C16 or C24? A Buyer's Guide to Structural Softwood Grades
Structural softwood is strength-graded so a designer can rely on how it performs. In this region you will mostly meet two strength classes, C16 and C24, and the difference between them is smaller than most buyers assume, but it lands squarely on your bill of quantities.
What the numbers mean
The number is the characteristic bending strength in newtons per square millimetre. C24 is stiffer and stronger than C16, with a higher modulus of elasticity, so it deflects less over the same span. Both are visually or machine graded to BS EN 338 and stamped accordingly.
Where each earns its place
- C16 suits general carcassing, wall plates, noggins, studwork and short span joists where loads are modest.
- C24 suits longer floor and roof spans, higher point loads, and anywhere the engineer has specified it outright.
Specifying C24 everywhere feels safe but adds cost you may not need; dropping to C16 where the design allows can trim a timber package meaningfully. The right answer is per member, not per project.
Moisture and treatment
Grade is only half the story. Kiln dried stock holds its shape; treated timber (UC3 / UC4) is essential for anything exposed or in ground contact. We supply both graded and treated to order, with certificates on request.
Tell us your spans and loads and we will help you land the leanest compliant grade. Start an enquiry →