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Publication - Advice and guidance

Building Standards technical handbook 2017: domestic buildings

Published
1 March 2017
Topic
Building, planning and design
ISBN
978-1-78544-328-2

The Building Standards technical handbooks provide guidance on achieving the standards set in the Building (Scotland) Regulations 2004 and are available in two volumes, domestic buildings and non-domestic buildings. This publication is available in html and also in PDF format (in 'supporting documents' ).

View supporting documents Supporting documents

Annex 2.C Vulnerability of roof coverings

2.C.0 Introduction

This annex provides guidance on the vulnerability of roof coverings and is concerned with the performance of roofs when exposed to fire from neighbouring buildings.

Commission Decision 2005/823/EC amending Decision 2001/671/EC establishing a classification system for the external fire performance of roofs and roof coverings allows the classification of performance by either:

  1. BS 476: Part 3: 2004 (National Test), External fire exposure roof tests, or

  2. BS EN 13501-5: 2005 (European Test), Fire classification of construction products and building elements, Part 5 - Classification using test data from external fire exposure to roof tests.

2.C.1 Vulnerability of roof coverings

The level of vulnerability is established from the guidance to Standard 2.1 to 2.15. Reference throughout this document to a low, medium or high vulnerability, will be satisfied by following the guidance in the table below. The British Standard classification does not automatically equate with the equivalent classifications in the European standards column, therefore products cannot typically assume a European class, unless they have been tested accordingly. The designer is free to choose materials or products, which satisfy either the British Standard Tests or the Harmonised European Tests.

Transitional period - British and European fire tests will co-exist in use until the British Standard classifications are withdrawn.

2.C.2 British Standards and associated specifications

The national test for roof coverings is BS 476: Part 3: 2004 which measures the capability of a roof to resist penetration from fire and flame spread when the external surface is exposed to radiation and flames.

BS 476: Part 3: 2004 sets out a classification system based on external penetration and flame spread as set out in the following table. The first letter of the designation indicates fire penetration performance i.e. the time at which any glowing or flaming [other than that from the gas pilot flame] appears on the underside of the specimen. The second letter of the designation indicates flame spread performance. The addition of the suffix ‘X’ indicates dripping from the underside of the specimen, any mechanical failure or development of holes in the specimen. The angle of the specimen in the test is designated by the prefix ’S’ [slope] or ‘F’ [flat].

Table 2.9. Roof Coverings: Penetration from fire and flame spread

Penetration Flame spread

  1. Those specimens which have not been penetrated within 60 minutes

  2. Those specimens which are penetrated in not less than 30 minutes

  3. Those specimens which are penetrated in less than 30 minutes

  4. Those specimens which are penetrated in the preliminary test

  1. Those specimens on which there is no spread of flame

  2. Those specimens on which there is not more than 525mm spread of flame

  3. Those specimens on which there is more than 525mm spread of flame

  4. Those specimens which continue to burn for more than 5 minutes after the withdrawal of the test flame or spread of flame more than 375mm across the region of burning in the preliminary test


2.C.3 Harmonised European Standards

The European test method has been published as DD ENV 1187: 2002, ‘Test methods for external fire exposure to roofs’, which specifies four methods for determining the performance of roofs to external fire exposure:

  • Test 1 : with burning brands

  • Test 2 : with burning brands and wind

  • Test 3 : with burning brands, wind and supplementary radiant heat

  • Test 4 : two stage test method incorporating burning brands, wind and supplementary radiant heat.

Only test method 4 evaluates penetrability in a satisfactory way to satisfy the fire performance requirements in the United Kingdom. For this reason, (t4) has been added to the European test designations to add clarity.

The performance criteria in terms of vulnerability to external fire exposure can be satisfied where the roof covering follows the guidance in the following table. The classification methodology is contained in BS EN 13501-5: 2005.

Table 2.10. Classification for roofs / roof coverings exposed to external fire

Classification for roofs / roof coverings exposed to external fire
Broof (t4)

  1. No penetration of roof system within 60 minutes

  2. In preliminary test, after withdrawal of the test flame, specimens burn for less than 5 minutes

  3. In preliminary test, flame spread less than 0.38m across region of burning

Croof (t4)

  1. No penetration of roof system within 30 minutes

  2. In preliminary test, after withdrawal of the test flame, specimens burn for less than 5 minutes

  3. In preliminary test, flame spread less than 0.38m across region of burning

Droof (t4)

  1. Roof system is penetrated within 30 minutes but is not penetrated in the preliminary test

  2. In preliminary test, after withdrawal of the test flame, specimens burn for less than 5 minutes

  3. In preliminary test, flame spread less than 0.38m across region of burning

Eroof (t4)

  1. Roof system is penetrated within 30 minutes but is not penetrated in the preliminary test

  2. Flame spread is not controlled
Froof (t4)

  1. No performance determined

Table 2.11. Vulnerability of roof coverings

1 2 3
Vulnerability British Standards European Standards
Low

  1. Designation AA, AB or AC when tested along with the substrate in accordance with BS 476: Part 3: 2004, or

  2. Glass at least 4mm thick, or

  3. A roof covering or rooflight of plastics materials which is in an open canopy or over a substantially open area such as a loading bay which is a single-skin polycarbonate sheet not more than 3mm thick or multi-skin polycarbonate sheet, or a thermoplastic material (see clause 2.5.4): a specimen of which when tested in accordance with Method 508A in BS 2782: 1970 (1974), performs so that the test flame does not reach the second mark within 2 minutes, the specimen thickness to be more than 1.5mm and not more than 3mm, or

  4. A thermoplastic sheet with a low or medium risk (see table to annex 2.C) or a rigid solid PVC (uPVC), or a polycarbonate rigid solid sheet at least 3mm thick, or a multi-skin polycarbonate sheet at least 10mm thick overall.

The material has achieved a classification of Broof(t4) in accordance with BS EN 13501-5: 2005 when tested to DD ENV 1187: 2002 + A1:2005, test 4.
Medium

  1. Designation BA, BB, BC, CA, CB or CC when tested along with the substrate in accordance with BS 476: Part 3: 2004, or

  2. A roof covering or rooflight of plastics materials which is a single-skin polycarbonate sheet not more than 3 mm thick or multi-skin polycarbonate sheet, or thermoplastic material, a specimen of which when tested in accordance with Method 508A in BS 2782: 1970 (1974), performs so that the test flame does not reach the second mark within 2 minutes, the specimen thickness to more than 1.5mm and not more than 3mm.

The material has achieved a classification of Croof(t4) and Droof(t4) in accordance with BS EN 13501-5: 2005 when tested to DD ENV 1187: 2002 + A1:2005, test 4.
High Any designation other than low or medium vulnerability, including for example, timber shingles or thatch. The material has achieved a classification of Eroof(t4) and Froof(t4) in accordance with BS EN 13501-5: 2005 when tested to DD ENV 1187: 2002 + A1:2005, test 4.

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