Timber Strength Class C18: Properties and Uses
Strength class C18 timber carries a characteristic bending strength of 18 newtons per square millimeter. These are the numbers structural design starts from.
Characteristic bending strength: 18 N/mm²
| Strength class | C18 |
| Characteristic bending strength | 18 N/mm² |
| Mean elastic modulus | 9 GPa |
| Characteristic density | 320 kg per cubic meter |
| Typical source | better general softwood |
Notes for design and site
C18 sits in the catalog between the mass market classes and is often the machine graded output of decent spruce. Specify it where C16 fails a deflection check by a whisker, but check availability first: many suppliers stock only C16 and C24, and a C24 substitution is never wrong structurally.
Related Calculators and Reference
- Property Library: the full materials reference on this site.
- Bill of Quantities Builder: price the timber package properly.
- Eurocodes at the JRC: the design standards behind these classes.