Loft conversions and fire safety: escape routes, fire doors and alarms

Everything turns on one measurement: 4.5 metres. Where an upper storey is no more than 4.5 metres above ground level, every habitable room can escape by an emergency window or external door, or by direct access to a protected stairway. Above 4.5 metres, windows are no longer enough.

The house needs a protected stairway, and no habitable room on that storey may be an inner room, reached only through another room. In a typical two-storey house, the first floor sits around 2.7 metres up and can use windows. Add a loft room and its floor is usually over 5 metres, so the whole escape route has to be protected.

A protected stairway is a stair enclosed by fire resisting construction at every storey, to at least REI 30, that is, 30 minutes of load bearing, integrity and insulation. The doors from rooms into it are fire doorsets, to at least E 20. The enclosure runs all the way to a final exit.

Or, where that's not possible, to two ground level exits separated from each other by fire resisting construction and fire doors, so a fire in the kitchen doesn't close both. Above the stair, where it rises into the roof space, there should be cavity barriers or a fire resisting ceiling, so fire in the loft void can't drop into the escape route.

Paragraph 2.21 applies this to conversions. Where a new storey is created above 4.5 metres, the full extent of the escape route should be addressed, not just the new floor. That means fire resisting doors and partitions along the whole route, upgrading existing doors where necessary.

Where the ground floor is open plan, new partitions should be provided to enclose the escape route. If the existing doors have historic or architectural merit, the guidance asks for them to be retained and upgraded where possible, rather than thrown away.

Many homes have an open-plan ground floor, and nobody wants to wall it off. Paragraph 2.23 gives an alternative, and all three parts are needed. First, sprinkler protection to the open-plan areas.

Second, a fire resisting partition and door separating the ground storey from the upper storeys, placed so that someone coming down from the loft can still reach a first floor escape window. Third, the cooking facilities separated from the open-plan area by fire resisting construction.

Escape windows matter for the storeys up to 4.5 metres, including the first floor your loft route passes through. Paragraph 2.10 sets the sizes. An unobstructed openable area of at least 0.33 square metres, at least 450 millimetres high and 450 wide, with the bottom of the opening no more than 1100 millimetres above the floor.

The window must stay open without being held, and it must lead somewhere free from danger. Locks and child-resistant stays are allowed. And when you replace a window that could serve as an escape window, the new one must give at least the same chance of escape.

Adding a habitable room above the ground storey also triggers the alarm rules. Section 1 asks for a fire detection and alarm system to at least Grade D2, Category LD3: mains powered smoke alarms with a backup battery, in the circulation spaces, meaning the hall and every landing including the new one, and interlinked so they all sound together. A heat alarm in the kitchen avoids false alarms from cooking.

Alarms must conform to the British Standards named in the guidance, and be installed and tested by someone competent.

One more case. If the house will have two or more storeys above 4.5 metres, for example a loft on a three-storey townhouse, paragraph 2.6 adds a further requirement. Either an alternative escape route from each storey more than 7.5 metres above ground, with the protected stairway separated from the lower storeys by fire resisting construction at that level, or a sprinkler system throughout the house, designed and installed to BS 9251.