Decking Installation

Handling and Installation

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 approx 100mm from ground.

Installation Details

Below are the installation details for the following sizes of decking.


The maximum suggested span for 19mm hardwood decking is for joists to be at 450mm centres.

Board spacing

Board spacing should allow for air circulation and drainage and also take into account seasonal movement. All timber will shrink as the timber dries and swell as it takes on moisture. The degree to which this occurs will vary depending on timber species and whether the timber is supplied air-dried or kiln-dried.

As a guide to allow for this movement, space boards as follows:

Board width Minimum spacing
(dependent on degree of ventilation provided)
65 & 90mm 4mm
140mm 6mm


Adequate ventilation of the deck is essential for long term stability. 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.



All decking boards should have two pre-drilled pilot holes per joist. Pilot holes should penetrate through the decking and not the radiata joist.

For fastening air-dried 140x19mm decking it is recommended to use 10g x65mm stainless steel decking screws. Pilot holes should be 15mm from the edge.

For fastening 65 or 90x19mm decking, 10gx50mm stainless steel decking screws can be used or alternatively 65mm annular grooved decking nails. If nailing, pilot holes should be 12mm from board edge.

These appropriate fixings are available from Rosenfeld Kidson, along with counter sunk screw bits to suit. Screws are available with either square or star drive and decking nails are available with a countersunk or jolt head.

End Sealing

End checking and splitting can occur when decking boards are cut to length. After you cross cut the decking, it is recommended to re-seal the cut ends. Seal the ends immediately after cutting with a suitable end grain sealer.


Decking can be coated on all four sides prior to delivery with exterior wood oil using Rosenfeld Kidson’s FactoryOil service. Coating will help to minimise surface checking, reduce potential cupping of the boards and slow discolouration. Any coating used should be tested first on a small sample to ensure compatibility and always follow the manufacturer’s application instructions.


UnCoated Timber

Maintenance of your hardwood deck will vary depending on the location of the deck, its construction and many other factors like aspect, drainage, coating, profile and usage etc. Your deck should be cleaned twice annually to remove debris, accumulated dirt and surface mould etc. A hard bristled brush or low pressure water blast will give best results. Chemical cleaning products that can be effective are also available.

Coated Timber

Maintenance is the same as for an uncoated deck but also inspect the deck annually for signs of peeling, discolouration or excessive wear to the coating. At least annually or as the coating shows signs of wear; apply a fresh coat or two of the last product used as per product manufacturer’s application instructions.

NB. These guidelines should be read in conjunction with the New Zealand Building Code. When building a deck please refer to the following standards: NZS3602, NZS3604, NZS3605, NZS3640 and NZS4203. Other recommended references include BRANZ Bulletin Issue 489 (Timber slat decks/balconies).

Rosenfeld Kidson, as timber merchants acknowledge the importance of conserving the world’s greatest renewable resource.

We are pleased to advise that we carry Chain-of-Custody (CoC) certification that enables us to sell timber that carries either FSC certification (SGS-COC-006703) or PEFC certification (SGS-PEFC/COC-0993).

FSC certified timber and PEFC certified timber undergo independent, third-party audited certification procedures at every step of the supply chain. This provides designers, specifiers, architects and consumers absolute assurance that those forest and wood products labelled as FSC certified or PEFC certified originate from legal sources, which are managed to prescribed social, economic and environmental standards.

As a New Zealand timber supplier offering the country’s largest range and quantity of specialist certified timbers we believe that stocking FSC & PEFC certified timber is essential for our continued growth. A major part of our timber range has FSC or PEFC certification and we are continually striving to increase this.

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