What is the difference between kiln-dried and air-dried timber?

Kiln-dried timber is dried in controlled chambers (typically 60–80°C) to a target MC of 12% (±2%) in 1–3 weeks. Air-dried timber is stacked outdoors under cover and dried by natural air circulation over 3–12 months, typically reaching 18–22% MC (cannot reach 12% in most European climates).

Kiln-dried timber is dried in controlled chambers (typically 60–80°C) to a target MC of 12% (±2%) in 1–3 weeks. Air-dried timber is stacked outdoors under cover and dried by natural air circulation over 3–12 months, typically reaching 18–22% MC (cannot reach 12% in most European climates). For structural use in heated buildings, kiln-dried timber is essential — air-dried timber is too wet and will shrink in service.

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

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

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.