rethatch

Rethatch is the process of applying new thatch to a thatched roof in order to replace worn or damaged material and restore weatherproofing and insulation. It can involve renewing the entire roof or targeted sections, depending on the extent of decay and the roof's design. Rethatching is typically carried out by specialist thatchers due to the skill required to lay, bind, and dress the thatch.

Thatching materials include water reed, longstraw, combed wheat reed, and, in some regions, heather. The choice depends on climate, tradition, roof slope, and local availability. Water reed tends to be durable; straw is lighter and cheaper. The new thatch is installed in courses from the ridge down to the eaves, secured with binder twine, wire, or spars, and dressed to form a tight seal and a water-shedding surface. The ridge is finished with a raised, weatherproof cap.

Often, traditional thatched roofs require rethatching every 15 to 40 years, though this varies with material and exposure; partial repairs between full rethatches are common. Proper underlay and ventilation, along with regular checks for leaks, moss, or vermin, extend life. In many regions, rethatching is a skilled trade and may be subject to conservation rules for listed buildings.