Thatched home inspection: Surveying a thatched property.

Buying a thatched property? We undertake specialist thatched roof surveys.

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Nothing resonates more in the eyes of homeowners of traditional buildings more than a chocolate box thatched cottage in the countryside. With its uneven slopes, curved dormers and detailed ridges make the perfect postcard and picturesque setting, however, many homeowners do not understand the maintenance and long term implications of owning a thatched building.

Thatch was the most common roof covering in almost every part of Britain in the medieval period, and remained a popular roofing material in rural areas until the late 19th century when mass production and the expansion of the railway network gradually reduced the price of other roofing materials such as clay tiles, slates and corrugated iron.

Thatch was a cheap by product of the harvest and not associated with high value, country cottages that we see today, infact, most common agricultural and low value dwellings were thatched! Things have changed of course and you should be aware that thatch is not a cheap roofing material.

There are three common methods of thatching in this part of the country namely combed wheat reed, long straw and water reed (sometimes known as Norfolk reed).

Combed Wheet Reed: Combed wheat reed is one of the accepted varieties of winter wheat which having been cut and stooked at harvest is put through a threshing machine which also combs the stems. The process prepares the material so that it can be used for thatching.

Typical lifespan of combed wheet reed is around 30 – 35 years

Long Straw: Longstraw is produced from straw specifically grown for thatching. This was the most popular form of thatch until around the 1960s when changes in agriculture made it less common and was gradually replaced by reed.

Long Straw thatch typically lasts for around 20 – 30 years.

Water Reed: Water reed is used extensively in the West Country and East Anglia. New properties are almost always thatched in water reed since it is the most durable of the thatching materials, and tends to give the longest life.

The life span of water reed if well maintained is around 40 – 50 years, however, this can exceed this greatly dependant of location, maintenance and quality of installation.

You will find that all of these varieties will require re-ridging every 10 years or so and require regular maintenance, clearing of moss, carrying out patching etc.

In general terms the largest single reason for thatch to deteriorate is directly related to the length of time that moisture is retained on the surface. Microbiological activity takes place in wet, warm conditions, causing the reed or straw to break down. Thus, the drier the climate, the more exposed the roof and the steeper its pitch the longer the material will last. Accelerated wear will take place in those areas where rainwater is channelled, namely to each side of any dormers or chimneys. Also where the pitch changes to below 50 degrees wear will also be accelerated.

Maintenance is the key, little and often is definitely the best policy. Annual inspection and maintenance log should be undertaken by a master thatcher. Most areas, towns or villages will have a local thatcher who has probably worked on your building historically. Making contact with them is a good idea. As with any profession of course there are good ones and bad ones.

There is no overseeing body or qualification. Anyone can setup as a thatching business and call themselves a master thatcher so do be wary. Make sure your thatcher is recommended and ask to see examples of work undertaken, both recently and after a few years.

Are you thinking of buying a thatched property, unsure of the current state of your thatch or are just in need of an inspection? Smith Heritage Surveyors carry out thatched home inspections throughout Wiltshire and the West Country. We are regulated by the Royal Institution of Chartered Surveyors and have all attained thatched home inspector certification having attended relevant training. We also work with and can recommend good master thatcher’s who will be able to give accurate costs for maintenance and rethatching.

General points:

– It is possible that buildings insurance may be higher due to the thatched roof and you are advised to check this with your preferred insurance company. When insuring the property, the presence of the thatch must be declared.

– You are advised not to light garden fires near the property.

– Blowlamps or heat guns should not be used in roof spaces or near the thatch externally.

– Ensure a hose pipe is constantly available and that it reaches the full perimeter of the building.

– Regular checks on the safety of the electrical system should be made.

– Consider adding mains powered inter-linked smoke detectors in the roof space.

– There is plenty of information about living with thatch on the internet: you are strongly recommended to take advantage of this.

One of the most common concern we hear from clients buying a thatched prperty is about fire risk and what they can do to reduce the risks. 70% of fires in thatched homes are caused by solid fuel burning appliances. Installation of a woodburners or a multi fuel appliances requires great caution due to the extreme temperatures generated over long periods of use. to put it simply, we would recommend not installing a log burner to mitigate against this risk.

What has been done to reduce the risk of fire and the spread of fire?

The Dorset Model has been jointly produced by the Local Authorities across Dorset in conjunction with Dorset Fire & Rescue Service, 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.This uniform approach to thatched buildings is now being recommended where compensatory requirements are considered acceptable to achieve compliance with the Building Regulations.

Building Control requirements

• rafters are to be overdrawn with a minimum 30 minute fire barrier (integrity and insulation) which should be water resisting
• 50 x 25 battens are recommended on a micro-porous boarding to allow the thatch to breathe (Dorset Fire and Rescue Service recommend a 60 minute barrier)
• the use of a flexible material or cavity foam as a fire resisting barrier is not acceptable for the purposes of the Dorset Model
• the chimney, including the pot, should end at least 1.8m above the height of the ridge
• due to the risk of condensation forming as hot gases cool, chimney pots should be limited to a maximum height of 600mm
• a domestic mains and battery powered, interlinked smoke alarm system will be required with one smoke alarm fitted in the roof void
• the smoke alarm system should be in accordance with Approved Document B to B.S. 5839 Pt. 6: 2004
• a terrace may not consist of more than three thatched dwellings together
• the use of intumescent mastic is required to help seal the fire barrier along all its junctions

The written comments of the adjoining property owner may be requested by the local authority for consideration.

Further recommendations

• the provision of a loft hatch is recommended for fire fighting purposes (the minimum recommended size is 600mm x 900mm)
• advice should be sought from an approved electrical contractor regarding the most appropriate type of wiring system
• effects from rodent damage and straw debris need to be considered by the approved electrical contractor
• it is NOT recommended to install recessed lighting into the ceilings below the thatch
• light fittings within the roof space to be in a bulkhead fitting
• external floodlights should not be located under the eaves of the thatch
• spark arrestors on the flues are NOT recommended because they can clog and restrict the flow of flue gases
• it is recommended that an external water tap supplied from the rising main is fitted with a hose capable of reaching all parts of the roof
• any metal plumbing in roof space should use compression joints to avoid the use of blow torches
• in order to achieve a ‘U’ value of 0.2w/m²K for thatched roofs, the following was taken from CIBSE Guide A3:
  • reed = thermal conductivity 0.09 and a resistivity of 11.1
  • straw = thermal conductivity 0.07 and a resistivity of 14.3
  • this gives a ‘U’ value of 0.2/m²K for 450mm of reed and 350mm of straw. On this basis ceilings may require additional insulation.

Problems with the Dorset Model.

One of the ways that thatch dries is from the warmth of the internal areas reaching the underside of the thatch. The fire barrier reduces this and e have seen thatch decay from the bottom up because of this. This has been picked up by a few surveyors and thatcher’s and there are steps to produce a new method known as the Devon Method.

Listed thatched properties

There are estimated to be 35,000 thatched roof properties in England; 24,000 are listed buildings.

If your building is listed then you will usually have to rethatch in the same material as when it was listed. If the building has recently been rethatched, you may be able to find a previous picture of the building on Rightmove or on the listing.

If the building has been rethatched in a different material then this may be considered a non lawful change to a listed building.

If you have any questions about thatched roof building surveys or buying a home with a thatched roof contact us here or call 01722 445 405 and ask for David.