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Thatched Buildings


Occasions arise when surveys are conducted of old premises (and occasionally modern buildings) which are roofed of thatch. This mainly involves, but not exclusively, public houses, restaurants, hotels and high net worth dwellings. This Technical Bulletin is intended to provide Consultants with guidance on the special hazards associated with thatched property and the fire safety measures which should be employed.

Not only is thatch highly combustible, but fires involving thatched roofs are extremely challenging. The majority of thatch fires occur from September to Easter; particularly during cold snaps and bank holiday periods. Once alight, thatch fires are almost impossible to control, with salvage the only option for the Fire and Rescue Service. Consequently, MD EML’s for thatched premises shall always be set at 100%.


As well as the specific fire precautions detailed below, fire safety management in thatched premises should adopt a high profile with suitable attention given to matters such as correct electrical maintenance, general fire hazards including cooking, arson prevention, where appropriate the completion of a fire risk assessment in accordance with the Regulatory Reform (Fire Safety) Order and other fire safety legislation, and the correct maintenance of fire safety equipment and means of escape.

Dealing specifically with the hazards posed by thatched roofs, key considerations are summarised in the following pages.


1.        Chimneys

It is reliably reported that the majority of thatch property fires that have occurred in recent years have been caused by chimney related issues in conjunction with the increasing use of enclosed wood burning/multi-fuel stoves. In addition to the obvious transmission of hot flue gases through a brick stack with open or porous joints, evidence also points towards the presence of thick beds of thatch positioned directly against chimneys associated with high flue gas temperatures, which over time allows sufficient heat transfer to a point (at around 200⁰C) where the thatch will char and ignite.


Hot spots within the thatch

Arising from the severity of this issue, the FPA has been commissioned to carry out a test and research programme, the findings of which very much support the ‘Heat Transfer Theory’ are referred to in the Appendix.

Traditionally, chimneys in older thatched properties were designed to be used with open fireplaces through which cold air was drawn, with the effect that flue gases became diluted and overall flue gas temperatures cooled. Modern enclosed solid fuel appliances, by comparison, burn cleanly and efficiently, generating flue gas temperatures in excess of 300⁰C.

(It is not uncommon for stoves to be oversized for their application, especially where small rooms with large inglenook fireplaces exist and the installation of a small, yet correctly sized stove would look out of place.)

Chimneys built before the 1960’s are most likely to be of single brick thickness and parged (commonly a mix of plaster and roughcast), not lined. This parging crumbles and disintegrates with age, leaving the brick or stonework to the chimney exposed. Coupled with this is the risk of a chimney fire, the effects of which can be increased if tar deposits formed by the burning of wood (particularly unseasoned logs) are allowed to accumulate. 

Black or brown localised deposits on the chimney and/or the presence of soot in the loft is likely to indicate that the chimney is unsound. This may also be visible externally.

Fires can also be caused by hot embers from the chimney falling onto the adjacent thatch.

These hazards are addressed in The Building Regulations (England & Wales) Approved Document J (reprinted 2015) which applies to all new buildings, or in cases where a material change of any part of the combustion system (appliance or chimney) is planned. It can also be applied retrospectively as ‘best practice’ where considered appropriate. Remedial measures in Approved Document J include:

  • Ensuring that the flue outlet (top of chimney pot) is positioned in areas that are (A) at least 1.8m vertically above the thatch and at least 0.6m above the ridge, and (B) are at least 1.8m vertically from the thatch and at least 2.3m horizontally from the thatch (as per diagram below), and


  • Ensuring that the risk of ‘Heat Transfer’ is reduced by adopting measures such as the cutting back of thatch from the chimney by at least 40mm and constructing a heat resistant shield away from the face of the chimney, or the installation of a factory made system chimney tested to European Standards and which have declared distances to combustible materials. System chimneys are available with stainless steel or ceramic liners, surrounded by high performance insulation and a stainless steel outer casing.

Positioning of flue outlet in compliance with Building Regulations


An example of a common cut-back arrangement in compliance with Building Regulations

Full details of these measures, together with diagrams can be found in Section 2 of Approved Document J which can be downloaded from  There is also an excellent publication (Thatch Article 1-007) available from HETAS (Heating Equipment Testing and Approvals Scheme) at (HETAS is the official body recognised by Government to approve biomass and solid fuel domestic heating appliances, fuels and services, including the registration of competent installers.)

