Decking screws

What do you need to fix a timber deck?

WoodSolutions’ TDG 21 says framing bolts, screws and nails should be hot-dipped galvanised or stainless steel, and that electroplated fasteners are unsuitable because the plating breaks down early. For preservative-treated decking boards, use hot-dipped galvanised, stainless or fixings coated for treated timber decking.

When must fixings be stainless?

Within a pool splash zone, which TDG 21 treats as within 1.0 m of the pool edge, and within 1 km of the coast. See pool decking.

304 or 316?

The design guide doesn’t name a grade. AIMS Industrial, an Australian fastener supplier, explains that 316 (A4) contains molybdenum, which resists chlorides better than 304 (A2), and says 316 is the usual choice near the coast, around pools and in marine environments.

How do you fix the boards?

• At least two nails per joist for each board, flush and staggered. Screw requirements are proprietary, so follow the screw maker.
• At least 12 mm from edges and board ends.
• Pre-drill, with nail holes at 80 percent of the nail diameter. AIMS also advises pre-drilling near board ends and in dense hardwood, where merbau and spotted gum split easily.

Which board widths does this assume?

TDG 21 says 19 mm thick Australian species boards usually come in 64 and 86 mm widths, and imported hardwood decking in 70 or 90 mm.

What about composite boards?

Composite boards are fixed with the maker’s clips or screws, and other fixings can affect the warranty. NewTechWood, for example, says its Metal Fix screws suit steel joists up to 2 mm thick, and its clips aren’t covered on double-wall profiles such as Stratco Probeam. See the NewTechWood page and installing composite decking.