6.1 External masonry walls

6.1.4 Fire resistance

External cavity walls shall adequately resist the passage of fire.

The cavity in the masonry cavity wall of a building can provide a route for the spread of smoke and flames. Cavities should be closed with cavity barriers, in accordance with Building Regulations.

Cavity barriers should be provided:

  • at the edges of cavities, including around openings eg window and doors,
  • where the cavity abuts compartment walls and floors,
  • where to break up extensive cavities which could act as a route for fire spread.

Cavity barriers need to achieve a minimum of 30 minutes’ integrity (E 30) and 15 minutes’ insulation (I 15).

Vertical cavity barriers, where required, should extend below the DPC and care should be taken to ensure continuity of cavity barriers where cavity barriers are installed at DPC level.

Where cavity barriers are used, they should be sized appropriately for the dimensions of the cavity. Normally they are installed under compression and as such maintaining the design cavity width is critical.

Significant reduction in cavity width will mean that the barrier cannot be fitted without creating problems for the following leaf of masonry. Significant widening in the cavity width will mean that the barrier may not be fitted with the appropriate level of compression and its performance may be impaired.

Concealed spaces#

Where cladding is fitted to a masonry substrate wall, cavity barriers should be provided. Cavity barriers to concealed spaces behind external cladding should be positioned:

  • at the edges of cavities including eaves and verges, around openings such as windows and doors and entry/exit points for services
  • at the junction between an external cavity wall and every compartment floor and compartment wall.

Last updated: 2nd January 2024

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