Timber Decking Boards can expand and contract so make sure you leave a sufficient gap when laying them. Decking Boards that are 130mm or wider will expand about 0.5mm for every 1% increase in moisture content. During winter the increase in moisture content can be around 4-6%. Therefore each board could expand up to 2-3 mm. Recommended gaps for timber decking boards that are up to 90mm is 4-6mm and for boards 130mm or wider the gap should be 7-9mm.
Decking must have enough room below it to allow for good sub deck ventilation. Allowance should also be made to ensure good cross flow ventilation. Try to avoid solid perimeter walls as they can cause a damp sub deck which will result in the bottom of the timber decking boards taking up moisture and develop cupping. If there must be solid perimeters, there are specially designed vents and fans that are available for ventilation.
This keeps the joists dry, limits the chance of rotting and gives you a better fixing for your nails or screws.
Drill a pilot hole or countersunk hole first and then drill the holes for the decking screws. This will help in reducing the stress the decking experiences when it expands and contracts during seasonal changes. Pre-drilling should limit the chance of the timber decking boards cracking and splitting. If you are using a decking nail, ensure that the board ends are pre-drilled.
Always use properly designed decking nails and screws. They should be either hot dipped galvanised or stainless steel if you’re close to saltwater. 19mm deck nails should be at least 65mm and with decking screws, a minimum of 10 gauge is advised for softwood joists. For boards 130mm and wider, 14 gauge is recommended.
It is recommended that oil based preservatives be applied to all timber surfaces including the trimmed ends before installation. This assists in reducing the amount of moisture penetration. After installation a second coat to the exposed surfaces is recommended.