Thatching

"Thatch" redirects here. For other uses, see Thatch (disambiguation).

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A thatched pub (The Williams Arms) at Wrafton, near Braunton, North Devon, England

Thatching is the craft of building a roof with dry vegetation such as straw, water reed, sedge, rushes and heather, layering the vegetation so as to shed water away from the inner roof. It is a very old roofing method and has been used in both tropical and temperate climates. Thatch is still employed by builders in developing countries, usually with low-cost, local vegetation. By contrast in some developed countries it is now the choice of affluent people who desire a rustic look for their home or who have purchased an originally thatched abode.

History

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Thatch during renovation.

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 Hawaiian Hale shelter made from the local ti leaves and 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

• Closeup of thatching Ben W Bell 31 7 2005.jpg

  A closeup of the thatching.

• Thatching Knots.jpg

  Bundling technique used in straw thatching.

• Thatched Roof Inside View.jpg

  Inside view of a straw-thatched house.

• Thatched Roof Moss.jpg

  Outside layer of moss and lichen growing on thatch.

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’ (2.1m) 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' (1.5 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 (COHT) Committee website www.historicthatch.org.

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.

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Palmetto-leaf thatching on chickees.

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.

Maintenance in temperate climates

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Thatched roof in Narita, Japan

Good thatch will not require frequent maintenance. In England a ridge will normally last 10–15 years, and re-ridging will be required several times during the lifespan of a thatch. Covering thatch with wire netting is no longer recommended, as this will slow evaporation and reduce its longevity. Moss can be a problem if it is very thick, but is not usually detrimental.

The thickness of the thatch decreases over the years as the surface is gradually eroded. A thatched roof can be thought to be nearing replacement when the horizontal fixings of each course are close to the surface. “A roof is as good as the amount of correctly laid thatch covering the fixings.”

Flammability

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River houses on the River Kwai

Thatch roofs do not catch fire any more frequently than roofs covered with 'hard' materials, but thatch fires are difficult to extinguish once they take hold. Old buildings often have poor quality chimneys, and most fires occur in the winter when hot gases ignite the thatch surrounding the chimney. Insurance premiums are higher than average because when a fire does occur, the damage is more severe and the thatch is more expensive to replace than with a standard tiled/slate roof. Workmen should never be allowed to use an open flame near thatch, and nothing should be burnt that could fly up the chimney and ignite the surface of the thatch. Spark arrestors usually cause more damage than good as they are easily blocked and reduce air flow.

A spray-on fire retardant or pressure impregnated fire retardant is available that can reduce the spread of flame, and lower the radiated heat output of the fire.

On new buildings a solid fire retardant barrier can be applied over the rafters making the thatch sacrificial in case of fire. If fireboards are used, it is essential that a ventilation gap be left between the boarding and the thatch so that the roof can 'breathe', as condensation can be a significant problem in thin, single layer thatch. Condensation is much less of a problem on thick straw roofs, and because they do not need to be ventilated provide much better insulation.In Ireland and the Isle of Man, turf is laid upon the rafters to form a fire barrier and this is called scraw.

Performance

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Ihōan, a tea house at Kōdai-ji in Kyoto, Japan

The performance of thatch depends on roof shape and design, pitch of roof, position — its geography and topography — the quality of material and the expertise of the thatcher.

Thatch has some natural properties that are advantageous to its performance. It is naturally weather-resistant,and when properly maintained does not absorb a lot of water. There should not be a significant increase to roof weight due to water retention. A roof pitch of at least 50 degrees allows precipitation to travel quickly down slope so that it runs off the roof before it can penetrate the structure.

Thatch is also a natural insulator, and air pockets within straw thatch insulate a building in both warm and cold weather. A thatched roof will ensure that a building will be cool in summer and warm in winter.

Thatch also has very good resistance to wind damage when applied correctly

Advantages

Thatching materials range from plains grasses to waterproof leaves found in equatorial regions. It is the most common roofing material in the world, because the materials are readily available.

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Farm-house in Holland near Alkmaar. The combination of thatch and roof tiles is quite common in that area.

Thatch is a versatile material when it comes to covering irregular roof structures. This fact lends itself to the use of second-hand, recycled and natural materials that are not only more sustainable, but need not fit exact standard dimensions to perform well.

Disadvantages

Thatched houses are harder to insure because of the perceived fire risk, and because thatching is labour intensive it is much more expensive to thatch a roof than to cover it with slate or tiles. Birds can damage a roof while they are foraging for grubs, and rodents are attracted by residual grain in straw.

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Thatched hut in Lesotho

Thatch has fallen out of favour in much of the industrialised world not because of fire, but because thatching has become very expensive and alternative 'hard' materials are cheaper — but this situation is slowly changing. There are almost 100,000 thatched roofs in the UK, and many more are being built every year.

New thatched roofs were forbidden in London by the Normans in the 12th century, and existing roofs had to have their surfaces plastered to reduce the risk of fire. The Great Fire of London in 1666 had nothing to do with thatch. The modern Globe Theatre is one of the few thatched buildings in London (others can be found in the suburb of Kingsbury), but the Globe's modern, water reed thatch is purely for decorative purpose and actually lies over a fully waterproofed roof built with modern materials. The Globe Theatre, opened in 1997, was modeled on the Rose which was destroyed by a fire on a dry June night in 1613 when a burning wad of cloth ejected from a special effects canon during a performance set light to the surface of the thatch.

Examples of thatched building forms

• Roundhouse (dwelling), pre-Roman European
• Black house, Scotland, Ireland
• Attap dwelling, Singapore
• Chickee, Seminole
• Teito, Asturias, Spain

See also

• Woodway House A thatched cob cottage orné in Devon, England.

External links

• The Thatcher's Craftbr:Plouz

sv:Stråtak