Requirement B4: External fire spread

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.