Dictionary Definition
thatch
Noun
1 hair resembling thatched roofing material
2 plant stalks used as roofing material
3 an English pirate who operated in the Caribbean
and off the Atlantic coast of North America (died in 1718) [syn:
Teach, Edward
Teach, Edward
Thatch, Blackbeard]
4 a house roof made with a plant material (as
straw) [syn: thatched
roof] v : cover with thatch; "thatch the roofs"
User Contributed Dictionary
English
Pronunciation
- /θætʃ/, /T
Extensive Definition
Thatching is the craft of
covering 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 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.
History
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 tropical
regions.
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.
Records of European thatch
date back to before the Middle Ages,
when the first villages
were 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.” 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 plaster daub.
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 the early
years of the 19th 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 readily available. To
compound this, the Napoleonic
Wars raised the price of wheat and straw to a prohibitive level in
Europe. The
number of thatchers declined, as the tradition became regarded as
unfashionable.
Technology in
the farming industry has had a negative
impact on the popularity of thatching. 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. The
increased loss of water
plants and wildlife occurred with the
shift from open ponds to cattle troughs and piped water for
animals. With it came the decline in availability of rushes, and
other wetland vegetation
used in thatching.
With renewed interest in
historic architecture and the trend
towards using more sustainable materials,
thatching is once again in the ascendancy.
Thatch material
There are more thatched roofs in the United Kingdom than in any other European country. The traditional material in most of England is 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.Water reed, which was used in
East
Anglia and 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 Turkey and 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.
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.” Water penetration,
when it occurs is minimal and is usually due to capillary
action. The presence of moss is 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.
3. Trees should 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.
5. Television
aerial 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.
Flammability
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. 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 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.
Performance
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. 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
States and Britain, offers an
insulation or R-value of 40.
Conventional building
insulation, such as fiberglass, usually rates
between 30 and 50.
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 rural environment. Thatch has an
ecological advantage because it is produced by natural processes
that do not use scarce and expensive resources of energy.
Disadvantages
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. Insurance costs 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 decomposition and
precautions must be taken to minimize the possibility of this
process taking place. In warm, wet climates thatch is prone to
fungal
attacks.
Animals can cause damage.
Birds looking
for food, gathering nest-making materials or nesting in the roof
itself becomes a greater possibility when the plant material is not processed
appropriately for its intended use. Rodents can 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 thatched.
New thatched roofs were
forbidden in London by 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 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 waterproof roof built with
modern materials.
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.
References
External links
thatch in Czech:
Došek
thatch in Danish:
Stråtag
thatch in German:
Reet
thatch in French:
Chaume
thatch in Dutch: Rieten
dak
thatch in Japanese:
茅葺
thatch in Polish:
Strzecha
thatch in Swedish:
Stråtak