Fire Safety Requirements for Basement Dwellings

What This Requirement Covers

Basements present particular fire safety challenges because occupants must travel upwards to escape, smoke naturally rises and can quickly fill escape routes, and firefighting access is more difficult. Approved Document B contains specific provisions for basements in both dwellings and non-domestic buildings.

Key Requirements

Basement Rooms in Houses

1. A habitable room in a basement requires either direct access to a final exit (e.g., a door to a light well or external area at basement level) or an emergency egress window meeting the standard requirements (0.33 m² minimum opening, 450 mm minimum dimension)
2. Where the only escape from the basement is via an internal stairway, the stairway must be a protected stairway enclosed with 30-minute fire-resisting construction
3. A fire detection and alarm system (Grade D1 LD2 minimum) must be provided, including detection in the basement rooms, hallway, and stairway
4. The basement stairway should ideally be separated from the ground-floor stairway by a fire door at ground level

Basement Flats

1. A flat located wholly below ground level must have its own independent escape route to a place of safety
2. The escape route must not pass through any other flat, common room, or car park
3. Basement corridors require emergency lighting and fire-resisting construction
4. Smoke ventilation must be provided to the escape route (natural via a light well or mechanical extraction)

Basement Car Parks

1. Car parks below residential or commercial buildings must be separated from the rest of the building by compartment construction
2. Ventilation must remove smoke and fumes: natural ventilation (open sides providing 5% of floor area) or mechanical ventilation to BS 7346-7
3. A sprinkler system may be required in enclosed basement car parks

Fire Service Access to Basements

1. Basements with a floor area exceeding 600 m² require smoke ventilation outlet shafts accessible from outside the building
2. The fire service must be able to ventilate the basement before entering for firefighting
3. In large basement areas, firefighting access points should be provided at regular intervals

Practical Compliance Tips

1. Always provide an independent means of escape from basements where possible; relying solely on an internal stairway is the least favourable option
2. Ensure light wells used for escape are large enough for a person to climb out and are accessible from the street or garden
3. Smoke ventilation for basements is often overlooked; plan duct routes and vent positions at design stage
4. Fire-rate the ceiling of any basement car park to the full compartmentation standard for the building
5. Emergency lighting in basements is essential; plan for maintained fittings on the escape route
6. Consider the structural implications of creating escape openings in existing basement walls
7. In basement conversions, check that the existing structure can achieve the required fire resistance