Fire requirements for straw roofs according to BR18
Fire-safe or not — this is how 5 and 10 meters determine how close you can build
Thatched roofs are beautiful and traditional, but they are also flammable, and a burning thatched roof produces both high heat and flying sparks that can ignite neighbouring buildings. Therefore, the building regulations (BR18) place special demands on where thatched houses may be located and how they must be constructed. The thatcher and carpenter must know the rules to be able to build legally.
§Fire-safe or non-fire-safe
Decisive for the distance requirements is whether the straw roof is fire-protected or not. A fire-protected straw roof is laid directly on an adjacent building part that has at least fire resistance EI 30 — that is, there is a fire-retardant board or structure immediately under the straw. A non-fire-protected straw roof, on the other hand, is built with, for example, a ventilated air gap under the straw, without a fire-separating adjacent building part.
§Distance to boundary
For a building with fire-safe straw roof the distance requirement to the property line is in principle 5 metres. For a building with non-fire-safe straw roof the requirement is 10 metres to the property line. The requirement must limit the risk of fire spreading to or from the neighbour's property. Secondary buildings — such as smaller outhouses and carports — with fire-safe straw roof can be placed at least 5.0 m from neighbour boundaries.
§Distance between buildings
When two buildings both have thatched roofs, the distance requirements are added together. If both buildings have fire-safe thatched roofs, the distance between them must be at least 5 + 5 meters. If one has a non-fire-safe roof, the requirement becomes 5 + 10 meters, and if both have non-fire-safe roofs, 10 + 10 meters is required. The logic is that each building contributes its own risk and the distances are therefore summed.
| Situation | Distance requirements |
|---|---|
| Fire-safe straw roof to boundary | 5 m |
| Non-fire-resistant straw roof to boundary | 10 m |
| Two fire-rated roofs between buildings | 5 + 5 m |
| A fire-safe + a non-fire-safe. | 5 + 10 m |
| Two non-fire-rated roofs | 10 + 10 m |
§Roofing class BROOF(t2)
Beyond the distance requirements, the roof covering must be installed at least as roofing class BROOF(t2). The class describes the roof's resistance to flying embers and sparks from outside — that is, the ability not to ignite from a fire in the neighbourhood. For thatched roofs, the class is achieved through approved construction where the thatch is combined with the correct substrates and solutions as recommended by manufacturers and the Thatchers' Guild.
Fire regulations for straw roofs may seem restrictive but they exist for a good reason: historically fires in thatched villages could lay several farms waste in one night. By knowing the rules and building fire-safe, the thatcher can preserve the beautiful roof and at the same time keep it within the law — even where plots are small.