Approved Document B (Fire Safety): What Homeowners Need to Know

Approved Document B is split into two volumes: Volume 1 (B1) covers dwellinghouses (the kind of work most homeowners do); Volume 2 (B2) covers other buildings. For residential projects, B1 is the relevant volume.

The key areas B1 addresses are:

• Means of warning and escape — smoke alarms, heat alarms and protected escape routes.
• Internal fire spread (linings) — wall and ceiling materials must limit the spread of flame.
• Internal fire spread (structure) — floors and walls between dwellings or between a house and an attached garage must provide fire resistance.
• External fire spread — external walls and roofs must resist fire spreading from one building to another.
• Access and facilities for the fire service — vehicle access routes and dry risers in larger buildings.

Part B applies to any building work covered by the Building Regulations. Key trigger projects for homeowners include:

• Loft conversions — the most significant trigger. A three-storey dwelling requires a protected escape route (a fire-protected hallway and staircase) from the new room to the exit.
• Extensions — new habitable rooms must have smoke alarms; the extension must not block escape from existing rooms.
• Garage conversions — if the garage is attached and is being converted to a habitable room, fire separation between it and the house must be provided.
• Internal alterations — removing a fire door or reducing ceiling height can compromise fire resistance and must comply with Part B.

A fire door is rated by the time it can resist fire. The most common rating in domestic buildings is FD30 — a door that provides at least 30 minutes of fire resistance. FD30S doors also have smoke seals.

Part B requires FD30S doors in these locations within a dwellinghouse:

• Between a habitable room and the protected stairway in a loft conversion (three-storey house)
• Between an integral garage and the house
• In some cases between a new ground-floor extension room and the rest of the house

Fire doors must be self-closing (fitted with a door closer) and must be installed with the correct intumescent strips and smoke seals. A standard interior door does not qualify as an FD30 door.

Part B requires smoke alarms on every storey of a new dwelling or when material alterations are carried out. For loft conversions, the requirements are:

• At least one smoke alarm on each floor level, including the new loft room
• All alarms must be interlinked — when one sounds, all sound simultaneously
• Alarms should be mains-powered with battery back-up (Grade D, Type LD2 as a minimum)
• A heat alarm is required in the kitchen (not a smoke alarm, which would generate false alarms)

Where a loft conversion creates a three-storey house, building control may require an enhanced alarm system or a protected escape route as an alternative to full sprinkler protection.

For loft conversions, building control will typically inspect:

• The fire door installation (correct rating, self-closer, intumescent strips)
• The alarm system wiring and interconnection
• Any fire-protected plasterboard enclosing the staircase
• The escape window in the loft room (minimum opening area 0.33 m², minimum 450 mm high and 450 mm wide)

For extensions, the main checks are that smoke alarms are fitted and that any new wall or floor between the extension and garage (if applicable) achieves the required fire resistance.

The most frequent fire safety problems on domestic projects are:

• Missing self-closers on fire doors — a fire door propped open is no longer a fire door. Fit a proper door closer.
• Incorrect plasterboard — standard 9.5 mm plasterboard provides little fire resistance; use 12.5 mm fire-rated (Type F) board for protected staircase enclosures.
• Alarm not interlinked — fitting separate battery-only alarms does not meet the requirement for a loft conversion.
• Blocked escape window — a Velux-type escape window in a loft room must open wide enough (0.33 m²) and not be obstructed by furniture.