Forget about crop tops, power suits and denim jackets making a comeback, let’s talk about the traditional craft of thatched roofs coming back into fashion!

More and more people are looking towards traditional roofing techniques to give a more rustic feel to a property.

So if you are thinking of constructing a thatched roof on a new build or conversion/refurbishment project, check out our recommendations and what to look out for.

The three main thatching materials in use today are water reed, often known as Norfolk Reed, long straw and combed wheat reed. Sedge, a grass-like plant is also used extensively in ridging.

Things to consider when constructing a thatched roof

Water

A common misconception with a thatched roof is the idea that it absorbs large amounts of water. This is not the case at all. Water is transferred down the roof from stem to stem until it drops from the cave. The steep pitches associated with thatched roofs allow for water to be shed at a very fast rate.

Recommendations

  • When designing for thatch, ample allowance should be made for the projection of the caves and gables so water can run clear of the building.

  • The ground should be well drained.

Fire

One of the main causes for concern is the risk of fire in a thatched property, however evidence shows genuine thatch fires are extremely rare and are usually caused by the same kinds of hazards affecting all housing. Figures from the Dorset Fire Brigade indicate that out of 3,000 fires each year, only 8-10 of these involved thatched buildings and in the majority of these incidents, the fire will have started within the building itself.

The reality is that all thatched building owners tend to be more careful about the dangers and employ a number of fire prevention measures.

Recommendations

  • Installation of a fireboard which is fitted to the rafters and gives at least 30 minutes fire resistance. Depending on the material and position of the building, this might then be counter battened to provide air movement between the material and fire retardant.

  • The fire barrier material used to overdraw the rafters should have some form of accreditation to prove that it is fit for purpose and will provide the 60 minute fire resistance as recommended by the Dorset Fire and Rescue Service. This exceeds the minimum standard set out by Building regulations of 30 minutes.

  • Smoke/fire warnings in the building should comply with Part B of Building Regulations.

  • Isolate any chimneys or flues from solid fuel burning appliances to avoid transferring heat to the thatch.  The Thatched Property Safety Guide suggests a 6mm aluminium sheet between the thatch and the chimney/flue, where the distance from the inside of the flue liner to the outside of the brickwork is less than 200mm.

  • Thatch has a designated AD/BC/CD performance class for roof coverings. The recommended minimum distance from any point on a relevant boundary is at least 6m. This distance can be reduced if additional safety measures such as extending the smoke alarm installation to include the loft space are put in place.

  • The use of flush ceiling mounted downlighters is not permitted in the ceiling below the thatched roof space.

It is important to ensure that the detailing and materials used when constructing a thatched roof are appropriate for the particular site and geographical location and must follow the recommendations of the Dorset Model and the Thatched Property Safety Guide.

Where alterations to an existing thatched roof are planned or when designing a new thatched roof it is imperative that consultation with a Master Thatchers Association is sought and in the case of a listed building, liaise with the conservation officer at the local council.

References:

The ‘Dorset Model’
National Society of Master Thatchers – “Fire in Thatch – A Guide to its Prevention”

By Frzana Ferguson