DOMESTIC DECK DESIGN GUIDEDOMESTIC DECK DESIGN GUIDESCOPEThis guide outlines key design and construction considerations for light domestic timber decksfor both raised and close to or on-ground timber decks that are exposed to the weather.It covers decks that are associated with Class 1 (detached houses, villas, townhouses etc) andClass 10 (garages, sheds, swimming pools etc) structures according to the National ConstructionCode (NCC). For the design and construction of decks for commercial, industrial or marineapplications or where a deck has to take heavier loads such as tiles, spas or even vehicles, astructural engineer will have to be consulted.Terminology used in domestic deck design and construction are illustrated in Figure 1.Figure 1: Components used to make up a timber deckHand tingConcrete padSteel brackets(hot-dip galvanised)Front Cover ImageProject: Castlecrag ResidenceArchitects: CplusC Architectural WorkshopPhotographer: Murray FredericksFacingjoistDeckingboardsPoststirrups

DOMESTIC DECK DESIGN GUIDE3HOW TO USE THIS GUIDESection A of this guide provides general information applicable to all types of light domesticdecks. Information relevant to specific types of decks is contained in Section B.SECTION A - GENERAL INFORMATIONThe following information is applicable to all deck systems.BEARERS AND JOISTSBearers and joists come in a variety of sizes, timber types and stress grades and their availabilitywill vary from one region to the next.Generally speaking the available stress grades in unseasoned hardwood are F11 and F14whilst seasoned hardwoods are available in F17 or F27 stress grades. Treated softwoods arepredominately available in F7 stress grade however F5 and MGP10 are available is some regions.The correct bearer sizes can be found in span Table 49 in AS1684. These tables assume a minimumend bearing of 50 mm by bearer width, and intermediate bearing of 100 mm by bearer widthfor continuous bearers. Joists that are at least 45 mm wide (seasoned hardwood and treatedsoftwood) or 50 mm wide (unseasoned hardwood) are recommended in order to avoid splittingwhen receiving nails or screws from placement of decking boards. This is particularly relevantwhere decking boards abut over the joist as the fixings can be placed further from the board’send. Joist sizes can be found in the span Tables 50 in AS1684. Joists of 35 mm or 38 mm width areonly suitable where proprietary deck fixings are used which a fixed to the side of joists.Placing a layer of 110 mm malthoid dampcourse or proprietary protection system on top of thejoists will increase the service life of the joist, refer Figure 2.Figure 2: Protection strip over deck joistsProtection systemJoistNote that the recommended timber sizes for the bearer and joist are for where decking boardsonly are being used. Where tiles are used as a deck covering, the sizes in AS1684 are notapplicable. In this circumstance advice should be sought from an engineer.

DOMESTIC DECK DESIGN GUIDESTRUCTURAL JOINTS AND CONNECTIONSThe joints between posts, bearers and joists need to be able to transfer load efficiently throughthe structure, refer to AS1684 for design of these elements.All connections should be of sufficient durability. All framing bolts, screws, nails, and otherhardware should be hot dipped galvanised, plastic coated or stainless steel. Electroplatedfasteners are not suitable due to early breakdown of the plating. Fixings within the splash zones(minimum 1.0 m from pool edge) of swimming pools must be stainless steel.Fixings for preservative treated decking boards should be hot dipped galvanised, stainless steelor with a coating approved for use on decking boards.Timber washers need to be appropriately sized, refer to Table 1.Table 1: Timber washer selection guide for coach screws or boltsWasher sizeBoltThickness (mm)Round Washer Minimum Dia.(mm)Square Washer Min.SideLength 575Note: Source AS1720.1Due to moisture potentially being trapped at the interface of a bearer and post connection atimber sealer should be used between the interfacing elements.4DECKING BOARDSThere are three main types of decking board profiles available; plain, pencil round and ribbed,refer Figure 3.Plain profile is not common as the square edges of the boards are more prone to splintering.Pencil Round has significantly less chance of splintering compared to plain boards. Ribbed boardprofile can be used faced up or down. Ribbed facing down provides maximum surface area forgrip however care should be taken in moist areas that the boards are kept free of mould andmoss build up which can make the boards slippery.Figure 3: Common decking board profilesPlain ProfilePencil Round ProfileReeded Profile