(Important Note:  In respect of listed building, under no circumstances should alterations to the chimney arrangements be made without obtaining listed buildings consent from the local planning authority.)

The traditional approach of fitting chimneys with spark arrestors is no longer recommended, owing to the fact that these can become blocked. Where spark arrestors are fitted, it is essential that these are taken down and cleaned once every 3 months.

Chimneys should be swept at regular intervals by a professional chimney sweep. HETAS recommends that chimneys are swept at least twice a year when burning wood or bituminous house coal and at least once a year when burning smokeless fuels. The chimney should be swept just before the start of the heating season and after any prolonged period of shutdown. If sweeping twice, the second time should be after the peak of the main heating season. In order to ensure competency, a HETAS Approved Chimney Sweep should be employed, and the chimney swept in accordance with the National Code of Practice for Chimney Sweeps. On completion of sweeping, a certificate should be issued.

In addition to regular sweeping, it is important that the flue and chimney is inspected at least once every 3 years to ensure that the brick or stonework and any flue lining are in sound condition and fit for purpose. This work, which invariably will involve the use of CCTV, should be carried out by a HETAS registered engineer or a member of the National Association of Chimney Engineers.


2.        Stove Pipe Temperature Gauge


In the case of wood burning/multi fuel stoves, the provision of a stove pipe temperature gauge is an essential accessory to optimise safe burning conditions. Too hot conditions will compromise the temperature gradient between the chimney bricks and flue gases even with a liner, whereas, too cold will result in a build-up of tar increasing the risk of chimney fires. This device, which in its simplest form is magnetically attached to the flue (normally at least 300mm above the top of the stove), allows the performance of the stove to be monitored. (Also, as with all appliances burning gas, oil, solid mineral fuel and biomass, CO alarms should be provided.)


A typical stove pipe temperature gauge

3.       Chimney Alarms

In response to the risk of Heat Transfer, chimney temperature monitoring and alarm systems have been devised, the two main products being:


  • TAS-33 Thatch Alert. Marketed by Thatching Advisory Services Ltd, this consists of a system of battery powered temperature probes installed at the interface between the chimney and the thatch, connected to a receiver from which temperatures can be monitored and a critical audible alarm raised - 


  • ‘Phoenix’ Chimney Monitor System devised by Thatch Fire Protection Ltd. This system employs linear heat detection cable installed around the chimney at the chimney to thatch interface, hardwired to a control panel which continuously monitors the detection cable for alarm and fault conditions. The system is mains power operated with battery backup, and is capable of remote monitoring - 


Despite claims that a number of Insurers provide premium discounts for such systems, which in the case of the Phoenix system is endorsed by NFU Mutual, market penetration has been extremely limited, with both companies quoting low annual unit sales.  


The installation of chimney temperature monitoring and alarm systems must not be taken as a substitute for correct chimney design and should only be considered in circumstances where despite the application of conventional remedies, concerns regarding the risk of Heat Transfer remain.


4.       Electrical Installation

The following precautions should be observed:

  • Ensure that periodic electrical inspection and testing extends to wiring and equipment in the loft.

  • All wiring connections, including aerial leads and supply cables positioned at least 300mm away from the thatch and any wire netting.

  • Bulkhead light fittings positioned away from the thatch to be provided in the loft and all wiring suitably protected, preferably with the use of mineral insulated cable.

  • Avoid cutting recessed lighting into ceilings below the thatch.


  • Ensure that all external lights are positioned at least 1m clear of any part of the thatched roof and that there are no floodlights under the eaves.

  • Overhead electric supply cables and telecoms lines to be prevented from coming into contact with the thatched roof or nearby trees.


5.       Fire Detection and Alarm Systems

Where there is automatic fire alarm protection to the premises, detectors should be incorporated in the loft or roof void.

(In response to the enhanced risk posed by  thatched building, the FIA has published Fire Detection and Alarm Systems in domestic buildings with thatched roofs which can be accessed here.)


6.        TV Aerials 

Owing to the risk of lightning, TV aerials and satellite dishes should not be fitted to the chimney but should be installed on a mast at least 6m from the building.


7.        Hot Work

Hot work of any kind in a thatched building should be avoided wherever possible. If this is not possible, a strict hot work permit shall apply. Under no circumstances should work to be carried out in the roof space.


8.   Loft Storage

Storage in the loft space below a thatch roof should be avoided or, where this is not possible, kept to an absolute minimum.


