Similar To This And Related Others
Spark Arrestor Plans
My own opinion on the
reduction of risk of fire in thatched property.
television or radio aerials should be, where possible be sited in the
attic or externally on a gable end and not on the chimney so as to have
the cable routed as far away from the thatch as possible. They should
never be routed through the roof. Apart from minimising the risk from
lightning strikes this will reduce undue strain on the chimney structure
and remove the need for ladders on the roof for aerial maintenance.
that any netting on the roof is fixed in such a way that it can be removed
easily in case of fire. Twisting the tension strip of one panel to the next fastens
most wire netting, a single twist will undo with minimum force making
the easier rapid removal to provide fire crews access to the surface of
electrical wiring in the loft space should ideally be routed in appropriate
fire retardant ducting to prevent possible rodent damage to cables and
help contain a short circuit cable fire.
linked mains and battery powered smoke alarm should be fitted in the roof
space in each bay. The use of these are not recommended in a normal attic
by the manufactures but the insulating effect of thatch minimises the
chances of false alarm through ambient temperatures fluctuations affecting
5839 Pt. 6) http://www.newryandmourne.gov.uk/environment/building_control/smoke_detection.asp
chimney should be, if used by any appliance producing flue gases be lined
according to the manufactures specification and in the case of solid fuels
be swept regularly. The top of the stack should be no closer than 1.8
m from the ridge vertically and in the case of a stack in the wall 4 m
vertically from any thatch surface. Spark arrestors on the flues should
be treated with caution because they can clog and restrict the flow of
flue gases. A stainless steel welders spark guard mesh made in two
sections is my personal recommendation, the inner tube being fixed so that
the flue brush enters it, an air gap to trap debris and allow cooling and
the outer tube removable to allow for manual cleaning. Good quality smokeless fuel is preferable to ordinary coal
or peat and any wood should be resin free (hard woods) and very well seasoned
and dry to prevent build up of tars. Any building work requiring ladders
or scaffolding resting on the thatch, in particular the ridge should be
padded (for example rolled old carpet) this will minimise possible damage.
Any building work that will result in rubble or mortar dust being shed
onto the roof should have that area completely covered full length of the
roof so that no building materials such as paint or mortar become lodged
in the thatch. The lime in mortars are particularly harmful.
not cut recessed lighting into the ceilings below the thatch. Light fittings
within the roof space should be in a bulkhead fitting. External floodlights
should not be located just under thatch overhangs.
provision of a loft hatch will be required for fire fighting purposes.
The minimum recommended size is 600mm x 900mm ensuring that access can
be gained to all roof void areas.
would be advantageous to have an external water tap and hose reel supplied
from the rising main, appropriately lagged against frost and capable of
reaching all parts of the roof, both externally and internally with adequate
pressure and fitted with a pump if needed.
common sense is the best guide, although thatch in a well maintained condition
is difficult to light, when it is allowed to decay or has been loosened,
it is similar to the lighting of a solid block of wood, if this is half
rotten or split into small pieces it will burn more readily.
not burn garden waste, and try and persuade your neighbours not to do
so particularly in dry and windy weather. The greatest area of risk is
under the eave and in the roof void, never allow paint burning in these
areas, and only have compression joints on plumbing to avoid the use of
If you are thatching a new roof, or one that has
had to have the rafters renewed, my advice would be to build in a fire
retarding barrier - see PLANS
this will at least give a measure of protection to the rest of the house
and isolates the roof from possible internal source of ignition. It is
possible to very effectively fire retard all the materials but if it will
wash off, or does not penetrate the entire thickness I consider it to be
of very limited value. For good protection the material has to be soaked
in retardant, dried and then used - this will be very expensive but is
Remember that thatch, as we know it has been in use for hundreds of years,
most properties, even today, do not fulfil all the above criteria. Unfortunately
when a thatch does catch fire it invariably makes the news, could it be
the rarity of occurrences? In nearly 40 years if thatching I have had to
re roof only one and repair three with minor damage. (none of them
thatched by me!) Most incidents are
due to glaring omission of common sense rather than any inherent flammability
It is also worth noting that most thatch fires seem to happen to roofs
that require re thatching but I expect this is also a coincidence !
To be extra careful note the latitude and
longitude of your property, this can be vital for the services to find you
quickly, the site of the nearest fire hydrant
(yellow 'H') and stream, pond for water.
The objective of the research being carried out by the team at RHM Technology
is to identify' and eliminate the major causes of preventable fires in
houses with thatched roofs.
Thatch fires make up a minor position of all domestic fires in the UK.
Unlike other fires there is seldom loss of life. The only question currently
asked, at the time of a thatch fire, is "what is the source of ignition"
(malicious or otherwise)?
Research has shown that a high proportion of thatch fires are chimney
related, probably as many as 90%.
Fire brigades with a large number of thatched properties in their area
have special problems. Each has its own strategy for dealing with thatch
fires, though experience shows, whatever the initial response, thatch
ultimately demands a high level of manpower and equipment in attendance.
Fighting thatch fires is problematical, properties can be in isolated
rural locations and difficult to find, especially in the depths of winter.
The fire is often well alight before it is detected and the brigade called.
Fighting thatch fires carries a high risk of injury for firemen.
Fire fighting is frustrated for a variety of reasons. Pouring water onto
thatch is ineffective (a thatched roof is designed to repel water). The
insulating properties of thatch counteract any cooling benefit from water.