DOMESTIC DECK DESIGN GUIDEDecking boards are also available in various widths. In all cases it is recommended that boardswith a narrow width are selected because it is easier for water to drain through the deck. Wherewider boards are selected they will need to be thicker to reduce the possibility of cuppingdeveloping.Tongue and grooved timber, plywood or particleboard sheet flooring products are notrecommended for use as decking in weather exposed situations.SPAN CAPACITYVarious timber decking boards have different span capacity. Table 2 gives maximum span of thecommon decking board timbers and thicknesses.Table 2 Maximum joist spacing for various decking boardsDeckingStress GradeThickness (mm)Maximum joist spacing (mm)HardwoodStandard Grade (AS 2796.1)1950019400214501940022450CypressGrade 1 (AS 1810)Treated SoftwoodStandard grade (AS 4785.1)Source: AS1684Decking boards must be supported over at least three joists and butt joints in boards should bestaggered. Refer to Figure 4.Figure 4: Illustration of staggered decking boards5

DOMESTIC DECK DESIGN GUIDE6NAIL FIXINGEach board must be fixed at each joist with at least two nails which should be finished flush withthe top of the boards (rather than punched) to prevent moisture being trapped. Where the fixingoccur other than at the ends of the board, nails should be staggered across the joist to avoidcracks caused by moisture movement in the decking, refer Figure 5.Figure 5: Illustration of nail fixing timber deckingNails offsetNails finished flushwith board surface(not punched down)To obtain a tight fit at joints for abutting boards, a slight under-cut is recommended, refer Figure6. To reduce the splitting of the decking board, nails or screws must be kept a minimum of 12mm from edges and the boards end. The drilled nail holes should be 80% of the nail diameter.Figure 6: Nailing at board endsNails to be12mm min. from endsBoard endsunder-cutfor tight fit

DOMESTIC DECK DESIGN GUIDE7Table 3 describes the minimum nails that can be used for decking up to 22mm thick and the deckjoists.Table 3: Minimum nail size for various timber species decking and joist combinationsDeckingHardwood orcypressTreated softwoodNailing2 nails per board crossingJoistsHardwood orcypressTreated softwoodHand driven50 x 2.5 flat or dome-head50 x 2.8 bullet-head50 x 2.5 flat-headdeformed shankHardwood orcypressTreated softwoodMachine driven65 x 2.5 flat-head or 50 x 2.8 bullet-head65 x 2.8 bullet-headdome-headdeformed shank50 x 2.5 flat or dome-head50 x 2.5 flat-headdeformed shank65 x 2.5 flat-head50 x 2.8 flat or dome-head50 x 2.8 flat headdeformed shank65 x 2.8 flat-headMACHINE DRIVEN NAILSGenerally machine driven nails are proprietary to the nailing gun manufacturer and are notreferenced in AS1684. Machine driven nails can be used as long as the nail has the same capacityas the hand driven nails detailed in Table 3. T-nails should not be used. Care is also required inusing machine driven nails to ensure that the top of the nail head is not driven below the surfaceof the board.SCREW FIXINGLike machine driven nails, screw requirements are not referenced in AS1684. The principlesdescribed above for nails should be followed for screw fixings. Types of screws are generallyproprietary and reference to the manufacturer specification is required.FIXINGS TO STEEL JOISTSScrews used normally for timber decks are not suitable for fixing decking to steel joist due to theseasonal and differential expansion and contraction of timber decking and steel substructuremay cause the screws to fail in shear. It is recommended that a timber batten is affixed aboveor beside the steel joist so the decking boards is nailed or screwed to this batten. Size of timberbatten is to allow adequate fixing for the decking to batten as well as the batten to the steel joist.

DOMESTIC DECK DESIGN GUIDEHIDDEN FIXINGSThere a number of proprietary systems available that fixes the decking at the side of the board,refer Figure 7. Most systems require a groove into the side of the decking for fixings whilst someuse spikes. In all cases the fixing systems are proprietary and manufacturers’ recommendationmust be followed.Figure 7: Hidden timber deck fixingsDeckingHidden fixingsJoistFINISHING8As a minimum, a protective finish should be applied to all surfaces (including any freshly cutends) of each decking board, preferably before fixing to the joists. A protective finish includesproducts which penetrate the surface of the timber and products which provide a film or coatingto the surface of the timber.This protective finish of the timber surface will reduce the effects of weathering of any timber(treated or untreated) in an exposed situation. From a durability perspective the main functionof the finish is to slow down the rate at which the timber will take up or lose moisture. By slowingthat rate down, the severity of any checking is considerably reduced. The finish should contain afungicide to prevent mould growing on any sugars or starches that may be in the finish.Further information can be found in WoodSolutions’ Guide No 13 – Finishing Timber Externally.TIMBER DURABILITYThe recommended durability of the timber for deck sub-structure and decking boards arecontained in Section B of this guide. In all cases either a recommended natural durability class orpreservative treated timber hazard level are given.

