1
4
IronbarkRedorGrey
Qld,NSW,Vic
4
4
Jarrah
WA,SA,Vic
SeeNote1
4
Kwila(Merbau)
Allstates
MahoganyRed
Qld,NSW
SeeNote1
4
MahoganyWhite
Qld,NSW
4
4
MessmateGympie
Qld,NSW
4
4
Tallowwood
Qld,NSW
4
4
Turpentine
Qld,NSW
4
4
4
AboveGroundDurabilityClass2
Ensure timbers
used for external
stair construction
have the required
durability.
AshSilvertop
Vic,NSW
4
GumSouthernBlue
Vic,NSW
4
GumSydneyBlue
Vic,NSW
4
GumMountainGrey
Vic,NSW
4
Jarrah
WA,SA,Vic
Kapur
Allstates
4
Karri
WA,SA,Vic
4
MahoganySouthern
Vic,NSW
4
StringybarkBlue-Leaved
NSW
4
StringybarkYellow
Vic,NSW
4
SeeNote1
4
Notes:
1.Thesetimbersshouldonlybeusedforin-groundapplicationsiftheycanbeeasilyreplacedifdegradeoccurs.
2.InQueensland,timberspeciesusedinstructuralapplicationsincludingstairs,balustradesandhandrailsshall
complywith‘ConstructionsTimbersinQueensland’asreferencedbytheBuildingCodeofAustralia.
Page 14
3.2 Timber Grade
Structural members
should be free of
any major strength
reducing features.
Asstairstringers,treadsandposts,etc,arestructuralmembers,theyarerequiredtobestressgraded
andshouldbefreefromanymajorstrength-reducingfeatures.Inaddition,timberforstairconstruction
shouldalsobestraightgrainedandfreefromanyimperfectionsthatmaydetractfromdurabilityor
serviceabilityperformancerequirements.Stringers,treadsandpostsshouldbeinaccordancewiththe
followingtable.
Table 3.2: Timber grade.
Species
AustralianStandard
Grade
Hardwood
AS 2082
Structural Grade 1, Appearance grade
Softwood (Caribbean, Radiata,
Slash and imported softwood)
AS 2858
Structural Grade 1, Appearance grade
Hoop Pine
AS 2858
F8 Appearance grade
Cypress Pine
AS 2858
F7 Appearance grade
Note:Inaddition,finger-jointedtimbershallcomplywithAS5068–Timber–‘Fingerjointsinstructuralproducts’
andlaminatedtimbershallcomplywithAS1328–‘Gluedlaminatedstructuraltimber’.
3.3 Moisture Content
Allowance should
therefore be made
for shrinkage in
unseasoned stringers,
treads and any
associated newel
posts, landing bearers
and joists, etc.
Traditionally,timberusedforexternalstairconstructionisunseasoned.Dependingonlocationand
species,theamountofshrinkageoccurringinunseasonedtimberwillvary.Generally,about6%
shrinkage(6mmper100mm)shouldbeexpectedforunseasonedopenforesthardwoods.Allowance
shouldthereforebemadeforshrinkageinunseasonedstringers,treadsandanyassociatednewel
posts,landingbearersandjoists,etc,andforthegapsthatwilldevelopbetweenjointssuchas
betweenstringerhousingsandtreads.
ExternalstairtimbersexposedtotheweatherwillreachEquilibriumMoistureContent(EMC)withtheir
surroundingsafteraperiodof9-18months,dependinguponprevailingweather,sizeandtypeof
timberused.
ForcoastalAustralia,stairsthatarewellventilatedshouldreachanEMCofapproximately16%.For
stairsclosetoandoverwater,EMCswillnormallybealittlehigher(18-21%)andfordryinlandareas
considerablylower(10-12%).
Note:Ifseasonedtimberisusedforexternalstairscoastalareas,considerationmustbegiventothe
expansionofthetimberastheEMCrisesfrom12%uptoabout16%,particularlyatjoints–suchas
wheretreadsarehousedintostringers–andmaycausesplitting.
3.4 Joint Priming
Onecoatofawater-repellentpreservativeoranoil-basedprimerisrecommendedtobeappliedto
jointsandhousings,etc,priortofabrication.
3.5 Corrosion Protection of Fasteners
Except in severe
environments, hot
dipped galvanised
fasteners will afford
the necessary
protection from
corrosion.
Havingensuredthatthemaximumservicelifewillbeachievedinthetimbercomponent,itisequally
importanttomatchthiswithnails,screws,boltsandothermetalconnectorsofequivalentservicelife.
Formostsituations(uptoandincludingcloseproximitytoprotectedbays/mildmarine)inexposed
environments,hotdippedgalvanisedfastenerswillaffordthenecessaryprotectionfromcorrosion.
Theservicelifeofhotdippedgalvanisedcoatingswillbeproportionaltotheirmass/areaorthickness
ofgalvanisingandaminimumthicknessof42micronsisrecommendedforaservicelifeofaround
30years.Formoreextremecorrosiveenvironmentsorwhereotherconditionsdictatesuchasin
contactwithmoistCCA/ACQ,etc,treatedtimberorincloseproximitytoswimmingpools(within
600mmofedge),guidancecanbeobtainedfromTable3.3.
Page 15
Table 3.3: Selecting corrosive resistant fasteners.
Application/Environment
FastenerMaterial
Remarks
Chemical,industrialand
marinesurfbeachor
largebays
Grade316stainless
steel
Grade304stainlesssteelmayrequire
additionalprotectivecoatingssuchas
epoxypaints.
Splashzonecloseto
pools
Monelmetal,silicon
bronzeandbrass.Self
drillingscrewstobe
Class4finish.
Monelnailsandscrewsavailable,usually
usedforboatbuilding,areagoodoption
closetopools.Silicabronzenailsaregood
foracidicspeciessuchaswesternred
cedar.
Mildmarine,industrial
andother
Hotdippedgalvanised
ormechanicallyplated,
minimumthickness
42microns.Selfdrilling
screwstoClass3finish.
Wherehotdippedgalvanisedbolts,etc,
areincontactwithmoistCCA/ACQ,etc,
treatedtimber,additionalprotectionusing
plasticsheaths,bituminousorepoxypaints
isrequired.
3.6 Termite Protection
Physicaland/orchemicalbarriersmustbeprovidedtoprotectthestairsandtoensuretermitesdonot
bypassprotectionsystemstoadjacentstructures.Termitebarriersmustbedesignedsothattheycan
bereadilyinspectedandmaintained.
Figure 3.1: Typical termite protection methods.
Page 16
3.7 Slip Resistance
TheBCArequiresstairtreadstohaveaslipresistantfinishorananti-skidstripnearthenoseofthe
tread.Anumberofproprietary‘paints’and‘strips’areavailabletosatisfythisrequirement.
3.8 Sizes
ThesizesandspansforstringersandtreadsforexternalstairsshallbeinaccordancewithTable3.4
and3.5.
Table 3.4: Stair stringers (maximum stair width 1800 mm).
TimberType
Stringer–[Depth(mm)xThickness(mm)](1)
200x38
200x50
250x50
300x50
3600
3900
4500
3100
3400
3700
4300
2600
3000
3300
3600
4200
DouglasFir(NthAmerican) F11
2400
2700
3000
3400
3900
Radiata,Hoop,Slash,etc
F8
2300
2600
2900
3200
3700
H3treatedpine
F5
1600
2200
2400
2800
3400
Species/Group
Grade(2)
Messmate,SpottedGum,
Blackbutt,Kwila,etc
F27
2900
3200
VicAsh,TasOak,Jarrah
F22
2800
SpottedGum,Blackbutt,
Ironbark,Kwila,etc
F17(3)
Maximum Stringer Span
250x38
(mm)(4)
Notes:
1.ThesizeofstringersgivenintheTablearenominalsizes.Designallowanceshavebeenmadefor
dressing(depth10mmmax,thickness5mmmax).Allowancehasalsobeenmadefortrenchingstringersto
accommodatetreads(10mmmax).
