Items where Subject is "B4: External fire spread"
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- B4: External fire spread (83)
Book Section
The external envelope of a building should not contribute to undue fire spread from one part of a
building to another part. This intention can be met by constructing external walls so that both of
the following are satisfied.
a. The risk of ignition by an external source to the outside surface of the building and spread of
fire over the outside surface is restricted.
b. The materials used to construct external walls, and attachments to them, and how they are
assembled do not contribute to the rate of fire spread up the outside of the building.
The extent to which this is necessary depends on the height and use of the building.
The external envelope of a building should not provide a medium for undue fire spread to
adjacent buildings or be readily ignited by fires in adjacent buildings. This intention can be met by
constructing external walls so that all of the following are satisfied.
a. The risk of ignition by an external source to the outside surface of the building is restricted.
b. The amount of thermal radiation that falls on a neighbouring building from window openings
and other unprotected areas in the building on fire is not enough to start a fire in the other
building.
c. Flame spread over the roof and/or fire penetration from external sources through the roof is
restricted.
The extent to which this is necessary depends on the use of the building and its position in relation
to adjacent buildings and therefore the site boundary.
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 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.
The following assumptions enable a reasonable standard of resistance to the spread of fire to be specified.
a. The size of a fire depends on the compartmentation within the building. A fire may involve a complete compartment, but will not spread to other compartments.
b. The intensity of a fire is related to the building use, but can be moderated by a sprinkler system.
c. Fires in ‘residential’ and ‘assembly and recreation’ buildings (purpose groups 1, 2 and 5) represent a greater risk to life.
d. A building on the far side of the relevant boundary meets both of the following conditions.
i. Has a similar elevation to the one in question.
ii. Is the same distance as the one in question from the common boundary.
e. The radiated heat passing through any part of the fire resisting external wall may be discounted.
In an otherwise protected wall, small unprotected areas may be ignored where they meet the conditions in Diagram 11.5.
Where both of the following apply, separation distances may be determined from the wall rather than from the edge of the canopy (Diagram 11.6).
a. The canopy is attached to the side of a building.
b. The edges of the canopy are a minimum of 2m from the relevant boundary.
Canopies that fall within class 6 or class 7 of Schedule 2 to the regulations (Exempt Buildings and Work) are exempt from the Building Regulations.
Space separation may be disregarded if a canopy is all of the following.
a. Free-standing.
b. Above a limited risk or controlled hazard.
c. A minimum of 1000mm from the relevant boundary.
This method applies to small buildings intended to be used for blocks of flats or dwellinghouses.
The building should not exceed three storeys in height (excluding basements) or 24m in length. Each side of the building should meet the limits stated in Diagram 11.7. Any small unprotected areas falling within the limits shown in Diagram 11.5 can be ignored.
This method may be used for buildings or compartments for which method 1 is not appropriate.
Where regulation 7(2) applies, that regulation prevails over the provisions within this section.
The building should not exceed 10m in height. Each side of the building should meet the limits stated in Table 11.1. Any areas falling within the limits shown in Diagram 11.5 can be ignored.
If a building is fitted throughout with a sprinkler system in accordance with Appendix E, either of the following is permitted.
a. The boundary distance can be halved, to a minimum distance of 1m.
b. The amount of unprotected area can be doubled.
If a reduced separation distance between buildings, or increased amount of unprotected area, is required, smaller compartments should be considered.
The fire resistance of a wall depends on its distance from the relevant boundary (see Diagram 11.1). Separation distances are measured to boundaries to ensure that the location and design of buildings on adjoining sites have no influence on the building under consideration.
The boundary that a wall faces is the relevant boundary (Diagram 11.2). It may be one of the following.
a. The site boundary.
b. The centre line of a space where further development is unlikely, such as a road, railway, canal or river.
c. An assumed notional boundary between two buildings on the same site (Diagram 11.3) where either of the following conditions is met.
i. One or both of the buildings are in the "residential" or "assembly and recreation" purpose groups (purpose group 1, 2 or 5).
ii. The buildings will be operated/managed by different organisations.
Parts of an external wall with less fire resistance than the appropriate amount given in Appendix B, Table B4, are called unprotected areas.
Where a fire resisting external wall has an external surface material that is worse than class B-s3, d2 and is more than 1mm thick, that part of the wall should be classified as an unprotected area equating to half its area (Diagram 11.4).
Unprotected areas should meet the conditions in Diagram 11.5, and the rest of the wall should be fire resisting from both sides.
External surface materials facing the boundary should be class B-s3, d2 or better.