DOMESTIC DECK DESIGN GUIDE9NATURAL DURABILITY CLASSESThere are two natural durability classes used in this guide “above-ground (AG) and “in-ground(IG)”. A number of Australian Standards list the above-ground and in-ground durability class forvarious timbers. These Standards are – AS1684 Parts 2 and 3 Residential timber-framed construction,– AS5604 Timber—Natural durability ratingsOther sources of information on timber durability can be found in:– Keith Bootle’s Wood in Australia– WoodSolutions Technical Guide #5 Timber Service Life Design – Design Guide for DurabilityThe durability class of many imported timbers can also be found in the Australian Standardsreferenced above. Where there is no durability class given for a timber species an indicator ofperformance can be found for a number of timber species from the paper; Natural Durabilityof Wood: A Worldwide Checklist of Species, Scheffer and Morrell 1998. In this publication theoffered durability classes do not correspond with Australia’s system but it does indicate betterperforming species.PRESERVATIVE TREATED TIMBER HAZARD LEVELSAustralian Standard AS 1604 Timber - Preservative-treated - Sawn and round define the retentionrates for various timber preservatives for various exposures and hazard levels.Note that timber treated with the preservative Copper Chrome Arsenate (CCA) is not allowedto be used in areas where children could come into frequent or intimate contact with it. Thatis handrail or decking boards. CCA treated timber is still OK to be used in other locations of thedeck such as framing, balustrades, posts and so on. Timber treated with other preservatives suchas ACQ (alkaline copper quaternary), copper azole or LOSP (light organic solvent preservatives)are OK to be used as handrails and decking boards. Note that timber treated with LOSPs is notsuitable for in-ground use.

DOMESTIC DECK DESIGN GUIDE10BUSHFIRE CONSTRUCTION REQUIREMENTSIn all parts of Australia that are prone to bushfires there are limitations on the use of timberin deck construction. This limitation varies depending on the risk of bushfire attack and theelements of the deck under consideration.Appendix A of this guide contains a list of common timber species used for timber decks and themaximum Bushfire Attack Level (BAL) that the species can be used in a deck, in accordance withAS 3959 Construction of buildings in bushfire-prone areas.Refer to WoodSolutions Technical Guide #4 Building with Timber in Bushfire-prone Areas - BCACompliant Design and Construction Guide for further information. It also should be noted thatSouth Australia and NSW have some differing requirements than that of AS 3959 and theserequirements need to be followed in those states.HANDRAILS AND BALUSTRADESIf the deck is more than one metre off the ground handrails or balustrades are required. Thechoice of appropriate handrails and balustrades will depend on the design and application andeven location in relation to other structures. For example balustrades for decks next to a poolvary from that of balustrades required in the NCC for fall protection. Further information can befound in Wood Solutions Technical Guide #8 Stairs, Balustrades and Handrails – Class 1 Buildings– Construction.MAINTENANCE AND WEARAll decks will benefit from regular maintenance. When cleaning the deck avoid hosing it down,instead use a broom or a blower. Pot-plants or other items should be elevated off the deck andbe placed in drip trays. They should also be moved regularly, to even the weathering of the deck.Timber is a natural product and as your deck timbers weathers, small cracks are likely to appearon the surface of the boards. These cracks are caused by the intermittent wetting and drying ofthe wood and are part of the character of wood and have no structural effect. This natural ageingprocess can be slowed by the use of finishes discussed above that reduce moisture movementsin timber.

