If the problem is severe or longstanding, the moisture can penetrate through the depth of the wall to rot timber lintels and the ends of joists and roof timbers.
Os yw'r broblem yn ddifrifol neu wedi bodoli ers tro, gall y lleithder dreiddio drwy'r wal gyfan gan bydru capanau drysau pren a phob pen i ddistiau a thrawstiau to.