There's another such house in my part of Finistere, built on gvt land. In Finistere at least it is built on the coastal side of the coastal road, an area which was (still is) left untouched/unbuilt for the Coast Guards and Custom and Excise officers to patrol and easily monitor the sea (illegal off-loads, centuries ago). It is consequently very exposed, hence I guess the construction. I believe these houses may well have been Coast Guard houses.