Unprotected areas should not exceed the result given by one of the methods in paragraph 11.16, and the rest of the wall (if any) should be fire resisting but only from the inside of the building.
To restrict the use of materials which ignite easily, which have a high rate of heat release and/ or which reduce the time to flashover, maximum acceptable 'fire propagation' indices are specified, where the National test methods are being followed.
These are determined by reference to the method specified in BS 476-6:1981 or 1989 Method of test for fire propagation of products. Index of performance (I) relates to the overall test performance, whereas sub-index (i1) is derived from the first three minutes of test.
‘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.
In a building with a storey 18m or more above ground level any insulation product, filler material (not including gaskets, sealants and similar) etc. used in the external wall construction should be of limited combustibility (see Appendix A). This restriction does not apply to masonry cavity wall construction
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.
The highest National product performance classification for lining materials is Class O. This is achieved if a material or the surface of a composite product is either:
a. composed throughout of materials of limited combustibility; or
b. a Class 1 material which has a fire propagation index (I) of not more than 12 and sub-index (i1) of not more than 6.
Note: Class O is not a classification identified in any British Standard test.
The external envelope of a building should not provide a medium for fire spread if it is likely to be a risk to health or safety. The use of combustible materials for cladding framework, or of combustible thermal insulation as an overcladding or in ventilated cavities, may present such a risk in tall buildings, even though the provisions for external surfaces in Diagram 40 may have been satisfied.
In a building with a storey 18m or more above ground level, insulation material used in ventilated cavities in the external wall construction should be of limited combustibility (see Appendix A). This restriction does not apply to masonry cavity wall construction which complies with Diagram 32 in Section 10. Advice on the use of thermal insulation material is given in the BRE Report Fire performance of external thermal insulation for walls of multi-storey buildings (BR 135, 1988).
Guidance on the design and construction of fire mains is given in BS 9990.
In low rise buildings without deep basements, access for firefighting personnel is typically achieved by providing measures for fire service vehicle access in Section 13 and means of escape.
For building work involving the erection or extension of a relevant building (i.e. a building to which the Regulatory Reform (Fire Safety) Order 2005 applies, or will apply), or the relevant change of use of a building, fire safety information should be given to the responsible person at one of the following times.
a. When the project is complete.
For building work involving the erection or extension of a relevant building (i.e. a building to which the Regulatory Reform (Fire Safety) Order 2005 applies, or will apply), or the relevant change of use of a building, fire safety information should be given to the responsible person at one of the following times.
b. When the building or extension is first occupied.
Basic information on the location of fire protection measures may be sufficient. An as-built plan of the building should be provided showing all of the following.
a. Escape routes – this should include exit capacity (i.e. the maximum allowable number of people for each storey and for the building).
Basic information on the location of fire protection measures may be sufficient. An as-built plan of the building should be provided showing all of the following.
b. Location of fire-separating elements (including cavity barriers in walk-in spaces).
Basic information on the location of fire protection measures may be sufficient. An as-built plan of the building should be provided showing all of the following.
c. Fire doorsets, fire doorsets fitted with a self-closing device and other doors equipped with relevant hardware.
Basic information on the location of fire protection measures may be sufficient. An as-built plan of the building should be provided showing all of the following.
d. Locations of fire and/or smoke detector heads, alarm call points, detection/alarm control boxes, alarm sounders, fire safety signage, emergency lighting, fire extinguishers, dry or wet fire mains and other firefighting equipment, and hydrants outside the building.
Basic information on the location of fire protection measures may be sufficient. An as-built plan of the building should be provided showing all of the following.
e. Any sprinkler systems, including isolating valves and control equipment.
Basic information on the location of fire protection measures may be sufficient. An as-built plan of the building should be provided showing all of the following.
f. Any smoke control systems, or ventilation systems with a smoke control function, including mode of operation and control systems.
Basic information on the location of fire protection measures may be sufficient. An as-built plan of the building should be provided showing all of the following.
g. Any high risk areas (e.g. heating machinery).
Details should be provided of all of the following.
a. Specifications of fire safety equipment provided, including routine maintenance schedules.
Details should be provided of all of the following.
b. Any assumptions regarding the management of the building in the design of the fire safety arrangements.
Details should be provided of all of the following.
c. Any provision enabling the evacuation of disabled people, which can be used when designing personal emergency evacuation plans.
A detailed record should be provided of both of the following.
a. The fire safety strategy.
A detailed record should be provided of both of the following.
b. Procedures for operating and maintaining any fire protection measures. This should include an outline cause and effect matrix/strategy for the building.
Further guidance is available in clause 9 and Annex H of BS 9999.
