Insidious

Some rotted wood in a little log cabin:

You can see that the end of the eave log is ragged on the left, but the better view is the end of the side-wall top beam in the center of the photo. The center of the beam is completely rotted out, but the edges are slightly better. In this case, with this type of log construction, the end grain is fully exposed for a number of major beams. Exposed to rot, and exposed to our view.

In more ordinary wood construction – both stick-built and with large timbers – you sometimes find the same kind of end-grain rot, but you have to go looking for it. In ordinary wood construction, little end grain is exposed like this. It is possible to have the nasty surprise of finding out that the center of a piece of wood is rotted even though the exterior looks pretty much okay. It is also possible to have a suspicion that there might be a problem, stick a knife into the wood and have the blade sink in to the hilt, rather than stop after a shallow cut.

It’s bad enough when structural damage is hidden by non-structural elements. Structural damage hidden within itself – which can happen with almost any common material – is worse.