2.TimbergradingshouldbeinaccordancewiththeappropriateAustralianStandardformilledproducts(i.e.AS
2792andAS4785).ThestressgradesusedfordesigninaccordancewiththeloadingrequirementsoftheBCA
areasindicatedandcanbedeterminedforAS2082andAS2858asappropriate.
3.TheF17gradeincludedintheTableisintendedforunseasonedhardwood,tobeusedforexternalstairsonly.
4.Stringerspanisthecentrelinelengthofthestringer.
Table 3.5: Stair treads (with open flights).
Stringer span is the
centre line length of
the stringer
TimberType
StairWidth[Treadspan](mm)
750
1000
1500
1800
38
48
58
34
40
50
60
28
36
42
53
65
DouglasFir(NthAmerican) F11
31
40
46
58
70
Radiata,Hoop,Slash,etc
F8
32
42
50
62
73
H3treatedpine
F5
40
46
54
70
N/A
Species/Group
Grade(2)
Messmate,SpottedGum,
Blackbutt,Kwila,etc
F27
26
32
VicAsh,TasOak,Jarrah
F22
28
SpottedGum,Kwila,
Ironbark,etc
F17(3)
1200
Minimum Thickness of Tread
(mm)(1)
Notes:
1.ThethicknessesintheTableareminimumdesignthicknessesandmaynotrepresentcommerciallyavailable
thicknesses.
2.TimbergradingshouldbeinaccordancewiththeappropriateAustralianStandardformilledproducts(ieAS
2792andAS4785).ThestressgradesusedfordesigninaccordancewiththeloadingrequirementsoftheBCA
areasindicatedandcanbedeterminedforAS2082andAS2858asappropriate.
3.TheF17gradeincludedintheTableisintendedforunseasonedhardwood,tobeusedforexternalstairsonly.
Page 17
4
Materials for Internal Stairs –
With and Without Riser Boards
(Open and Closed Stairs)
Interiorstaircaseworkisconsideredtobeaspecialisedsectionofcarpentryandjoinery.
Flightsareoftenpreparedinaworkshopmakingfulluseofavailablemachinesand
equipment.Interiorstairsdifferconsiderablyindesign,fromsimplestraightflights,
commonlyusedindomesticwork,tomoreelaboratestairsconstructedpurposelyasan
attractivefeatureinpublicandcommercialbuildingsandineleganthomes.
Manyinteriorstairsarebuiltfromjoineryqualitytimbercutandseasonedspeciallyforstairs.
Thespecifiedfinishisoftenclearpolish/polyurethane,etc,thereforebothmaterialand
workmanshipshouldbeoftheveryhigheststandard.
4.1 Timber Durability and Species
Hardness may need
to be considered for
uncovered treads.
Forinternaluse,timberofanydurabilityclassissuitable,howeverhardnessmayneedtobe
consideredforuncoveredtreads.
Thespecieschosenwillgenerallydeterminetheoverallcolourofthestairs.Asaguide,Table4.1
indicatestherangeofcoloursthatmaybeexpected.Thesapwoodofmanyhardwoodscanbemuch
lighterthanadjacentheartwoodandsometreads,risers,strings,etc,maycontainbothlightanddark
colours.
The selection
of a hard timber
species ensures
improved resistance
to indentation and
abrasion.
Lyctidsusceptiblesapwoodofsomehardwoodspeciese.g.SpottedGumisrequiredbysomestate
legislation,includingQueenslandandNewSouthWales,tobepreservativetreated.Sometreatments
mayimpartabrownorgreen-greytingetosapwood,whileboronpreservativeisnon-colouring.LOSP
treatmentisalsoused.InthisinstanceaH3treatmentmaybeusedinlieuofH2treatmenttoavoidthe
colourfromdyesoftenusedwithH2LOSPtreatments.
Hardnessindicatesaspeciesresistancetoindentationandabrasion.Damagetotimberstairsmay
occurduetoheavyfoottrafficandinparticular‘stiletto-heel’typeloading.Theselectionofahard
timberspeciesensuresimprovedresistancetoindentationandabrasion.Softtimberspecies,ifused
forsteptreads,canbeexpectedtoindent.
Page 18
Table 4.1: Species guide.
Species
Availability
Colour
Hardness
Blackbutt
Qld, NSW
golden yellow to pale brown
very hard
Brushbox
Qld, NSW
mid brown even colour
hard
Forest Red Gum
Qld, NSW
dark brown or dark red brown
very hard
Ironbark
Qld, NSW, Vic
dark brown or dark red brown
very hard
Jarrah
WA, SA, Vic
dark red brown
hard
Karri
WA, SA
rich reddish-browns to pale pinks
hard
Manna/Ribbon Gum
Vic
pale straw pinks
moderately hard
Messmate
Vic
pale yellow to pale brown
moderately hard
New England Blackbutt
Qld, NSW
straw to pale brown
very hard
Rose Gum
Qld, NSW
straw pink to light red
hard
Southern Blue Gum
NSW
pale brown with some pink
hard
Spotted Gum
Qld, NSW
brown, dark brown, light sapwood
very hard
Stringybark
Qld, NSW, Vic
yellow brown with pink tinge
hard
Sydney Blue Gum
Qld, NSW
pink to dark red
hard
Tallowwood
Qld, NSW
pale straw to light brown
hard
Tasmanian Oak
All states
pale straw to light brown, pink
moderately hard
Victorian Ash
All states
pale straw to light brown, pink
moderately hard
Kwila / Merbau
All states
dark brown
hard
Northern Box
Qld, NSW
mid brown even colour
hard
Cypress
All Eastern states
straw sapwood, dark brown heartwood
moderately hard
Hoop Pine (Araucaria)
All states
straw
soft
Radiata
All states
white to straw
soft
Australian Hardwood
Imported Hardwood
Softwoods
4.2 Timber Grade
Asstairstringers,treadsandposts,etc,arestructuralmembers,theyarerequiredtobestressgraded
andshouldbefreefromanymajorstrength-reducingfeatures.Inaddition,timberforstairconstruction
shouldalsobeseasoned,straightgrainedandfreefromanyimperfectionsthatmaydetractfrom
serviceabilityperformancerequirements.Forinternalstairs,stringers,treadsandpostsshouldbein
accordancewithAS2792,AS4785andthefollowing:
Table 4.2: Timber Grade
Type
Australian
Standard
Grade
Hardwood
AS 2082
Structural Grade 1, seasoned, Appearance grade
Softwood (Caribbean, Radiata,
Slash and imported softwood)
AS 2858
Structural Grade 1, seasoned, Appearance grade
Hoop Pine
AS 2858
F7 seasoned, Appearance grade
Cypress Pine
AS 2858
F7 seasoned, Appearance grade
Note:Inaddition,fingerjointedtimbershallcomplywithAS5068–Timber–‘Fingerjointsinstructuralproducts’
andlaminatedtimbershallcomplywithAS1328–‘Gluedlaminatedstructuraltimber’.
Page 19
4.3 Moisture Content
All components of
internal stairs should
be seasoned.
Unless the staircase
is in a permanently
controlled
environment, the
timber will always
move in response
to changing
environmental
conditions.
Unlessotherwisespecified,allcomponentsofinternalstairsshouldbeseasoned.Seasonedtimberis
usuallysuppliedatanaveragemoisturecontentbetween11%and13%.Whereconditionsaredrieror
inair-conditionedbuildings,moisturecontentoftimbermayvaryfrom7%to12%.Inthesesituations
thetimbermayneedtobeacclimatisedon-sitepriortofabrication.
Timberisanaturalproductthatrespondstochangesinweatherconditions.Duringperiodsofhigh
humiditytimberwillabsorbmoisturefromtheaircausingittoswellorincreaseinsize.Conversely,
duringdriertimeswhenhumiditiesarelow,timberwillshrink,reducinginsize.Unlessthestaircase
isinapermanentlycontrolledenvironment,thetimberwillalwaysmoveinresponsetochanging
environmentalconditions.Gapsbetweentreadsandhousings,treadsandriserboards,etc,can
beexpectedasthetimberaccommodatesseasonalchanges.Additionalshrinkagetothatnormally
expectedmayalsooccurwhenastaircaseisexposedtoheatsourcessuchasfireplacesorsunlight
throughlargedoorsorwindows.
