 On Dartmoor, blowing houses were rectangular buildings between around in length and around half this in width.They were made of unmortared granite blocks with walls often or more thick and probably had turf or thatch roofs which were periodically burnt to retrieve the particles of tin that would have been driven into the roof through the blast from the bellows.Blowing houses are typically located on or near the bank of a stream where the fall of water was enough for a leat to be built to work a small () diameter overshot water wheel which developed around to operate the bellows.