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A U S T R A L I A NHARDWOOD & CYPRESS

T E C H N I C A L & D E T A I L I N G G U I D E


…quality you can build on!T E C H N I C A L & D E T A I L I N G G U I D E

Section One1

Section Two2

Section Three3

Section Four4

Section Five5

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AUSTRALIAN HARDWOOD AND CYPRESS2


Table of ContentsIntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Using Hardwoods & CypressWhat do the Terms Hardwood & Cypress Include? . . . . . . . . . . . 4Parts of the Tree . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Processing the Tree into Timber Products . . . . . . . . . . . . . . . . . . 5Managing Moisture, Seasoning & Shrinkage . . . . . . . . . . . . . . . . 7

Designing for AppearanceColour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Grain & Texture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Natural Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Sawing Patterns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Sizes and Availability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Internal Timber Finishes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Checking Your Appearance Selection . . . . . . . . . . . . . . . . . . . . 14

Designing for Structural StrengthStructural Properties & Grading . . . . . . . . . . . . . . . . . . . . . . . . 15Sizes & Availability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16Span Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17Timber Joints & Connectors . . . . . . . . . . . . . . . . . . . . . . . . . . . 17Adding Timber Size to Insulate Against Fire . . . . . . . . . . . . . . . 20Checking Your Structural Selection . . . . . . . . . . . . . . . . . . . . . . 22

Designing for DurabilityPerformance Criteria for Durability . . . . . . . . . . . . . . . . . . . . . . 23Natural Timber Durability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Using Preservative Treatments to Increase Durability . . . . . . . . 24Coatings to Protect Timber and Connectors . . . . . . . . . . . . . . . 25Detailing Construction to Protect Timber . . . . . . . . . . . . . . . . . 27Maintenance Strategies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27Bushfire Prone Areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27Checking Your Durability Selection . . . . . . . . . . . . . . . . . . . . . . 28

Formalising the Specification (and Reference Material)Writing the Specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29Glossary of Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30Bibliography and Regulatory Documents . . . . . . . . . . . . . . . . . 32Linked Guides Supporting this Document . . . . . . . . . . . . . . . . 32Acknowledged Documents . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

AUSTRALIAN HARDWOOD AND CYPRESS 3


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IDE Introduction

Wood begins as a natural resource and passesalong the production chain until it is convertedinto end user products. This guide describescommon principles for specifiers to use inconverting hardwoods and Cypress intoappropriate end products. The content conveysthemes that can be applied to buildingconstruction, interior design, fit-out, civilstructures and landscaping. It will also benefitthose who simply wish to learn more about thecorrect use of timber.

This guide acts as an over arching documentwhich is to be read in conjunction with a seriesof linked technical guides for specificapplications, such as flooring, decks, stairs and

handrails, piles and poles, cladding, fit-out andfurniture. It also links to information on differenthardwood and Cypress species, and relatedtimber producers.

The guide starts with basic principles of timberusage, then breaks into three streams. Onedealing with using timber for its appearance,another dealing with structural applications,while the third deals with durability issues. Theguide ends by detailing how to prepare a timberspecification, and also contains regulatoryreferences, a glossary of terms and a list of thepreviously mentioned link documents. The overalldocument structure is shown in Figure 1.

Figure 1: Information flow

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U S I N G H A R D W O O D S & C Y P R E S S

Hardwood and Cypress take in a huge range of species. Some are more commerciallyavailable than others, and in addition, some are only used in certain parts of Australia.Table 1 defines the main species, source and common applications.

Since timber is a natural material it is best to work with it, rather than against it.

This section looks at a few basic principles when using hardwoods and Cypress.

Common NameAsh, Alpine/Mountain

Blackbutt

Brushbox

Coastal species(Bloodwood, Grey Box,Grey Gum, YellowStringybark, RedMahogany)

Cypress (softwood )

Flooded Gum

Ironbarks (Grey, Red)

Jarrah

Karri

New England Blackbutt

River Red Gum

Spotted Gum

Sydney Blue Gum

Tableland species(Brown Barrel, MannaGum, Messmate,Silvertop Stringybark)

Turpentine

Tallowwood

White Mahogany

SourceNSW, Tas, Vic

NSW, Qld

NSW, Qld

NSW, Qld , Vic

NSW, Qld

NSW, Qld

NSW, Qld

WA

WA

NSW, Qld

NSW, Vic, Qld

NSW, Qld

NSW, Qld

NSW, Vic, Qld

NSW, Qld

NSW, Qld

NSW, Qld

Common ApplicationsGeneral framing, flooring, and panelling, joinery, furniture

Poles, sleepers, general framing, decking, flooring, furniture

Heavy engineering, panelling, cladding and flooring

Heavy engineering, marine structures, general framing , panelling,cladding, flooring, decking, poles, sleepers, piles, cross arms (refer toSpecies Guide referenced in Section 5 for specific details).

General framing, flooring, panelling, joinery, furniture

General framing, flooring, panelling, joinery, furniture

Heavy engineering, marine structures, poles, boat building, generalframing, flooring, decking, sleepers

Flooring, joinery, panelling, sleepers, poles and piles, heavyengineering, general framing

Flooring, joinery, panelling, plywood, sleepers, shipbuilding, heavyengineering, general framing

Flooring, building general framing, joinery

Heavy engineering, general framing, sleepers, flooring, panelling,joinery, furniture

Flooring, joinery, heavy engineering, general framing, piles, poles,sleepers, plywood, tool handles.

Flooring, joinery, furniture, general framing and heavy engineering,cladding, panelling and boat building.

Protected construction applications, general framing, flooring,panelling, tool handles, joinery, furniture (refer to Species Guidereferenced in Section 5 for species specific details)

Heavy engineering, marine structures and piling, ship building,sleepers, poles, general framing, panelling, cladding, flooring, decking

Decking, flooring, general framing, heavy engineering, sleepers, marinestructures, poles, piles, bridges

Heavy engineering, poles, marine structures, boat building, generalframing, panelling, cladding, flooring, decking

WHAT DO THE TERMS HARDWOOD & CYPRESS INCLUDE?

Note: For further information refer to the ‘Species Guides’ referenced in Section 5 of this document.

Table 1: Types of Hardwoods and Cypress

Section One

Using Hardwoods & Cypress 1



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For any species, each passing year brings newgrowth rings in the tree trunk (refer to Figure 2).The centre of the tree is often referred to as the‘pith’ and is rarely used except in poles, piles andwhere very large sections are required, e.g.,girders. The heartwood (or truewood) is usuallydarker in colour, and extends from the centre (orpith) in the tree out to the sapwood. The sapwoodis usually lighter in colour, and extends from theheartwood to the cambium layer. The sapwoodis the living part of the wood, and conducts waterand nutrients upwards from the roots to theleaves, and also acts as a storage area for sugarsand starches. As the tree grows, the innersapwood is converted to heartwood. Each hasdifferent properties relevant to constructionapplications.

• Sapwood has lower natural decay resistancethan heartwood, but where necessary can beboosted by adding preservative treatments,

• Sapwood and heartwood have similar strengthand dimensional stability,

• Both heartwood and sapwood may co-occurin timber used for appearance and structuralpurposes, but in some applications sapwoodmay be removed or limited in content.

PROCESSING THE TREE INTO TIMBER PRODUCTSThe natural characteristics of timber placeconstraints on how it is used and offered tospecifiers. Issues include sawing, milling, gradingand quality control constraints.

Log Products Log products involve the minimum amount ofprocessing, and are commonly used for pole, pileor landscape applications. The sapwood of logproducts may be preservative treated to help meetdurability requirements. This involves leaving thesapwood in place to accept preservatives, whilein other instances – such as in power poles –sapwood is purposely removed (i.e ‘de-sapped’).Basic types of log products are shown in Figure 3.

