A Rotting Timber Frame Foam sheathing, too much moisture, and a broken vapor barrier almost spelled disaster for a four-year-old timber-frame house in southern Vermont. by Steven Bliss "If you don't put in a vapor barrier, your house is going to rot away." You've heard this many times, but it's not so simple. Thousands of insulated houses with no vapor barrier (or a lousy vapor barrier such as kraft paper) have not rotted away. Furthermore, sticking a sheet of poly in the wall is no guarantee against problems. Take the rotting timberframe house that I visited in southern Vermont last November... The 1,800-square-foot, 1-1/2-story Cape is four years old. The walls are framed with 8x8 timbers, which are exposed on the interior