The blackhouses on Lewis have roofs thatched with cereal straw over turf and thick, stone-lined walls with an earthen core. Roof timbers rise from the inner face of the walls providing a characteristic ledge at the wall head ("tobhta"). This gives access to the roof for thatching. Both the animals and occupants shared the same door, living at different ends of the same space. Several long ranges, or rooms, were usually built alongside each other, each one having its own ridgeline giving them the very distinctive look of the Lewis blackhouse.