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 direct flame impingement or radiant heat flux from a fire in an adjoining building or other external source.
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).
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. Therefore, the construction of external walls in taller buildings should not contribute to the development of fire or contribute to vertical fire spread up the facade of the building. The 11m storey height in clause 2.7.1 and clause 2.7.2 is based on the reach capability of a fire and rescue service ground mounted water jet where there is sufficient pressure and flow in the water main. Designers are encouraged to seek early advice from the fire and rescue service if they wish to vary from the guidance where, for example, the facade is accessible to high reach appliances. Also, see annex 2.B for exceptions.
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.
Green walls (also called living walls) have become popular in recent years. Best practice guidance can be found in ‘Fire Performance of Green Roofs and Walls’ published by the Department of Communities and Local Government.
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).
2.7.1 External wall cladding
External wall cladding includes non load-bearing external wall cladding systems attached to the structure, for example, composite panels, clay or concrete tiles, slates, pre-cast concrete panels, stone panels, masonry, profiled metal sheeting including sandwich panels, timber panels, weather boarding, thermally insulated external wall rendered systems, and other ventilated cladding systems. For the purposes of compliance with Standard 2.7, external wall cladding includes spandrel panels and infill panels.
External wall cladding more than 1m to the boundary may be constructed from combustible products more than 1mm thick which is European Classifications B, C, D or E (see annex 2.B). This guidance does not apply to domestic buildings having a storey more than 11m above ground level.
External wall cladding not more than 1m from a boundary should achieve European Classification A1 or A2 except cladding to a house where:
the cladding achieves a European Classification B, and
the wall behind the cladding has the appropriate fire resistance duration from both sides.
Storey height more than 11m – Where the building has a storey at a height of more than 11m above the ground the external wall cladding system should be constructed of products achieving European Classification A1 or A2.
Alternative guidance - BR 135, ‘Fire Performance of external thermal insulation for walls of multi-storey buildings’ and BS 8414: Part 1: 2015+A1: 2017 or BS 8414: Part 2: 2015+A1: 2017 provides guidance on fire spread on external wall cladding systems. The guidance provided in these publications may be used as an alternative to European Classification A1 or A2 external wall cladding and for European Classification A1 and A2 products exposed in a cavity. BS 9414: 2019 (Draft June 2019) provides additional information on the application of results from BS 8414 tests.
There is a risk of vertical fire spread from specified attachments to an external wall including balconies, solar panels and solar shading. Solar shading are devices attached to an external wall to reduce heat gain within a building by deflecting sunlight. Fire-fighters may not be able to apply a water jet from a fire-fighting hose directly onto a fire that has spread onto specified attachments high above the ground.
Where the building has a storey at a height of more than 11m above the ground, specified attachments should be constructed of products achieving European Classification A1 or A2.