Items where Subject is "Section 10: Resisting fire spread over external walls"
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- Section 10: Resisting fire spread over external walls (21)
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The external wall of a building should not provide a medium for fire spread if that is likely to be a risk to health and safety. Combustible materials and cavities in external walls and attachments to them can present such a risk, particularly in tall buildings. The guidance in this section is designed to reduce the risk of fire spread as well as the risk of ignition from flames coming from adjacent buildings.
Regulation 7(1A) prohibits the use of relevant metal composite materials in the external walls of all buildings of any height.
Relevant metal composite materials are defined (in regulation 2(6)(c)) as any panel or sheet, having a thickness of no more than 10mm which is composed of a number of layers two or more of which are made of metal, alloy or metal compound and one or more of which is a substantial layer made of a material having a gross calorific value of more than 35MJ/kg when tested in accordance with BS EN ISO 1716. A substantial layer is defined as a layer which is at least 1mm thick or has a mass per unit area of at least 1kg/m².
Regulation 7(1)(a) requires that materials used in building work are appropriate for the circumstances in which they are used. Regulation 7(2) sets requirements in respect of external walls and specified attachments in relevant buildings.
NOTE: Further guidance on regulation 7(1) can be found in HM Government’s Manual to the Building Regulations.
Regulation 7(2) applies to any building with a storey at least 18m above ground level (as
measured in accordance with Diagram D6 in Appendix D) and which contains one or more
dwellings; an institution; or a room for residential purposes. It requires that all materials which become part of an external wall or specified attachment achieve class A2-s1, d0 or class A1 in accordance with BS EN 13501-1, other than those exempted by regulation 7(3).
NOTE: The above includes student accommodation, care homes, sheltered housing, hospitals, dormitories in boarding schools, hotels, hostels and boarding houses. See regulation 7(4) for the definition of relevant buildings.
NOTE: Transposition to national class (Table B1) does not apply to the classification in this paragraph.
External walls and specified attachments are defined in regulation 2(6) and these definitions
include any parts of the external wall as well as balconies, solar panels and solar shading.
Regulation 7(3) provides an exemption for certain components found in external walls and specified attachments.
Regulations 5(k) and 6(3) provide that, where the use of a building is changed such that the building becomes a building described in regulation 7(4), the construction of the external walls, and specified attachments, must be investigated and, where necessary, work must be carried out to ensure they only contain materials achieving class A2-s1, d0 or class A1, other than those exempted by regulation 7(3).
Regulation 7(2) requires that the curtain and or slats of solar shading devices in a relevant building (as defined in regulation 7(4)) achieve class A1 or A2-s1, d0. The curtain of solar shading devices cannot be classified as a membrane in accordance with regulation 7(3).
Solar shading devices installed up to 4.5m above ground level are not required to meet the requirements of regulation 7(2).
This section provides guidance on resisting fire spread over external walls; however, it does not deal with fire resistance of external walls. An external wall may need fire resistance to meet the provisions of Section 3 (Means of escape – flats), Section 6 (Loadbearing elements of structure – flats), Section 11 (Resisting fire spread from one building to another) or Section 15 (Access to buildings for firefighting personnel – flats).
The provisions of regulation 7 apply in addition to requirement B4. Therefore, for buildings described in regulation 7(4), the potential impact of any products incorporated into or onto the external walls and specified attachments should be carefully considered with regard to their number, size, orientation and position.
