Thatching is the craft of covering a
roofwith 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 probably the oldest roofing material 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 well-to-do people who want their home to have a rustic look.
The tradition of thatching has been passed down from generation to generation for thousands of years. Few descriptions of the building techniques exist, especially in
In equatorial countries thatch is the prevalent local material for
roofs, and often walls. There are diverse building techniques from the HawaiianHale 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 caneleaf roofs and the Kikuyu tribal homes in Kenya. [ [http://www.polynesia.com/fiji/fijian-houses.htm] ] [Low-Tech Building Craze Hits Hawaii; Indigenous Thatched-Roof Hale Once Out of Favor, Now Seen as Status Symbol on the Islands. "Washington Post." Matt Sedemsky. Nov. 30, 2003] The colonisationof indigenous lands by Europeans greatly diminished the use of thatching.
Records of European thatch date back to before the
Middle Ages, when the first villageswere established. The creation of villages brought with it the need for readily available, inexpensive, and durable building material, such as thatch. “Thatch houses built in close proximity helped to account for the frequent and disastrous fires that swept through the narrow streets of medieval cities.”"Thatch." West, Robert The Main Street Press. Pittstown, New Jersey. 1987] Eventually the authorities wrote the Ordinance of 1212, arguably the first building regulation in force in London, prohibiting the building of new thatch roofs and demanding the whitewashing of existing ones with plasterdaub.
Early settlers to the
New Worldused thatch as far back as 1565. Native Americans had already been using thatch for generations. When settlers arrived in Jamestown, Virginiain 1607, they found Powhatan Indians living in houses with thatched roofs. The colonists used the same thatch on their own buildings. [http://www.thatch.com Non Standard Household Insurance Towergate Strovers ] ] In the early years of the 19th century thatching was in decline. The commercial production of Welsh slate had begun in 1820and the mobility which the canalsand then the railwaysmade possible meant that other materials became readily available. To compound this, the Napoleonic Warsraised the price of wheatand strawto a prohibitive level in Europe. The number of thatchers declined, as the tradition became regarded as unfashionable. Technologyin the farming industryhas had a negative impact on the popularity of thatching. Use of the material declined following the First World Warin particular, and with the invention of the combine harvesterand the need to develop shorter stemmed varieties of wheat, the long straw once produced was no longer available. The increased loss of water plantsand wildlifeoccurred with the shift from open ponds to cattle troughsand piped water for animals. With it came the decline in availability of rushes, and other wetlandvegetation used in thatching.
With renewed interest in historic
architectureand the trend towards using more sustainablematerials, thatching is once again in the ascendancy. [ [http://www.buildingconservation.com/articles/thatchrf/thatchrf.htm Thatched Roofs: An Introduction - catherine Lewis ] ]
There are more thatched roofs in the
United Kingdomthan in any other European country. The traditional material in most of Englandis wheat straw, which is now produced by specialist growers. 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. This has generated accumulations of thatch 2.0 m thick and in ancient buildings preserved lower layers of medieval thatch over 600 years old. [Letts, John 2000. Smoke Blackened Thatch: a unique source of late medieval plant remains from Southern England. Reading & London: The University of Reading and English Heritage]
Water reed, which was used in
East Angliaand Eastern England, is a one-coat material; weathered reed is usually stripped and replaced by a new layer. Almost half of England's thatched roofs are thatched with water reed, 90% of which is imported from Turkeyand Eastern Europe. Although water reed has been known to last for more than 70 years on steep roofs in dry climates, modern imported water reed on an average roof in most parts of England will not last any longer than good quality wheat straw. The lifespan of the thatch 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 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. [Andrews, Charles Mclean and Andrews, Evangeline Walker (1945). "Jonathan Dickinson's Journal or, God's Protecting Providence. Being the Narrative of a Journey from Port Royal in Jamaica to Philadelphia between August 23, 1696 to April 1, 1697". Yale University Press. Reprinted (1981) Florida Classics Library. P. 11.] [Charles W. Pierce (1970). Pioneer Life in Southeast Florida. University of Miami Press. Pp. 53-4.ISBN 0-87024-163-X] [ [http://waynesword.palomar.edu/traug99c.htm#bayleaf Thatching From The Bayleaf Palm Of Belize] - retrieved June 4, 2007]
Maintenance in temperate climates
Good thatch will not require frequent maintenance. Re-ridging will be required several times during the lifespan of a thatch. The life of a ridge will vary depending upon the type, pitch, location and other factors. An approximate guideline would be 15 years. It is normal practice to renew the wire netting when re-ridging.
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 fixings are close to the surface. “A roof is as good as the amount of correctly laid thatch covering the fixings.” [ [http://www.eamta.co.uk The Thatch & Thatching Of The East Anglia Master Thatchers Association ] ] Water penetration, when it occurs is minimal and is usually due to
capillary action. The presence of mossis not necessarily detrimental to the thatch.
The life of a thatch can be extended by appropriate repair. Some guidelines are:
1. Follow the advice of professional thatcher.
2. Do not move around on thatch unnecessarily.
Treesshould be kept well back from thatch and never allowed to overhang or brush against the roof.
4. Do not let non-thatchers fit netting, flashings, etc., without advice from an experienced thatcher.
Televisionaerial erectors etc., should be required to keep off the thatch as much as possible.