The records should include details of all of the following.
a. The fire safety strategy, including all assumptions in the design of the fire safety systems (such as fire load). Any risk assessments or risk analysis.
The records should include details of all of the following.
b. All assumptions in the design of the fire safety arrangements for the management of the building.
The records should include details of all of the following.
c. All of the following.
i. Escape routes (including occupant load and capacity of escape routes).
ii. Any provision to enable the evacuation of disabled people.
iii. Escape strategy (e.g. simultaneous or phased).
iv. Muster points.
The records should include details of all of the following.
d. All passive fire safety measures, including all of the following.
i. Compartmentation (i.e. location of fire-separating elements).
ii. Cavity barriers.
iii. Fire doorsets, including fire doorsets fitted with a self-closing device and other doors equipped with relevant hardware (e.g. electronic security locks).
iv. Duct dampers.
v. Fire shutters.
The records should include details of all of the following.
d. All passive fire safety measures, including all of the following.
i. Compartmentation (i.e. location of fire-separating elements).
The records should include details of all of the following.
d. All passive fire safety measures, including all of the following.
ii. Cavity barriers.
The records should include details of all of the following.
d. All passive fire safety measures, including all of the following.
iii. Fire doorsets, including fire doorsets fitted with a self-closing device and other doors equipped with relevant hardware (e.g. electronic security locks).
The records should include details of all of the following.
d. All passive fire safety measures, including all of the following.
iv. Duct dampers.
The records should include details of all of the following.
d. All passive fire safety measures, including all of the following.
iv. Duct dampers.
The records should include details of all of the following.
d. All passive fire safety measures, including all of the following.
v. Fire shutters.
The records should include details of all of the following.
e. All of the following.
i. Fire detector heads.
ii. Smoke detector heads.
iii. Alarm call points.
iv. Detection/alarm control boxes.
v. Alarm sounders.
vi. Emergency communications systems.
vii. CCTV.
viii. Fire safety signage.
ix. Emergency lighting.
x. Fire extinguishers.
xi. Dry or wet fire mains and other firefighting equipment.
xii. Other interior facilities for the fire and rescue service.
xiii. Emergency control rooms.
xiv. Location of hydrants outside the building.
xv. Other exterior facilities for the fire and rescue service.
The records should include details of all of the following.
f. All active fire safety measures, including both of the following.
i. Sprinkler system(s) design, including isolating valves and control equipment.
ii. Smoke control system(s) (or heating, ventilation and air conditioning system with a smoke control function) design, including mode of operation and control systems.
The records should include details of all of the following.
g. Any high risk areas (e.g. heating machinery) and particular hazards.
The records should include details of all of the following.
h. Plans of the building as built, showing the locations of the above.
The records should include details of all of the following.
i. Both of the following.
i. Specifications of any fire safety equipment provided, including all of the following.
• Operational details.
• Operators’ manuals.
• Software.
• System zoning.
• Routine inspection, testing and maintenance schedules.
ii. Records of any acceptance or commissioning tests.
The records should include details of all of the following.
i. Both of the following.
i. Specifications of any fire safety equipment provided, including all of the following.
• Operational details.
• Operators’ manuals.
• Software.
• System zoning.
• Routine inspection, testing and maintenance schedules.
The records should include details of all of the following.
i. Both of the following.
ii. Records of any acceptance or commissioning tests.
The records should include details of all of the following.
j. Any other details appropriate for the specific building.
Materials of limited combustibility are defined in Table A7:
a. (National classes) by reference to the method specified in BS476: Part 11:1982; or
b. (European classes) in terms of performance when classified as class A2-s3, d2 in accordance with BS EN 13501-1 :2002, Fire classification of construction products and building elements, Part 1 - Classification using data from reaction to fire tests when tested to BS EN ISO 1182:2002, Reaction to fire tests for building products - Non combustibility test or BS EN ISO 1716:2002 Reaction to fire tests for building products - Determination of the gross calorific value and BS EN 13823:2002, Reaction to fire tests for building products - Building products excluding floorings exposed to the thermal attack by a single burning item.
Table A7 also includes composite products (such as plasterboard) which are considered acceptable and where these are exposed as linings they should also meet any appropriate flame spread rating.
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External fire spread
B4.(1)The external walls of the building shall adequately resist the spread of fire over the walls and from one building to another, having regard to the height, use and position of the building.
(2)The roof of the building shall adequately resist the spread of fire over the roof and from one building to another, having regard to the use and position of the building.
