Introduction to external fire spread provisions - Control principles

The guidance in Section 5 which relates to the extent to which fire may spread over and between buildings depends on the size and intensity of the fire, the construction of the external walls and roof, and the distance between the buildings. Construction of walls – the fire resistance of an external wall and the combustibility of its external face are controlled to reduce its susceptibility to ignition from an external source and the danger from fire spreading up the external face of the building and the materials used for external walls and attachments to them, do not contribute to the rate of fire spread up the outside of a building. Construction of roofs – the combustibility of the external surface of a roof is controlled to reduce its susceptibility to ignition from an external source. Distance between buildings – adequate separation between buildings is achieved by relating the amount of unprotected area (e.g. windows, areas of combustible wall, etc.) in the wall of a building or compartment to the distance that wall is from its relevant boundary. It may be advantageous to reduce compartment sizes or to provide compartmentation where none would otherwise be necessary, as this will reduce the size of the fire and may permit a reduced boundary distance or alternatively, an increase in unprotected area.