Sawn ProductsSawn products are produced by cutting logs intolarge slabs, then re-sawing these into smallersections. There are two main categories – back-sawn and quarter-sawn sections (refer Figure 4)as well as a hybrid of the two. Each has a differenteffect on the way growth rings appear in the cuttimber. As discussed later, this affects theappearance and manner of shrinkage in thetimber. After sawing, joinery and visually exposedstructural timbers are usually kiln dried anddressed to actual size. The same is true for lintel,truss and other framing elements requiringdimensional stability. Other framing timbers and

Bark

Sapwood

CambiumHeartwood

Juvenile wood

Pith

Figure 2: Tree cross section

Figure 3: Types of log products

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certain types of cladding only require a ‘sawnfinish’ (off the saw), and are generally unseasonedand nominally sized. Exceptions occasionallyoccur. Some unseasoned hardwoods and Cypressmay be dressed when only partly seasoned. It isbest to enquire with suppliers for specificproducts for intended applications.

Figure 4: Types of sawn products

Nail Plated TimberNail plated timber makes greater use of small andshort timber sections. They are mechanicallyjoined to provide increased length or depth. Thetimber pieces are generally kiln dried andmachined to size before plating. The process iscarried out as a manufacturing operation toensure the quality of jointing. As the nail platesare exposed, these elements are usually used forstructures that are concealed from view. The nailplates may be affected by exposure to weatherand should only be used in protected locations.

Engineered Timber Products Engineered timber products offer the mostadvanced usage of raw timber. A commonexample is glue laminated beams which usesmall timber sections glued together as shown inFigure 6. The benefit of this approach is thatnatural imperfections in the timber can besignificantly reduced – creating a stronger,straighter, and more stable product – comparedto sawn timber. In addition, large beams can beproduced to suit standard or customised structuralsituations. For instance, beams can be producedwith curves, tapers and cambers to suit specificneeds. Advanced elements include portal framesand arches.

Back cut

Quarter cut

Figure 5:Nail plated kiln dried, dressed products

Figure 6: Glue laminated engineered timber products



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Sheet timber products and veneers take a differentapproach to utilising the raw material. Plywoodand decorative veneers are made by peeling orslicing logs. Peeling is usually for structuralpurposes and slicing for decorative applications.Plywood production involves gluing layers on topof each other until the desired thickness isachieved. The knots and other imperfections areisolated into single veneers rather than continuousas per a solid product. The grain of each veneer isrun in a perpendicular direction to adjacent layers.This creates strength in both length and width.Uses are mainly for formwork and decorativeflooring. Decorative veneers have multiple fit-outand furniture uses, and are often overlaid onplywood or medium density fibre board.

Another sheet application is hardboard. It is madeof fine hardwood fibres held together with naturallignin from the wood – applied under heat andpressure. It is commonly used for cladding,bracing and is also used for linings (especiallywhere sheets are perforated to reduce noise).

MANAGING MOISTURE, SEASONING AND SHRINKAGE Moisture management is used to minimiseshrinkage and movement in the timber. Forinstance, when wood comes from a newly felledtree it is virtually saturated with water. As moistureleaves the wood it influences strength,dimensional stability, stiffness, hardness, abrasionresistance, machineability, insulation value,resistance to decay and nail holding ability.

Measuring MoistureIn managing moisture it is necessary to be ableto measure moisture levels. Moisture content isdescribed in terms of the weight of watercontained in the wood expressed as a percentageof oven-dried wood weight. Key levels ofmoisture content are linked to simplified termssuch as ‘seasoned’ and ‘unseasoned’ timber.Seasoned timber relates to low levels of moisturecontent, less than or equal to 15%. Thisapproximates the equilibrium moisture content(EMC) of most timber. EMC is the moisture levelthat the timber wants to stay at once it has driedout and acclimatised to its environment. Timberwith a moisture content higher than 15% isregarded as unseasoned or green.

Shrinkage and SeasoningTimber should be specified as being seasoned orunseasoned for installation purposes. Thisdecision is very important since seasoned timberis generally stronger than unseasoned timber –all other things being equal. Unseasoned timberis also less dimensionally stable due to the effectsof potential shrinkage. Shrinkage is where woodfibres move closer together causing distortion ofthe three dimensional features of timber. This onlyoccurs once the timber dries out to fibresaturation point – a point between 25–35%moisture content that varies for each species.Longitudinal shrinkage is very small and generallydisregarded; radial shrinkage is about 2 to 7%;while tangential shrinkage is generally up to twicethis amount, at 4 to 14%. When this amount ofshrinkage takes place in an uncontrolled way, therisk of splitting in timber increases significantly.In addition, there is the risk of shape distortion,as shown for typical cuts of timber in Figure 7.

Figure 7:

Effects of shrinkage on common cuts of timber

Timber species with high shrinkage (e.g. NewEngland Blackbutt, Messmate, Mountain Ash,Silvertop Ash and Turpentine) require greater careif being used in an unseasoned state. Applicationswhere any radial and tangential shrinkage mayhave significant impact such as flooring,panelling, some cladding, mouldings, furnitureand joinery, require timber to be seasoned priorto use. Unseasoned timbers can be used in otherapplications but this involves a value judgementand creates the need for careful detailing andattention to expected shrinkage rates.

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Detailing Unseasoned TimberShow care where:

• materials with different shrinkagecharacteristics are combined, e.g. unseasonedtimber next to seasoned timber or non-timberproducts, end grain next to cross grain;

• large timber sections are involved;

• multiple stacked timber members e.g. joists ontop of bearers;

• large timber areas are involved e.g. flooring,cladding;

• clearance needs to be provided relative to brickveneer walls i.e. at lintels, eaves lining, windowsills and floor framing;

• multi-storey construction causes combinedshrinkage i.e. where each floor may add to theoverall effect;

• shrinkage affects fire resistant construction e.g.at gaps in walls.

Further perspective of the effects of shrinkage onunseasoned timber is shown by the figures inTable 2.

Seasoning Issues The seasoning process also requires care tomanage the effects of shrinkage. The surface driesfirst while the interior remains wet and abovefibre saturation point. As a result, the interiorremains in its expanded shape while the surfaceshrinks – causing checks and cracks. Largesections are most affected. In addition, ends offerthe highest risk as water can enter and leave thetimber more readily, which may result in largeamounts of differential shrinkage. The problemis increased where the addition of some waterborne preservative treatments create the need forsecondary seasoning. The problem can beremedied or minimised by good seasoningpractices, however there is a concurrent need fordesigners to acquaint themselves with what isrealistic – especially where large, treated sectionsare concerned.

Statutory and Regulatory SeasoningRequirementsTimber producers are obliged to meet standardsand statutory seasoning requirements. If nothingis specified, then statutory requirements takeprecedence e.g. the ‘NSW Timber Marketing Act’and the ‘Queensland Timber and UtilisationMarketing Act’. In the absence of a specifiedmoisture content, these acts require seasonedtimber to fall within a moisture content range of10 – 15%. If building standards or architecturalrequirements are written into specifications, thenless rigid requirements may prevail (i.e. as perprovisions in respective Acts). For instanceAS2082 calls for 90% of a parcel of timber to be15% moisture content or less, but no individualpiece can be more than 18%. In addition,moisture content is specified for specificapplications, as detailed in Table 3.

Member

Lintel

Plates (top and bottom)

Floor Joists

Floor Bearer

Total shrinkage

SeasonedHardwood/Cypress

0

0

0

0

0

UnseasonedCypress

10

3.6

4

4

21.6

UnseasonedHardwood

20

7.2

8

8

43.2

Depth(mm)

1 at 250

2 at 45

1 at 100

1 at 100

Typical Shrinkage (mm)

Table 2: Typical shrinkage in Hardwood and Cypress framing

Notes: 1. Shrinkage rates = 8% for unseasoned Hardwood; 4% for unseasoned Cypress (source: AS1684).



