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 |
| 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 |
| Spotted Gum | 1 | | Low | Low | | |
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 of increased slip resistance.
More information click here
Expansion Gaps
Timbers commonly used in New Zealand vary enormously in terms of stability (how much they shrink and swell). Three factors need to be considered in determining the gap between boards:
- Moisture Content: The moisture content of the framing must not exceed 20% at the time of fixing the decking as problems may occur later and cause excessive timber movement if framing is too wet.
- Species: Expansion gap for each species is different. Refer the following table for information. Decking species at ITI Timspec include Kwila, Vitex, Spotted Gum and Accoya®
- 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 |
| Spotted Gum | Not recommended | 4mm | Not recommended | 6-8mm |
| Vitex | 3mm | 4mm | Not recommended | 6-8mm |
For more information download our hardwood decking brochure, visit our downloads page.