Moisture in timber

Water is vital to a living tree. The weight of water in a tree is usually greater than that of the wood itself. After felling and seasoning the tree loses most of this water but because wood is hygroscopic it retains a moderate amount which continues to have an important bearing on many of the wood's properties, including strength.

In common with other hygroscopic materials, cellulose absorbs different amounts of water according to temperature and humidity and, in so doing, changes its dimensions. This is significant in designing and must be allowed for.

Moisture content

The moisture content of wood is conventionally expressed as a percentage, based on the weight of dry wood which means that moisture content can exceed 100 per cent, i.e.

Moisture content % =

weight of water in specimen dry weight of same specimen

x 100%