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Zone

Coastal

Inland

Air-conditioned

OutdoorAv. E.M.C. (%)

14

11

–

Indoor

Av. E.M.C. (%)

12

9

9

Seasoning Requirements for Specific ServiceEnvironmentSeasoning requirements only approximate theequilibrium moisture content on-site. Eachenvironment is different and so some adjustmentmay be necessary to get the best result –especially where appearance is important. In suchinstances conditioning of the timber beforeinstallation to limit the chances of movement maybe necessary. Different service environmentsshould also be considered – especially airhumidity. Humidity changes for coastal and aridenvironments, interior and exterior environments,air conditioned or heated environments. Each ofthese will change the stability of moisture in thetimber.

Generally the moisture content of timber productssuch as flooring should be approximately suitedto ‘normal’ environments. If they are not suitedto normal conditions or the conditions on-siteare unusual, then they should be acclimatised tothe expected in-service equilibrium moisturecontent level before installation. This may meanthat timber products are conditioned on-sitebefore fixing. For instance, it is not uncommon

for floor fixers to leave timber appropriatelystacked on-site for three or more weeks prior tofixing.

Another approach, although rare, is to predictthe EMC prior to taking the timber to site (e.g.condition it at the timber manufacturer’spremises). To assist, Table 4 provides the averagemoisture content for coastal, inland and air-conditioned environments. In order to determinewhich applies to your situation refer to Figure 8which shows three climate zones. ‘Inland’ refersto Zones 1 and 2, while ‘coastal’ refers to Zone 3.Specifiers must be mindful that the figures derivedfrom Table 4 are still approximate becausehumidity is constantly changing in the distinctmicro-climate of each service environment. Somedegree of moisture induced shrinkage (orswelling) is hard to avoid – even if only due toseasonal climate change. The only tool for dealingwith such movement is to limit restraint of thetimber in-situ – thus allowing freer movement.Movement joints or specialist connectors can beintegrated into the construction to achieve thisresult.

Application

Strip flooring

Parquet flooring

Light decking

Lining boards

Dressed boards, joinery and Moulding

Cladding, Fascia and Barge Boards

MC Range Hardwoods

9 to 14%

8 to 13%

10 to 18%

9 to 14%

9 to 14%

10 to 14%

MC Range Cypress

10 – 15

10 – 15

10 – 15

10 – 15

10 – 15

10 – 15

Table 3: Moisture content for different applications

Table 4: Seasoning for specific environments

Notes: 1. Cladding may have higher moisture content where the profile allows for shrinkage.2. Source: AS2796.1/AS1310.

Notes: 1. The moisture content values for air-conditioned and heated situations are appropriate regardless of the zonelocation.2. E.M.C. zones do not bear the same significance to farming timbers as appearance or feature products.

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Alice Springs

Roma

Dubbo

Cairns

Townsville

Bundaberg

Brisbane

Coffs Harbour

SydneyCanberra

Bega

Hobart

Melbourne

Adelaide

Perth

ZONE 3

ZONE 2

ZONE 1

ZONE 1 – 9am RH <60%

ZONE 2 – 9am RH >60% and 3pm RH >40%

ZONE 3 – 9am RH >70% and 3pm RH >60%

RH = Relative Humidity ZONE 3

Onslow

Darwin

Figure 8: Climate Zones based on relative humidity


D E S I G N I N G F O R A P P E A R A N C E

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COLOUR Colour is arguably the first thing to consider whenselecting timber for appearance. It is best to thinkin terms of basic colour groups such as blond,brown, red and yellow, then choose an individualspecies that meets these criteria. Table 5 showscommon species grouped according to basiccolour categories. These categories are based oncommon heartwood colours rather than thelighter and less used sapwood. Some degree ofvariation still exists within the heartwood and soTable 5 is a guide only. Variation can be balancedby grading timber during installation. Thisprovides a more consistent overall appearancecompared to randomly placed pieces but requiresgreater attention to workmanship. Another issueis that timber changes colour slightly on thesurface during its serviceable life. Sunlight has ableaching effect on dark colours and a yellowingeffect on blond colours. Weathering has anadditional effect on unprotected external timberscausing them to ultimately turn silvery grey incolour. Care should be taken in the selection ofapplied timber finishes to manage these effects.

GRAIN AND TEXTUREGrain refers to the direction, size andarrangement of fibres in the timber. Differentspecies have different grain patterns and this cantransform appearance. In generic terms, grainscan be described as: straight, sloping, spiral,interlocking, irregular and wavy grains, and maybe accentuated by the type of cut used whensawing the timber (i.e. back sawing or quartersawing).

Texture is associated with grain, and refers towhether the wood is coarse, fine, even or uneven.Much of this is related to the size andarrangement of the wood cells. Such features tendto be important when viewing the timber at closerange. For details on grain and texture ofindividual species, refer to the Species Guide asreferenced in Section 5 of this document.

Timber has natural appeal that makes it a sought after material – especially for joinery, furniture andinterior design purposes. Australian hardwood and Cypress offer a truly unique, interesting andbeautiful appearance. This section of the guide helps designers utilise colour, grain, texture, knots,sawing patterns, natural features and decorative finishes.

ColourBlond

Brown

Yellow

Red

SpeciesAsh (Silvertop, Mountain and Alpine), Blackbutt, Messmate, White Mahogany

Brown Barrel, Brushbox, Grey Box, Manna Gum, New England Blackbutt, Spotted Gum, Stringybark (Yellow, Red, Silvertop), Grey Ironbark

Cypress, Tallowwood

Forest Red Gum, Flooded Gum, Grey Gum, Red Ironbark, River Red Gum, Sydney Blue Gum, Turpentine, Red Mahogany, Bloodwood

Table 5: Species colours

Section Two

Designing for Appearance2

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NATURAL FEATURESNatural features come from branches andirregularities in the tree, and affect the finishedappearance of timber. They include things likeknots, gum veins, checks and pin holes. If thereis a desire to limit or control natural features, thenthe appropriate grade of timber should bespecified. For hardwoods, this includes optionssuch as: select, medium feature and high featuregrades – as defined by AS2796.2. For Cypress thisincludes Grade 1 and 2 – as defined in AS1810.These grades objectively define the number, typeand spacing of knots and imperfections. As anexample, variation in grades for hardwoods areshown in Figure 9 and summarised below:

Select Grade – (SEL)

• permissible features: small holes and smalltight knots,

• not permitted: enclosed termite galleries,shakes, splits, decay, loose knots, gum pocket,narrow gum veins, want, wane or mechanicaldamage and non natural stains or sticker marks.

Medium Feature Grade – Standard (MF)

• permissible features: tight knots, small holes,tight and loose gum veins, limited gum pocketand checks,

• not permitted: enclosed termite galleries,shakes, splits, decay, want, wane ormechanical damage and non natural stains orsticker marks,

High Feature Grade – (HF)

• permissible features: knots, holes, tight andloose gum veins, limited gum pocket andchecks,

• not permitted: enclosed termite galleries,shakes, splits, decay, want, wane ormechanical damage and non natural stains orsticker marks.

Before selecting a grade it is useful to comparethe relative features expected in each species.Some are more prone to knots, holes, gum veinsand insect attack, than others. This can beexplored by referring to the Species Guidereferenced in Section 5.

Figure 9: Various appearance grades in hardwood

Select Medium Feature High Feature



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Sawing patterns represent another factorinfluencing appearance. Logs are sawn accordingto practical and economic necessity. Though thistends to dictate what is available in the market,each sawing pattern adds a different appearanceto the grain. For instance back sawing expressesgrowth rings in the wide face of the wood, whilequarter sawing shows growth rings in the narrowface (refer Figure 10). If necessary inquire withsuppliers about what to expect for differentspecies

SIZES AND AVAILABILITYSizes of dressed timber are influenced byavailability. Many are derived from structural orrough sawn sizes which are then re-processedfor dressed timber usage (Note: stress gradebranding is usually lost during re-processing,which is permitted by State regulations as longas appropriate arrangements have been madebetween the supplier and purchaser).

