15 Oct Fire in Thatch
“Prevention is essential; detection is nearly always too late”
28 serious fires in 2019!
Thatch Fires are disastrous; every thatch fire is a piece of our heritage destroyed and if rebuilt only a pastiche of the original. The distress to owners is deep and long lasting and cost to our fire services high in effort, manpower and financial considerations. However, homeowners can do something to help reduce the numbers of thatch fires through understanding and taking responsibility for managing risk to avoid unnecessary destruction.
Over the years, the National Society of Master Thatchers (NSMT) in conjunction with the fire services and specialist thatch insurers, has put great effort into the understanding and control of thatch fires. Currently, the largest number of serious thatch fires is in older thatched properties often with multi-layered thatch, unsuitable chimneys and wood burning stoves.
There is a booklet on the Society’s website which you can find here: https://nsmtltd.co.uk/wp-content/uploads/2019/01/3.-Fire-Prevention-in-Thatched-Properties-Advice-Notes-to-Download.pdf
What is the cause of fire in thatch? Undoubtedly fires start in or around chimneys. Chimneys need to be inspected regularly and swept twice a year in early autumn before the winter starts and early spring before the late cold snaps hit. This removes soot and bird nests. As thatch is often very thick, any issues with the integrity of the chimney can only be seen through camera inspection and should be used periodically so defects, such as eroded masonry and holes in the chimney, can be identified.
Burning the right fuel is essential to keep a healthy chimney as it slows down the build-up of dangerous tar deposits. Preferably hardwood which has a moisture content less than 20% is best.
Bird guard or Spark Arrestor? To prevent birds nesting in the flue, fit a bird guard to the chimney. This allows clear passage for smoke and the build up of soot is avoided and stops burning twigs being emitted from the flue. Spark arrestors can do the same but can easily soot up affecting the efficiency of the fire and increase the risk of Carbon monoxide poisoning.
Improving the alerting time to property occupants. This is an issue under constant review. Although smoke alarms within the house are an excellent way to alert occupants to the danger of a fire, they are less effective with the thatch. The problem is that fire and smoke alarms are not triggered at the time a thatch fire starts. By the time there is sufficient smoke to trigger an internal or external alarm, the fire will be well advanced and it is usually too late to save the property.
This is because of the nature of thatch: fire initiated at the surface (e.g. by burning brands from a chimney) will burrow into the thatch and proceed unseen and with many chimney related fires the fire can start deep within the layers of thatch round the chimney. A fire will develop very slowly as it is limited by oxygen availability. In deep tightly packed thatch a fire can burn for many hours before it reaches the surface, when more air availability will cause a flash over and visible flames at the surface. By then, the fire will have proceeded too far and it is too late for the fire services to save the property.
Fire advance in thatch is slow, varying from 1.3m/hr in calm conditions to 4m/hour in a gentle breeze. Spread is slowed by denser packing and longer air paths at the base of the ridge. It is largely unaffected by ridge type. Sadd (2001) CACFOA report.
Improve the initial fighting of the fire at source. The NSMT has been working very closely with Hampshire Fire and Rescue Service. There is a training video available used by many fire services with thatch in their areas. It is also available for public use from the NSMT website. The video covers thatch roof construction and how to take it apart quickly during a fire situation and how to use compressed air foam systems (CAFS) in controlling a fire. For fire fighters it is very difficult to gauge where to cut a fire break in deep thatch; heat seeking cameras only operate efficiently at the surface and will not reveal the presence of fire, even a few centimetres below the surface, because thatch is such a good insulator.
If a fire is detected, waste no time dial 999. When contacting the emergency services make sure they have good directions to the property and know where the fire hydrant and supplementary water supplies are (pond, river, swimming pool) and a description of the thatch e.g multi-layer, single coat, fire board, fire barrier, water reed, straw, netted main coat or just the ridge. Any other information which could be of use to the fire service so they can plan a course of action which could save your home and salvage your treasured possessions.
Reduce the destruction and damage of property. Unfortunately, in the event of a thatch fire damage to property is often severe, caused as much by water as by the fire. In new build properties with thatch this problem has been designed out through the “Dorset Model”. The principle of the Model is achieved by separating the thatch and the remainder of the property by using fire and water resisting boards to create a physical barrier against both fire and water. Flexible membranes do not conform to the building regulation.
Angold R E., Sadd P A, Sanders M (1998) Fire and Thatch, Specifications for Materials and Treatments for Thatch Vol.1 (Partners in Technology reference C1 39/3/286)
Benjamin K (2016) A survey of 148 fires between December 2008 and May 2016. Burgoyne’s report.
Dorset Building Control Technical Committee ‘The Dorset Model’. The Dorset Model has been jointly produced by Local Authorities across Dorset in conjunction with the Dorset Fire and Rescue Service, The Dorset Master Thatchers Association and the Building Research Establishment Ltd: https://www.dorsetcouncil.gov.uk/planning-buildings-land/building-control/advice-and-guidance/thatched-buildings-the-dorset-model.aspx
Hampshire Fire and Rescue Service /NSMT (2018) thatch removal and fire-fighting techniques. https://nsmtltd.co.uk/fire-service-training-video/
Glockling J. D. M (2018) Fires In Thatched Properties With Open Fires And Wood Burning Stoves.
Historic England & NFU Mutual report
NSMT, Fire Prevention in Thatched Homes. (2017) www.nsmtltd.co.uk
Sanders M., Angold R. E., (2012) Thatches and Thatching, A Handbook for Owners, Thatchers and Conservators. Ch.7 pp79-98. Crowood press