LumberBank is one of New Zealand’s leading hardwood decking and timber suppliers. offering a variety of hardwood and structural solutions to meet both residential and commercial applications. LumberBank prides itself on sourcing and supplying timbers from certified and renewable resources.

Timber species suitable for decking are given in NZS 3602:2003. The most commonly used timbers in New Zealand are shown in Table 1. They are: • radiata pine (must be treated H3.2) • kwila • vitex (also known as vasa) • cypress species such as heart macrocarpa • jarrah.

Product Description and Specification

Kwila is an excellent hardwood timber species that’s perfect for exterior decking and joinery, it has all the advantages a stable and durable hardwood can offer with the added reassurance of coming from an environmentally responsible source. Kwila’s surface hardness, strength and durability make it an excellent choice for New Zealand’s harsh climate.

Environmental Colour Texture and Grains Density (Dry) Durability Sizes Dried
Kwila (Instia Bijuga, Instia Palembanica) FSC® 100% Dark reddish brown with light goldy flecks Moderately coarse texture with slightly interlocked grain 870kg/m3 Class 1-2 Grip Tread/Smooth 90/140 x 19 Kiln

Storage & Handling

Decking should be kept dry and out of the weather in an area out of direct sunlight until installation. On site each pack should be kept flat and off the ground, elevated on bearers at a minimum of 100mm allowing good air flow.



Decking at 19mm thick should be installed at maximum 450mm joist centres. Where Radiata joists are used the screws should penetrate at least 45mm to achieve good holding. The spans and spacings for joists and bearers must be read from the ‘wet in service’ tables in NZS 3604:2011. SG8 is the default timber grade used.


With the climatic conditions in New Zealand the recommendation for 90x19mm should be spaced 3-4mm apart and 140x19mm spaced 4-6mm apart. The specified gap will allow the deck to drain and allow air circulation under and around the decking. NB: These are recommendations only and the installer should always factor in new Kiln dried timber vs Shipping dried with the regional climate and environments taken into account.   


Pre-drilling and countersinking for fixings is essential to avoid face and end splits. Its recommend that 90×19 & 140×19 Decking should be fixed to every joist with 10g x 65mm Stainless Steel Decking Screws. Pre-drill pilot holes slightly smaller than the screw and countersink. Drill pilot hole 12.5mm for 90mm wide decking & 15mm for 140mm wide decking in from the edge of the boards.


Proper airflow beneath the decking is crucial in minimizing cupping and warping of the timber. Good ventilation reduces the moisture difference between the top face and underside of the boards, extending the deck’s life and performance. The sub deck should have a clearance of at least 450mm from the ground and proper drainage. Additionally, the perimeter of the deck should remain open to airflow and must not be fully enclosed. In wet areas or over water, additional clearance is recommended. Failure to provide suitable ventilation is a common cause of early decking failure. Other measures to minimize moisture difference include using a ground-level vapor barrier with slit drainage and applying a suitable surface coating on all four sides of the decking boards (refer to coating section).


Deck timbers may be left unfinished or may be given some protection from weathering and UV light. This involves the application of decking oil, timber stain, non-slip paint or non-pigmented sealer (which does not protect against UV light). To enhance the performance of the decking,  avoid dark stains, ensure the space under the deck is well ventilated.To minimise surface checking, cupping and discolouration we recommend the decking be coated on all four sides. Sealing all four sides of the boards will reduce potential cupping and checking by slowing moisture transference into and out of the wood, maintaining a more even moisture content through the timber. Suitable coatings will vastly decrease the maintenance required on your decking. We recommend clear or light colours, dark colours will require additional maintanance as well as stress the timbers with expansion and contraction caused by moisture and sun exposure. With the harsh NZ weather and UV rays it is almost impossible to keep your decking from silvering off over time.

Maintenance Uncoated Timber

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

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

Note: 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)

DISCLAIMER: LumberBanks Hardwood Decking is manufactured with care and continually inspected to ensure quality. It is a natural wood product and subject to variations in weight, density, colour, grain and performance. Care must be taken during installation and the ongoing maintenance of the deck.