9.   Bonfires

Bonfires, barbeques, fireworks or Chinese lanterns should not be lit where there is a risk of embers or burning material landing on the thatch.


10. Fire Retardant Sprays and Barriers

Fire retardant spray coatings are available which have been specifically formulated for both internal and external thatch protection. Such products include “Thatchsayf” marketed by Thatching Advisory Services -  and “Magma Firestop” recommended by the Thatch Advice Centre under the brand of “Thatch-Safe”

As with all such products, correct application is essential if the desired results are to be obtained and therefore only ‘certified’ contractors should be employed. In order to remain effective, routine re-treatment is required, normally at least once every five years. Whilst fire retardant sprays have a role to play in providing external protection to the thatch, they are unlikely to have any impact on protecting the inner layers of thatch from Heat Transfer.

The above companies, amongst others, also market a range of fire-retardant barrier systems in the form of membranes and boards for fixing to the rafters below the thatch for application in new build and re-thatched projects, in compliance with the Dorset Model (see below).

Another product devised by Thatch Safe Ltd. is marketed under the brand of ‘Thatch-Safe ATTIX’. This comprises of an automatic fire suppression system for installation and protection of the loft space, activated by linear heat sensors positioned around the chimney and along the underside of the ridge and employs what is stated to be an to be an environmentally friendly chemical agent. Owing to the fact that this product is only designed to suppress a fire incepting in the loft space and does nothing to protect against the two main causes of thatch fires, it is not surprising that it has achieved very limited market penetration.


The ‘Dorset Model’ has been jointly produced by the Local Authorities across Dorset in conjunction with Dorset and Wiltshire Fire and Rescue Service (DWFRS), the National Society of Master Thatchers, and after consultation with the National Inspection Council for Electrical Installation Contracting and the Building Research Establishment Ltd on the basis that evidence has shown that thatch can be made sacrificial in the event of fire.

The ‘Dorset Model’ is quoted in Approved Document B of Building Regulations as a method of dealing with issues of external fire spread, with the aim of providing guidance for extensions and new buildings with thatch roofs that are within 12m of a boundary.

One of the main requirements of the model is that roof rafters are overdrawn with a minimum 30-minute fire barrier (integrity and insulation) with the objective of providing the Fire and Rescue Service with the time to extinguish or remove the thatch. (DWFRS recommend a 60-minute barrier for property protection).

In addition, a domestic mains and battery powered, interlinked smoke alarm system is required to be installed in accordance with Approved Document B to BS 5839: Part 6, with at least one smoke detector installed in the roof void.

Details of the ‘Dorset Model’ are available at


The life expectancy of a thatched roof will vary according to several factors. These factors include regular maintenance, the quality of materials used, the skill of the Thatcher, the proximity of trees, pollutants in the environment and even the geographical location, as a high humidity level shortens the life-span of the thatching materials.  The following figures, allowing five years either way, are a reasonable guide to any thatched roof which is not exposed to great extremes.

  • Water Reed (also known as Norfolk Reed) - 50-60 years.

  • Combed Wheat 25-40 years

  • Long Straw 15-25 years.

Ridges, whatever their design or type, have a life-span of 10-15 years.



Consultants surveying a thatched building should pay particular attention the following:

  • Age of the building, listed building status and when last re-thatched.

  • The general external condition of the thatch and chimney, with particular regard to the presence of black or brown localised deposits on the chimney and/or the presence of soot in the loft space. Where safe to do so, access to the loft should be obtained.

  • Height and position of the chimney outlet in relation to the thatch. A minimum height of 1.8m is normally recommended (as per Approved Document J) which can be achieved by replacing or extending the pot. However, it has to be recognised that thatched buildings will commonly be ‘listed’ and approval for such measures may not be easily obtained.

  • Presence/cleaning of bird guards and spark arrestors, where fitted. 

  • Frequency of inspection and sweeping of the chimney by a HETAS Approved Chimney Sweep and availability of completion certificates.

  • Where wood burning/multi fuel stoves are encountered, enquiries should be made as to when the stove was installed and the availability of a HETAS Certificate of Compliance, confirming that the installation meets the requirements of Building Regulations. In cases where such information is unavailable, a risk improvement requirement shall be made that the stove installation and chimney be promptly inspected by a HETAS registered installer or a member of the National Association of Chimney Engineers for fire safety and a report submitted.