Asmallamountofnoisecanbeexpectedfrommosttimberstairswhenwalkedon.Noisescanoccur
frommovementoftreadsinhousings,treadsagainstariserboardorfromtreads,risers,etc,moving
onnails.
4.4 Termite Protection
BecausetermiteprotectionofthehouseisrequiredundertheBCAinareaswheretermitesare
present,thereisnospecificrequirementforindividualtermiteprotectionofinternalstairsunlessthe
onlymethodoftermiteprotectionforthehouseistheuseoftermiteresistantmaterial.Inthiscase,
termiteresistanttimbershouldbealsochosenforthestairs.RefertoAS3660.1.
4.5 Slip Resistance
TheBCAperformancerequirementsstatethatstairtreadsornearthenosingshallbeslipresistant.A
numberofproprietary‘paints’and‘strips’areavailabletosatisfythisrequirement.
4.6 Span Tables
For feature stairs,
30 mm is suggested
as a minimum
thickness for all
treads, irrespective
of stair width.
Thesizesandspansforstringersforinternalstairswithandwithoutriserboardsshallbethesameas
forexternalstairs(Table3.4).
Note:Forinternalstringersandtreads,seasonedtimberonlyshouldbeused.
Thesizeoftreadsforinternalstairswithoutriserboardsshallbethesameasforexternalstairs(Table3.5).
Thesizeoftreadsforinternalstairsfullysupportedbyriserboardsshouldbeaminimumof19mm
thickforstairsupto1000mmwideand30mmfor1000-1800mmwide.
Note:Forfeaturestairs,30mmissuggestedasaminimumthicknessforalltreadsirrespective
ofstairwidth.
Page 20
5
Stair Construction Procedure
Beforecommencingthemarkoutforstairs,thecalculationsforgoingandrisecanbe
determined(seeAppendixB).Fromthese,makeamargintemplateandpitchboardorsetup
asteelsquarewithclampsreadytomarkoutstrings.
5.1 Margin Template and Pitch Board
5.1.1 Pitch Board
Usingapieceofplywood,masonite(suchasplyormasonitebracing)orsimilar,markoutandcuta
pitchboardusingthegoingandrisecalculated(Figure5.1).
Figure 5.1: Pitch board.
5.1.2 Margin Template
Beforethemargintemplatecanbeprepared,thewidthofthemargin(X)mustbeknown.Themethod
offindingthemarginwidthisasfollows(Figure5.2):
i) Placethepitchboardonthestring,withthehypotenuseofthepitchboardflushwiththestring
edge.
ii) Useoff-cutpiecesoftreadandriserboardtodrawintothistrialposition,thetread,andalsoriser
andwedgesifused.
Note:Forstairswithriserboards,placetheoff-cutpieceoftreadupsidedownandalignthefrontedge
oftheriserhousingwiththeedgeofthestringasshowninFigure5.2.
iii)Drawalinejustbelowthetread(orwedgesifused)andparalleltothestringedge.
iv)ThedistanceXisthewidthrequiredforthemargintemplate.
Figure 5.2: Determination of margin line.
Page 21
Asuitablemargintemplatecannowbeconstructedusingoff-cutsfrommouldings(Figure5.3).
Figure 5.3: Margin template.
Note:Thismethodmaybefollowedtodeterminethewidthoftimberrequiredforstrings.
5.1.3 Steel Square
Anylargemetalsquaresuchasaroofingsquarecanbeusedasanalternativetoapitchboardand
margintemplate,butanunderstandingoftheproceedingmethodsisnecessarytobeabletosetthe
squareupcorrectly.
Usethesteelsquareandmetalstopstofindthemarginlineasper5.1.2andFigure5.4.
Figure 5.4: Using steel square to determine margin line.
Page 22
Resetmetalstopsonsteelsquareincorporatingmarginline(Figure5.5).
Figure 5.5: Using steel square as combined margin template and pitch board.
5.2 Marking Out Strings
A good practice
is to always mark
out the same hand
string first.
Whenmarkingoutstairstringsaroutinewillpreventmistakesandthewastingoftime.Agoodpractice
istoalwaysmarkoutthesamehandstringfirst.
Thispracticeshoulddevelopaclearerrecognitionofthecorrectpositioningofmembers.
Note:Theacceptedpracticeofmarkingrighthandorlefthandstringfirstvariesfromstatetostate
andregiontoregion.Theprocedurebelowisbaseduponmarkingthelefthandstringfirst.
Step1
Thestringhandingisdeterminedbylookinguptheflightorattheflightfromthebottom.Thestringto
theleftistheleft-handstring.Thetwostringsinoneflightareapair;oneleftandoneright-handstring.
Step2
Placestringsinpairsonsawtoolsandmarkinsidefaceandtopedges–considertheeffectofany
springorbow.Forshortflightswithonestepbolt,placethehollowofthebowinandforlongerflights
withtwostepboltsplacethehollowofthebowout.Stringedgesshouldberoundsup(springup)
(Figure5.6).
Figure 5.6: Pairing strings.
Page 23
Step3
Havingpairedthestringsbyfaceandedgemarkingthem,commencemarkingouttheleft-hand
string.Drawthemarginlinewiththemargintemplate,thenusingthepitchboard,startatthebottomof
theflightandmarkthepositionofthefloor,thefirstriseandgoing(Figure5.6).
Beforecontinuingtomarkthestring,apairofwingdividerssettodistance‘H’inFigure5.6shouldbe
usedtomarkalongthemarginline,thenumberofremainingstepsintheflight.Thisactionwillserveto
equalisesuccessivemarkingwiththepitchboardandavoidpossiblelossorgain.
Step4
Aftercompletingthemarkingofthefirststring,placebothstringstogetherasapairandsquarethe
pointsonthemarginlineacrossfromonetotheother.Thismethodwillpreventlengthdifferences
betweenthetwostrings(Figure5.7andFigure5.8).
Figure 5.7: Marking out left string.
Page 24
Figure 5.8: Marking out right string.
Gauge depth =
tread thickness
minus housing depth.
Step5
Whensatisfiedthattheinitialmarking,asinFigure5.8,iscorrect,proceedtocompletethemarking
forthehousings.Numbereachtreadandriser.Selecttreadsandrisers(ifused)innumericalorder
andscribethicknessandshapeontostrings.Usingagauge,markthehousingdepth(15mm)onto
thebackedgeofthestring.Alwaysgaugefromtheoutsideofthetread.Thiswillaccountforany
differencesinthicknessofthetreadparticularlywhenusingunseasonedroughsawntimber.
Note:Gaugedepth=treadthicknessminushousingdepth(Figure5.9).
Figure 5.9: String marked out for housings.
Page 25
5.3 Housing Strings
Theactualhousingoutofthestringscanbeachievedbyseveraldifferentmethods.
Thesimplestmethod,suitableforexternalstairsusingroughsawntimber,istouseapowersawtocut
alongthelinesmarkedforthetreads.
Setthedepthofthesawtothehousingdepth,15mm.Runthesawanumberoftimesbetweenthese
cutsandthenuseamallet/hammerandchiseltoremovetheremainingmaterial(Figures5.10
and5.11).
Figure 5.10: Housing strings.
Arouterwithatemplateguidefittedcanbeusedandispossiblythebestandneatestmethodfor
housingstringsonsite(Figure5.11).
Figure 5.11: Housing string practices.
Page 26
5.4 String End Joints
The joint used will
depend on the type
of stair and the
structure it is being
attached to.
Themarkingfortheappropriatejointsattheendsofthestringscannowalsobecompleted.