DOMESTIC DECK DESIGN GUIDE11TANNIN, IRON STAIN AND RESIN BLEEDTANNIN BLEEDMost hardwood timber species contain water-soluble extractives which provide colour and somenatural decay resistance to the timber. Water-soluble extractives may be leached to the surfaceof the timber whenever moisture leaves the timber. Because the discolouration is water-soluble,it can be washed to other surfaces and leave an unsightly stain which can be difficult to removefrom brickwork, concrete or any paving which is underneath the deck unless they are sealed. Tolessen the likelihood of such extractives bleeding and staining, use seasoned timber and apply awater repellent finish to all surfaces including any freshly cut ends. Also seal pavers or concreteelements underneath.IRON STAINAny iron filings that are not cleaned from the surface are likely to react with moisture and thetimber extractives to create unsightly black staining on the timber. Avoid using any tools on, nearor above an uncovered deck which may deposit fine iron filings or dust on the timber surface.Particular care should be taken with cutting metal, masonry, brick or ceramics with an anglegrinder. An angle grinder cutting bricks or tiles creates iron filings from the metal mesh whichforms the base of the cutting disk.RESIN BLEEDSome softwood timber species boards such as radiata and slash pine can be prone to resin bleed.Ideally if a board shows obvious signs of resin bleed then it is preferable not to use board or tocut out the affected area. If it has to be fixed in the deck, fix it in a position where the resin bleedwon’t be a problem. Sometimes it may not be obvious that a board is prone to resin bleed untilafter the finished deck has been exposed to a period of hot weather. In such circumstances theresin can be cleaned up or the offending board replaced.

DOMESTIC DECK DESIGN GUIDESECTION B - SPECIFIC REQUIREMENTSRAISED TIMBER DECKINGThis is any timber deck where the decking boards are over 400 mm above the finished ground.It is assumed that there is appropriate drainage available for water and adequate cross-flowventilation underneath the deck, refer Figure 8. Note that adequate cross–flow ventilation fordecks is regarded as the same as the minimum requirement for raised timber floors in houses.For the minimum cross-ventilation requirements refer to NCC, Volume 2 Part 3.4.1.Figure 8: Raised Timber Deck 400mmSpacer blockDouble bearerconstruction12Notched postsSUB DECK SUPPORTSThe purpose of the sub deck supports is to transfer horizontal and vertical loads into the groundand sometimes includes uplift forces particularly where decks are covered with a roof.FOOTINGSFootings for supporting posts are generally designed in two ways. The most common methodis concrete footings with galvanized stirrups embedded or fixed in the footings to support theposts, refer Figure 9. An alternative method to support the deck post is by embedding the postdirectly into the concrete footing. When this method is used care is required to use no-finesconcrete, have adequate concrete under the post, and slope the top of concrete footing awayfrom the post, refer Figure 10.

DOMESTIC DECK DESIGN GUIDEFigure 9: Post stirrups in concrete footingsTimber postGalvanised stirrupTimber postTop of footingsloped away75mmMin.‘No-Fines’concrete footingConcretefooting100mmMin.Figure 10: Post embedded into a concrete footingPosts supporting roofloads to be continuous ordirectly over deck supportsJoists fixed to buildingwith galvanised joist hangersor on timber ledger13Gap refer to table 3Bearer housed 10mminto posts (typically)Hot-dipgalvanisedpost bracket75mm minclearanceConcretefooting

DOMESTIC DECK DESIGN GUIDE14Figure 11: Proprietary Metal stirrupsThe design of footings is outlined in AS2870 or AS1684. Generally the soil classification andexpected loads on the deck are required to be known. Decks designed to AS2870 and AS1684 arefor decks used for housing with average loads and ground conditions. If these conditions are notmeet, for example the deck needs to support a spa or the deck is to be tiled, the design needs tobe considered by a structural engineer.DECK FRAMING AND DECKING BOARDSTIMBER SELECTIONUnless the deck is completely protected by a roof the timber framing and boards will be exposedto the weather; therefore it is essential that timber is chosen which can provide good service lifein these conditions.Those timbers used above the ground (framing, boards and posts on stirrups) should behardwoods rated above-ground natural durability class 1 or 2 or, if softwood is used, preservativetreated to H3 hazard level. Softwood timber that is treated to H2 hazard level is not suitable foruse in the construction of decks.Timber embedded in the ground (embedded posts) should have be in-ground natural durabilityclass 1 or be preservative treated to H5 hazard level.Refer to Appendix A for a list of common timbers and their above-ground and in-ground naturaldurability ratings.There is a wide variety of engineered wood products now available on the market such as gluelaminated timber, finger-jointed timber and LVL products. If using these products referenceto specific manufacturer recommendations is required as in most cases there are additionalrequirements or limits when these are used in applications such as decks where they areexposure to the weather. Note that timber I-beams (treated or untreated) are not suitable foruse in the construction of decks.

