Screws

Screws for decking, cladding and garden buildings

Screws give a stronger and more adjustable fixing than nails, and they can be removed if a board needs replacing. For outdoor use the main choice is the material of the screw, because the wrong one will corrode and stain the timber around it.

Stainless A2 or A4

• A2 stainless suits most inland UK projects, including cladding and decking away from the sea and from chlorinated water.
• A4 stainless (marine grade) is better for coastal sites, swimming pool surrounds and very wet situations, because it resists chloride corrosion more effectively.

Avoid zinc plated screws on oak, larch and western red cedar, as tannins can attack them and leave dark streaks. Our screws, nails and accessories category lists the options by size and finish.

Size and spacing

For decking, choose a screw about two and a half times the board thickness, so a 28mm board takes a 65 to 70mm screw. For cladding, a screw length of twice the board thickness is a sensible starting point. Use two screws per board at each joist or batten, set 15 to 20mm in from the edge, and always pre-drill in hardwoods and thermally modified timber to prevent splitting. A countersunk head sits flush, and a small pilot hole keeps boards from cracking at the ends.

How many to order

Count the boards, multiply by the supports and by two, then add 10%. As a very rough guide, decking needs about 40 to 50 screws per square metre.

For other fixing methods see secret fixing clips or read our cladding guide. Call 0161 504 0011 if you want advice on the best screw for your timber.