Brief History of Thatch and Thatching
Source: http://en.wikipedia.org/wiki/Thatching
The tradition of thatching has been passed down from generation to generation for thousands of years, and numerous descriptions of the materials and methods used in England over the past three centuries survive in archives and early publications.
In equatorial countries thatch is the prevalent local material for roofs, and often walls. There are diverse building techniques from the ancient Hawaiian hale shelter made from the local ti leaves, lauhala or pili grass of fan palms to the Na Bure Fijian home with layered reed walls and sugar cane leaf roofs and the Kikuyu tribal homes in Kenya. The colonisation of indigenous lands by Europeans greatly diminished the use of thatching.
Thatch has probably been used to cover roofs in Europe since at least the Neolithic period, when people first began to grow cereals. Wild vegetation, especially water reed (Phragmites australis), was probably used before this but no records or archaeological evidence for this have survived ”.
Early settlers to the New World used thatch as far back as 1565. Native Americans had already been using thatch for generations. When settlers arrived in Jamestown, Virginia in 1607, they found Powhatan Indians living in houses with thatched roofs. The colonists used the same thatch on their own buildings.
In most of Europe and the UK, thatch remained the only roofing material available to the bulk of the population in the countryside, and in many towns and villages, until the late 1800s. The commercial production of Welsh slate had begun in 1820 and the mobility which the canals and then the railways made possible meant that other materials became readily available. The number of thatched properties actually increased in the UK during the mid-1800s as agriculture expanded, but then declined again at the end of the 19th century because of agricultural recession and rural depopulation. Gradually, thatch became a mark of poverty and the number of thatched properties gradually declined, as did the number of professional thatchers.
Thatch has become much more popular in the UK over the past 30 years, and is now a symbol of wealth rather than poverty. There are now approximately 1,000 full time thatchers at work in the UK, and thatching is becoming popular again because of the renewed interest in preserving historic buildings and using more sustainable building materials.
Thatch material
There are more thatched roofs in the United Kingdom and Ireland than in any other European country. Good quality thatching straw can last for more than 45–50 years when applied by a skilled thatcher. Traditionally, a new layer of straw was simply applied over the weathered surface, and this ‘spar coating’ tradition has created accumulations of thatch over 7’ (2.1 m) thick on very old buildings. Over 250 roofs in Southern England have base coats of thatch that were applied over 500 years ago, providing direct evidence of the types of materials that were used for thatching in the medieval period. Almost all of these roofs are thatched with wheat, rye, or a 'maslin' mixture of both. Medieval wheat grew to almost 6 feet (1.8 m) tall in very poor soils and produced durable straw for the roof and grain for baking bread. Information on UK thatching materials, methods and traditions, and the work that is being done to preserve them, is available on the Conservation of Historic Thatch
Technology in the farming industry has had a significant impact on the popularity of thatching. The availability of good quality thatching straw declined in England after the introduction of the combine harvester in the late 1930s and 1940s, and the release of short-stemmed wheat varieties. The increasing use of nitrogen fertiliser in the 1960s-70s also weakened straw and reduced its longevity. Since the 1980s, however, there has been a big increase in straw quality as specialist growers have returned to growing older, tall-stemmed, 'heritage' varieties of wheat such as Maris Wigeon, in low input/organic conditions.

All of the evidence indicates that water reed was rarely used for thatching outside of East Anglia. It has traditionally been a 'one coat' material applied in a similar way to how it is used in continental Europe - weathered reed is usually stripped and replaced by a new layer. It takes 4-5 acres of well-managed reed bed to produce enough reed to thatch an average house, and large reed beds have been uncommon in most of England since the Anglo-Saxon period. Over 80% of the water reed used in the UK is now imported from Turkey, Eastern Europe and China. Although water reed might last for 50 years or more on a steep roof in a dry climate, modern imported water reed on an average roof in England will not last any longer than good quality wheat straw. The lifespan of a thatched roof is also dependent on the skill of the thatcher, but other factors need to be taken into account, such as climate, quality of the materials used, and the pitch of the roof.

Thatch is fastened together in bundles with a diameter of about two feet. These are then laid on the roof with the butt end facing out and secured to the roof beams, after which they are pegged in place with wooden or steel rods. The thatcher adds the layers on top of each other, finishing with a layer to secure the ridgeline of the roof. This method means thatch roofs are easy to repair, can endure heavy winds and rain and only need a stable supporting structure.
In areas where palms are abundant, palm leaves are used to thatch walls and roofs. Many species of palm trees are called "thatch palm", or have "thatch" as part of their common names. In the southeastern United States, Indian and pioneer houses were often constructed of palmetto-leaf thatch. The chickees of the Seminole and Miccosukee Indians are still thatched with palmetto leaves.
http://en.wikipedia.org/wiki/Thatching