What is equilibrium moisture content?

Equilibrium moisture content (EMC) is the MC at which timber neither gains nor loses moisture to the surrounding air. It depends on ambient temperature and relative humidity.

Equilibrium moisture content (EMC) is the MC at which timber neither gains nor loses moisture to the surrounding air. It depends on ambient temperature and relative humidity. In UK centrally heated buildings (20°C, 40–60% RH), EMC is approximately 10–12%. In unheated spaces, EMC is 14–18%. Externally exposed timber reaches 16–22% depending on climate and exposure. Timber should be delivered as close to its service EMC as possible.

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.