Internal walls

Also see:

6.3.6Fire resistance

Internal walls shall have adequate resistance to the spread of fire. Issues to be taken into account include:

  1. fire resistance
  2. typical construction
  3. services
  4. materials.

The guidance below does not apply to Scotland, and reference should be made to the Technical Handbooks.

Fire resistance

Internal walls should provide fire resistance in accordance with building regulations.

Typical construction

Internal walls of hollow or cavity construction (fire-resisting or otherwise) should have cavity barriers installed at:

  • the perimeter
  • junctions with fire-resisting floors and walls.

Fire-resisting walls should be fire stopped or constructed to resist fire spread at:

  • their perimeter
  • junctions with other fire-resisting walls, floors and roofs
  • openings for doors and pipes, etc.

Where fire-resisting walls are of:
■ masonry construction with a cavity, they should be closed at the top
■ framed construction, they should have wire reinforced mineral wool cavity barriers at junctions with floors and ceilings.

At junctions between a separating or compartment wall and a pitched roof or flat roof:
■ adequate precautions should be provided to prevent fire spread
■ the separating wall should stop approximately 25mm below the top of adjacent roof trusses
■ soft packing such as mineral wool should be installed above and below the roofing underlay to allow for movement in roof timbers to prevent ‘hogging’ of the tiles.

A wire reinforced mineral wool blanket cavity barrier should be provided within boxed eaves and be:
■ a minimum 50mm thick
■ carefully cut to shape to seal the boxed eaves fully
■ fixed to the rafter.

The wall dividing an integral, or attached, garage and the floor above should be designed to act together to provide adequate resistance to fire spread. Where the garage has either no ceiling or there is no floor in the space above, vertical fire separation may be required.

For timber constructions, fire stopping material should be compressible, e.g. mineral wool, to accommodate timber shrinkage without affecting fire stopping.


Where services such as pipes, cables and ducting pass through fire-resisting walls, penetrations should be fire stopped. Services should not penetrate plasterboard layers of separating walls.

Fire stopping should be:

  • in accordance with building regulations and the design information
  • completed neatly.


Suitable fire stopping materials include:

  • mineral wool
  • cement mortar
  • gypsum plaster
  • intumescent mastic or preformed strip
  • proprietary sealing systems assessed in accordance with Technical Requirement R3.