Before 1849, when Sir James Matheson began to re-lot the Island, the one-roomed houses were to be found in clusters, some having their walls overlapping, but the new type of house (examples of which can still be seen in Arnol), were built into the dykes which separated the arable land from the common pasture. The front wall of the house was part of the protective dyke.

The typical black house was a long, rectangular building forty to fifty feet in length, with an interior width of ten to twelve feet. There was a  fosgalan, porch, round the front door, with a small barn usually a third of the size of the house at the rear. As a rule, the walls were two drystone dykes, four to six feet apart, with the intervening space tightly packed with earth. In some cases, the outer walls were of turf or of alternate rows of turf and stones. The  fosgalan provided the only entrance to the house, although there was, in the outer wall of the barn, a  toll-fhasgaidh, a small rectangular hole which was opened when grain was being winnowed. There were no windows in the walls. Inside the  fosgalan, a tunnel led to a small kiln for drying the grain, while on the other side was usually the stable door. The door of the  fosgalan was about fifteen feet from the lower end of the house.

All the corners in the outside walls were rounded, and great care was taken to ensure that the outer walls, which were of undressed stone, had a slight slant, to allow the rain to drip off and not seep into the interior. There were also no gables on the house, the walls being from five to six feet in height all round, with projecting stones left in one wall to form a  staran, type of ladder to provide access to the wide, turf-covered wall-tops for thatching purposes.

The couples for the roof were placed at wide intervals on the inner walls. A cross-piece was fixed near their apex, while a  gath droma, ridge-pole, was laid along their tops. For the further strengthening of the roof, a  corra-thulchain, strong piece of timber, was placed between the middle of each end wall and the apex of the adjacent couples. Two rows of side timbers or purlins, about three feet apart, were laid lengthwise on the couples. Occasionally, a stick was fixed to the tops of the corner couple, to which the ropes that bound the end thatch could be fixed. Smaller pieces of wood were laid between the ridge-pole and wall-tops to support the thatch, once wholly composed of overlapping slabs of turf. Later, rushes, fern, heather, straw or potato shaws were used as additional thatch. No nails were used for this roof structure, except latterly, for the couples. Straw or heather ropes and sometimes tangle fastened the various pieces together, until they were displaced by coir rope, locally called  siaman Thearlaich, Charles' rope, after Stornoway merchant, Charles Morrison, who first introduced it into the Island. The thatching rope was looped round anchor stones, slightly above the wall-tops, below which there was another row of stones covering the bottom section of the thatch. When securing the thatch, the ball into which the rope had been coiled was thrown backwards and forwards across the roof and looped round the anchor stones.

Thatching required much skill, otherwise the owner might have to quote the proverb:

"Fuadach ort a' ghaoth an iar-dheas,
'S tu gheibh lorg air tigh gu shioman."

"Curse you, o south-west wind,
You always search out a ropeless house."