Thatch Building Regulations

Listed in this section of our website are the main areas relating to building control requirements for new builds and extensions with thatched roofs.

Extract from – The Building Regulations 2010 Fire Safety Approved Document B

Volume 1 – Dwelling houses 2006 Edition incorporating 2010 and 2013 amendments
B4 Section 10: Roof Coverings
Thatch and wood shingles

10.9 Thatch and wood shingles should be regarded as having an AD/BD/CD designation or EROOF (t4) (European class) classification in Table 5 if performance under BS476-3:2004 (or 1958) or BSEN 1187 cannot be established.

Note: Consideration can be given to thatched roofs being closer to the boundary than shown in Table 5 if, for example, the following precautions (based on Thatched buildings. New properties and extensions (the ‘Dorset Model’) are incorporated in the design:

  1. The rafters are overdrawn with construction having not less than 30 minutes fire resistance;
  2. The guidance given in Approved Document J Combustion appliances and fuel storage is followed; and
  3. The smoke alarm installation extends to the roof space.

Table 5       Limitations on roof coverings*

Designation† of covering of roof or part of roof
Minimum distance from any point on relevant boundary

National Class European Class Less than 6m At least 6m At least 12m At least 20m
AA, AB or AC Broof (t4)        
BA, BB or BC Croof (t4)        
CA, CB or CC Droof (t4)   (1)(2)  (1)  
AD, BD or CD Eroof (t4)   (1)(2)  (1)  (1) 
DA, DB, DC or DD Froof (t4)       (1)(2)

Not acceptable

  1. Not acceptable on any of the following buildings:

    a. Houses in terraces of three or more houses.
    b. Any other buildings with a cubic capacity of more than 1500m³.

  2. Acceptable on buildings not listed in Note 1, provided that part of the roof is no more than 3m² in area and is at least 1500mm from any similar part, with the roof between the parts covered with a material of limited combustibility.


  • See paragraph 10.9 for limitations on thatch and wood shingles.
  • The designation of external roof surfaces is explained in Appendix A. (See Table A5 for notional designations of roof coverings.)

    Separation distances do not apply to the boundary between roofs of a pair of semi-detached houses (see para 10.5) and to enclosed/covered walkways. However, see Diagram 11 if the roof passes over the top of a compartment wall.

    The National classifications do not automatically equate with the equivalent classifications in the European column, therefore products cannot typically assume a European class unless they have been tested accordingly.

© Crown Copyright 2011 – The Building Regulations 2010 Fire Safety Approved Document B

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Supporting Information

The designation of roof subject to conditions of external fire shall be according to both the time of penetration and the distance of spread of flame along their external surface.

Each category designation shall consist of two letters, e.g. AA, AC, BB, these being determined as follows:

First Letters:
A. Those specimens which have not been penetrated within 1 hour.
B. Those specimens which are penetrated in not less than ½ hour.
C. Those specimens which are penetrated in less than ½ hour.
D. Those specimens which are penetrated in preliminary flame ignition test.

Second Letters:
A. Those specimens on which there is no spread of flame.
B. Those specimens on which there is not more than 533mm spread of flame.
C. Those specimens on which there is more than 533mm spread of flame.
D. Those specimens which continue to burn for 5 minutes after the withdrawal of the test flame or spread more than 381mm across the region of burning in the preliminary test.

A U-value is a measure of heat loss. It is expressed in W/m²K, and shows the amount of heat lost in watts (W) per square metre of material (for example wall, roof, floor etc.) when the temperature (K) outside is at least one degree lower.

The lower the U-value, the better the insulation provided by the material.

The standard in Part L of the Building Regulations (2010) for replacement roofs is 0.18 W/m²K.