|Thatch can be defined as any vegetation used to roof a structure. The vegetation is gathered, bundled, and secured to a framework on top of a building. Thatch functions both as a shingle and underlayment; very rarely is there anything beyond simple framework between the thatch and the inside of the structure. For that reason, thatchers have to understand the qualities of the thatching material they use – its value as insulation and, particularly, its ability to withstand snow, wind, and rain.The two most common types of European and American thatch are straw and reed. Both are tried-and-true choices and each brings slight different qualities to a completed roof. They are not, however, the only materials suitable for thatching. Thatched roofs appear on every continent except Antarctica, and thatching materials rage from plains grasses to waterproof leaves found in South American rainforests or on South Pacific islands.
European thatch dates back to before the Middle Ages, when the first small, permanent villages were established. The creation of villages brought with it the need for readily available, inexpensive, and durable building material. One of these materials was thatch. Early settlers to the New World used thatch as far back as 1565, but Native Americans had already been using thatch for generations. When settlers arrived in Jamestown in 1607, they found Powhatan Indians living in houses with thatched roofs. The colonists used the same thatch on their own buildings.
Today, thatch is generally acknowledged for its visual appeal and as a way to add a historic or whimsical touch to a home. While it does impart a storybook quality to many structures, thatch also retains the practical aspects of its past. In addition to its beauty, one of its best qualities is its ability to act as an effective insulator. And believe it or not, repairing a thatched roof is much easier than you would think. In addition, today’s thatched roofs benefit from the efforts of modern science – they can be made fire retardant. In recent years, thatch has been gaining popularity because of the current trend towards using more natural materials.
:: Reed and Straw ::
|In Europe, a roof made of reed is more durable than one made of straw. Plants such as Norfolk reed – so called because it was harvested in the Norfolk fens – were commonly used along coastal areas in the Southeast of England and along the west coast of Scotland. Other reeds are harvested all over the world and are commonly referred to by the generic name “water reed.” The availability of reed accounts for the concentration of thatched buildings along coasts and in marshy areas.Before it can be used, reed must be thoroughly dried to prevent it from shrinking once it is in place. Once dry, it is gathered in bundles and attached to the prepared frame of the roof. The bundles have a circumference of 24 to 27 inches, or “3 hands.” Depending on the size of the project and the part of the roof, a bundle is anywhere from 3 to 7 feet long.
Straw is another common thatching material. While readily available, straw thatch does not last as long as reed. Collecting it is also more labor-intensive, since it has to be cut and trashed before it’s drawn by hand into workable bundles, known as “yearns.” Because straw is so brittle, the thatcher must continually wet it while working, to keep it from breaking. The straw will not shrink as it dries, so the thatcher must gauge during the process what the finished roof will look like.
The layer of thatch that covers a roof is at least a foot thick. In addition, any building to be thatched must have a roof that is set at a minimum pitch of 45 degrees. Precipitation travels down the steep slope of the completed roof and reaches the ground long before it has the chance to penetrate the rooms below. In fact, the top inch or so of the thatch is the only part that ever feels the effects of the elements.
Easy to Repair
If a thatched roof is in need of repair, a fresh layer of thatch can be applied directly on top of the original layer. The result can be an old, and very thick, layer of thatch. Although new thatch is usually 12 inches thick, up to 4 feet of material can accumulate on old roofs. Unless the original roof was destroyed by fire, the bottom layer of thatch is as old as the structure itself.
Thousands of pockets of air exist between and within the stems of the vegetation that makes up a thatched roof. These air pockets give the roof the ability to insulate a building in both warm and cold weather. Norfolk reed, which is commonly used to thatch roofs in the United States and Britain, offers an insulation or R-value of 40. Conventional insulation, such as fiberglass, usually rates between 30 and 50.
Text from http://www.thatching.com/thatching.html