Technical Booklet E Fire Safety·Page 12·36
External fire spread
External walls and roofs must be designed and constructed to prevent fire from spreading over them or between buildings, considering the building's use, position, and height.
The external walls and roof of a building shall be so designed and constructed that they afford adequate resistance to the spread of fire over them, and from one building to another, having regard to—
(a) in the case of an external wall - the use, position and height of the building; and
(b) in the case of a roof - the use and position of the building.
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