What are the dimensional tolerances for structural timber?

Dimensional tolerances for structural timber depend on the surface finish: Sawn timber: ±1 mm on thickness, ±2 mm on width (EN 336 tolerance class 1); Regularised timber: ±1 mm on all dimensions (EN 336 tolerance class 2); Planed (CLS) timber: ±0.5 mm on all dimensions. Length tolerance is typically ±5 mm for standard lengths.

Dimensional tolerances for structural timber depend on the surface finish: Sawn timber: ±1 mm on thickness, ±2 mm on width (EN 336 tolerance class 1); Regularised timber: ±1 mm on all dimensions (EN 336 tolerance class 2); Planed (CLS) timber: ±0.5 mm on all dimensions. Length tolerance is typically ±5 mm for standard lengths. For timber frame construction, regularised or CLS timber is specified because consistent dimensions are essential for panel fabrication and airtightness. Measure dimensions at multiple points along the length — timber may vary due to taper or distortion.

Why this matters

This question relates to Timber Quality Control: Inspection, Grading & Acceptance Criteria, which covers the broader topic in detail. Understanding this specific aspect helps architects, builders, and timber dealers make informed specification decisions.

For full context and additional technical detail, see our comprehensive guide:

→ Timber Quality Control: Inspection, Grading & Acceptance Criteria

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About this answer

This answer is part of the PuurModulair Knowledge Base — comprehensive timber specification guidance for architects, builders, and dealers across the UK, EU, and Scandinavia.