Swelling is a physical process in which a substance (usually a liquid, but also a gas or vapor) penetrates a solid body and causes an increase in volume of the solid body.
In civil engineering, stresses can be induced by swelling of unrestrained structural components (especially timber), which must be considered in the structural analysis. Moisture absorption in timber can only take place if the air humidity deviates from the timber equilibrium moisture content. There must be a moisture gradient between the timber and the environment.