As described previously posts are generally connected to concrete footings via a stirrup. Theyare generally preservative treated softwood (H3 hazard level) or naturally durable (above groundClass 1 or 2) hardwood timber.AS1684 span tables have the required timber sizes for posts. These are dependent on deckarea, roof area (if any), the post height and stress grade of the timber selected. Common crosssectional sizes for posts vary but generally commence at 88 mm and upwards. Minimum sizes forposts are also governed by the distance between the ground and the underside of the bearers.The maximum height of a deck above the ground for a given post dimension is 15 times the facewidth of the post.Deck posts need to be braced and AS1684 has various bracing methods. These methods areeither cross bracing between posts, refer Figure 12 or as a cantilever timber stump, refer toFigure 13.1800mm max.Figure 12: Braced Timber posts30to60153600mm max. (2 post system)Figure 13: Cantilever timber stumpPED150mmmin.WMax. Stump Height to Width Ratio 15:1DOMESTIC DECK DESIGN GUIDEPOSTS

DOMESTIC DECK DESIGN GUIDEDeck board spacingThe purpose of spacing decking boards is to allow seasonal movement of the timber deckingboards so that a gap is maintained to allow water to freely drain between the boards. The gap isnot to be too far apart that it forms a trip hazard. The gap between the boards will be dependenton a number of elements;– whether it is a hardwood or softwood timber species,– the decking board cover width, and– the moisture content of the timber during the installation process, i.e. unseasoned deckingboard requires less of a gap than seasoned decking boards.A gap of 3 to 4 mm is ideal over the long term. Table 3 shows the recommended spacing at thetime of decking board installation.Table 3: Recommended decking gaps at installationDecking cover width (mm)Seasoned or unseasonedRecommended decking gap86 to 90Seasoned3 - 4 mm91 to 140Seasoned4 - 5 mm86 to 90Unseasoned2 mm91 to 140Unseasoned2 mm70 to 90Seasoned4 mm91 to 120Seasoned5 mmHardwoodSoftwoodNote: In South Australia construction practices in bushfire-prone areas require a gap between decking boards of a set distance.Refer to NCC Volume 2.16DECKS CLOSE TO OR ON-GROUNDWhere the decking is less than 400 mm off the ground additional consideration to ensureadequate performance and service life of the timber is required. These include increasedventilation, subsurface drainage, increased timber durability/preservative treatment and accessfor termite inspection and maintenance.Where any of the conditions described in the guide cannot be met performance may be affectedand the service life of the deck will be reduced.Figure 14: Timber deck close to the groundGroundLineAllow ventilationand inspection 400mm Additionaltimbertreatment

DOMESTIC DECK DESIGN GUIDESUB-DECK AREA PREPARATIONIt is important that the ground beneath the deck is completely cleared of all building rubbish,garden debris, or obstructions to water or air movement. Water must not be able to pool underthe deck and the ground must be sloped away from the foundations of the house or othernearby buildings. Agricultural drainage pipes may be required in some instances so that watercan properly flow away from beneath the deck.Plastic sheeting acting as a water proof membrane should be placed on the cleared ground. Iftimber bearers are to be placed directly on the ground, the plastic sheet should then be coveredwith compacted gravel or sand to provide a solid base, refer Figure 16.FOOTINGSThere are a two main ways these can be arranged: – Concrete beams, with joists sitting on top, with no need for bearers, refer Figure 15.– Bearers placed straight on to the ground or soil, refer Figure 16.Figure 15: Concrete beam footingGap refer to table 3Concrete beamPlastic membrane‘No-Fines’concrete footing17Figure 16: Bearer directly on to groundHouseframe40mm minimum gapmembraneJoistCompact sand or gravel baseConsider drainage whenapplying membrane

DOMESTIC DECK DESIGN GUIDE18Concrete foundations and bearers should be placed so that they do not restrict the flow ordrainage of water. Preferably a decking system should be designed so that it is panelised. Thepanels need to be sized so that they can be easily lifted to allow for easy maintenance andinspection. The perimeter of the deck should be kept open to allow for ventilation.TERMITE INSPECTIONOnly termite resistant timber should be used (see below) and a gap between the house and deckof at least 40 mm maintained to allow for pest inspection, refer Figure 16.DECK FRAMING AND DECKING BOARDSTIMBER SELECTIONTimbers used close to or on the ground require additional durability as well as termite resistance.Framing timbers more than 150 mm above the ground should be termite resistant and aboveground durability Class 1 or 2 (plus sapwood removed or H3 treated) or softwood preservativetreated to at least H3 hazard level.Framing timbers on the ground or lower than 150 mm should be termite resistant and in-grounddurability Class 1 (plus sapwood removed or H4 treated) or preservative treated to H4 or better.Decking boards should be termite resistant above-ground natural durability Class 1 or 2 (plussapwood removed or H3 treated) or preservative treated to H3 or better.DECKING BOARD SPACINGThe decking should be the minimum width available and have a minimum spacing betweenboards (long term) of 5 mm to allow water to flow between the boards and ensure adequateventilation.