Machined thicknesses include 20, 35 and 45mmoptions. The latter is limited in supply due to thetime and difficulty in seasoning high densityhardwoods. Lamination offers a practicalalternative. Widths include 65, 90, 140, 190, 235and 285mm (depending on species). Widthsgreater than 140mm are also limited in supplybecause of the lack of appropriate quality logs.Tolerances for thicknesses and widths varydepending on shrinkage and recovery rates fromrough sawn sections – sizes 1–2mm smaller thanthe above may occur. Lengths are available in300mm increments but 100mm increments maybe available for short lengths (e.g. less than 2.4m).

Large orders require lead time for preparation.Special runs may also be possible for unusual orlarge section sizes. In addition, sheet veneerproducts are available to use in conjunction withthe above from specialist stockists. It isrecommended that producers be contacted fordetails about sizes and availability (refer to theProducers Guide referenced in Section 5).

INTERNAL TIMBER FINISHESTimber finishes provide the final influencingfactor to the finished timber appearance. Finishesfor internal uses can be classified as clearpolyurethanes, oils and stains.

Polyurethanes create a clear film over the timberin satin, semi gloss and gloss sheen levels. Lowerlevels of sheen (satin) help hide imperfections inthe flatness of large areas such as floor boards.In contrast high gloss has the opposite effect dueto increased reflectivity. Even so it allows easiercleaning and there is less likelihood of mouldgrowth caused by the condensation of steam, fatsand oils which occur in kitchens and wet areas.All gloss levels can be formulated to have anti-yellowing agents to prevent the discolouringbrought about by long term exposure to ultra-violet light. (Note: only light coloured timberspecies are noticeably affected). Clear finishescan also be formulated to provide various levelsof impact resistance and therefore some are moreapplicable than others where high traffic usageis involved (e.g. floors).

Oils differ from clear finishes as they soak intothe timber and therefore lose the featuresassociated with a protective film. They also tendto create a different appearance by looking morenatural and creating a flat lustre.

Stains are similar to oils in the way they soak intothe timber and provide a relatively flat, unsealedappearance. Perhaps the main difference is thatstains have a colouring agent that aims to tint thenatural timber to provide an altered appearance.It is also possible to use stains in conjunctionwith clear finishes where the latter is used toprovide gloss and a protective film over the stain.

Figure 10: Features attainable via different saw cut methods

Quarter sawn Back sawn

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Checking the previously discussed timber selection factorsis perhaps best summarised in the flow chart shown inFigure 11. Its aims is to ensure all appropriate factors aretaken into account for different specification scenarios.

Figure 11: Process for selecting timber for appearance

CHECKING YOUR APPEARANCE SELECTION


D E S I G N I N G F O R S T R U C T U R A L S T R E N G T H

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STRUCTURAL PROPERTIES AND GRADINGWhen considering structural properties it isimportant to realise there are many commerciallyavailable species. Strength varies for eachdepending on whether it is tested in thelongitudinal, tangential or radial axes. The timberindustry has simplified these variables bydeveloping a system of timber stress grading.Stress grades give an indication of strength ‘inbending’. The process of grading begins byidentifying a timbers ‘strength group’ whichclusters species of similar strength together (e.g.based on modules of rupture and elasticity).‘Structural grades’ separate the strength groupsinto smaller groups to deal with reduced strengththrough natural imperfections in the tree. Fromthis, a stress grade is assigned (signified by an ‘F’for sawn timber or ‘GL’ for glue laminated timber).Twelve grades exist, and those relating tohardwoods and Cypress are shown in Table 9.These grades are utilised by structural designersto assess the capacity of elements to perform ingiven applications (with the assistance ofAS1720.1).

Approaches to Stress GradingGrading can be carried out at any stage in thechain of production, e.g. on logs, unseasoned orseasoned sawn timber. It can be carried out inany one of the following three ways, accordingto need and circumstance.

Visual gradingVisual grading involves a trained ‘grader’ whofirst identifies the timber strength group, thenlooks for characteristics that influence structuralgrade, then assigns a stress grade. The two mainguiding documents for this are: AS2082 (forhardwood) and AS2858 (for Cypress).

Machine GradingMachine grading utilises a computer controlledmachine that measures the stiffness of timber.This can be directly correlated to strength whereupon a grade is assigned. Individual pieces arefed into the machine in a longitudinal direction,which continually deflects the timber by a givenload. Stress grades are assigned based on themeasured stiffness. The main guiding documentfor this method is AS1748.

Proof GradingProof grading allocates a stress grade based on apiece of timber being able to sustain a specificproof bending stress. The proof stress is generally2.2 to 2.4 times the actual design stress. The mainguiding document for this method is AS3519.

Grading in PracticeMachine grading is useful where economies ofscale and the characteristics of the timber permit.It allows grading to take place as an in-line partof the milling process and is less reliant on humanerror. Even so, machine grading is sometimeshard to undertake on high strength hardwoods –the machines have difficulty bending the timber.In addition, machines cannot check for decayand susceptibility to the Lyctus borer. As such itis not necessarily the most efficient approach andso visual grading is still common. Table 8 providesan account of common methods and commonlyavailable stress grades for Cypress and hardwoods(seasoned and unseasoned).

Hardwoods and Cypress have been used since early settlement in Australia for all types of structures.They have proven to be sustainable and readily available resources. Design principles have nowdeveloped to deliver highly adapted products. Hardwoods and Cypress offer strength, fire resistanceand natural durability. Careful design and detailing can optimise these properties in structures asdiscussed in this section of the guide.

Section Three

Designing for Structural Strength3

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SIZES AND AVAILABILITY There are standardised sizes for structural timber which serve to assistdesign, production, pricing and quality control requirements – sizesare presented in Tables 7, 8 and 9.

Common stress grades

Occasional achievable stress grades

Common grading method

Cypress

F4 and F5

F7

Visual and Proof

UnseasonedHardwoodsF14 and F17

F8, F11 and F22

Visual and Proof

SeasonedHardwoodsF17 and F27

F34

Visual

Table 6: Stress grades for hardwoods and Cypress

Dimension

mm

35

45

70

✓

✓

90

✓

✓

120

✓

✓

140

✓

✓

170

✓

✓

190

✓

✓

240

✓

✓

Table 7: Sizes for seasoned hardwood

Notes: 1. Commonly available sizes – marked ✓.2. Lengths are generally available in 0.3 m increments, up to 6 m; Longer lengths may be

available where structurally joined with nail plates.3. Tolerances +2, -0mm.4. 70 and 90mm widths are generally made up by vertically nail laminating.

Structural and ????? applicable.5. Preservative treatment branding on each piece of timber.6. 270 and 290mm limited availability.7. 45mm is of lower availability.

50

✗

✗

✗

✓

✓

75

✗

✓

✓

✓

✓

100

✗

✓

✓

✓

✓

125

✗

✓

✓

✓

✓

150

✗

✓

✓

✓

✓

175

✓

✓

✓

✓

✗

200

✗

✓

✓

✓

✗

225

✓

✓

✓

✓

✗

250

✓

✓

✓

✗

✗

275

✓

✗

✗

✗

✗

300

✓

✗

✗

✗

✗

Table 8: Sizes for unseasoned hardwood

Notes: 1. Commonly available sizes – marked ✓; Additional sizes usually available on order – marked ✗.

2. Lengths are generally available in 0.3m increments, up to 6m readily available; 6 to6.9m frequently available; 6.9m and over – check with supplier.

3. Tolerances for lengths up to 6 m long and up to 200mm in width: ±3mm. For lengthsover 6m long, increase tolerances by one-third.

4. Posts – 125 x 125mm and 150 x 150mm are also available.5. Sized or gauged timber tolerances: +2, -0mm.6. Preservative treatment branding on each piece of timber where applicable.

