What is equilibrium moisture content?
Equilibrium moisture content (EMC) is the percentage of moisture a hygroscopic material — such as wood — absorbs or releases until it reaches equilibrium with the temperature and humidity of its surrounding air. It is a key parameter in timber construction, parquet floors, joinery and wooden furniture.
Why is EMC important?
Wood swells when it absorbs moisture and shrinks when it dries out. If wood is installed at the wrong moisture content, problems can arise after installation:
- Shrinkage cracks — the wood dries out and splits
- Swelling and warping — caused by moisture absorption
- Sticking doors and windows — especially in wet seasons
- Loose parquet — gaps in winter, buckling in summer
Application
The EMC depends on climate conditions:
| Situation | Temp/RH | EMC of wood |
|---|---|---|
| Sheltered outdoor climate | 12 °C / 80% RH | 16–18% |
| Unheated room | 15 °C / 70% RH | 13–15% |
| Heated home | 20 °C / 50% RH | 9–11% |
| Heated home (winter) | 22 °C / 30% RH | 6–8% |
| Underfloor heating | 23 °C / 40% RH | 6–8% |
In practice with parquet and joinery
- Parquet in a heated home: install at 8–10% moisture content
- External joinery in larch or meranti: 14–16%
- Internal joinery in pine: 10–12%
- Solid wood furniture: 8–10%
Acclimatising
Wood needs time before installation to adjust to the room climate. This is called acclimatising:
- Solid parquet — at least 5 days to acclimatise
- Internal joinery — leave a week in the dry building
- Floorboards — open packaging in the actual room
Measuring moisture content
A wood moisture meter measures the current moisture. Compare this with the expected EMC of the final location. If there is a large difference, do not install the wood until it has had a chance to adjust.
Related terms
- Hygroscopic
- Wood
- Drying
- Shrinkage
- Relative humidity
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