Once you move past the standard 19 mm decking board, the sizes stop being interchangeable. 135x35, 140x35 and 140x42 are three different boards for three different jobs, and the gap between them is not just a few millimetres of width. This guide sets out what we actually supply at each size and what the differences mean on site.
What we supply
| Size | Species | Origin | Notes |
|---|---|---|---|
| 135x35 mm | Ironbark, Spotted Gum, Forest Red Gum, Gympie Messmate | Australian grown | Each of these four also has a genuine 140x35 mm width option at the same rate. Select the width on the product page. |
| 140x35 mm | Blackbutt | Australian grown | Supplied at 140 mm only. |
| 140x42 mm | Merbau | Imported | A heavier section again, 7 mm thicker than the 35 mm boards. |
The 140x35 mm option on those four products is worth reading twice, because it is the answer to a question we are asked often. If you want a 140x35 mm board in Ironbark, Spotted Gum, Forest Red Gum or Gympie Messmate, you do not need a different product. It is a width option on the 135x35 mm listing, priced at the same rate per linear metre.
Width: 135 mm or 140 mm
At 35 mm thick the width choice behaves the same way it does on a standard board. Assuming the calculator's 4 mm starting gap, a 135 mm board covers 139 mm and a 140 mm board covers 144 mm. These are calculation figures; the gap you lay comes from your product's installation guide. Over a 20 m2 area that is about 144 linear metres against about 139, a difference of roughly 3.5 percent before wastage. The visual difference on a finished surface is negligible. The difference matters when you are matching existing boards or fitting whole boards to a fixed deck width. The same arithmetic at standard thickness is set out in 135x19 vs 140x19 hardwood decking.
Thickness: 35 mm or 42 mm
This is the real distinction, and it is not a small one. At the same width and length, a 42 mm board contains about 20 percent more timber than a 35 mm board. That shows up in three places: the price per linear metre, the weight your team is lifting, and the effort of cutting and pre-drilling. In dense hardwood a thicker section is noticeably harder work on tools.
What extra thickness does not automatically buy you is span. Our supplier documentation does not publish span tables for these profiles, so do not design joist centres around board thickness on the assumption that a thicker board bridges further. Confirm spans with your certifier or engineer, and take joist spacing from the installation instructions for the boards you choose.
Treat 140x42 as a materially different product from the 35 mm boards, not as a slightly thicker version of them.
A note on 140x42 and 140x45
Our 140x42 Merbau is an imported hardwood decking board. 140x45 Treated Pine Framing is MGP10 structural pine sold in set lengths for framing. The sizes are close, but they are not alternatives to each other: they differ in species, treatment, how they are sold and what they are for.
Choosing between them
- Start with the species and the durability you want, then take the sizes that species is offered in. The Australian Class 1 hardwoods carry supplier-published Class 1 above-ground durability; Merbau is listed as Class 2.
- If Blackbutt is on your shortlist, the thick board is 140x35 mm. There is no 135x35 mm Blackbutt.
- If you want 140 mm in an Australian species other than Blackbutt, use the 140 mm width option on the 135x35 mm product.
- Do not step up to 42 mm for span. Step up for mass at an exposed edge, for a more substantial walking surface, or because a specification calls for it.
- Price both before deciding. The thickness step is the largest cost variable at these sizes.
Working out quantities
Thick boards are still sold per linear metre in random lengths, so the method does not change: deck area, gap, cover width, linear metres, then an allowance for cuts. Use the timber calculator and check the working in the calculator guide, or read how decking board sizes are measured if cover width is new to you. If you are deciding between a standard 19 mm board and a thick one at the same width, the 135x19 vs 135x35 guide covers that step directly. The whole size decision is walked through in how to choose hardwood decking board sizes in Sydney, and the range is in the decking collection.