Thejointusedwilldependonthetypeofstairandthestructuretowhichitisbeingattached.For
example,forasimpleexternalflightthestringisgenerallynotchedoverthebearer(orlandingplate)or
tenonedintoanewelpostatthetopandbirdsmouthedoverthebottomtread(Figure5.12).
Figure 5.12: Supporting stringers.
Page 27
Wherenewelpostsareused,tenonsarecutontheendofthestringsandthenewelsmorticedtosuit
(Figures5.13and5.14).
Stringers lift
and separate!
Figure 5.13: Tenons at ends of stringer.
Insomecases(usuallyinternalstairsonly)thefacesofthefirstandlastrisersshouldbeinthecentre
ofthenewelposts.
Figure 5.14: Fixing strings to landing newels.
Page 28
Cuttreadsandriserstolengthandnumberfrombottomtotop–makeallowanceforextralengthon
bottomtreadifspecified–removearrises(edges)asrequired.Ifrisersarebeingusedandthetreads
arenotpre-grooved,groovethetreadsforrisers.
5.5 Step Bolts (Tie Bolts)
Unless the stairs fit
between two walls,
step bolts will be
needed.
Unlessthestairsfitbetweentwowalls,stepboltswillbeneeded.Borethestringerstotake12mm
stepboltsatamaximumof1350mmcentres.Positionthemtocoincideascloselyaspossibletothe
centrelineofthestringerandundersideofatread,leavingagapbetweentheundersideofthetread
andthebolt(Figure5.15).
Figure 5.15: Position of step bolt.
Page 29
5.6 Assembly
Beforestartingtoassembleexternalstairs,primepaintoroilalljointsandsurfacesthatwillbe
concealed,enclosedorunabletobepaintedafterassemblyincludingthenewels,bearerorjoist
wherethestairsaretobefixed.
Apracticalwaytofindthepositionofthestumpsunderthebottomtread–ratherthanbycalculation–
istotakeoneofthecutstrings,placeitinpositionandthenlevelthetreadhousingswithaspiritlevel
(Figure5.16).Makeanyadjustmentsnecessarybypackingunderthelowerendofthestring.Usepilot
pegstolocatethecentreandtopofthestumpsasshowninFigure5.16.
Figure 5.16: Finding position of stumps.
When using
unseasoned timber
it is good practice
to temporarily nail
treads and risers.
After allowing
as much time
as possible for
shrinkage to take
place, withdraw
the nails, close the
joints then complete
nailing and punching.
Fittopandbottom(orsecondbottom)treadsand,forflightswithrisers,thebottomriseronlyto
stringsandnailtogether.Nailtogetherwiththree100x4.5mmnailsperjoint.Pre-drillifnecessary.For
externalstairs,allnailsusedshouldbehotdippedgalvanised.
Fitandlooselytightenstepboltsifrequired.
Liftthispartlyassembledjobintopositionfitthestringerstothenewels,bearersorjoistsasrequired.
Fittheremainderofthetreadsandriserswhereusedandnailwiththreenailsperhousing.
Tightenthestepbolts.
Note:Whenusingunseasonedtimberitisgoodpracticetotemporarilynailtreadsandrisers.After
allowingasmuchtimeaspossibleforshrinkagetotakeplace,withdrawthenails,closethejointsthen
completenailingandpunching.
Page 30
6
Balustrades and Handrails
ForallClassesofbuilding,balustradesandhandrailsarerequiredtocomplywiththe
BuildingCodeofAustralia(BCA).TheBCArequirementsincludedesignandconstruction
provisionsforthevariouscomponentsincludingcompliancewiththeloadingprovisionsof
AS1170.1‘StructuraldesignactionsPart1:Permanent,imposedandotheractions’.
Forbalustradesandhandrails,theBCAisprimarilyconcernedwiththesafetyofbuilding
usersandoccupants.Designandconstructionmustthereforetakeintoconsideration
boththestrengthanddurabilityofmaterialsandcomponentsaswellasthe‘geometric’
constraints.
SeeSection2forguidanceonBCArequirements,includingthoseforwherethefloor
surfaceismorethan4mabovethefloor/groundbelow.
6.1 Loads
Balustrades and
railings must resist
0.9 kN inward,
outward and
downward load at
any point.
AS1170.1requiresbalustradesandrailingstogetherwithmembersandconnectionswhichprovide
structuralsupporttobeabletoresistthefollowingfactoredlimitstateloads–0.9kNinward,
outwardanddownwardloadatanypoint.Italsorequiresbalustradesandhandrailstobeableto
resistafactoredhorizontalorverticalloadof0.53kN/mforallareaswithinorservicingexclusively
onedwellingincludingstairsandlandingsexcludingexternalbalconies,and1.13kN/mforexternal
balconiesindomesticandotherresidentialbuildings.Infill,includingbalusters,shouldbecapableof
resisting0.75kNinanydirection.
6.2 Materials
6.2.1 Durability
Inweather-exposed,above-groundapplicationsorwheresubjectedtoothersourcesofmoisture,
stringers,treads,risers,handrails,posts,newels,balustersandinfillshouldbe:
Use Above Ground
Durability Class 1
or H3 treated
pine species for
weather exposed
applications.
(i)Warm,humidtropicalnorthernclimates:eitherAboveGroundDurabilityClass1specieswithany
sapwoodpresenttreatedtoH3(orhigher)orH3(orhigher)treatedsoftwoodsuchasSlash,Hoop
orRadiataPine.PreservativetreatmentshallcomplywithAS1604.
Page 31
(ii)Temperate,coolsouthernclimates:eitherAboveGroundDurabilityClass2orbetterspecies
withanysapwoodpresenttreatedtoH3(orhigher)orH3(orhigher)treatedsoftwoodsuchas
Slash,HooporRadiataPine.PreservativetreatmentshallcomplywithAS1604.Lowerdurability
speciescanalsobeutilisedalthoughcarefuldetailingofjointswithapplicationandmaintenanceof
protectivecoatings(paints,stains)and/orinstallationofprotectiveshielding(e.g.malthoid)ontop
ofexposedtimberedgesneedstobeutilised.
SuitablespeciesarelistedinTable3.1.
Careshouldbetakentoensurethatwaterisnottrappedbyendgrainabuttinghorizontalsurfaces
(i.e.slopeendgraincutstopandbottomofbalustersandbottomrailswherebalustersabut,provide
drainageholes,etc).
Forinternaluse,timberofanydurabilityclassissuitable.
6.2.2 Timber Grade
Thetimbershouldbefreefromanymajorstrength-reducingfeatures,bestraightgrainedandbein
accordancewiththefollowing:
Table 6.1: Timber grade.
Type
Australian
Standard
Description
Grade
Hardwood
(IncludingMeranti)
AS2796
Sawnandmilled
products
Clearorselectgrade
Softwood(Including
importedsoftwood)
AS1786
Joinerytimbermilled
fromAustraliangrown
conifers
Cleargrade
Inaddition,fingerjointedtimbershallcomplywithAS5068–Timber–‘Fingerjointsinstructural
products’andlaminatedtimbershallcomplywithAS1328–‘Gluedlaminatedstructuraltimber’.
Notes:
1.MaterialsusedinaccordancewiththefollowinginformationmustsatisfyrelevantAustralianStandardsandhave
therelevantminimummechanicalpropertiesincludingthefollowing:
Hardwood –StressGradeF22,(characteristicbendingstrengthf’b=65MPa,ModulusofelasticityE=16,000
MPa)andJointGroupJD2.Examples–SpottedGum,Ironbark,Blackbutt,KwilaandMerbau.
Meranti and Australian Softwood – (characteristicbendingstrengthf’b=25MPa,ModulusofelasticityE=
9100MPa)andJointGroupJD4.Examples–Radiata,HoopandSlashPineandMeranti.
Imported Softwood – (characteristicbendingstrengthf’b=25MPa,ModulusofelasticityE=6,900MPa)and
JointGroupJD4.Examples–NewZealandRadiataPine.
