Thatching is a traditional British craft of the use of straw or grasses as a building material. Using thatch for roofing goes back as far as the Bronze Age in Britain. Thatched cottages and farm buildings were the norm in rural Britain for a millennium or more.
The building practices used lightweight, irregular materials and this cottage probably has cob walls. These walls were not made to take much weight, and thatch was the lightest weight material available. People used whatever was available locally, this meant materials as diverse as broom, sedge, sallow, flax, grass, and straw. Most common is wheat straw in the south of England.
Thatch was primarily used by the poor. Much later, in the late 18th century thatched cottages became an extremely popular theme with the "picturesque" painters, who tried to portray an idealized version of nature. Today a thatched cottage is seen as an idyllic home.