Decking Know How Tips & Advise
|Species ||Durability Class ||Movement In Use ||Bleeding ||Splintering ||Length Specification ||Notes |
|Accoya ||1 ||.0.8 - 1.5% ||Low ||Low ||2.4 - 4.8M || |
|Jarrah ||2 ||5.0 - 7.5% ||Low ||Low ||0.9 - 5.4M (2.4M avg) ||Watch swelling |
|Kwila ||2 ||1.5 - 3.0% ||High ||Low ||1.8 - 5.4M (3.0M avg) ||Watch bleeding |
|Macrocarpa ||2 - 3 ||3.0 - 5.0% ||Low ||Low ||1.8 - 5.4M (2.7M avg) ||Not recommended |
|Pilularis/Blackbutt ||2 ||4.0 - 7.0% ||Low-Medium ||Low ||1.8 - 4.5M (2.7M avg) ||Watch swelling |
|Radiata (treated) ||2 ||3.0 - 4.5% ||Low ||Medium ||1.8 - 6.0M (3.0M avg) ||More likely to check and splinter |
|Rosewood ||1 ||1.0 - 2.0% ||Low-Medium ||Low ||1.5 - 4.5M (2.4M avg) || |
|Saligna ||2 - 3 ||5.0 - 9.0% ||Low-Medium ||Low ||1.8 - 4.5M (2.7M avg) ||Watch swelling |
|Vitex ||2 ||2.0 - 4.0% ||Low-Medium ||Low ||1.5 - 3.6M (2.4M avg) ||Shorter lengths |
|Western Red Cedar ||2 ||1.5 - 3.0% ||Low ||Low-Medium ||1.8 - 6.0M (3.0M avg) || |
|Yellow Cedar ||1 ||3.0 - 6.0% ||Low ||Low ||1.8 - 4.8M (3.3M avg) || |
More about Slip Resistance
The Department of Building and Housing advises that decks not on the route to the main entrance do not require a slip resistance of 0.4 to meet the Building Code clause D1 (Access Routes).
However any exposed timber decking on the route to the main entrance will probably need to have some form increased slip resistance, this is most easily achieved by either fixing a weatherproof matting to the timber or coating the timber with a sand/grit impregnated coating.
More information click here.
Timbers commonly used in New Zealand vary enormously in term of stability (how much they shrink and swell). Three factors need to be considered in determining the gap between boards:
- Moisture Content: Decking is supplied in a range of moisture contents to the New Zealand market, from near green to kiln dried. Generally speaking, a kiln dried will swell more than a green board.
- Species: Kwila is a very stable species which does not shrink and swell a lot however, other species like Jarrah, Saligna, Greenheart, and others all shrink and swell a lot.
- Size (width of the board): Wider boards will shrink/swell more than narrower boards so require a larger expansion gap.
This table gives recommended expansion gaps for Timber Decking:
| ||90-120mm Wide ||130-140mm Wide |
|Species ||Green / Shipping Dry ||Air Dried / Kiln Dried ||Green / Shipping Dry ||Air Dried / Kiln Dried |
|N/A ||3-4mm ||N/A ||4-6mm |
|Blackbutt ||3mm ||4mm ||Not recommended ||6-8mm |
|Jarrah ||Not recommended ||5mm ||Not recommended ||Not recommended |
|Kwila ||3mm ||4mm ||Not recommended ||6-8mm |
|Saligna ||Not recommended ||5mm ||Not recommended ||Not recommended |
|Vitex ||3mm ||4mm ||Not recommended ||6-8mm |
For more information download our hardwood decking brochure, visit our downloads page.