2.Unlesscertifiedbythesuppliertoidentifythatitis‘AustralianGrown’softwood,handrail(balustrades)spans
shallbedeterminedfromthe‘ImportedSoftwood’spansgiveninTable6.2.
6.3 Member Sizes
6.3.1 Handrails
HandrailsizesandspansshallbeinaccordancewithTable6.2.
6.3.2 Posts/Newel Posts
PostsandnewelpostsshallhaveaminimumstressgradeofF5.Wheresupportinghandrails/
balustradesonly,theminimumsizeofpostsandnewelpostsshallbe80x80mm(maximumpost
spacing3600mmandheightof2700mm).Wheresupportingroofandorfloorloads,refertoAS1684
todetermineminimumsize,butshallbenotlessthan80x80mm.
6.3.3 Infill/Balusters
Theminimumsizeofinfill/balustersshouldbeasfollows:
Hardwood–19x19mmor21mmdiameter
Softwood–19x42,32x32or25mmdiameter.
Page 32
Table 6.2: Handrail sizes.
Timber
Hardwood
Merantiand
Australian
Grown
Softwood
Softwood
Imported
orUnknown
Origin
Size/Description MaximumspanofHandrail(mm)
(mmxmm)
Withinorexclusively
OtherareasinResidential
servicingoneDwelling
Buildings(includingexternal
(excludingexternalbalconies) balconies)
65x65(profiled)
3000
3000
3000
3000
42x65(profiled)
2200
2700
2200
2700
42x85(profiled)
2400
3400
2400
3400
35x70
2100
3000
2100
3000
35x90
2200
3600
2200
3600
35x120
2400
3600
2400
3600
45x70
2500
3200
2500
3200
45x90
2700
3600
2700
3600
45x120
2900
3600
2900
3600
70x70
3500
3500
3500
3500
70x90
3600
3600
3600
3600
65x65(profiled)
2700
2700
2200
2200
42x65(profiled)
1400
2000
1400
1800
42x85(profiled)
1800
3000
1700
2400
35x70
1200
2400
1200
2000
35x90
1600
3200
1600
2500
35x120
2100
3600
1800
3400
45x70
2000
2800
1800
2200
45x90
2400
3400
2000
2900
45x120
2600
3600
2400
3600
70x70
3200
3200
2800
2800
70x90
3400
3600
3200
3600
65x65(profiled)
2400
2400
2200
2200
42x65(profiled)
1400
2000
1400
1800
42x85(profiled)
1800
2700
1700
2400
35x70
1200
2400
1200
2000
35x90
1600
2900
1600
2500
35x120
1900
3600
1800
3400
45x70
2000
2600
1800
2200
45x90
2200
3100
2000
2900
45x120
2300
3600
2300
3600
70x70
2900
2900
2800
2800
70x90
3000
3400
3000
3400
Notes:
1.Handrailswithnointermediateverticalsupportsmaybeusedonflatoronedge(Figure6.2).
2.Handrailswithintermediateverticalsupportsshallbeinstalledonflatwithintermediateverticalsupports
spacednotgreaterthantheallowablespansgivenforthesamehandrailwithnointermediateverticalsupports
(Figure6.2andNote:ForTypeEconnectionsrefertomanufacturers’specifications).
3.Figure6.4.
4.Whereatoprail(minimumsize42x65)iswithin150mmofthemainhandrailandisrigidlyfixedtoit(using
blocks,orbalustersordowelsthatpassthroughthemidrailandarefixedtothetoprail)atleastonceatmid
span,theallowablespanofthehandrailmaybeincreasedby300mm.
5.Handrailspanshavebeenlimitedto3600mmmaximum.
6.Profiledsectionstypicallyincludebreadloaf,ladieswaistandcolonialprofiles.
7.Thereisnonegativetolerancepermittedonthebreadthordepthdimensions(overalloutsidedimensionsof
profiledshapes)givenintheaboveTable.
Page 33
Figure 6.1: Intermediate vertical support.
Figure 6.2: Handrails – on flat and on edge.
Page 34
6.4 Connections
6.4.1 Posts
Postsandnewelpostsshouldbeconnectedtofloorframing/stringersinaccordancewithFigure6.3.
Figure 6.3 (a): Posts and newel posts.
Figure 6.3(b)
Page 35
Figure 6.3(c)
6.4.2 Handrails
Table 6.3: Loads on handrails.
Span
Type
Handrail
Span
(mm)
HandrailConnectionLoads(kN)
Withinor
exclusively
servicingone
Dwelling
(exc.external
balconies)
OtherAreas
inResidential
Buildings
(inc.external
balconies)
Single
Span
1800
0.90
1.0
2100
0.90
1.2
2400
0.90
1.4
2700
0.90
1.5
3000
0.90
1.7
3300
0.99
1.9
3600
1.1
2.0
Continuous 1800
Span
2100
1.1
2.0
1.3
2.4
2400
1.4
2.7
2700
1.6
3.0
3000
1.8
3.4
3300
2.0
3.7
3600
2.2
4.1
ExampleOfDetermining
HandrailConnection
TheshadedareasinTables
6-3and6-4provideaguideto
theselectionofanappropriate
connectionforacontinuousspan
softwoodhandrailspan
of2400mm.
Step1.FromTable6-3determine
theloadonthehandrail=2.7kN
Step2FromTable6.4andFigure
6.4,determineaconnectionwith
thecapacitytoresist2.7kN.
Step3Acceptablesolutions
determinedfromTable6-4are:TypeAconnection,1M10boltor
TypeBconnection,2No10
screwsor
TypeDconnection,2No10
screwsperlegofbracket.
Page 36
Table 6.4: Capacity of handrail connections.
Timber
Hardwood
(JD2)
Softwood
andMeranti
(JD4)
CapacityofConnections(kN)
TypeA
TypeB
TypeC
No.
Bolts
No.
ScrewSize
Screws (Type17)
Screws
BoltSize
(Cuphead)
M10
M12
1
13
14
2
26
1
2
TypeD
Nails
2/Screws
perlegof
bracket
No10 No14 2/
2/
2/3.15 2/3.75 No10
No10 No14 dia
dia
No14
1
3.4
4.4
28
2
6.8
8.8
8
9
1
2.0
2.6
16
18
2
4.0
5.2
1.9
2.3
1.6
1.8
4.9
7.6
1.1
1.3
0.9
1.0
2.8
4.3
Notes:
1.ForTypeAconnectionsquantitiesaregivenforbothfacemountedhandrails(worstcase)andhandrailsflush
fullorhalfcheckedtopost.
2.ForTypeBconnections,minimumscrewpenetrationintopostis38mmandhandrailsflushfullorhalfchecked
topost.
3.ForTypeCconnectionstheminimumscrewpenetrationintopostis40mmandtheminimumnailpenetration
intopostis38mm.
4.Midrailsandbottomrailsshallbefixedwithaminimumof2/3.15dia.skewnails.
Figure 6.4: Handrail connections.
Note:ForTypeEconnectionsrefertomanufacturers’specifications.
Page 37
7
Application and
maintenance of
finishes should
not be considered
as a substitute for
ensuring that the
inherent durability of
the underlying timber
is appropriate to the
service life required.
Weathering, Finishes and
Maintenance
Thelong-termdurabilityandvisualappealandaestheticsofbothinternalandexternalstairs
andbalustradescanbegreatlyenhancedbyapplicationandmaintenanceofsuitableand
appropriatefinishes.
7.1 External Stairs and Balustrades
Otherthanforaestheticreasons,themainobjectiveofapplyingandmaintainingfinishes(paintsand
stains)ontimberusedinexternalapplicationsistominimisetheeffectsofweatheringandtherefore
tomaximisetheservicelifeofthetimber.Exposuretosunandrainleadstowettinganddryingand
subsequentchecking,splittinganddistortion.
Applicationandmaintenanceoffinishesshouldnotbeconsideredasasubstituteforensuringthatthe
inherentdurability(naturalorbytreatment)oftheunderlyingtimberisappropriatetotheservicelife
requiredfortheapplicablehazardlevel.