Dimension

mm

25

38

50

75

100



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SPAN TABLESStress grades and timber sizes combine todetermine the spanning ability of load carryingmembers. Span tables allow users to choose anappropriate size and stress grade to achievespanning needs. For simple construction – suchas domestic construction – this can be determinedfrom span table supplements in AS1684.2 andAS1684.3. For multi-unit residential construction,span tables can be down loaded from theNational Timber Development Council web sitewww.timber.org.au/mrtfc. For decks, stairs,handrails and balustrades, refer to the applicationguides referenced in Section 5 of this document,to obtain specific span tables. For other loadconditions, spans can be determined fromproprietary computer programs commonly usedby timber producers.

TIMBER JOINTS & CONNECTORS Timber must be able to make strong joints as wellas having strong spanning ability. This isdetermined by strength developed parallel orperpendicular to grain. If one direction is weakerthan the other then joint strength is reduced.Splitting may occur if connectors are placed tooclose to the edge or too close to each other. TheSpecies Guide referenced in Section 5 of this

document advises on the ‘joint group’ to whicheach species belongs. This is a measure of thetimbers ability to hold fasteners and bear jointloads. For domestic construction AS1684 adviseson connector arrangements for various jointgroups in standard framing situations. In otherinstances, joint group information must be usedin conjunction with AS1720.1 and structuralengineering principles, to confirm jointing andconnector requirements.

Choosing an Efficient Connector betweenTimber MembersAn efficient connector maximises structuralperformance, minimises cost, and minimisesinstallation effort. Many small connectors spacedclose together – such as nails – are generally moreefficient than fewer large connectors spacedfurther apart – such as bolts. In addition, nailshave the added benefit of being fast to install,especially when used with a nail gun and nailingtemplate.

Connector efficiency can also be aided by thedesign of the timber joint. For instance, beamsthat bear directly onto columns are more efficientthan cleat joints. If a cleat joint can not be entirelyavoided then the derivation shown using a corbelsupport is preferable (refer Figure 12).

Width

mm

38

50

75

100

75

✓

✓

✓

✓

100

✓

✓

✓

✓

125

✓

✓

✓

✗

150

✓

✓

✓

✗

175

✗

✓

✓

✗

200

✗

✗

✗

✗

225

–

✗

✗

✗

250

–

✗

✗

✗

Table 9: Sizes for unseasoned Cypress

Notes: 1. Commonly available sizes – marked ✓Additional sizes usually available on order – marked ✗.

2. Lengths are generally available in 0.3m increments, up to 6m readily available; over 6m – check with supplier.

3. Tolerances for lengths up to 6m long and up to 200mm in width: ±3mm; up to 6m longand over 200m in width: +9, -3mm; over 6m long tolerance increased by one-third.

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Types of ConnectorsAn advantage of timber is its ability to make useof a wide range of connectors, including nails,spikes, screws, bolts and nail plates.

NailsNails are the most common form of mechanicalfasteners used in construction. There are manytypes, sizes and forms. When using nails, thenumber, spacing, depth of penetration, pull outstrength, and resistance to lateral movement,influences overall connection strength. Nailoptions include bullet head, flat head, hardboard,wallboard, fibre cement, clout and plasterboardnails – as shown in Table 10. Different types ofcorrosion resistant materials can be matched withcertain nail types including stainless steel, siliconbronze, monel and galvanised coating. Nails havea tendency to split timber when being driven,and the use of blunt or chisel headed nails mayalleviate the problem, as will pre-drilling of kilndried timber. The metal in some nails can reactwith the extract from timbers, forming stains. Forinstance, uncoated steel nails can cause blackstains while copper can produce green stains. Toavoid this problem, galvanised nails arerecommended.

ScrewsScrews are commonly classified by head typeand by the method of drive. They are mainly usedfor light to medium scale structural situations.They offer superior pull-out strength comparedto nails but take longer to install. In recent yearsself drilling screws – especially Type 17 screws– have made installation faster. Types includecountersunk, raised counter sunk, round headhexagon, washer head – as shown in Table 11.

Screws are manufactured from low-carbon steel,brass and stainless steel. The latter two are often

used for highly corrosive environments. Analternative is to make use of hot-dip galvanising.Yet another alternative – for low corrosion risksituations – is electroplating in either zinc,zinc–chrome, cadmium nickel or chromium.

BoltsBolts function by bearing on the surface of thetimber and the shearing action within the boltitself. Common types are shown in Tables 12, andin most instances should be accompanied withwashers. Common washer sizes for timber areshown in Table 13.

Bolts are commonly used to fix large timbermembers together, or timber to steel. Coachscrews are used for slightly lower strengthsituations and are essentially heavy duty screwsbut are sized similar to bolts. They are usefulwhere nuts cannot be placed onto bolts and areonly suitable for timber to timber joints, or steelto timber joints.

Bolts can also be used to attach timber toconcrete or masonry. This is typically through theuse of special masonry or chemical anchors. Hereno nuts are used on the end in the concrete ormasonry. Instead the bolts rely on friction oradhesion to the substrate. Care is required tomake sure the anchor strength is sufficient to resistpull out loads. In addition, washers at the boltheads must be large enough to prevent timberfibres from crushing when exposed to pull-outloads.

In general, bolts and coach screws are made fromlow-carbon steel, and in some instances brass orstainless steel. The choice is often driven by theneed for corrosion resistance. Where steel is used,this can be improved using hot-dip galvanisingand electro-plating.

Pole notched toprovide bearingfor beam

Minimum contactbetween beam and pole

Corbel supports beam

Figure 12: Typical structural connections



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Type

Bullet Head Nail

Type Application

Hexagon Washer Headexternal hexagon drive

Countersunk Headcross-recessed drive

Wafer Headcross-recessed drive

Bugle Headcross-recessed and hexagonal

recessed head

Roof sheet fixing. Used with neoprenewasher under head

General fixing in wood to woodconnections

General fixing of proprietary metalfastener to wood connections, where

roof sheeting rests on fasteners

General fixing in wood to woodconnections where uplift may be

severe

Flat Head Nail

Hardboard Nail

WallBoard Nail

Cement Sheet Nail

Flex Sheet Nail

Soft Sheet Nail

Clout

Plasterboard Nail

Decking Spike

Duplex Nail

Roofing Nail

Fencing Staple

Timber framing and general finishing

Metal connectors, containers and softwood framing

Hardboard fixing

Wallboard fixing

Cement sheeting

Galvanised sheeting, other flexible sheeting

Low density materials, e.g Plastics

General fixing of thin sheets, not recommended forstructural connectors such as framing anchors

Plasterboard fixing

Timber deck fixing

Concrete framework can be withdrawn

Fix galvanised roof or wall sheeting(non-cyclonic areas only)

Fix fencing wire

Application

Table 10: Nail selection guide

Table 11: Screw selection guide

Table 12: Bolt selection guide

Illustration

Illustration

Type Application

Hexagon Head Bolt General structural purposes

Cup Head Bolt Occasional structural purposes where head must beflush with surface

Coach Screw Used to replace bolts where nut is inaccessible or to improve appearance

Threaded Rod Applications where it is difficult to specify boltlength beforehand, e.g tie-down rods, pole

construction and cross-bracing

Illustration

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ADDING TIMBER SIZE TO INSULATE AGAINST FIREFire confronts the performance attributes of anystructure. Many people do not realise that largesolid timber sections perform well in fires – evenbetter than steel. Timber chars slowly which hasan insulating effect on the unburnt timberbeneath. This makes it possible to design timberto resist burning or collapse for a given period oftime. For instance, the rate of charring and hencethe rate of reduction of load carrying capacitydue to loss of cross section, can be calculated.As a result it is possible to design slightly largermembers in order to resist fire. The need for thisdepends on the class of building as defined inthe Building Code of Australia (it tends to beunnecessary for many residential buildings). Themeans for establishing the additional sizerequired for charring is determined usingAS1720.4 which addresses fire resistance forstructural timber members. For instance, bysubstituting appropriate values into the equationsbelow, the residual cross section for constructionelements can be calculated with sufficientaccuracy to meet the compliance requirementsof the BCA (refer Specification A2.3 Clause 3).

