Historic Preservation Blog

Traditional Roofing Materials: Thatch

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Thatching is the craft of building a roof with dry vegetation such as straw, water reed, sedge (Cladium mariscus), rushes, or 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.

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.

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 website.

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.

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.

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.” 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.

Because thatch is lighter less timber is required in the roof that supports it.  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.