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 – Dwellings 2019 Edition

B4 Section 12: Resisting fire spread over roof coverings

Thatch and wood shingles

12.9 If the performance of thatch or wood shingles cannot be established, they should be regarded as having an EROOF (t4) (European class) classification in Table 12.1 Note: Consideration can be given to thatched roofs being closer to the relevant boundary than shown in Table 12.1 if, for example, all of the following precautions (based on the LABC publication Thatched Buildings. (the ‘Dorset Model): New properties and extensions are incorporated in the design:

a. The rafters are overdrawn with construction having not less than 30 minutes fire resistance.

b. The guidance given in Approved Document J is followed.

c. The smoke alarm installation (see Section 1) extends to the roof space.

Table 12.1 Limitations on roof coverings Minimum distance from any point on the relevant boundary

AcceptableNot acceptable

Notes: Separation distances do not apply to the boundary between roofs of a pair of semi-detached dwelling houses and to enclosed/covered walkways. However, see Diagram 5.2 if the roof passes over the top of a compartment wall. Polycarbonate and uPVC rooflights that achieve a class C-s3, d2 rating by test may be regarded as having a Broof (t4) designation.

1. The designation of external roof surfaces is explained in Table B2 below.

2. 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.

3. Acceptable on buildings not listed in 1 if both of the following apply.

a. Part of the roof is no more than 3m² in area and is at least 1500mm from any similar part

b. The roof between the parts is covered with a material rated, class A2-s3, d2 or better.

B15 – Performance of the resistance of roofs to external fire exposure is measured in terms of penetration through the roof construction and the spread of flame over its surface.

B16 – Roof constructions are classified within the European system as Broof (t4),Croof (t4), Droof (t4), Eroof (t4) or Froof (t4) in accordance with BS EN13501-5. Broof (t4) indicates the highest performance and Froof (t4) the lowest.

B17 - BS EN13501-5 refers to four separate roof tests. The suffix (t4) used in paragraph B16 indicates that Test 4 is to be used for the purposes of this approved document.

B18 – This document uses the European classification system for roof covering set out in BS.

EN13501-5; however, there may be some products lawfully on the market using the classification system set out in previous editions. Where this is the case.

Table B2 (below) can be used for the purposes of this document.

Table B” Roof covering classifications: transposition to national class

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

Supporting Information Designations

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.

Contains public sector information licensed under the Open Government Licence v3.0.