Notional Charring Rate

C = 0.4 + (280/D)2

where C = notional charring rate, inmillimetres per minute (mm/min)

and D = timber density at a moisturecontent of 12% in kilograms per cubicmetre (kg/m3)

Note: species of higher density char more slowly(i.e. reduction in charring is roughly inverselyproportional to increase in density)

Effective Depth of Charring (in millimetres)

dc = Ct + 7.5

where dc = calculated effective depth ofcharring in millimetres (mm)

and C = notional charring rate in millimetresper minute(mm/min) as calculated

and t = period of time, in minutes (min)

Note: The effective depth of charring will dependon the number of faces of the member exposedto the fire – 1, 2, 3, or 4. If all faces are exposed,then charring depth must be added to all facesof the structurally required cross section size.

Thickness (mm)2.0

2.5

3.0

4.0

5.0

Round WasherMinimum Dia. (mm)

36

45

55

65

75

Square WasherMin. Side Length (mm)

36

45

55

65

75

Bolt

M8

M10

M12

M16

M20

Table 13: Washer selection guide

Washer Size

Note: Source: AS1720.1



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Sample: Calculation to determine the size of a 60/–/– FRL Blackbutt post

Step 1: Determine the size of the post required to support the floor using timber design methods inAS1720.1. Reference to AS1720.4 (Clause 2.8) may also be useful as it defines ‘fire limitstate’ load conditions. This state may allow lower load conditions than when a fire is absent.As a result, the increase in timber size for charring may go part/full way to meeting sizesrequirements for normal load conditions. Say a 55 x 55mm post is required for the example.

Step 2: Determine the notional rate of char for Blackbutt.

Step 3:

Step 4:

Thus for a Blackbutt post with an FRL of 60/ – / –, the most practical size is probably 150 x150mm unseasoned timber which will season in-situ (i.e. this is being selected as a substitutefor seasoned Blackbutt, which is hard to obtain). Another option is a glue-laminated Blackbuttpost at least 130 x 130mm.

Species: Blackbutt – Density @ 12% M.C. =

Notional charring rate C =

=

=

900kg/m3

0.4 + (280)2

(Density)

0.4 + (280)2

(900 )

0.5mm/min

Charring depth for 60 minutes. =

=

=

=

=

Ct + 7.5

(0.5 x 60) + 7.5

0.4 + (280)2

30 + 7.5

37.5mm each side (assume all sides effected).

Size of column required =

=

55 + 37.5 + 37.5

130 x 130mm

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Figure 13: Process for selecting timber in structurally oriented situations

CHECKING YOUR STRUCTURAL SELECTIONAs with appearance needs, it is a good idea to check yourstructural selection by using the decision flow chart shownin Figure 13. Its aims is to ensure all appropriate factors aretaken into account for different specification scenarios.


D E S I G N I N G F O R D U R A B I L I T Y

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PERFORMANCE CRITERIA FOR DURABILITY Durability considerations are important inensuring the service life of all timber products.Designers need to choose timber and details thatsuit the service environment. The main factorsinclude weathering, fungal decay, and termite orborer attack. These issues have been combinedinto hazard classes, as shown in Table 14.

These service conditions can be accommodatedby one or more of the following:

• select naturally durable timbers,

• use timber that has been preservative treated,

• detail construction to provide protection,

• use protective coatings,

• uphold an appropriate maintenance strategy.

NATURAL TIMBER DURABILITY Cypress and many hardwoods show great naturaldurability. For instance, Turpentine has a proventrack record in tough marine environments suchas wharf construction. Timber species are dividedinto four durability classes as shown in Table 15.The tabulated data indicates how long eachspecies will resist decay and termite attack underdifferent hazard conditions. These classificationsrelate specifically to untreated heartwood ratherthan the less durable sapwood (which is generallyregarded as Class 4 durability).

Irrespective of structural or appearance requirements, durability has overriding importance. Thissection systematically deals with durability issues. It starts by setting-up performance criteria fordurability and then suggests ways of addressing these criteria. This includes the use of naturallydurable timber, preservative treatments, detailing construction to protect timber, protective coatingsand maintenance strategies

Section Four

Designing for Durability

Exposure/ServiceCondition

Inside, above ground.Completely protected from theweather , well ventilated and

protected from termites

Inside, above ground Protectedfrom wetting, nil leaching

Outside above ground i.e.periodic wetting and leaching,

borers and termites

Outside, in-ground Subject tosevere wetting and leaching

Outside, in-ground contact withor in fresh water.

Subject to extreme wetting andleaching and/or where the

critical use requires a higherdegree of protection.

Marine watersSubject to prolonged immersion

in sea water

BiologicalHazard

Lyctid borers

Borers and termites

Moderate decay, borers andtermites

Severe decay, borers and termites

Very severe decay, borers andtermites

Marine wood borers and decay

TypicalExample

Framing, flooring, interior fit-out,furniture

Termite resistant framing

Pergolas, decks, fences,weatherboards, window joinery

Fence posts, garden edging,landscaping timbers

Building poles constantlyexposed to fresh water, retaining

walls, piles, stumps, coolingtowers

Boat hulls, marine piles; jettycross bracing, landing steps and

similar

HazardClass

H1

H2

H3

H4

H5

H6

Table 14: Durability hazard classes

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USE OF PRESERVATIVE TREATMENTS TO INCREASE DURABILITY The durability of timbers with low naturaldurability can be enhanced by the use ofpreservative treatments. Preservatives are addedto the timber to meet the previously describedhazard classes.

The use of preservatives involves the introductionof stable chemicals into the cellular structure ofthe timber. This protects it from wood destroyingorganisms such as fungi and insects. Preservativesare mainly used in sapwood as heartwoodcontains resins and other extracts that preventthe uptake of preservative solutions. Timbers suchas Cypress cannot be treated.

There are many types of preservatives, each withindividual advantages. These include three maingroups: Oil-borne, Water-borne and LightOrganic Solvent borne.

Oil-borne PreservativesOil-borne preservatives include creosote ormixtures of creosote, petroleum oil andinsecticides. These chemicals are generallylimited to heavy engineering structures such asroad bridges and power poles. They aresometimes added as a double treatment to marinepiles e.g. with CCA treatment.

Water-borne PreservativesWater borne preservatives include CopperChrome Arsenic (CCA), Ammonia CopperQuaternary (ACQ) and Boron compounds.

The copper-chrome-arsenic compounds cover awide biological spectrum and are not subject tosignificant leaching. The copper is a fungicideand the arsenic is both an insecticide and back-up fungicide. The chrome acts as a fixing agentto render the copper and arsenic chemicalsinsoluble. CCA treated timber is odourless andcan be readily painted or stained once dry. It hasa characteristic light green colouring.

ACQ is a newer form of timber treatment that issimilar in performance to CCA. The copper andquaternary ammonium compounds provideprotection to timber against decay, fungi, termitesand wood boring insects. The timber appearsgreen when freshly treated but mellows to agolden brown with exposure to the weather.Boron is used specifically to protect sapwoodagainst borer attack and is aimed predominatelyat the Lyctid borer in many hardwoods. It remainswater soluble after application and is onlysuitable for interior use where leaching does notoccur.

