Many were still roofed until the 1970s[5] but without the necessary annual repairs deteriorated rapidly; as people moved into more modern dwellings with indoor plumbing and better heating, most have fallen into ruin.
The blackhouses on Lewis have roofs thatched with cereal straw over turf and thick, stone-lined walls with an earthen core.
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.
One reason for this is that, unlike their later counterparts, the early examples may have been made of turf and thatch and quickly returned to the earth once abandoned.
As one of the most primitive forms of the North Atlantic longhouse tradition, it is very probable that the roots of the blackhouse, in which cattle and humans shared the same roof, is well over 1000 years old.