  • Also, the extent to which a routine CCTV survey of the chimney has been conducted, checking the suitability and condition of the flue/liner. Specialist inspection of the flue should be conducted at least once every 3 years. Until this inspection has been carried out and any necessary fire safety remedial work completed, our recommendation would be that the stove should not be used. (This, however, would be a matter for Underwriters and is not to be included in the wording of the risk improvement. Reports on such cases are to be ranked as ‘contentious’.) 

  • The presence of a stove pipe temperature gauge and chimney temperature alarms.

  • Policyholder aware the stove manufacturer’s operating and maintenance instructions including, where recommended, undertaking an annual service at the end of the burning season, preferably by a HETAS registered servicing engineer.

  • Presence of CO detection.

  • Compliance with the ‘Dorset Model’ in respect of new build and rethatch property. (Whilst having no bearing on the EML, this may be considered by some Underwriters to be a favourable risk feature.)

  • In the event of any queries or concerns regarding thatched buildings relative to a specific case, Consultants should contact the Technical Helpline.



Sources of information include:


Thatching Advisory Services

Thatch Advice Centre

National Society of Master Thatchers

National Association of Chimney Sweeps

Guild of Master Chimney Sweeps



FPA Study - Fires in Thatched Properties with Wood Burning Stoves

Sponsored by Historic England and NFU Mutual, the FPA has conducted an important study into the fire hazards associated from the operation of wood burning and multi-fuel stoves in thatched properties, the report of which has become freely available from the FPA at

The key recommendations of this report together with diagrams are transcribed below.

The research conducted confirms that wood burning and mutli-fuel stoves represent a greater hazard in thatch roofed buildings than open fires and as such are NOT a recommended form of heating.



The report accepts that the efficiency advantages of wood burning, and multi-fuel stoves are attractive to householders and provides the following guidance to assist in reducing the risk of fire where such stoves are used.


Sparks and embers, apart from those generated by chimney fires, are generally of low energy with a short lifespan. Increasing the distance between the top of the chimney and the thatch (by raising the height of the chimney, adding a chimney pot, or reducing the thickness of the thatch) will result in fewer active sparks reaching the thatch thereby reducing the probability of ignition.

Tar and soot build-up can lead to chimney fires resulting in extreme flue gas temperatures and burning material being emitted from the chimney top. Chimney fires may cause ignition of building fabric and contents, damage chimney liner and brickwork, and may set fire to thatch directly by radiation or by ejecting burning material that lands on the thatch.


The introduction of a nest of twigs into the chimney provides an assured and proven means of generating heavy, high intensity burning brands, issuing from the chimney that could set thatch alight even after long distances of travel from the pot top. Sweeping alone will not mitigate this risk as birds may build a nest after the chimney has been swept. The chosen device must not impair the function of the chimney; be capable of blocking under any circumstances; and must not impair normal chimney sweeping activities.


All stove chimneys should be lined, ideally with twin-walled insulated rigid stainless liner. Where not possible due to chimney geometry and access issues, a quality twin-walled

flexible stainless liner should be used in its place. The transport of hot fire gases and sparks to internal thatch layers via imperfect chimney brickwork has been demonstrated to be an assured means of starting in-thatch fires. The risk from this mechanism of fire raising may be wholly mitigated by the provision of a liner.


During ignition, when the stove controls may be set to a maximum ventilation to get the fire going, there is the potential to lift heavy burning materials, such as paper and card, from the fire box and for it to be ejected from the chimney over the thatch. The use of firelighters and kindling in preference to paper and card will reduce the risk. The wood burning stove should NEVER be used as an incinerator, e.g. for sensitive paperwork and rubbish.


When the ventilation to the stove is increased to boost the fire during ignition or refuelling it is essential that the stove is attended until the controls are re-adjusted to their normal settings. Failure to do so may result in very high uncontrolled stove and chimney temperatures in association with high flue gas velocities. These factors may act to initiate chimney fires (if tar and soot is present), lift burning material out of the chimney, and raise fires through gas escape under thatch if the brickwork is imperfect and the chimney unlined.


Stove temperature monitoring is an essential user aid to understanding if the stove is working within its safe limits. Operating at too low a temperature risks coating the chimney with soot and tars which may later lead to chimney fires. Operating at too high a temperature risks fire raising through the ejection of burning material; the starting of chimney fires if tar and soot has built up; and the internal ignition of thatch through faulty brickwork if the chimney is unlined. All members of the household should be aware of the meaning of the gauge sections and know how to control the stove to maintain ideal operating limits.

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