Roofs - An Introduction
The predominant thatching material in use in this country up until the 19th Century was
straw - either longstraw or combed wheat reed. Norfolk Reed (or water
reed) was traditionally used in the counties of East Anglia and other
wetland areas. A diversity of styles had developed over time and, coupled
with different materials, distinct regional characteristics became apparent.
The combed wheat reed roofs of the West Country for example, are shallow
pitched and 'pudding basin' in appearance compared with the steeply pitched
longstraw roofs of East Anglia. The treatment of ridges, eaves and gables
varies in different parts of the country and in those areas where there
is a strong thatching tradition a departure in style today would look
out of place.
In the early years
of this century thatching was in decline. 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 far more
readily available than ever before. Use of the material declined following
the First World War in particular, and with the invention of the combine
harvester and the need to develop shorter stemmed varieties of wheat,
the long straw once produced was no longer available.
With renewed interest
in our historic architecture, thatching is now, once again, in the ascendancy.
The three main thatching materials in use today are water reed (often
known as Norfolk Reed although a large amount is imported from Eastern
European countries), longstraw and combed wheat reed. Sedge, a grass-like
plant which grows in wetland areas, is also used extensively in ridging.
Water reed is used extensively in parts of the West Country and East Anglia. New properties
are almost always thatched in water reed since it is the most durable
of the thatching materials, and tends to give the longest life. Many factors
influence the longevity of a thatched roof and it is therefore unwise
to generalise on the subject. However a Norfolk Reed roof situated in
one of the counties of East Anglia where there is a tradition of very
steep pitches, could be expected to last an average of 50-60 years although
there are instances of roofs lasting much longer than this.
When re-thatching with water reed, the existing material will be completely removed back
to the roof timbers, although in the south-west of the country, where
roof pitches tend to be less steeply pitched, thatchers often lay water
reed on top of a base coat. The new reed is carried on to the roof in
bunches and, starting at eaves level, is fixed directly into the rafters
with the butts of the stalks exposed. Each layer of reed is held in place
with either steel or hazel sways and once in position it is dressed into
shape with the use of a legget.
once extensively used throughout the main corn crop regions from Dorset
northwards, but is now confined mainly to the counties of East Anglia,
although examples of it exist up and down the country. It is harvested
with a binder. Old-fashioned long-stemmed varieties of wheat are grown
and cut whilst still slightly green. After being allowed to dry, the wheat
is threshed in a threshing drain and the resultant straw leaves the drum
in a fairly mixed state.
Before longstraw can
be used for thatching it needs to be made into yealms. A yealm can be
described as a tight, compact layer of straw, which has been 'tidied'
and is level at both ends. Yealming is a lengthy procedure which takes
place on the ground and is basically carried out in order to straighten
the straw and prepare it into manageable amounts for use on the roof.
When re-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.
(left), long straw (right)
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 (see above). Longstraw also has exterior
hazel rodding at eaves and gables - a feature seldom seen on the reed
types. As it is more easily attacked by birds, netting is usually fitted
to the whole of the roof.
COMBED WHEAT REED
reed, or 'Devon' reed is predominantly used in the south and west of the
country. Although very similar in appearance to water reed, it is in fact
straw. The grain is removed from the straw through a combing machine which
is fitted to the top of an ordinary threshing drum. The straw does not
then have to pass through the drum and comes from the machine with the
butts all laid in one direction. It is then tied into bundles and stacked
ready for use.
Combed wheat reed
is applied to the roof in a similar fashion to water reed, dressed into
shape with a legget. However, as with longstraw, it is not necessary to
remove all the existing material from a roof prior to re-thatching.
Although there are
national average figures quoted for the longevity of each type of material,
these are of little use as judgements on performance - or likely performance
- can only be made in individual circumstances. The performance of thatch
depends on many factors such as roof shape and design, the pitch and its
position (geographically and topographically), the quality of the material
and the skill of the thatcher.
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 sedge.
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.
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
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.
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 eave. 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 eaves
and gables to project water clear of the building, and the ground should
be well drained.
Wind damage should
not usually be a problem. The experience of the 1987 winds in the south-east
of the country showed thatch to be more secure than many other forms of
roofing materials. 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
When alterations to
an existing thatched roof are planned or when designing a new thatched
roof it is imperative that consultation with a Master Thatchers Association
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.