Once established, a thatch fire can be sustained by oxygen diffusing from
beneath the roof. Wire netting on the outside of the roof, restricted
loft access and barrier boards add to the difficulties of dealing with
a thatch fire. Under these circumstances the brigade strategy can often
only be one of salvage. Thatch has an ability to burn unseen, making the
cutting and placing of fire breaks difficult.
Insurers are becoming alarmed by the increasing number of fires associated
with thatched properties. The level of damage from a thatch fire means
that claims are high, the average cost per claim in 1995 was £8 5k. From
insurance records it can be seen that the incidence of thatch fires is
seasonal, occurring in early autumn, late spring, during cold snaps, weekends
or holiday periods. Problems seldom start in unoccupied houses. For CGA
50% of claim payments are fire related, but these constitute only 7% of
the total number of claims submitted.
Current advice to thatched property owners is in containing or retarding
a fire rather than in identifying the most likely cause. Because many
thatched houses are listed buildings and because there is inconsistency
in advice given across county borders, planning requirements vary. Some
conservation officers favour the installation of "thatch batts"
and barrier foil as "underlay" for thatch. Research elsewhere
is examining this practice in relation to moisture migration through thatch
and its effectiveness as a fire barrier.
In some areas, unless straw or reed is treated with chemical fire retardant,
thatching a roof would not be allowed. This requirement has led to some
thatching projects going ahead where otherwise an alternative roofing
material would have to be found. Only limited records are available to
indicate the effectiveness of chemical treatments as a means of controlling
The modern thatching industry faces a variety of challenges. Many thatched
properties are listed buildings forming a valued part of our heritage.
A fire in a listed building is doubly distressing not only to the current
owners but in the irretrievable loss of a unique structure. In formulating
conservation strategies it may be necessary to sublimate some entrenched
views to ensure that the building can be protected from fire as well as
other modern types of wear and tear. The formula quoted by the National
Trust is "to conserve and preserve a property in the right way, following
what has gone before". This would involve maintaining the building
in perpetuity, giving value for money and following the best methods to
Results from a mathematical model of the processes of heat transfer in
thatch have produced a series of temperature, time and condition profiles
indicating conditions which are likely to result in a thatch fire.
Few thatched properties are new buildings, many of them have listed building
status. The majority of thatched properties have chimneys built prior
to the 1960s when chimney construction was of only a single brick thickness.
At this time many thatched properties had large inglenook fire places,
where flue gases would be mixed with large quantities of cooling air,
drawn in through ill fitting doors and windows.
Traditional thatch maintenance techniques often require a spar coating
to be applied over existing thatch. Under these circumstances, and over
a long period of time, the depth of thatch can reach up to 2 metres, 1
metre is not uncommon. Under these conditions the insulating characteristics
are such that little heat is lost through the body of the thatch. On the
other hand 10 cm thickness of chimney brick is a relatively poor insulator
and even in circumstances when the brick work is sound, heat is easily
transferred into the thatch.
The temperature profiles which can develop in thatch, a metre deep, when
flue gases reach 300~C. This level of heat transfer into the thatch can
occur after only 12 hours of continuous use.
Once a sustainable temperature of over 200~C has been reached within
the thatch, conditions are favourable for the first stages of slow breakdown
and charring. Under these circumstances, over a period of
time, changes can occur which may lead to a potential for fire. Because
these changes occur within the deep body of thatch, a fire generated in
this way may be well alight before discovery. Prolonged, high temperatures
can lead to ignition of thatch even with an intact chimney. Where a faulty
flue allows gases to escape the risk is increased.
Heat generated by a woodbuming stove was so intense that, over a period
of time, the whole chimney had become distorted and cracked.
Enclosed solid fuel stoves are becoming very popular with thatch property
owners. Under normal operating conditions it is not unreasonable to expect
flue gas temperatures to reach 300~C, when a fire is burning strongly
temperatures can rise to 600~C and higher. In properties with double glazing
and extensive draught proofing, flue gas temperatures remain high for
the entire length of the chimney. Changes in the way people live, double
glazing, wood burning stoves to replace open fires, has probably led to
the steady increase in the number of thatch fires.
Thatch adjacent to a single skin brick chimney will reach 85% of the
flue gas temperature after one day of continuous use, with little cooling
across the brick work.
Findings predicted by the model have been supported by evidence from
fire brigades and "post mortem" examinations carried out following
fires in thatched properties. All the fires investigated in 1996 appear
to have been chimney related.
LOOK FOR THE WARNING SIGNS
Spark arrestors, up to now, seem to be
given tentative approval, though in this investigation even thatch
fire visited had some type of device on the chimney pot. If fitted, spark
arrestors must be cleaned regularly.
Soot is a powder! Any solid material or tar removed from a chimney during
sweeping a should be investigated.
Thatch separating from the chimney could be drying out from excessive
heat. Ask your thatcher to inspect the condition of the thatch and chimney.
Check pointing and flashing regularly particularly where the chimney
is surrounded by thatch.
Sweep chimneys regularly and thoroughly.
Burn only dry and seasoned wood.
Install a chimney liner, advice can be obtained from the National Association
of Chimney Lining Engineers, telephone: 01785 811732.
Whilst essential, smoke alarms in a thatched property alert the owner
often too late.
In thatch fire prevention is essential, detection is usually too late!
© This article is a summary of research being undertaken at RHM Technology,
High Wycombe as part of the "Partners in Technology" initiative
funded through the Department of the Environment. CGA Select (a division
of CGA Direct Insurance Brokers) and supported by in-kind contributions
from the thatching industry.