Items where Subject is "Section 12: Resisting fire spread over roof coverings"
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- Section 12: Resisting fire spread over roof coverings (13)
Book Section
‘Roof covering’ describes one or more layers of material, but not the roof structure as a whole.
Provisions for the fire properties of roofs are given in other parts of this document.
a. Requirement B1 – for roofs that are part of a means of escape.
b. Requirement B2 – for the internal surfaces of rooflights as part of internal linings.
c. Requirement B3 – for roofs that are used as a floor and for roofs passing over a compartment wall.
d. Section 11 – the circumstances in which a roof is subject to the provisions for space separation.
Separation distance is the minimum distance from the roof, or part of the roof, to the relevant boundary (paragraph 11.4). Table 12.1 sets out separation distances by the type of roof covering and the size and use of the building.
In addition, roof covering products (and/or materials) defined in Commission Decision 2000/553/ EC of 6 September 2000, implementing Council Directive 89/106/EEC, can be considered to fulfil all of the requirements for the performance characteristic ‘external fire performance’ without the need for testing, provided that any national provisions on the design and execution of works are fulfilled, and can be used without restriction.
The performance of rooflights is specified in a similar way to the performance of roof coverings. Plastic rooflights may also be used.
Table 12.2 and Diagram 12.1 set the limitations for using plastic rooflights whose lower surface has a minimum class D-s3, d2 rating.
Table 12.3 sets the limitations for using thermoplastic materials with a TP(a) rigid or TP(b) (see also Diagram 12.1) classification. The method of classifying thermoplastic materials is given in Appendix B.
Other than for the purposes of Diagram 5.2, polycarbonate or uPVC rooflights achieving a minimum rating of class C-s3, d2 can be regarded as having a BROOF(t4) classification.
When used in rooflights, unwired glass a minimum of 4mm thick can be regarded as having a BROOF(t4) classification.
If the performance of thatch or wood shingles cannot be established, they should be regarded as having an EROOF(t4) 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 spaces.
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NOTES:
1.There are restrictions on the use of plastic rooflights in the guidance to requirement B2 in Section 4.
2.Surrounding roof covering to be a material of class A2-s3, d3 or better for at least 3m distance.
3.Where Diagram 5.2a or 5.2b applies, rooflights should be at least 1500mm from the compartment wall.
See paras 12.5 and 12.6
NOTES:
Separation distances do not apply to the boundary between roofs of a pair of semi-detached dwellinghouses 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 Appendix B.
2. Not acceptable on any of the following buildings.
a. Dwellinghouses in terraces of three or more dwellinghouses.
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 has a maximum area of 3m2 and is a minimum of 1500mm from any similar part.
b. The roof between the parts is covered with a material rated class A2-s3, d2 or better.
NOTES:
None of the above designations are suitable for protected stairways.
Polycarbonate and uPVC rooflights that achieve a class C-s3, d2 rating by test (see paragraph 12.7) may be regarded as having a BROOF(t4) classification.
Where Diagram 5.2a or 5.2b applies, rooflights should be a minimum of 1500mm from the compartment wall.
If double-skinned or laminate products have upper and lower surfaces of different materials, the greater distance applies.
1. See also the guidance to requirement B2 in Section 4.
2. The designation of external roof surfaces is explained in Appendix B.
3. Single-skinned rooflight only, in the case of non-thermoplastic material.
4. The rooflight should also meet the provisions of Diagram 12.1.
NOTES:
None of the above designations are suitable for protected stairways.
Polycarbonate and uPVC rooflights that achieve a class C-s3, d2 rating by test (paragraph 12.7) may be regarded as having a BROOF(t4) classification.
Where Diagram 5.2a or 5.2b applies, rooflights should be a minimum of 1500mm from the compartment wall.
If double-skinned or laminate products have upper and lower surfaces of different materials, the greater distance applies.
1. See also the guidance to requirement B2 in section 4.
2. No limit in the case of any space described in 2a, b and c.
3. Single-skinned rooflight only, in the case of non-thermoplastic material.
4. The rooflight should also meet the provisions of diagram 12.1.