Timber Material Strength Grade Classification: What the Marks Mean
A practical guide to timber strength grades — covering EN 14081, ASTM O86, and how modified timber is classified
Strength grading is what makes timber material usable in structural calculations. Without a grade, you can't design with it. If you're specifying timber for a structural application, here's what the grade marks mean and how to verify them.
We supply machine-graded timber products for structural use. Here's how the grading systems work and what to check before you accept delivery.
EN 14081 (Europe): C16, C24, and What Comes Between
| Grade | MOR (N/mm²) | MOE (N/mm²) | Typical Use |
|---|---|---|---|
| C16 | 16 | 8,000 | General framing, non-critical |
| C24 | 24 | 10,000 | Floor joists, roof trusses |
| C30 | 30 | 11,000 | Glulam, engineered structural |
Keep in mind: Modified timber may have different strength values than untreated timber of the same species. Always use test data for the modified product — not generic species data from span tables.
Machine vs. Visual Grading: Which Matters for Your Order
- Machine grading (EN 14081-2): Measures MOE by deflection under load, then assigns grade. More consistent for volume production — and required for CE marking in Europe.
- Visual grading (EN 14081-1): Trained grader assesses knots, slope of grain, wane. Acceptable for smaller orders; grader certificate must be traceable to a certified grading body.
How to Verify on Delivery
Strength Grade Verification Checklist
- Grade stamp on every piece: EN 14081 requires each piece >100mm wide to carry the grade mark. For smaller sections, bundle tags are acceptable.
- Request test certificate: Machine-graded timber should come with a certificate showing the machine settings and grade yield for the production run.
- Check third-party audit: Reputable machine grading setups are audited by a certification body (BM TRADA, SPIB, etc.). Ask for the audit report reference.
Our insulating laminated wood products are supplied with grade documentation and test reports for structural applications.
Need Strength-Graded Timber for Your Project?
We provide machine-graded timber with full grade documentation and CE marking where applicable.
Or contact our technical team for grade specification support.
