Section 11: Special provisions for car parks
11.1 Car parks call for different measures to restrict fire spread within buildings for the following reasons.
a. The fire load is well defined.
b. The probability of fire spreading from one storey to another in a well ventilated car park is low. Guidance is therefore given for three ventilation scenarios.
Open sided car parks
Natural ventilation
11.2 For the purposes of assessing fire resistance, a building, compartment or separated part containing a car park may be regarded as open-sided when it complies with all of the following.
a. There are no basement storeys.
b. Each storey is naturally ventilated by permanent openings at each car parking level. The aggregate vent area is a minimum of 1/20 of that level’s floor area, at least half of which is provided equally by two opposite walls.
c. Where one element of structure supports, carries or stabilises another, the fire resistance of the supporting element at least matches the minimum period of fire resistance for the other element.
d. In mixed use buildings, the fire resistance of any element that supports, carries or stabilises an element in the other part of the building should at least match the minimum period of fire resistance for the other element.
e. All materials used in the construction should be class A1 rated, except for the following.
i. Any surface finish applied to a floor or roof of the car park (or within any building, compartment or separated part adjoining the structure enclosing it), if the finish meets requirements B2 and B4.
ii. Any fire doorset.
iii. Any attendant’s kiosk not exceeding 15m2 in area.
iv. Any shop mobility facility.
Car parks that are not open sided
11.3 For car parks that do not have the ventilation set out in paragraph 11.2, the required fire resistance is given in Appendix B, Table B4. Ventilation should be either natural or mechanical. See Approved Document F for additional guidance on ventilation of car parks.
Natural ventilation
11.4 Each storey should be ventilated by permanent openings at each car parking level. The openings can be at ceiling level. The aggregate free vent area should be a minimum of 1/40 of that level’s floor area, at least half of which should be provided equally by two opposite walls (1/160 on each side). The remaining free area can be distributed wherever possible.
Mechanical ventilation
11.5 If the minimum standard of natural ventilation is not possible, a system of mechanical ventilation should be provided that complies with all of the following.
a. The system should be both of the following.
i. Independent of any other ventilating system (other than any system that provides day to day ventilation to the car park).
ii. Designed to operate at 10 air changes per hour during a fire.
b. The system should run in two parts, each of which is:
i. capable of extracting 50% of the rates set out in item (a)
ii. able to operate alone or with the other part
iii. provided with an independent power supply capable of operating if the main supply fails.
c. 50% of the outlets should be at high level and 50% at low level.
d. The system should use E, I and S ductwork in accordance with BS EN 1366-8.
For further information on equipment for removing hot smoke, refer to BS EN 12101-3. An alternative method of providing smoke ventilation from enclosed car parks is given in BS 7346-7.
Requirement B4: External fire spread
These sections deal with the following requirement from Part B of Schedule 1 to the Building Regulations 2010. Section 12 also refers to regulation 7(2) of the Building Regulations 2010. Guidance on regulation 7(1) can be found in Approved Document 7.
Requirement
Requirement
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.
Limits on application
Regulation
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 Class 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.
Intention
Resisting fire spread over external walls
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.
Resisting fire spread from one building to another
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.