7.1.1 Unprimed Timber
Nailholesshouldbestoppedwithanexteriorgradewoodfiller.Dirtoranyloosematerialshouldbe
removedpriortocoating.Allsurfaces,endsandjointsshouldbeprimedpriortoassemblywitha
qualitysolvent-basedalkydprimerorstain,inaccordancewiththemanufacturers’recommendations.
Finaltopcoatsofexteriorpaintorstainshouldthenbeappliedinaccordancewiththemanufacturers’
recommendations.
7.1.2 Pre-primed LOSP Treated Timber
Pinkpre-coatedhandrailandbalustradecomponentsshouldbesandedbackanddustedoffto
removeanylooseorpowderycoatingspriortofinishing.Nailholesshouldbestoppedwithanexterior
gradewoodfiller.
Allsurfaces,endsandjointsshouldbeprimedpriortoassemblywithaquality,solventbased
alkydprimer.Whentheprimerhasdriedinaccordancewiththemanufacturersrecommendations,
applytwofullcoatsofpremium100%acrylicexteriortopcoatinaccordancewithmanufacturers
recommendations.
Darkcolouredpaintsandstainsshouldbeavoidedastheyheattimbertoelevatedtemperatures
whichcausegreaterlossofmoistureandsubsequentshrinkageandchecking.Decayisalsomore
activeathighertemperatures.
7.2 Internal Stairs
Thefinishforinteriorstairsisoftenclearpolish,lacquer,etc,thereforebothmaterialandworkmanship
shouldbeoftheveryhigheststandard.
Ifclearfinishesaretobeused,extracareshouldbetakenwhenmarkingoutthatpencilmarks,etc,
arekeptlightanddonotleaveanindentationinthetimber.
Anynailsshouldbepunchedaminimumof3mmbelowthesurfaceoftheboards.Thepunchednail
holescanthenbefilledwitheitheroilornon-oilbasedfiller.Oil-basedfillersmaybleedoilintothe
timberandaffectthecolourofthewoodsurroundingthenailhole,ormaynotbecompatiblewith
variouscoatingproducts.
Thecolourofthefillershouldbecarefullyselectedtominimiseanyvisualimpactofthefiller.Many
oftheseproductsaresoldincolourspre-matchedtospecificspecies.Generallyallfillersareslightly
darkerandthisallowsfortheboardstodeepenincolourfollowingfinishingandUVexposure.
Page 38
Table 7.1: Clear finishes for stairs.
OilbasedAlkyds
Tung
oil
Generally all fillers
are slightly darker
and this allows for
the boards to deepen
in colour following
finishing and UV
exposure.
Linseed
oilbased
varnishes
Composite
Solventbased
Oil
modified
Urethanes
(OMU)
Waterbased
Urethane 2pack
Singlepack
oil/alkyd
‘Tung
Polyurethane Polyurethane
oil’
(moisture
cured)
Lesswearresistantfinishrequiringmore
Highwearresistantfinish
frequentmaintenance
Polyurethane
6-24hourdryingbysolventevaporation
1-4hourdryingbychemical
reaction
2-4hourdryingbyevaporation
andreaction
Sometolerancetowaxes
Nottoleranttowaxes
Nottoleranttowaxes
Moderatetostrongodouronapplication
Strongodouronapplication
Minimalodouronapplication
Avoidinhalationandcontact
Avoidinhalationandcontact Avoidinhalingcross-linkersand
hardeners
Matttoglosslevels
Matttoveryhighglosslevels Matttoglosslevels
Darkenswithage
Darkenswithage
Lessdarkeningwithage
Generallyreadyforuse2-5daysfrom
completion*
Generallyreadyforuse2-3
daysfromcompletion*
Generallyreadyforuse2days
fromcompletion*
Acrylic
Singleand
twopack
Moderatetohighwearresistant
finishes
*Varieswithweatherconditionsandproduct.Fullcuringmaytakealongertime.
Page 39
A
Appendix A – Glossary
RefertoFiguresA1andA2forillustrationsofmostterms.
A1 General
Stair,Stairs:Anassemblyofstepsorflightsincludingallnecessarylandings,balustrades,etc,
constructedfortheeasy,convenientandsafepassagefromonefloortoanother.
Staircase:Meansthesameasstairorstairsbutincludesthatpartofthebuildingenclosingthestairs.
Stairway:Generallymeansthespaceprovidedforthestairsincludingtheopeninginthefloor.
Stairwellorwellhole(theopeningintheupperfloorforthestairs):Theverticalspaceseendown
betweentheouterstringsofstairshavingoneormorereturnflights.
Step:Acombinationofatreadandriser.Oneunitinstairs.
Flight:Thatportionofstairsthathasacontinuousseriesofrisers,includingrisersofwinders,not
interruptedbyalandingorfloor.
Riser:Theheightbetweenconsecutivetreads(topoftreadtotopofnexttread).
Totalrise(Riseofflight,Riseofstair):Theverticalmeasurementfromthetopofthefirst(lowest)floor
orgroundtothetopofthelast(highest)floorregardlessofthenumberofflightsinthestair.
Going:Thehorizontaldimensionfromthefronttothebackofatreadlessanyoverhangfromthenext
treadabove(frontofariserlinetofrontofthenextriserline).
Totalgoing(Goingofflight,Goingofstair):Thehorizontaldistancemeasuredinonedirectionover
oneormoreflights,includingintermediatelandings,andtakenfromthefrontedgeofthefirstor
bottomtreadinthelowerflighttothefrontedgeofthefloororlandingatthetopofthestairs.Again,if
risersarefitted,thehorizontalmeasurementfromthefaceofthefirstorlowestrisertothefaceofthe
lastortopriserinthestairs.
Stairwidth:Theunobstructedwidthmeasurementbetweentheinsidefaceofthehandrails,orthe
stringersiftherearenohandrails.(Note:TheBCAdoesnotprescribeaminimumwidthforstairs.)
A2 Members in a Staircase
String,stringersorstringboards(sidesofthestair):Theinclinedmembersinastairwhichusually
actasabeamandwhichspanfrombottomtotopofeachflightandsupporttheendsofthetreads
andrisers.
Treads:Thehorizontalmembersinaflightonwhichthefootisplacedwhenascendingordescending
theflight.
Stepbolt(tiebolt):Ahorizontalthreadedrodcommonlyusedtotiethestringerstogetherinexternal
openflightstairs.
Riserboards:Theverticalboardsfixedbetweensuccessivetreads.Theirpurposeistoclosethe
openingsbetweenandhelptosupportandstiffenthetreads.
Nosing:Thefrontedgeofatreadthatmayormaynotbeprojectingovertheriser.Itisusually
rounded.
Scotia:Asmallmouldinghavingaconcaveface.Itmaybefittedagainstthetopfaceoftheriserand
underthenosingofsomeboxedstairs(rarelyusedthesedays).
Newels:Thepostsatthetopandbottomofflightstowhichstringsandbalustradesarefixed.Newels
mayalsosupportlandingsandformpartofbalustrades.
Landing:Anarea(floororrestingplace)atthetoporbottomofaflightorbetweentwoflights.
Page 40
A3 Members in a Balustrade
Balustrade:Acopingorhandrailwithsupportingbalusters.Anopenbalustradecomprisesbalusters,
handrail,bottomrailorstringcapping.Asolidbalustrademayhavepanelling,glassorperspex
insteadofbalusters.
Balusters:Verticalmemberswhichinfillthespacebeneathandsupportthehandrail.
Handrail:Thesupportforthehandsatthesideofthestairsorlandings/decks,etc.
Bottomrail(string):Thelowesthorizontalmemberinabalustradethatsupportsthebalusters.
Midrail:Arailparalleltoandbetweenahandrailandbottomrailorstring.
Handrailsupport:Averticalpieceoftimberfixedbetweenthestringandhandrailtostrengthenthe
handrailandmidrail.
