2.7 Spread on external walls
There is a risk of fire spread on the external walls of a building. Fire could break out through a window or door opening and spread onto the external walls. External walls close to the boundary are also at risk as they may be exposed to radiant heat flux from a fire in an adjoining building.
Horizontal or lateral fire spread between houses or between flats and/or maisonettes will be inhibited by the construction of separating walls. Vertical fire spread between flats and maisonettes will be inhibited by the construction of separating floors (see Standard 2.2).
High rise domestic buildings - fire-fighters may not be able to apply a water jet from a fire-fighting hose directly onto a fire that has spread onto or within an external wall high above the ground. This is because the external wall is either inaccessible or is out with the reach capability of fire-fighting equipment such as hydraulic platforms or turntable ladders. The construction of external walls in high rise domestic buildings should not contribute to the development of fire or contribute to vertical fire spread up the façade of the building.
The guidance for fire spread on external walls should not be assessed in isolation and reference should be made to the guidance to Standard 2.4 for fire spread in cavities and the guidance to Standard 2.6 for fire spread to neighbouring buildings.
Conversions - in the case of conversions, as specified in regulation 4, the building as converted shall meet the requirements of this standard in so far as is reasonably practicable, and in no case be worse than before the conversion (regulation 12, schedule 6).
External wall cladding includes non load-bearing external wall cladding systems attached to the structure, for example, clay or concrete tiles, slates, pre-cast concrete panels, stone panels, masonry, profiled metal sheeting including sandwich panels, weather boarding, thermally insulated external wall rendered systems, glazing systems and other ventilated cladding systems.
External wall cladding more than 1m to the boundary may be constructed from combustible products more than 1mm thick which is low, medium, high or very high risk (see annex 2.B). This guidance does not apply to high rise domestic buildings.
the cladding achieves a low risk reaction to fire classification, and
the wall behind the cladding has the appropriate fire resistance duration from both sides.
However an insulation product need not achieve a non-combustible classification where:
Alternative guidance - BR 135, ‘Fire Performance of external thermal insulation for walls of multi-storey buildings’ and BS 8414: Part 1: 2002 or BS 8414: Part 2: 2005 has been updated to include the most up-to-date research into fire spread on external wall cladding. The guidance provided in these publications may be used as an alternative to non-combustible external wall cladding as described above and for materials exposed in a cavity, as described in clause 2.4.7.