6. Do not allow standing on the ridges or the use of ridges as working platforms.
7. Long Straw thatching should be securely netted to avoid bird penetration as is sometimes the case with combed wheat and some water reeds. [http://www.thatching.org thatching.org ] ]
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 break through a poor quality flue or chimney and ignite the thatch surrounding the chimney. Insurancepremiums 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 also usually cause more damage than good as they are easily blocked and reduce air flow (it should be noted that not all experts agree on this point).
A spray-on fire retardant or pressure impregnated fire retardant can reduce the spread of flame. Most thatch fires do not begin on the surface of the thatch (the surface is usually damp in the UK), but in the thatch surrounding the chimney. While it is true that some fire retardants may expedite the decay of the roof, it is not the case with all well formulated products.
On new buildings a solid fire retardant barrier can be constructed over the rafters making the thatch sacrificial in any fire. If fireboarding is used, it is essential that a ventilation gap is left between the boarding and the thatch so that the roof can 'breathe' and thus reduce the rotting of the thatch.
The performance of thatch depends on roof shape and design, pitch of roof, position — its
geographyand topography— the quality of material and the expertise of the thatcher.
Thatch has some natural properties that are advantageous to its performance. Firstly, it is naturally weather-resistant. When properly maintained, thatch does not absorb large amounts of water. There should be no large increase to roof weight due to water retention. In a well-designed roof, the uppermost inch or so of the thatch is the only portion that feels the effects of the elements. A roof pitch of 45 degrees or more allows precipitation to travel down the steep slope of the roof and reach the ground long before it can penetrate the structure.
Thatch is also a natural insulator. When whole vegetation is used, thousands of pockets of air exist between and within the stems of the grasses that make up a thatched roof. These air pockets give the roof the ability to insulate a building in both warm and cold weather. At least a foot thickness of thatch on top of a roof also helps thermal retention. Norfolk reed, commonly used to thatch roofs in the
United Statesand Britain, offers an insulation or R-valueof 40. Conventional building insulation, such as fiberglass, usually rates between 30 and 50.
Thatch is not by its nature prone to
winddamage. Experience of hurricaneforce wind tests up to 100 mph in Californiahas shown that, when applied correctly, thatch has good wind resistance. However, older thatched roofs, particularly in wind-prone areas can benefit from well-fitted netting.
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. With certain types of thatching, particularly low rounded roofs, good acoustic insulation can make extremely quiet living conditions.Thatch is a competitive
thermal insulatorwhen applied thickly. A thatched roof will ensure that a building will be cool in summer and warm in winter. Local techniques, such as the placement of a turfsubstratum by the Scottish, can reduce air movement and improve insulation even further.
Thatch is a versatile material when it comes to covering irregular roof structures. This fact lends itself to the use of second-hand,
recycledand natural materials that are not only more sustainable, but need not fit exact standard dimensions to perform well.
Thatching can be sustainable -- if crops are managed ecologically, then the resource can be renewed regularly. Many of the natural thatching materials are improved by regular harvesting. For example, reeds,
marram grass, broom, heather, and juniperall regrow in more usable forms. Thatch can be recycled to be an excellent fertilizer."Thatches and Thatching Techniques: A Guide to Conserving Scottish Thatching Tradition." Walker, Bruce. McGregor, Christopher. Stark, Gregor. Historical Scottland. 1996]
As local materials always tend to harmonize with the landscape surrounding their place of origin, thatch, as a natural material, will blend well with a
ruralenvironment. Thatch has an ecological advantage because it is produced by natural processes that do not use scarce and expensive resources of energy.
Thatched houses are more vulnerable to fire risk than those covered with other materials, and it is imperative that precautions be taken to reduce the risk.
Insurancecosts can be higher due to this factor. The process of thatching is more labor intensive than other methods of roofing, affecting the overall cost.
Being an organic material, thatch is susceptible to decay and
decompositionand precautions must be taken to minimize the possibility of this process taking place. In warm, wet climates thatch is prone to fungalattacks.
Animals can cause damage.
Birdslooking for food, gathering nest-making materials or nesting in the roof itself becomes a greater possibility when the plantmaterial is not processed appropriately for its intended use. Rodentscan cause extensive damage when present in the house. The quality of design and building can greatly affect the performance of the roof. If built and/or maintained inadequately, then problems such as vulnerability to wind damage and prolonged damp conditions are issues.
Thatch can be maintenance intensive. The maintenance cycle varies based on thatch type, roof pitch, the degree of shade or exposure and the kinds of materials used.
Thatch has fallen out of favour in much of the industrialized 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 in some parts of England 1 in 4 new roofs are being thatchedFact|date=May 2008.
New thatched roofs were forbidden in
Londonby the Normans in the 12th century, and existing roofs had to have their undersides (within the roof space) plastered to reduce the risk of fire. The Great Fire of Londonin 1666 had nothing to do with thatch. The modern Globe Theatreis 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 waterproof roof built with modern materials.
Examples of thatched building forms
Roundhouse (dwelling), pre-Roman European
Black house, Scotland, Ireland
Attap dwelling, Singapore
Teito, Asturias, Spain
Woodway HouseA thatched cob cottage ornéin Devon, England.
* [http://www.buildingconservation.com/articles/thatchrf/thatchrf.htm Building Conservation.com]
* [http://www.ballybegvillage.com/thatching.html Thatching in Ireland]
* [http://www.thatching.pl/ Thatching in Poland]
* [http://www.countryside.gov.uk/LAR/archive/publications/thatchers_craft.asp The Thatcher's Craft]
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