LOGS as BUILDING MATERIAL

© 2008, Kenton Shepard

Unlike many building materials which go through a complicated and energy-intensive manufacturing process, logs are simply dried tree trunks (also called the "stem" or "bole") which are adapted for use in log walls using cutting tools and machinery. Inspectors examining them and those who buy them will see evidence of the natural growth process and the effects of the environment in which the trees have grown and the conditions under which the logs have dried.

Checks, spiral grain, knots, insect holes and logs with sweep and taper are commonly found in log homes. These imperfections are not defects and are to be expected in most homes. It's only when they cause problems that they become defects.

Sweep- is bowing in a log. No naturally-shaped logs are perfectly straight. Logs too radically bowed shouldn’t be used in log homes, however occasionally inspectors will see logs which look excessive. There's no harm in commenting on a wall log with extreme sweep, in fact it's a good idea, because the client may be wondering whether it's a problem.

The inspector should examine it carefully in an effort to determine which its use is causing problems or may cause problems, although inspectors are not responsible for identifying logs which may cause problems in the future.

If the house appears to be well along in the settling process, inspectors should be watching for gaps which may allow air leakage, moisture intrusion or insect infiltration? If the home is fairly new, extreme sweep may be a problem in the future, depending on how the log in question and the logs in the courses (called “rounds”) above and below it react as they dry. If the sweep has reduced the amount of contact area between logs, it may not take much movement to open a gap.

Taper- is the difference between log tip and butt diameters. Log tips and butts alternate in a wall and built correctly, log walls can accommodate logs with considerable taper.

Knots- indicate where branches grew in the live tree and may be tight or loose. Knots affect the angle of grain as wood fibers bend to grow around the limb and so may have an effect on log strength, but determining the extent to which this condition is a problem would require the services of a certified log grader.

This photo to the right is an example of logs with lots of taper used in a wall. These logs are Western Red Cedar. By alternating the direction of taper in successive rounds of logs, the builder was able to provide a level surface at the top of the wall to support roof framing.

All photos are courtesy of  Kenton Shepard