Regulation 7 – Materials and workmanship
(1)Building work shall be carried out—
(a)with adequate and proper materials which—
(i)are appropriate for the circumstances in which they are used,
(ii)are adequately mixed or prepared, and
(iii)are applied, used or fixed so as adequately to perform the functions for which they are designed; and
(b)in a workmanlike manner.
(2)Subject to paragraph (3), building work shall be carried out so that materials which become part of an external wall, or specified attachment, of a relevant building are of European Classification A2-s1, d0 or A1, classified in accordance with BS EN 13501-1:2007+A1:2009 entitled “Fire classification of construction products and building elements. Classification using test data from reaction to fire tests” (ISBN 978 0 580 59861 6) published by the British Standards Institution on 30th March 2007 and amended in November 2009.
(3)Paragraph (2) does not apply to—
(a)cavity trays when used between two leaves of masonry;
(b)any part of a roof (other than any part of a roof which falls within paragraph (iv) of regulation 2(6))if that part is connected to an external wall;
(c)door frames and doors;
(d)electrical installations;
(e)insulation and water proofing materials used below ground level;
(f)intumescent and fire stopping materials where the inclusion of the materials is necessary to meet the requirements of Part B of Schedule 1;
(g)membranes;
(h)seals, gaskets, fixings, sealants and backer rods;
(i)thermal break materials where the inclusion of the materials is necessary to meet the thermal bridging requirements of Part L of Schedule 1; or
(j)window frames and glass.
(4)In this regulation—
(a)a “relevant building” means a building with a storey (not including roof-top plant areas or any storey consisting exclusively of plant rooms) at least 18 metres above ground level and which—
(i)contains one or more dwellings;
(ii)contains an institution; or
(iii)contains a room for residential purposes(excluding any room in a hostel, hotel or boarding house); and
(b)“above ground level” in relation to a storey means above ground level when measured from the lowest ground level adjoining the outside of a building to the top of the floor surface of the storey.
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.
Wall sufficiently distant from relevant boundary to be a 100% unprotected area
Wall on or very close to the relevant boundary: very limited amounts of unprotected area
Wall not on, or not very close to, but not sufficiently far from relevant boundary that it can be a wholly unprotected area
Amount of unprotected area dependent on distance from relevant boundary
See para 11.4
NOTES:
Intermediate values may be obtained by interpolation.
1.The total percentage of unprotected area is found by dividing the total unprotected area by the area of a rectangle that encloses all the unprotected areas, and multiplying the result by 100.
This boundary coincides with and is therefore relevant to side A
The boundary is parallel to side B2
But the relevant boundary may be the centre line of a road, railway, canal or river
NOTES:
This boundary is at less than 80 degrees to side C and is therefore relevant to side C
This diagram sets out the rules that apply in respect of a boundary for it to be considered as a relevant boundary.
For a boundary to be relevant it should comply with one of the following:
a. Coincide with the side of the building (A).
b. Be parallel to the side of the building (B1 or B2).
c. Be at an angle of maximum 80 degrees to the side of the building (C).
This boundary is parallel to and therefore relevant to side B1
See para 11.5
NOTES:
The notional boundary should be set in the area between the two buildings using the following rules:
1. The notional boundary is assumed to exist in the space between the buildings and is positioned so that one of the buildings would comply with the provisions for space separation having regard to the amount of its unprotected area. In practice, if one of the buildings is existing, the position of the boundary will be set by the space separation factors for that building.
2. The siting of the new building, or the second building if both are new, can then be checked to see that it also complies, using the notional boundary as the relevant boundary for the second building.
Notional boundary
Site boundary
Compliance with the provisions for space separation in respect of building A
Compliance with the provisions for space separation in respect of building B
See para 11.5
Area of fire resisting wall with materials more than 1mm thick and with a reaction to fire performance worse than class B-s3, d2 = a x b
Area of wall counted as unprotected area = 0.5a x b
Area of fire resisting wall with materials having a reaction to fire performance better than class B-s3, d2
See para 11.7
The unprotected area of the external wall of a stairway forming a protected shaft may be disregarded for separation distance purposes
Roofs pitched at an angle of less than 70 degrees may be disregarded for separation distance purposes
Represents an unprotected area of not more than 1m2 which may consist of two or more smaller areas within an area of 1000mm X 1000mm
Represents an area of not more than 0.1m2
See para 11.11
NOTE: Projections from the building line, such as a canopy or a loading platform, can be ignored when assessing separation distance. This does not apply where the canopy is enclosed by side walls.
Distance to relevant boundary measured from building line
See para 11.12
Minimum distance (a) between side of building and relevant boundary (m) Maximum total area of unprotected areas (m2)
See para 11.18
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.