Thatch is an ancient technique for lightweight roofing over buildings with weak walls of mud brick or wattle-and-daub (woven branches covered with clay or mud) construction. Bundles of straw, reeds, heather or bracken fern were tied into layers on a light frame. Smoke rose through the thatch, so no chimney was necessary. Soot preserved the lower layers of thatch, and new layers were added as needed. Preserved medieval thatch layers are currently studied for medieval crop and climate data.
The oldest English archaeological find is Culverwell Mesolithic Habitation Site at Isle of Portland in Dorset, on the south coast 60 miles west of Portsmouth. The site dates back 7,500 years. The village included three or four huts housing fewer than 30 people up to 20 years. Huts were wetland reed thatch over bent hazel branches. The community included thatch-roofed pit storage houses paved with Portland limestone cobbles.
Thatch was common in the ancient Levant, even on public buildings. In the 7th century B.C.E., low-pitch, terra cotta roofing tiles first replaced thatch at a large stonewalled temple in Corinthia, Greece. A model of a temple found at Perachora and dated a few generations earlier depicts a thatched roof. Rural and smaller town houses continued to have mud walls and high-pitched, lightweight thatched roofs supported by wooden rafters.
Medieval and Early Modern
Cereal farming reached England by 2000 B.C.E. During medieval times, 400 to 1400 C.E., rye straw was the preferred roofing material, compared to wheat straw, marsh reeds, heather or bracken ferns. In west England, specialized roofing crops were selectively threshed only at the grain head. Thatched roofs became fire hazards in growing towns. In 1212, London banned new thatch construction and required whitewash on existing thatch as a flame retardant. Still, in 1613, the thatch-roofed Globe Theater, in Southwark across the Thames from London, burned to the ground in one hour. Thatched roofs spread the Great Fire of London in 1666.
Thatched roofs sparked by wooden chimneys burned most buildings at the Virginia Company's Jamestown settlement during the Starving Time winter of 1607. The nearby Powhatan native Virginians lived in cozy, cocoon-shaped, extended family long houses of movable thatch mats layered over bent poles. New waves of European settlers brought their own thatch techniques to America. The Pennsylvania Dutch built to economize on nails, with light-weight rafters supported on collar-ties and without ridge poles. They traditionally laid thatch roofs only when the horns of the rising crescent moon pointed down. German thatched barns persisted in rural New Jersey into the 20th century.
In the 19th century, rail transportation for slate and tile roofing materials made thatch obsolete, but thatch enjoyed a 20th-century aesthetic revival for English country cottages. About a thousand thatchers currently work in England, where there are about 40,000 thatched buildings. Formal accreditation is awarded through two English master thatcher professional associations. Formal training leading to national vocational certification is available to journeymen at Knuston Hall, an adult residential college in Northamptonshire.