Stringcapping:Atimbermemberfixedtothetopedgeofthestringtoreceivethebalusters.
Falsetenon:Apieceofhardwoodinsertedintoamorticeinthenewelpostandamorticeorgroovein
thehandrailandnailedinposition.Thistypeofjointallowseasyassemblyofrailstonewelposts.
A4 Construction Terms
Goingrod:Arodonwhichismarkedthegoingofeachstep,thegoingandthepositionofthe
landingsi.e.thelengthoftheflight.
Heightrod:(storeyrod)Arodonwhichismarkedtheriseofflightsandtheriseofeachtread.
Pitchboard:Atriangulartemplate,usuallymadeofgalvanisedironorplywood,oneofitssidesequal
tothegoing,asideatrightanglestothegoingequaltotheriser.(Aroofsquareplusfencewouldbe
analternative).
Marginline:Alinemarkedontheinsidefaceofthestring38to50mmparalleltothetopedge.From
thislinethehousingsareusuallypositioned.
Margintemplate:Agaugeusedagainstthetopedgeofthestringtomarkthemarginline.Itisused
inconjunctionwiththepitchboardtomarkoutthelocationsofthetreadsandrisers.
Lineofnosingornosingline:Alinetouchingthefronttopedgeofallthetreads,landingand/or
floor.Itisaseparatelinetothemarginlinewhenthenosingofthetreadprojectsinfrontofthefaceof
theriserboard.
Landingjoist:Abeamthatrunsbetweenlandingtrimmerstosupporttheflooringordecking.
Landingtrimmer:Abeamatthefrontofalandingwhichsupportsthelandingjoists,newelpostsand
topofeachflight.
Undercarriageorcarriagepiece:Anadditionalheavytimbersupportsystemfittedbeneathwide
stairs.
Spandrelframing:Verticalframingandpanelswhichmayinfillthetriangularspacebetweenthe
undersideoftheouterstringandthefloor.
Stairsoffit:Plywoodorplasterboardlining,etc,usedtocovertheundersideofthestairs.
Page 41
Figure A1: Terminology – Stairs and landings.
Figure A2: Terminology – Balastrades and handrails.
Page 42
B
Appendix B – Stair Calculations
B1 General
Toobtainthefactsrequiredtobeabletosetout,ordermaterialandbuildstairs,somedetailed
measuringandcalculatingisnecessary.
Tosuitthestockwidthofmaterialavailable,stairsareusuallybuiltwitha240to250mmgoinganda
risefrom160to180mm.SeeSection2.
Therisecanonlybecalculatedfromthetotalrise.Thetotalriseshouldbemeasuredwithatapefrom
thelowerfloorleveltotheupperfloorlevel.Thetotalrisefoundmaynowbeappliedtoacalculation
(seeB2).
Todeterminethetotalriseforexternalstairswherethegroundisnotlevelandeitherslopestowardor
awayfromthebuilding,refertoAppendixC.
Thefollowingproblemsareexamplesofhowtofindtheunknownsuchasrise,going,numberofrises
andgoingsfromtheknownfacts,i.e.totalriseandasinsomecasestherestrictedspaceavailablefor
thetotalgoingofastairaswellasheadroom.
Page 43
B2 Example 1
Straightflightofexternalstairswiththetotalrise=2665mm.Thetotalgoingisunrestrictedandthe
proposedtreadswillbe250x38mmunseasonedhardwood.
Calculaterise:
Dividetheriseoftheflightbyatrialriseof170mm(forexternalstairstheriseisgenerallyabout180
mmandforinternalabout175mm)toobtaintheapproximatenumberofrises.
2665÷170mm=15.67.Thisgives15risersat170mmandoneat115mm.(2665–(170x15))
Althoughitisallowabletohaveadifferentriseatthebottomofexternalstairs,thisshouldbeavoided
wherepossible,soroundofftothenearestwholenumber=15.
Rise=(2665÷15)=177mm
Note:Theresultoftheabovecalculationis177.66butwecanrounddownupordowntothenearest
wholenumber.Ifroundeddown,theresultisthattheriseoftheflightwillbe10mmlessthanthetotal
riseof2665.However,whenthestairsarebuilttothisandputinplace,thetreadswillhaveaslight
slopetothefront,inthiscasejustlessthan1mmpertread.Thisisacceptableandforexternalstairs
canassistwatertorunoffthetreads.
Calculategoing:
Thetreadwidthis250mmsothiscanbeourgoing.(Whereanoverhangonthetreadisprovided,
thegoingwillneedtobeadjustedaccordingly.)
Calculatetotalgoing:
Thereisalwaysonelesstreadthanthenumberofriserssothegoingoftheflightwillbe:
250mm(thetreadwidth)x14(15risers-1)=3500mm.
CheckresultswithBCArequirements:
Rise:177mmiswithintherangeof115to190mm.
Going:250mmiswithintherangeof240to355mm.
Sloperelationship:177x2+250(risemultipliedby2+thegoing)=604iswithintherangeof
700to550mm.
AnotherrequirementoftheBCA,thata125mmspheremustnotpassthroughtreads,shouldalso
bechecked.Therise,177mm,lessthetreadthickness,38mm,mustbelessthan125mm.
177–38=137.Thisismorethan125andsoisnotwithintheBCArequirement.
Acleatcouldbefixedunderthetreadabovetocloseupthespacetocomply.
Figure B1
Page 44
B3 Example 2
Aninternalstairinastraightflighthasatotalriseof2500andthetotalgoingoftheflightis3200.
Inthisinstance,wehaveasingleflightwithboththegoingandtheriseoftheflightgiven.The
procedureismuchthesameasinthelastproblem.
Calculaterise:
Dividetheriseoftheflightbyatrialriseof170mmtoobtaintheapproximatenumberofrises:
2500÷170mm=14.70.Thisgives14risersat170mmandoneat120mm.(2500–(170x14))
Itisnotallowabletohaveadifferentriseatthebottomofinternalstairssoroundofftothenearest
wholenumber=14.
Rise=2500÷14=178mm
Note:Theresultoftheabovecalculationis178.57butwecanrounddowntothenearestwhole
number.Theresultisthattheriseoftheflightwillbe8mmlessthanthetotalriseof2500.However
whenthestairsarebuilttothisandputinplace,thetreadswillhaveaslightslopetothefront,inthis
caseabout0.5mmpertread.Thisisacceptable.Wheretheslopetothefrontwouldexceedthis,
roundingupwillbeabetteralternativeastreadswillthen‘slopein’andbesafer.
Calculategoing:
Inthisexample,thetotalgoingoftheflightis3200.Dividethisbythenumberoftreads
(onelesstreadthanthenumberofrisers).
Going=3200÷13=246mm.
Going:246mmiswithintherangeof240to355mm.
Numberoftreadsisgreaterthan3andlessthan18.
Sloperelationship:178x2+246(risemultipliedby2+thegoing)=602iswithintherange
of700to550mm.
TheotherBCArequirement,thata125mmspheremustnotpassthroughtreads,shouldalsobe
checked.Therise,178mm,lessthetreadthickness,38mm,mustbelessthan125mm.
178–38=140.Thisismorethan125andsoisnotwithintheBCArequirement.Addacleatunder
thetreadtocloseupthespace.
Figure B2
Page 45
B4 Example 3
Straightflightofexternalstairswiththetotalrise=3600mm.Thetotalgoingisunrestrictedandthe
proposedtreadswillbe250x50mmunseasonedhardwood.
Calculaterise:
Dividetheriseoftheflightbyatrialriseof170mm(170isanaverageriseforstairs)toobtainthe
approximatenumberofrises.
3600÷170mm=21.17–roundedofftothenearestwholenumber=21.
Rise=3600÷21=171mm(Roundeddownaspertheaboveexamples)
However,thenumberofrisersexceedsthatallowedbytheBCAinasingleflight(notmorethan18)so
alandingwillneedtobeincorporated.
Calculategoing:
Thetreadwidthis250mmsothiscanbeourGoing.
