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Materials
Long straw
Longstraw was once extensively used from Dorset northwards, but is now confined mainly to the counties of East Anglia. It is harvested with a binder.
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Before longstraw can be used for thatching it needs to be made into yealms. When thatching with longstraw, it is not usually necessary for all of the old material be removed from a roof. The thatcher will normally only remove existing material back to a base coat and the new straw is then fix to this with hazel spars.
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Longstraw thatch is easily distinguishable from the other two types of material. It has long lengths of straw visible on the surface and has the general appearance of having been poured on, contrasting with the closely cropped look of combed wheat reed and water reed. Longstraw also has exterior hazel rodding at eaves and gables - a feature seldom seen on the reed types.
Ridges
The ridge of a thatched roof bears the brunt of the weather and as the fixings are external, it requires attention on average every 10 to 15 years. The material used is usually the same as that used for the main coatwork however water reed is too stiff and brittle. As a result, the ridge of a water reed roof is often made with combed wheat reed.
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The patterned ridges which have become popular allow the thatcher some artistic licence, but they are a relatively new innovation and as such are thought to be unsuitable for the majority of historic thatched properties. Different considerations apply in the re-thatching of an old building and one of recent date and it is probably fair to say that a house built prior to the 19th Century requires good plain workmanship without too much embellishment.
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There are two main types of ridge - the 'wrap-over' which is used most widely, and the 'butt-up' which is found mainly in the south-west of the country where its use would appear to have developed from the stiffer nature of combed wheat reed. The 'butt-up' ridge has the butts of the material forced together from either side to form an apex whereas the 'wrap-over' is formed by folding a thick layer of material over the apex of the roof and fixing it on both sides.
Performance
With greater awareness of the vernacular materials and style of particular regions, conservationists have realised the importance of maintaining (and even returning to) the historically correct thatching style and material pertinent to the area. Local authorities actively discourage the use of a 'foreign' material and in any case, listed building consent is required for alterations to a listed building.
Furthermore, the awarding of grants for repairs and re-thatching is often dependent upon compliance with the thatching policy of the local council and consideration of a change of material will usually only be granted for exceptionally strong technical reasons.
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A common misconception with thatch is the idea that it absorbs large amounts of water. This is not the case at all. Water is transferred down the roof from stem to stem until it drops from the eaves. The steep pitches associated with thatched roofs allow for water to be shed at a very fast rate. When designing for thatch, ample allowance should be made for the projection of the caves and gables to project water clear of the building, and the ground should be well drained.
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A greater cause for concern is the risk of fire in a thatched properly, although the risk however is probably overstated. Evidence shows that thatch fires are usually caused by the same kinds of hazards affecting all housing and that genuine thatch fires are extremely rare. Figures from the Dorset Fire Brigade indicate that of 3,000 fires each year, only 8-10 of these involve thatched buildings and in the majority of these incidents, the fire will have started within the building itself. The reality is that all thatched building owners tend to be more careful about the dangers and employ a number of fire prevention measures. Nevertheless, many thatchers now recommend the installation of a fireboard which is fitted to the rafters and gives at least a half hour's fire resistance. Depending on the material and position of the building, this might then be counter battened to provide air movement between the material and fire retardant.
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When alterations to an existing thatched roof are planned or when designing a new thatch roof it is imperative that consultation with a Master Thatcher is sought and in the case of a listed building, with the conservation officer at the local council. Thatchers have no hesitation in recommending thatch as an ideal roof covering, provided that certain conditions are met. It is only those who work with the different materials and understand the complexities of thatch who are able to advise properly on the way thatch will work.
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