Durability Classheartwood only

Class 1 – HighlyDurable

Class 2 – Durable

Class 3 – ModeratelyDurable

Class 4 – Non-durable

Species

Bloodwood, Cypress, Grey Box,Grey Gum, Ironbark, White

Mahogany, Tallowwood,Turpentine,

Blackbutt, Jarrah, New EnglandBlackbutt, Red Mahogany, RiverRed Gum, Spotted gum, Yellow

Stringybark

Brushbox, Flooded Gum, Karri,Messmate

Brown barrel, Mountain and AlpineAsh, Manna Gum

H5In ground

25+

15 to 25

8 to 25

less than 8

H3 AbovegroundExposed

45+

30

15

5

H1Protected

50+

50+

50+

50+

Table 15: Service life of naturally durable timbers in different hazard classes



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Light Organic Solvent Preservatives (LOSP)actually describes the carrier of the preservativeand not the contents. As a result, LOSP’s varygreatly according to the preservative chemicalsadded. In general, LOSP’s are solutions of eitherinsecticides or fungicides and insecticides, andmay contain additional water repelling agents todevelop good weathering characteristics whereexposed. They are suitable for interior or exterior,but are limited to above ground situations only.They may also be protected by a coating such aspaint or oil based stain in order to extend orenhance the durability.

Irrespective of the type of preservative used thetreatment generally forms a protective envelope.As such, cutting and drilling of treated timbershould be avoided. Where this is not possible thetreatment should be patched on-site using paint-on preservatives.

In general, preservative treatments must complywith stringent statutory requirements, whethertreated within the state or imported from otherstates or overseas. State Acts take precedenceover all other documents including AustralianStandards (e.g. AS1604). Though State Acts vary,they generally cover:

• The types of preservatives that can be used.

• The minimum penetration of preservative intothe timber.

• The minimum retention of preservative in thetimber.

• The registered brand that must be applied tothe timber.

If necessary further detail on these issues shouldbe sought as required.

COATINGS TO PROTECT TIMBER & CONNECTORS Finishes provide an extended means of protectingagainst sun, rain, wind and frost. Withoutprotection, timber colour may be bleached;surface fibres may loosen; boards may cup orwarp; cross sectional sizes may slowly erode;continual shrinkage and swelling may causecracking in the timber. Without protection,structure may prematurely deteriorate.

Protective Coatings for TimberProtection can be provided by the application ofcoatings such as paints, water repellents,preservatives and pigmented stains. The mainobjective is to prevent or retard the uptake ofmoisture and the absorption of ultraviolet light.This applies to external claddings, posts, beamsand decks where there are the following optionsfor protective finishes:

• Clear water repelling treatments – thesetreatments are site applied and are essentiallysite based versions of the previously discussedpreservative treatments. Commonly theycontain an organic solvent medium, withadditives such as copper naphthanate or zincnaphthanate. In addition wax or resin is oftenadded. Where fully exposed these types ofproducts have a limited service life and re-application in 6–12 months may be required.In addition, solvent or water based finisheswith UV inhibitors are also available and giveimproved service life. Either way these finishesmust not be confused with internal clearfinishes.

• Semi transparent stains – these provide a highdegree of protection while enhancing thenatural beauty of the timber. Pigments providea UV screen and light colours are best as theyabsorb less heat. Stains utilising an oil base arealso useful in giving good moisture protection.Prior to applying stains all surfaces includingends should be given a coat of water repellentpreservative. Ideally, the first coat of stainshould be applied prior to installation, withfinal coat(s) upon completion. A service life of3–5 years can be expected depending upondegree of exposure to the weather. Re-application is relatively easy e.g. surfacesgenerally only require cleaning beforeadditional coats are applied.

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• Opaque Stains and Paints – when properlyapplied and maintained, these provide the bestprotection against weathering. Water borne(acrylic) and solvent borne (oil) paints canprovide a film which is substantiallyimpervious to water and gives maximumprotection against ultra-violet light. Thesefinishes offer a different appearance to theformer options – they hide the timbers naturalcolour and grain. Getting the most out of themis reliant on applying the recommendednumber of sealing, priming and finishing coats– as recommended by the manufacturer. Ifdone correctly a service life of between 5 and10 years can be expected from most opaquefinishes.

The above options can be used for mostapplications except decks. They occupy a specialcategory due to the amount of foot traffic,abrasion and exposure to the weather. As a resultproducts specifically manufactured for thispurpose should be used. Semi-transparent oilstains are generally the main option because theoil penetrates into the surface, providing moistureprotection. The pigments also filter the sun’s ultra-violet rays, thus reducing checking and fading.

Protective Coatings for ConnectorsPreventing chemical breakdown and corrosionat connections is another important componentof dealing with durability. The key issue is toprevent the interaction of moisture, chemicalsand metal, from causing corrosion or abreakdown of the wood fibres around metalfasteners. Most use protective coatings toconnectors, though some of the more expensiveoptions use a core corrosion resistant materialsuch as stainless steel. Options are shown inTable 16.

MaterialMild Steel

Plated (Zinc,Cadmium) and Gold

Passivated

Hot dip Galvanised

Silicon Bronze,Copper, Brass,

Monel

Stainless Steel

ApplicationFully protected from weather or

moisture

Exposed head but only whereinternal or protected from the

weather and corrosive environments

External exposed to weather andlow corrosive

Marine

Marine

Chemical, industrial, marine andpool

CommentsCheck for compatibility with preservative treated

timbers

Avoid damage during handling and installation

Bolts: Where in contact with moist CCA treated timber,additional protection using plastic sheaths or

bituminous epoxy coatings.

Nail and Screws: Usually used in boat building or foracidic timbers such as western red cedar. Not for use

when in contact with aluminium.

Nails and Screws: Used in boat building

Grade 316 preferred for marine environments.Additional coatings should be applied to Grade 304

Table 16: Connectors to prevent corrosion and chemical breakdown

Precautionary note: Many hardwoods have a low pH level (i.e. acidic) therefore increasing corrosion especially wheremoisture is present. As a result, it is best to err on the side of caution when using the above table. Specify higher ratherthan lower.



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MAINTENANCE STRATEGIESMaintenance of timber is crucial to the long termserviceability of timber structures. Timberprotected by an overhanging structure requireslittle or no maintenance, but where exposed tothe weather, some form of maintenance duringthe life of the structure is important. Designphilosophy here gives three options:–

1. Over design the element so it needs nomaintenance during its life.

2. Maintain elements as demanded.

3. Design the elements so that they are cyclicallymaintained.

Of these, strategy one is least preferred, whilestrategy three is most preferred. Strategy twoclearly offers an intermediate option. Having saidthis, the choice between all three will beinfluenced by access to the timber and budgetaryconstraints.

BUSHFIRE PRONE AREASBushfire prone areas require specialconsideration. These areas are usually defined bylocal council and require building materials thatperform well in fires. Timber species falling intothis category include Blackbutt, Red Ironbark,River Red Gum, Silver Top Ash, Spotted Gum andTurpentine. All satisfy the definition of fireretardant timbers (Warrington Fire Research).Reference should also be made to AS3959 forfurther details on regulatory requirements.

Strategy

Shedding water

Sacrificial Elements

Isolating timber fromHazard

Easy inspection andmaintenance

Method

Slope the element enough to allow waterrun-off.

Use protective elements over the top andside of critical elements. Here, sacrificial

options such as cladding or cappings, takethe direct weathering while the underlying

element is protected.

Use a barrier to prevent moisture or insectattack.

Detail elements so that they can beinspected or maintained i.e. ensure they are

assessable

Example

Handrail and balustrade with 5º slope

Cladding over beamsCaps power poles

Damp proof coursePost stirrups

Termite physical barriers

Post stirrups

Table 17: Strategies to improve timber durability

DETAILING CONSTRUCTION TO PROTECT TIMBERDetailing construction to enhance durability may include one or moreof the methods described in Table 17.

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CHECKING YOUR DURABILITY SELECTIONIt is appropriate to check your durability decisions beforecommitting to a specification as shown in Figure 14.

Figure 14: Process for selecting timber when designing for durability


F O R M A L I S I N G T H E S P E C I F I C A T I O N

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WRITING THE SPECIFICATIONOnce selection of timber has been completed itis important that the correct information ispresented so that all involved know what isrequired. This is also an important mechanism toprotect the designer from any deviations tospecification that may occur during the job. Aone line timber specification can be made up ofa series of abbreviated words and numbers, eachdescribing a particular characteristic of the timberelement. The basic principles are shown inTable 18 and an applied example is shown onFigure 15. Here it is notable that items are usually

shown on the side of the drawing with an arrow.Another option is to include the information ina key or table with member sizes. A third optionis to write the information in a separatespecification document. Under any of thesescenarios it is important to ensure that thematerials specified are cross referenced withcontingent information covering timber durabilityand workmanship. This may be linked to notescovering regulations, standards, legislation andon-going maintenance regimes.

