Glossary
Equilibrium Moisture Content (EMC)
It cannot be denied that wood exchanges moisture with air. The exact amount, e.g. the gain or loss of moisture, depends on the humidity and temperature of the air and the current amount of water in the wood. If the climate changes, the moisture content within the wood will change as well, because wood absorbs or emits moisture and thus the timber as building material either swells or shrinks. If the moisture content within the timber changes considerably, the timber volume will change as well. This is why the moisture relationship has an important influence on the properties and performance of timber as a building material.
Timber in service is exposed to seasonal and daily changes with regard to the humidity and the temperature of the surrounding air. Although the climate influences this moisture relationship, it is safe to say that an equilibrium condition will be reached gradually. This equilibrium condition is defined as Equilibrium Moisture Content (EMC) and describes the exact moisture content, at which wood neither gains nor loses moisture.
