This article is provided as a public service by the Geophysical Institute, University of Alaska Fairbanks, in cooperation with the UAF research community. Dr. Sue Ann Bowling is an Associate Professor of Physics at the Institute. Radial cracks in logs, clearly displayed in this corner of a log building, are an inevitable result of drying. They represent the only way a large whole log can manage to shrink more in circumference than radially. Logs crack, most often in long spirals.
Doors stick in damp weather, and chairs pull apart when it's dry.
Wood is a marvelous material in many ways, but it does have its problems under changing humidity conditions. The original function of wood, of course, was to hold up trees, not houses. Wood that is supporting a living, healthy tree is not subject to large, uncontrolled humidity changes. The inner part of the trunk is shielded from fluctuations by the outer part, which is carrying moisture between the leaves and the roots of the tree. Food travels in the living phloem tissue just under the bark.