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. 

Expansion Gaps

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
Accoya
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.

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