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.
Residential care buildings and hospitals also present a greater risk because the mobility, awareness and understanding of the occupants could be impaired and as a consequence, full evacuation immediately a fire is discovered may not be the most appropriate course of action.
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 façade is accessible to high reach appliances. Also, see annex 2.B for exceptions.
The guidance for fire spread on external walls of buildings 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).
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.
A cavity formed by external wall cladding should be protected in accordance with the guidance to Standard 2.4 and fire spread to neighbouring buildings in accordance with the guidance to Standard 2.6.
Where the cladding is more than 1m from the boundary and is constructed from combustible products more than 1mm thick, that has a European Classification B, C, D or E (as described in annex 2.E), the cladding should be constructed from products with a reaction to fire in accordance with the following table:
Table 2.9. Reaction to fire of external wall cladding more than 1m from boundary
|Building Use||Topmost storey height above ground ||European Classification |
|Entertainment and Assembly Building||Any||A1 or A2|
|Entertainment and Assembly Building with a total storey area not more than 500 m2||11m||B, C, D or E|
|Hospital and residential care building||Any||A1 or A2|
|Hospital and residential care building with a total storey area not exceeding 200 m2||11m||B, C, D or E|
|Any other building||More than 11m||A1 or A2|
|Not more than 11m||B, C, D or E|
Includes single-storey buildings
See exemptions in annex 2.E
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.