EMC – Equilibrium Moisture Content
From the US Department of Agriculture Wood Handbook: “Wood as an Engineering Material”
Recommendations for relative humidity in buildings range from 30% – 50%.
Recommendations for ambient temperature in buildings range from 60°F – 80°F.
If ambient conditions stay within the recommended ranges, the EMC – equilibrium moisture content of wood stays between 6% and 9%. Should the moisture content change within the given range, the amount of expansion and contraction of wood is limited.
Examples:
1) If kept at a relative humidity of 40% and a temperature of 70°F, lumber at 7.7% will not change its moisture content.
2) Conditions in a warehouse are 60% relative humidity at 50°F. If dry wood is left in the warehouse for an extended period of time, the wood will pick up moisture until 11.2% wood moisture is reached, regardless of wood species and initial moisture content.
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EMC Table for Equilibrium Moisture Content of Wood
| T | Relative Humidity | ||||||||||||||||||
| °F | 5 | 10 | 15 | 20 | 25 | 30 | 35 | 40 | 45 | 50 | 55 | 60 | 65 | 70 | 75 | 80 | 85 | 90 | 95 |
| 30 | 1.4 | 2.6 | 3.7 | 4.6 | 5.5 | 6.3 | 7.1 | 7.8 | 8.7 | 9.5 | 10.4 | 11.3 | 12.4 | 13.5 | 14.9 | 16.5 | 18.5 | 21.0 | 24.3 |
| 40 | 1.4 | 2.6 | 3.7 | 4.6 | 5.5 | 6.3 | 7.1 | 7.8 | 8.7 | 9.5 | 10.4 | 11.3 | 12.4 | 13.5 | 14.9 | 16.5 | 18.5 | 21.0 | 24.3 |
| 50 | 1.4 | 2.6 | 3.6 | 4.6 | 5.5 | 6.3 | 7.1 | 7.9 | 8.7 | 9.5 | 10.3 | 11.2 | 12.3 | 13.4 | 14.8 | 16.4 | 18.4 | 20.9 | 24.3 |
| 60 | 1.3 | 2.5 | 3.6 | 4.6 | 5.4 | 6.2 | 7.0 | 7.8 | 8.6 | 9.4 | 10.2 | 11.1 | 12.1 | 13.3 | 14.6 | 16.2 | 18.2 | 20.7 | 24.1 |
| 70 | 1.3 | 2.5 | 3.5 | 4.5 | 5.4 | 6.2 | 6.9 | 7.7 | 8.5 | 9.2 | 10.1 | 11.0 | 12.0 | 13.1 | 14.4 | 16.0 | 17.9 | 20.5 | 23.9 |
| 80 | 1.3 | 2.4 | 3.5 | 4.4 | 5.3 | 6.1 | 6.8 | 7.6 | 8.3 | 9.1 | 9.6 | 10.8 | 11.7 | 12.9 | 14.2 | 15.7 | 17.7 | 20.2 | 23.6 |
| 90 | 1.2 | 2.3 | 3.4 | 4.3 | 5.1 | 5.9 | 6.7 | 7.4 | 8.1 | 8.9 | 9.7 | 10.5 | 11.5 | 12.6 | 13.9 | 15.4 | 17.3 | 19.8 | 23.3 |
| 100 | 1.2 | 2.3 | 3.3 | 4.2 | 5.0 | 5.8 | 6.5 | 7.2 | 7.9 | 8.7 | 9.5 | 10.3 | 11.2 | 12.3 | 13.6 | 15.1 | 17.0 | 19.5 | 22.9 |
| 110 | 1.1 | 2.2 | 3.2 | 4.0 | 4.9 | 5.6 | 6.3 | 7.0 | 7.7 | 8.5 | 9.2 | 10.0 | 11.0 | 12.0 | 13.2 | 14.7 | 16.6 | 19.1 | 22.5 |
| 120 | 1.1 | 2.1 | 3.0 | 3.9 | 4.7 | 5.4 | 6.1 | 6.8 | 7.5 | 8.2 | 8.9 | 9.8 | 10.7 | 11.7 | 12.9 | 14.4 | 16.2 | 18.6 | 22.0 |
The EMC chart provides the correlation between moisture contents listed above and ambient relative humidity and temperature. Wood is stable at the given moisture and relative humidity ranges.
The EMC Calculator.com lists values for any relative humidity, temperature and the corresponding stable moisture content.
For changes in equilibrium moisture content by region and by season click for Moisture Map of North America
Measuring Moisture and Humidity
Lignomat offers a line of meters to measure moisture and humidity. Measuring moisture and humidity is the first step in avoiding moisture problems. Because if you don’t know, how can you prevent. If you have a question, call Customer Service at 800-227-2105 or go to www.lignomat.com
Lignomat offers a wide selection of different moisture meters and thermo-hygrometers.