I used my extending ladder, a very useful piece of kit, to inspect an otherwise hidden valley (roof slope junction) the other day. These are a notorious weak point in roof construction due either to defective design or blockage by leaf fall etc.
This is the side wall of two adjoining houses in Caldecott, Rutland. Local Ironstone and, interestingly, fairly ancient looking mud walling (probably wattle and daub). Luckily I was only surveying the stone cottage on the left of this picture.