Decking installation instructions

Timber is a natural product and is subject to variation in weight, colour, density, grain and performance. Care must be taken with decking installation and maintenance to allow for movement as some swelling , shrinkage, movement and checking can occur. Care should also be taken during use of the deck that items such as flower pots do not trap moisture against the surface which can cause discolouration and even premature rotting. Ventilation gaps must not be blocked by items such as landscaping materials as they are important for the good performance of the deck.

All decking should be kept dry before installation. Storage of decking on site should be in a cool dry place, out of direct sunlight and elevated on bearers 100mm off the ground (150mm if  ground unsealed).


The spans between joists for 19mm hardwood decking should be no more than 450mm centres.


Some of the boards may have defects so it is important to either cut out the defect or put the board to one side to use as a short later on. Sort out the lengths of the boards so you can obtain full usage without much waste.

Board spacing

Board spacing should allow for air circulation and drainage and take into account seasonal movement. All timber will shrink as the timber dries during warmer drier weather and expand during wetter weather. The degree to which this happens will depend on timber species and on site conditions, particularly relating to the degree of ventilation provided. 95mm boards should be laid with a  minimum 5mm gap and 140mm boards the gap should be a minimum of 7mm. If the board run exceeds 6m then a small expansion gap needs to be provided.


Adequate ventilation is essential for long term stability and performance of the deck. Allowing air to freely circulate around the deck will reduce the moisture differential between the top and underneath of the boards, minimising the likelihood of cupping and distortion following installation.

To achieve proper ventilation the deck should have at least 450mm clearance from the ground. Heights below this will require a special construction to achieve building code compliance.


All decking should have two predrilled holes per Joist. Pilot holes must only penetrate the deck not the joist. Pilot holes should not be less than 15mm from the edge. For Fastening 140mmx 19mm decking 10g x 65mm stainless steel screws must be used. For 95mmx 19mm decking 10g x 50mm stainless steel screws should be used.

End sealing

End checking and splitting can occur when boards are cut to length. After you cross cut the decking it is recommended to reseal all ends of the decking boards with a suitable end grain sealer.


We recommend boards to be coated with at least 2 coats of a suitable exterior oil prior to installation. Boards can be used uncoated however they will weather more than uncoated boards and be more susceptible to movement and moisture uptake. Any coating should be tested first on a sample to ensure suitability and always follow the manufacturers instructions.


Maintenance of your deck will vary according to the location of your deck, its construction and other factors like aspect, drainage coating profile and usage. Your deck should be cleaned twice a year (more if necessary)  to remove debris, accumulated dirt and surface mould etc. A hard bristled brush or low pressure water blaster will give best results. Coated decks should also be inspected for wearing of the coat  and a fresh coat applied as necessary.

These instructions should be read in accordance with the NZ building code. When building a deck please refer to the standards NZ3602, NZ3604, NZ3640, NZ4203.