Thatched roofing is waterproof roofing made from a natural reed grass. It can be made of rye, barley and oat straw or heathers, among other materials. Traditionally, thatchers use materials that are available locally.
When creating thatched roofing, a thatcher lays 5- to 6-foot bundles of reeds on top of each other in order to create the shell that covers a roof. Each layer is approximately 12 inches. In addition to its waterproof characteristics, thatched roofs also serve as effective insulators.
Because of the material used to create thatched roofing, it can be dressed into shapes that are unusual for roofs. The natural waterproof quality of the roofs is a result of the reeds used to make the roofs. Reeds have hollow insides, with tight overlapping cells on the outer layers that keep water out. By bundling enough of these plants together, water cannot penetrate. Typically, moisture does not absorb into these bundles more than 1 or 2 inches. The roofs are set at a minimum pitch of 45 degrees, allowing for precipitation to move down the slope of the roof before moisture can set in.
If a thatched roof is in need of repair, a fresh layer of thatch can be placed on the original roof. Over time, old roofs can accumulate up to 4 feet of material.