Timber durability & hardness
How timber is rated for durability, hardness and strength.
Natural durability
Durability classes (AS 5604) rate the expected life of a species' heartwood when exposed to the weather. Sapwood of all species is non-durable unless treated. Timbers are rated separately for use in ground contact and above ground.
| Class | In ground contact | Above ground |
|---|---|---|
| Class 1 (highly durable) | 25+ years | 40+ years |
| Class 2 (durable) | 15–25 years | 15–40 years |
| Class 3 (moderately durable) | 5–15 years | 7–15 years |
| Class 4 (non-durable) | up to 5 years | up to 7 years |
See the durability class of each species in our timber species guide, which can filter species by in-ground and above-ground class.
Hardness
Hardness indicates resistance to indentation and wear, which matters for flooring, decking and stair treads. It is closely linked to density (measured at 12% moisture content).
| Rating | Typical density |
|---|---|
| VS (very soft) | 480 kg/m³ or less |
| S (soft) | 485–560 kg/m³ |
| F (firm) | 565–680 kg/m³ |
| M (moderate) | 685–800 kg/m³ |
| H (hard) | 805–960 kg/m³ |
| VH (very hard) | 965 kg/m³ or more |
Strength groups
Species are grouped by strength for engineering design:
| Group | Applies to | Range |
|---|---|---|
| S | Unseasoned timber | Seven groups, from S1 (strongest) to S7 |
| SD | Seasoned timber | Eight groups, from SD1 (strongest) to SD8 |
Joint groups
Joint groups indicate a species' strength in fastened joints for engineering design. There are six groups, from 1 (strongest) to 6, with separate groups for unseasoned (J) and seasoned (JD) timber.
This information is general guidance only. See our disclaimer, and check current Australian Standards and the National Construction Code for your project. Questions? Ask our team.