Timber decking in Australia

What timber is used for decking in Australia?

The common choices are hardwoods such as merbau, blackbutt and spotted gum, cypress, and softwood (usually pine) treated against rot. WoodSolutions’ Technical Design Guide 21 says above-ground deck timber should be Class 1 or 2 hardwood (with sapwood removed or H3 treated), or softwood treated to at least H3.

Class 1 above ground means a life of more than 40 years in WoodSolutions’ system, and Class 2 means 15 to 40. These are lives for the timber itself under the standard’s conditions, not a warranty on your deck. The merbau, blackbutt and spotted gum entries are also listed as termite resistant and bushfire-resisting timbers for BAL-12.5, 19 and 29.

How far apart should the joists be for timber boards?

WoodSolutions’ Table 2 gives maximum joist spacing by board:

At 45 degrees to the joists, the example given is 19 mm standard-grade hardwood, which needs joists at 350 mm. For the frame as a whole, see how to build a deck.

Does merbau really stain?

Yes. WoodSolutions says most hardwoods contain extractives that can leach to the surface and stain brickwork, concrete or paving under the deck, and recommends seasoned timber and a water-repellent finish on all surfaces, cut ends included. One Australian presenter describes merbau as cheap and hard but very resinous, so untreated boards stain whatever is beneath them when it rains, and a finish put on too early can leach and run. His options are weathering the deck for about four to six weeks or using a tannin-removing prep product, and he expected about 18 months from the oil. Another presenter says a prep reviver lets you skip the usual 6 to 8 week wait. Those are their figures, not a standard. Our merbau and composite comparison puts it against composite.

What fixings should you use on timber decking?

Hot-dipped galvanised or stainless steel. Electroplated fasteners aren’t suitable. Within 1.0 m of a pool edge or within 1 km of the coast they must be stainless. Fix at least 12 mm from edges and ends, in pre-drilled holes. See decking screws for 304 against 316.

What does a timber deck need to last?

Raised decks (boards more than 400 mm above the ground) need drainage and cross-flow ventilation underneath, as for a raised timber floor in a house. A damp-proof strip on top of each joist adds service life. Oil or stain keeps the colour, and cleaning keeps it safe underfoot; see deck cleaning for the routine on merbau.

How much does timber decking cost?

We haven’t read a dated Australian price list for decking timber, so we don’t quote prices. Merchants quote by the lineal metre and the board profile. The cost calculator lets you enter your quote, and it won’t show a total until every required line has a price.

Is pool decking different?

Pool surrounds add slip, heat and chemical concerns. Fixings within 1 m of a pool edge must be stainless on a timber deck. See pool decking for what the makers say.