What moisture content should structural timber be?

Structural timber for internal use (heated buildings) should be delivered at 12% moisture content (±2%), which corresponds to the equilibrium moisture content in centrally heated buildings. Timber for external use (Use Class 3) should be 16–20% MC.

Structural timber for internal use (heated buildings) should be delivered at 12% moisture content (±2%), which corresponds to the equilibrium moisture content in centrally heated buildings. Timber for external use (Use Class 3) should be 16–20% MC. Timber delivered above these levels will shrink as it dries in service, causing gaps, distortion, nail pops, cracking finishes, and potential structural issues at connections.

Why this matters

This question relates to Structural Timber Moisture Content: Why 12% Matters, 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:

→ Structural Timber Moisture Content: Why 12% Matters

Related questions

• How do you measure timber moisture content?
• What happens if timber is installed too wet?
• What is equilibrium moisture content?

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. All technical content is reviewed by qualified timber technologists before publication.