- Design guides
- Flat roof design considerations
Fire protection and performance ratings
British Standards and Building Regulations for Roofs
In the UK, the hazard that exists of fire spreading to the roof of a building from a nearby fire outside the building itself is covered under Building Regulations ‘Fire Safety – Approved Document B’ and uses BS 476: Part 3 2004 - 'External Fire Exposure Roof Test' to assess representative systems of the roof construction (not individual comprising components) in their response to fire from outside the building. The test is not concerned with the behaviour of roofs when subjected to the effects of fire from its underside, i.e. from within the building.
The test covers two primary elements; the penetration of flame would give an A – D evaluation, and the surface spread of flame which would also be classified on an A – D score to produce a two letter code to identify the final rating. This rating would then signify whether the system could be used anywhere on the roof if it achieved an AA, AB or AC classification and therefore deemed ‘unrestricted’. If, however, the system should achieve any other rating this would be regarded as ‘restricted’ and not be utilised within at least 6, 12 or 20 metres of the boundary (depending on the two letter classification) as they do not provide adequate protection against the spread of flame through or over them.
Each classification letter represents a different result :
|A||Specimens not penetrated within 1 hour||A||Specimens with no spread of flame|
|B||Specimens penetrated in not less than half hour||B||Specimens with not more than 533mm spread of flame|
|C||Specimens penetrated in less than half hour||C||Specimens with more than 533mm spread of flame|
|D||Specimens penetrated in the preliminary flame test||D||Specimens which continue to burn for 5 minutes after the withdrawal of the test flame or spread more than 381mm in the preliminary test.|
Please Note: Separate fire standards apply to wall cladding and are covered in BS 8414 Fire Performance of External Cladding Systems
To advance and clarify the fire standards across Europe for External Fire Performance the industry has been going through a changeover from the test and classification of BS476-3:2004 to the tests of ENV1187 and classification using BS EN 13501-5. The standardisation into one European test proved indefinable as many countries within the EU had differing regulations and so four test standards were required to cover the legislation in place within the various member states at the time. As such the ENV1187 has four tests for roof covering systems: t1 for Germany, t2 for Scandinavia, t3 for France and t4 for the UK.
The results from testing under ENV1187 with BS EN 13501-5 are given as European Class ratings Broof(t4), Croof(t4), Droof(t4), Eroof(t4) and Froof(t4) and can be related to the longstanding BS 476 two letter ratings as follows:
|Minimum distance from any point on relevant boundary|
|AA, AB or AC||Broof(t4)||unrestricted and can be used anywhere on the roof|
|BA, BB or BC||Croof(t4)||at least 6m of the boundary|
|CA, CB or CC||Droof(t4)||at least 6, 12 or 20m of the boundary depending on the building type and use|
|AD, BD or CD||Eroof(t4)||at least 6, 12 or 20m of the boundary depending on the building type and use|
|DA, DB, DC or DD||Froof(t4)||at least 20m of the boundary depending on the building type and use|
For more information, please contact our technical department on 0845 271 8800, email@example.com