The risk of fire in thatched roofs is an issue that owners and others ignore at their peril. If the causes are properly understood and the appropriate measures taken, the risk of one occurring is low. However, it is clear that not all owners are aware of the risks they are taking.
Of the 50,000
to 60,000 thatched properties in the United Kingdom, approximately
24,000 are listed. Nationwide monitoring of thatched fires shows
that during the 1990s 60 to 70 serious thatch-roof fires were
recorded annually, and the figure is rising. Already in 2006 (to
the end of April) over 70 have been recorded and documented. With
few exceptions, these have all occurred in older, usually listed
properties. The figures include domestic dwellings and a number
of historic pubs, and 95 per cent are chimney-related.
is paralleled by the increasing use of multi-fuel stoves, sales
of which were running at an all-time high at the end of 2005.
Although it is counter-intuitive to believe that the two are related,
the installation and regular use of a multi-fuel stove or open
fire with a flexible metal liner can seriously increase the risk
of a fire. This is because modern enclosed solid fuel appliances
are designed to burn efficiently and cleanly at high temperatures.
Connecting these to old chimneys makes the thatch especially vulnerable
to the risk of slow char caused by the build-up of heat through
the brick and into the thatch.
transmission from an ordinary brick chimney into thatch: The
colours show the temperature contours through 115mm of brick.
Where the thatch surrounds the chimney, the insulating effect
of the thatch prevents heat loss from the brick outer surfaces
in contact with the thatch. If the flue gas temperature is
maintained at 300°C, the chimneybreast above the fire is barely
warm to the touch. However, where it passes through the thatch
the temperature rises, and in an area where the thatch is
around one metre deep, the bricks will heat through to the
point where the temperature will be high enough to ignite
the thatch after about 14 hours. The deeper the thatch, the
greater the risk.
most at risk are those with deep multi-layered thatch surrounding
a central chimney which has single-brick walls. Thatch separated
from the flue by the width of just one brick, as is the norm in
older thatched properties, can reach 85 per cent of flue gas temperatures
after only one day of continuous use. Modern flexible metal chimney
linings, even if faultlessly fitted, do not significantly reduce
the temperatures achieved through heat transfer into the thatch.
Badly fitted and inappropriate liners constitute a higher risk
than no liner at all and fitting too large an appliance for the
size of property also increases the risk. The risk is totally
dependent on how the consumer uses and understands the heating
system. Temperature monitoring can be carried out remotely by
fitting a device (Thatchgard for example) in the area of the thatch
which is most at risk, and enabling the effects of a stove to
be better understood and controlled.
combed wheat reed and long straw thatch is maintained by fixing
new spar coats on top of existing thatch layers. This gives the
poured on 'chocolate box picture' appearance much loved by traditionalists.
With time, the depth of thatch increases and, where the thatch
abuts a chimney, depths of 1-2 metres can easily be reached. In
this way, a considerable surface area builds up against the chimney
making the thatch more vulnerable. The recommended clearance from
the ridge to the top of a chimney stack is 1.8 metres (six feet).
However, even a cursory review of the most picturesque villages
will show many properties with thatch now level with the top of
the chimney. Just building a chimney extension makes the situation
worse as it allows even greater increases in thatch depths in
It is therefore
recommended that, when re-thatching, the opportunity is taken
to remove old wire netting and reduce the thatch depth. However,
removing old thatch is a controversial step to take. No thatcher
willingly strips a roof, as it is hard, skilled, dirty and expensive
work and disposal of discarded material is becoming an increasingly
difficult environmental issue. Furthermore, the surviving thatch
layers not only contribute to the character of the building, but
they may also contain important archaeological information about
the crops grown in the past and the way the building was used.
Nevertheless, some removal is essential, and to keep thatch depth
in proportion only the most recent layers need to be removed.
In this way archaeologically significant material may be left
of thatch is necessary, whether as a precaution against the risk
of fire, or for structural reasons, such as to enable timbers
to be repaired or replaced, thatch layers can always be recorded
and samples stored as they are removed. In all cases it is essential
to consult with all interested parties before removing existing
layers of thatch, including the local authority conservation officer.
thatched in water reed are less vulnerable than those thatched
in combed wheat reed or long straw, because when re-thatching
occurs, water reed is usually removed and cleaned back to the
rafters. (It is only likely to be spar coated in the West Country.)
Water reed stems are tough and packed more tightly together, making
them less flammable than cereal straw.
with deep thatch. This house in Hampshire has had numerous
spar coats and the thatch depth has increased progressively.
Originally, the top of the chimney pot would have been around
1.8 metres (six feet) above the ridge, and the thatch around
it is probably about 2.4 metres (eight feet) thick. The installation
of an enclosed multi-fuel stove employing this chimney would
result in a high risk of fire.
is well managed in those new homes which are now being built with
thatched roofs, as experience gained from studying old thatched
buildings has led to the development of built-in fire prevention
precautions. These include chimney flues being insulated and double
skinned to ensure that there is no contact between thatch and
the heat from hot flue gasses. In addition, the thatch is separated
from the house by a fire resistant barrier, so, in the unlikely
event that it does catch fire, the thatch becomes sacrificial,
while the occupants and the rest of the house are protected from
always be remembered that thatch is an organic material, subject
to different behaviour patterns depending on its surroundings,
treatments and choice of materials or styles. It has a finite
life span, measured in tens rather than hundreds of years and,
above all, it is combustible.
is the most common cause of thatch fires in the United Kingdom.
It is the combination of deep thatch and a central chimney in
conjunction with the use of multi-fuel stoves that put properties
most at risk. Proper maintenance, care and understanding are the
essential tools in protecting the national heritage and people's
homes. The National Society of Master Thatchers (NSMT), local
fire and rescue services, specialist insurance companies, local
authority conservation officers and, increasingly, the chimney
lining sector are all working together to reduce the risk of thatch
fires. Initiatives include a range of publications, and the NSMT
organises public seminars in conjunction with local fire services
in areas of the country where there are high numbers of thatched
insurance claim for each serious thatched fire is now close to
£250,000. Each fire service call out costs in the region of £40,000
in manpower and resources. While monetary cost is a calculation
that cannot be ignored, anyone who has experienced a thatch fire
will know that an insurance policy can only reinstate in a material
sense. Personal possessions and intimate memorabilia, like heritage,
is priceless and irreplaceable. These are the hidden costs in
any fire loss claim which cannot be revealed by statistics, and
most could be avoided.
article is reproduced from The Building Conservation Directory, 2006
SANDERS is Secretary & Chief Executive Officer of the National Society of Master Thatchers Limited (NSMT).
She has worked with the NSMT for 15 years, researching
and disseminating knowledge concerning the
longevity of thatch and the factors that affect it, including fire and fire prevention.
The society's aim is to provide a resource of first choice
for those who care about thatch as part of the nation's
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