Particular attention is drawn to the following points.
a. Membranes used as part of the external wall construction above ground level should achieve a minimum of class B-s3, d0. Roofing membranes do not need to achieve a minimum of class A2-s1, d0 when used as part of a roof connecting to an external wall.
b. Internal linings should comply with the guidance provided in Section 4.
c. Any part of a roof should achieve the minimum performance as detailed in Section 12.
d. As per regulation 7(3), window frames and glass (including laminated glass) are exempted
from regulation 7(2). Window spandrel panels and infill panels must comply with regulation 7(2).
e. Thermal breaks are small elements used as part of the external wall construction to restrict
thermal bridging. There is no minimum performance for these materials. However, they
should not span two compartments and should be limited in size to the minimum required
to restrict the thermal bridging (the principal insulation layer is not to be regarded as a
thermal break).
f. Regulation 7(2) only applies to specified attachments. Shop front signs and similar attachments are
not covered by the requirements of regulation 7(2), although attention is drawn to paragraph 10.21g.
g. While regulation 7(2) applies to materials which become part of an external wall or specified
attachment, consideration should be given to other attachments to the wall which could
impact on the risk of fire spread over the wall.
h. Any material achieving class A1fl or A2fl-s1 in accordance with BS EN 13501-1 is exempted when it
meets both of the following conditions.
i. It forms the top horizontal floor layer of a balcony.
ii. It is provided with an imperforate substrate under it which extends to the full size of the
class A1fl or A2fl-s1 material.
The external walls of buildings other than those described in regulation 7(4) of the Building Regulations should achieve either of the following.
a. Follow the provisions given in paragraphs 10.5 to 10.9, which provide guidance on all of the following.
i. External surfaces.
ii. Materials and products.
iii. Cavities and cavity barriers..
b. Meet the performance criteria given in BRE report BR 135 for external walls using full-scale test data from BS 8414-1 or BS 8414-2.
In relation to buildings of any height or use, consideration should be given to the choice of materials (including their extent and arrangement) used for the external wall, or attachments to the wall (e.g. balconies, etc.), to reduce the risk of fire spread over the wall.
The external surfaces (i.e. outermost external material) of external walls should comply with the provisions in Table 10.1. The provisions in Table 10.1 apply to each wall individually in relation to its proximity to the relevant boundary.
In a building with a storey 18m or more in height (see Diagram D6 in Appendix D) any insulation product, filler material (such as the core materials of metal composite panels, sandwich panels and window spandrel panels but not including gaskets, sealants and similar) etc. used in the construction of an external wall should be class A2-s3, d2 or better (see Appendix B). This restriction does not apply to masonry cavity wall construction which complies with Diagram 8.2 in Section 8. Where regulation 7(2) applies, that regulation prevails over all the provisions in this paragraph.
In buildings that include a ‘residential’ purpose (purpose groups 1 and 2) with a storey 11m or more in height (see Diagram D6 in Appendix D) any insulation product, filler material (such as the core materials of metal composite panels, sandwich panels and window spandrel panels but not including gaskets, sealants and similar) etc. used in the construction of an external wall should be class A2-s1, d0 or better (see Appendix B). This restriction does not apply to masonry cavity wall construction which complies with Diagram 8.2 in Section 8. Where regulation 7(2) applies, that regulation prevails over all the provisions in this paragraph.
Best practice guidance for green walls (also called living walls) can be found in Fire Performance of Green Roofs and Walls, published by the Department for Communities and Local Government. Where regulation 7(2) applies, that regulation prevails over all the provisions in this paragraph.
Cavity barriers should be provided in accordance with Section 5 in dwellinghouses and Section 8 in flats.
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Table 10.1 Reaction to fire performance of external surface of walls
‘Relevant buildings’ as defined in regulation 7(4) (see paragraph 10.10)
NOTES:
In addition to the requirements within this table, buildings with a top occupied storey above 18m should also meet the provisions of paragraph 10.6.
In all cases, the advice in paragraph 10.4 should be followed.
1. The restrictions for these buildings apply to all the materials used in the external wall and specified attachments (see paragraphs 10.9 to 10.12 for further guidance).
2. Profiled or flat steel sheet at least 0.5 mm thick with an organic coating of no more than 0.2mm thickness is also acceptable.
3. Timber cladding at least 9mm thick is also acceptable.
4. 10m is measured from the top surface of the roof.