This section gives guidance on writing a timber specification in drawings or documents. It alsoprovides references to underlying regulatory documents, technical application guides and technicalterms.

Characteristic

Application or Product

Size

Species or Species group

Surface Finish

Profile

Moisture Content

Treatment

Durability Class

Structural Grade

Appearance Grade

Special Features

Fixings

Fabrication details

Finishing details

Example of Key Words

Cladding, flooring, rafter, beam, joist, hand rail, etc

Width (mm) x Thickness (mm) x Length (mm or m)

Mixed hardwood, blackbutt, spotted gum, New England group

Sawn, dressed, sized, gauged, D.A.R., reeded finish, etc.

Tongue and Groove (T&G), End matched

Seasoned or unseasoned

Treated H1, H2, H3, H4, H5, H6 or untreated

Durability Class 1, 2, 3 or 4

F8, F11, F14, F17, F22, F27 etc.

Hardwood: Select, Medium feature, High featureCypress: Grade 1 or 2

e.g. density between 600 and 700 kg/m3

Fixed with 2/75 x 3.15mm diameter galvanised nails

To specific requirements

One flood coat of water repellent preservative

Table 18: One line specification guidelines

Section Five

Formalising the Specification5

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Figure 15: Typical specification on drawings

100 x 38mm F14 HWD top rail screwed to posts and edges arrised

90 x 45mm F14 HWD DAR with top edges arrised. Screw fixed to support frame

75 x 50mm F14 HWD support framing secured with 10mm Ø HDG cup head bolts

100 x 100mm F14 HWD supports skew nailed to decking

88 x 19mm select HWD decking

125 x 75mm F14 HWD bearer

Post fixed to 50 x 6mm HDG steel "W" bracket with 2/12mm Ø HDG bolts

100 x 100mm F14 HWD posts @ 1200mm cts

10mm Ø HDG cup head bolts

12mm ø HDG cup head bolts

75 x 50mm F14 HWD nogging @1200mm cts

900

400

400

45

Timber dried by exposure to air in a yard or shed, without artificial heat(also see seasoning).

The sharp intersection of two surfaces, e.g.. face and edge of a piece oftimber.

Cut so that the wide face of the piece is a tangential plane to the growthrings. Trade practice in Australia is to class timber as backcut when theaverage inclination of the growth rings to the wide face is less than 45degrees, and to class veneer as backcut when the growth rings are nominallyparallel to the face of the veneer.

The pith and the adjacent wood contained within the four surfaces of apiece of timber anywhere in its length

air-dried timber:

arris:

backcut:

boxed heart:

GLOSSARY OF TERMS



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The moisture content at which timber neither gains nor loses moisture from the surrounding atmosphere

The point in the seasoning or wetting of timber at which the cell cavitiesare free from water but cell walls are still saturated with bound water. It istaken as approximately 25–30% moisture content

Unseasoned, wet, with free water present in the cell

The portion of a log that includes the pith and the associated defectivewood

The wood making up the centre part of the tree, beneath the sapwood.Cells of heartwood no longer participate in the life processes of the tree.Heartwood may contain phenolic compounds, gums, resins, and othermaterials that usually make it darker and more decay resistant than sapwood

In situation

One of the principal chemical constituents of wood cellular tissue – thebinding agent

Generally parallel to the direction of the wood fibres

Larva of the family Lyctidae, commonly the species Lyctus brunneus Steph.,which attacks starch sapwood of some seasoned or partially seasoned,pored timbers. The adult beetle makes the flight hole. Syn. Powder-postborer

Timber is classified according to its susceptibility to attack by lyctid borer.Legislation governs the sale and use of lyctid susceptible timber in NSWand Queensland; Australian Standards limit the use of lyctid susceptiblesapwood throughout Australia

The weight of moisture contained in a piece of timber expressed as apercentage of the oven dry weight

The named size, or ordered size, which may vary from the actual size ofthe piece because of variations due to sawing, shrinkage and dressing andthe tolerances allowed on these operations

Timber in which the average inclination of the growth rings to the wideface is not less that 45 degrees

Coincident with a radius from the axis of the tree or log to the circumference

Timber sawn on the radius from the central axis of the tree or log to thecircumference, perpendicular to the growth rings. The resulting pieces aregenerally triangular in shape

Outer layers of wood which, in a growing tree, contain living cells andreserve materials such as starch. Under most conditions the sapwood ispaler in colour and more susceptible to decay than heartwood

Coincident with a tangent at the circumference of a tree or log, or parallelto such a tangent. In practice, it often means roughly coincident with agrowth ring

Timber in which the average moisture content exceeds 25%

equilibrium moisturecontent (EMC):

fibre saturation point:

green timber:

heart:

heartwood:

insitu:

lignin:

longitudinal:

lyctid borer:

lyctid susceptibility:

moisture content:

nominal size:

quarter sawn timber:

radial:

radially sawn:

sapwood:

tangential:

unseasoned timber:

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BIBLIOGRAPHY & REGULATORY DOCUMENTS1. AS1214 Hot-dip galvanised coatings on

threaded fasteners.

2. AS1604 Timber – Preservative treated – Sawnand round.

3. AS1684 Part 2 Residential timber frameconstruction – Non-cyclonic (including spantable supplements).

4. AS1684 Part 3 Residential timber frameconstruction – Cyclonic (including span tablesupplements).

5. AS1720 Part 1 Timber structures – Designmethods.

6. AS1720 Part 4 Timber structures – Fire-resistance of structural timber members.

7. AS1748 Timber stress grade – Productrequirements for mechanical stress gradedtimber.

8. AS2082 Timber – Hardwood – Visually stress-graded for structural purposes.

9. AS2796.1 Timber – Hardwood – Sawn andmilled products, Part 1: Product specification.

10. AS2796.2 Timber – Hardwood – Sawn andmilled products, Part 2: Grade description.

11. AS2858 Timber – Softwood – Visually gradedfor structural purposes.

12. AS3519 Timber – Machine proof-grading.

13. AS3959 – Construction of buildings inbushfire prone areas.

14. Building Code of Australia – BCA 1996.

15. Timber Technology – Wood Properties –Department of Employment, Education andTraining.

16. Wood in Australia KR Bootle – McGraw Hill.

17. Wood Handbook – United States Departmentof Agriculture.

18. Warrington Fire Research, The suitability ofthe use of various untreated timbers forbuilding construction in bushfire-prone areas,Dandenong

LINKED GUIDES SUPPORTING THIS DOCUMENT Hardwood & Cypress Application Guides

• Flooring

• Domestic Decks

• Non-domestic Decks, Boardwalks & LightVehicular Traffic Structures

• Stairs, Handrails & Balustrades

• Expressed Hardwood Structures

• External Cladding

• Fire Hazard Requirements for Non-domesticFit-out

• Joinery, Furniture and Fit-out

• Landscape Structures

• Round Timber – Piles, Poles & Girders

• Internal Lining Boards (Go to www.australianhardwood.net)

Hardwood and Cypress Species Guides

Hardwood and Cypress Producers Guide(Go to www.australianhardwood.net)

ACKNOWLEDGED DOCUMENTS • Timber Manual – National Association of Forest

Industries, Canberra

Sponsored by the NSW Native Timber Industry Marketing and Development Fund

T D AFor additional assistance please contact theTimber Advisory Service

1800 044 529or visit the following websites:

www.timber.net.auwww.australianhardwood.net

Timber DevelopmentAssociation (NSW) Ltd

www.timber.net.au

www.australianhardwood.net