DOMESTIC DECK DESIGN GUIDE19APPENDIX 1 - COMMON DECKING BOARDTIMBER shfireResistanceBlackbutt64 1986 1921YesBushfireResistingTimberRed Ironbark64 1986 1911YesBushfireResistingTimberGrey Ironbark64 1986 1911YesDensitygreaterthan 750kg/m3Spotted Gum64 1986 19136 3221YesBushfireResistingTimberMerbau /Kwila70 1990 19140 0 19140 25YesDensitygreaterthan 750kg/m31

DOMESTIC DECK DESIGN SizesJarrah65 1988 19Tallowwood64 1986 191Turpentine64 1986 19Treated Pine70 1990 19120 ireResistanceYesDensitygreaterthan 750kg/m31YesDensitygreaterthan 750kg/m321YesBushfireResistingTimberH3H3YesNoRed Mahogany21YesDensitygreaterthan 750kg/m3River Red Gum21YesBushfireResistingTimberYesNoCypress22

DOMESTIC DECK DESIGN GUIDEREFERENCESAustralian Building Codes Board, National Construction Code Series, Volume TwoAustralian Standards– AS 1604 Specification for preservative treatments Part 1: Sawn and Round timber– AS 1684.2 Residential timber-framed construction. Part 2: Non-cyclonic Areas– AS 1684.3 Residential timber-framed construction. Part 3: Cyclonic Areas– AS2870 Residential slabs and footings– AS 1810 Timber - Seasoned cypress pine - Milled products– AS 2796.1 Timber - Hardwood - Sawn and milled products - Product specification– AS 2870 Residential slabs and footings standard– AS 4785.1 Timber - Softwood - Sawn and milled products - Product specification– AS 5604 Timber—Natural durability ratingsWoodSolutions Technical Design Guides#4 – Building with Timber in Bushfire-prone Areas - BCA Compliant Design and ConstructionGuide#5 – Timber Service Life Design – Design Guide for Durability21#8 – Stairs, Balustrades and Handrails – Class 1 Buildings – Construction.#13 – Finishing Timber ExternallyBootle, Wood in Australia, Second EditionScheffer and Morrell, Natural Durability of Wood: A Worldwide Checklist of Species

The Timber Development Association of New South Wales (TDA) is an industry funded associationrepresenting all segments of the timber industry, from manufacture to supply. For over 75 years,the TDA has effectively promoted the educated use of timber and timber related products.The TDA was incorporated on the 21st October, 1938. Its original mission was to promote the useand sale of timber of all kinds — whether native to Australia or imported from abroad. It was alsomandated to promote the interests of all persons, firms or companies in Australia involved withtimber or wood technology, or engaged in forestry.The TDA mission has evolved considerably over the years. The TDA now concentrates on thetechnical advancement of the timber industry.FURTHER INFORMATIONInformation on timber use can be found from TDA’s website document has been prepared in good faith exercising due care and attention. However,no representation or warranty, expressed or implied, is made as to the relevance, accuracy,completeness or fitness for purpose of this document in respect of any particular user’scircumstances. Users of this document should satisfy themselves concerning its applicationto, and where necessary seek expert advice about, their situation. The Timber DevelopmentAssociation (NSW) Ltd, its agents and employees shall not be liable with respect to any liability,loss or damage caused or alleged to have been caused directly or indirectly by this document. Document copyright of Timber Development Association (NSW) LtdISBN: 978-0-646-90555-6Published July 2013BMS9968.0713

SPAN CAPACITY Various ti mber decking boards have diff erent span capacity. Table 2 gives maximum span of the common decking board ti mbers and thicknesses. Table 2 Maximum joist spacing for various decking boards Decking Stress Grade Thickness (mm) Maximum joist spacing (mm) Hardwood Stand