Calculatetotalgoing:
Flight1–250mm=9x250=2250mmplusFlight2–250mm=10x250=2500mmplusthe
landingwidth900mm=5650mm.
Going:250mmiswithintherangeof240to355mm
Wehavealreadyestablishedthenumberoftreadsisgreaterthan18andalandingneedstobe
incorporated.
SlopeRelationship:171x2+250(risemultipliedby2+thegoing)=592,withintherangeof550
to700mm.
TheotherBCArequirement,thata125mmspheremustnotpassthroughtreads,shouldalsobe
checked.Therise,171mm,lessthetreadthickness,50mm,mustbelessthan125mm.171–50=
121.Thisislessthan125andsoiswithintheBCArequirement.
Figure B3
Sloperelationshipcalculations:
Thecalculationstodeterminethesloperelationshipintheaboveexamplesworkedouttobewithinthe
BCArequirement.
Ifthegoingplustwicetheriseworkedouttolessthan550thiswouldindicatethatthestepwastoo
smallandthesolutionwouldbetoleaveoutonestepanddothecalculationalloveragain.
If,ontheotherhand,thefirsttrialriseandgoingcausedthesteptobetoolarge(i.e.ifthegoingplus
twicetheriseworkedouttolargerthan700)thesolutionwouldbetoaddanotherstep.
Page 46
B5 Headroom for Stairs
The BCA minimum
is 2000 mm, but 2100
mm is preferred.
Headroomorheadway:Provisionshouldalwaysbemadeforsufficientheightsothattheheadof
anyonewillnotstrikeagainsttheedgeofthelandingorsoffitabove.Thisverticalheightorspaceis
called‘headroom’anditshouldnotbelessthan2000mm.(TheBCAminimumis2000mm,but2100
mmispreferred).
TheheadroominthestairshowninFigureB4wouldbefoundbytakingthenumberofrisers
containedwithintheopeningofthefloor(14),multiplyingitbytheriseandsubtractingthedepthofthe
floor.Notealsothatthelengthoftheopeninghasthesamenumberoftreads(14)astherearerisersin
theheadroom.
AssumingthestairinFigureB4tohaveariseof177mmandthedepthofthefloor260mm,the
methodoffindingtheheadroomwouldbe:
Risexnumberofrisersintheheadroomportionofthestairminusthedepthofthefloor.
Headroom=177x14–260
=2478–260
=2218mm
Figure B4
Forstairsintwoflights,themethodoffindingtheheadroomisobtainedbystudyingFigureB5.Note
thattheheadroomistakenfromtheundersideoftheceiling,atthecornerofthetrimmer,vertically
downtothenosingline.
Counttherisersfromthetopofthestairsdowntothelowerarrowpointmarkingtheheadroom.There
are8risersfromthetopofthestairtothetopofthelanding,andfromthetopofthelandingtothetop
ofthetread(indicatedbythearrowpoint)thereare7risers(onelessthanintheupperflight)making
15inall.
Assumingariseof156mm,taketheheightofthese15risers:
156x15=2340
Nowsubtractthethicknessofthe225mmupperfloor:
=2340–225–Headroom=2115mm
Inotherwords,tofindtheheadroomdoublethenumberofrisersintheupperflight,subtractone,
multiplybytherisethensubtractthethicknessoftheupperfloor(FigureB5).Apartfromtheflight
showninFigureB5,thisappliestoanyflightwithalandingincludingastraightstair,dog-legflight,etc.
Page 47
Thismaybewrittenasaformulaas:HeadroomRx(Ux2–1)–T,where:
R=rise
U=numberofrisersInupperflight
T=thicknessofupperfloor
Thepreviousexamplecanbecalculatedthus:
Headroom=Rx(Ux2–1)–T
=156x(8x2–1)–225
=156x1.5–225
=2340–225
=2115
Figure B5
Note:AstudyofFigureB6willshowclearlytheaffectonheadroombytakingonerisefromthetop
flightandsoaddingonetothebottomflight;theresultisareducedheadroombytworises
(e.g.2115mm–(156x2)=headroomof1803mmwhichwouldnotbesuitable).
Figure B6
Page 48
B6 Practical Method for Calculating Number of Rises and the Rise
Aftermarkingthetotalriseontoastoreyrod,apairofcarpenter’swingdividersshouldbesettoatrial
rise(165to170mm)andthensteppedalongthestoreyrodtofinishwithinthetotalrise.Whiledoing
this,thenumberofspacesshouldbecountedandrecorded(FigureB7).
Figure B7
Thedistancebetweenthelastdividermarkandthetotalrisemarkonthestoreyrod(X)isnowdivided
bythenumberofspacescountedandtheresultaddedtothefirstsettingofthedividers.
IfX=60mmthen60÷12=5
Trialrise170mm+5mm
Rise=175mm
Restepthedividersalongthestoreyrodasacheck,butnowthelaststepshouldfinishexactlyonthe
totalrisemarkandthenumberofspacesorrisesshouldbeasbefore(FigureB8).
Figure B8
Youshouldnowhavethenumberofrisesandtheexactriseandconsequentlythenumberofgoings
whichisalwaysonelessthanthenumberofrises.Rememberthatalandingiscountedasagoing
sothatwhenalandingisrequiredinastairtherewillbetwoflightsandthenumberoftreadsinboth
flightswillbetwolessthanthetotalnumberofrisesinthestair.
B7 Quantity Calculations
B7.1 String Length Required
Thisisnormallydeterminedbymeasurementfromafullsizesetoutofasectionthroughtheflight,
showingthetreatmentofthestringatbothends;howeverfororderingpurposes,applicationofthe
rule‘numberoftreadsintheflightx300mm+500mm’shouldprovidesufficientmaterial.
Note:The500mmallowsforvariationsoftreatmentattopandbottomofthestring.
UsingExample1above:
No.oftreadsintheflightx300mm+500mm
15x300mm+500mm
4500mm+500mm
Stringlength=5000mm
Twostringsof5000mmarerequired.(i.e.order2of5.1m)
Page 49
B7.2 Number of Treads
FromthepreviouscalculationsinExamples1,2and3,thenumberoftreadsisknown.
Thelengthofeachtreadwilldependonthewidthofthestairs.
UsingExample1aboveandwidthofflight=900mm:
No.oftreadsintheflight=15
Treadlength=900mm
15treads@900mm.
Iftheseareorderedas15individualpieces,thisdoesnotallowverymuchmarginforerrororany
endsplitsthatmayneedtobecutoff.Ordering5pieces3000mmlongwillallowasuitableamount
withoutbeinguneconomical.
B7.3 Tread Cutting Length
Thecuttinglengthofatreadwillbetheoverallwidthofthestairminustwicethegaugedepth(Figure
B9).
Example:
Widthofstair=900mm
Housingdepth=15mm
Stringthickness=50mm
Treadcuttinglength=900–(2x(50–15))
=900–70
=830mm
Figure B9: Tread cutting length.
Page 50
C
These methods
have generally been
replaced by the use
of laser levels, etc.
Appendix C –
Total Rise Calculations –
Sloping Ground
C1 Determining Total Rise on Sloping Ground
Thefollowingguidancecanbeusedtodeterminethetotalriseforexternalstairswherethegroundis
notlevelandeitherslopestowardorawayfromthebuilding.
Note:Thesemethodshavegenerallybeenreplacedbytheuseoflaserlevels,etc.
Figure C1: Stairs without landing – Land sloping towards building.
Page 51
Figure C2: Stairs with landing – Land sloping towards building.
Figure C3: Stairs without landing – Land sloping away from building.
Note:thissituationtobeavoidedwhereverpossibleasitaddstothenumberoftreadsrequired.
Page 52
Figure C4: Stairs with landing – Land sloping away from building.
Note:thissituationtobeavoidedwherverpossibleasitaddstothenumberoftreadsrequired.
Page 53

Stairs, Balustrades and Handrails, Design Guide 8

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