Loft Conversion Fire Regulations: Protected Stair, Fire Doors, Alarms and Escape

The loft is the easy part of the fire strategy. The part that catches people out is downstairs.

A loft conversion turns a two-storey house into a three-storey one, and the regulations treat a three-storey house differently. Approved Document B Volume 1, paragraph 2.21a, says the full extent of the escape route has to be addressed. That route runs down your existing stairs, across the first-floor landing, through the hall and out of the front door. So doors on bedrooms nobody is touching may need upgrading or replacing. A kitchen that opens straight onto the hall becomes a design question. And an open-plan ground floor, the knock-through you may already have done, can turn into the biggest decision in the whole fire strategy.

The loft company designs the strategy and fits it, but the decisions land on rooms you live in. Understand the strategy before you sign the contract, while it is still a drawing.

These rules cover England. Wales has its own Approved Document B and Scotland uses its Building Standards Technical Handbooks, and both differ in detail.

Why a third storey changes how you get out

In a two-storey house with one stair, a bedroom window is a credible way out. Paragraph 2.2 lets every habitable room (excluding kitchens) on a storey no more than 4.5m above ground rely on either an emergency escape window or direct access to a protected stair (Diagram 2.1b). Above that height, Approved Document B stops counting on people climbing out of windows. The Planning Portal's loft guidance is blunter: escaping through windows from floors above first-floor level is too dangerous.

Paragraph 2.21 is the one written for lofts. Where a conversion creates a storey above that line, the escape route is normally the stair, protected all the way down to a final exit. Paragraph 2.5b allows the other arrangement: a top storey separated from the lower storeys by fire resisting construction, with an alternative escape route leading to its own final exit.

Height is measured from the floor surface of the top storey down to ground level on the lowest side of the building (Appendix D, Diagram D6). A house on a slope can be taller at the back than it looks from the street.

There's a second line to check in taller houses. Where two or more storeys sit above 4.5m, paragraph 2.6 adds to the protected stair: each storey more than 7.5m above ground needs either an alternative escape route or a sprinkler system throughout the house to BS 9251. In one MoneySavingExpert thread, the owner of a mews townhouse was told the new loft floor sat just over that line, and building control would only sign off with sprinklers or an equivalent. One public cost guide puts a whole-house sprinkler retrofit at £6,000 – £10,000. Ask the designer to show the height of the new floor on the drawings, measured the way Diagram D6 describes, before anyone prices the job.

Diagram 2.1c adds one more rule for a top storey above 4.5m: no inner rooms. Every habitable room in the loft must open onto the protected stair. A second bedroom you can only reach by walking through the first one fails.

The protected stairway, and what "final exit" means

Paragraph 2.5a describes a protected stairway as a stair separated by fire resisting construction of at least REI 30 at every storey, ending at a final exit. Appendix A defines a final exit as the end of an escape route that gives direct access to a street, passageway, walkway or open space, sited so people can get clear of the building. Windows never count. In practice that means your front door, or a side or back door you can walk away from.

Two details change how you should look at your own house.

The first is in the Appendix A definition: a protected stairway includes any passageway between the foot of the stair and the final exit. Your hall is part of the enclosure.

The second is an option. Paragraph 2.5a also accepts a stair that leads to two ground-level final exits, separated from each other by fire resisting construction and fire doors (Diagram 2.2b). That can help where the stair lands somewhere awkward.

Above the enclosure, paragraph 2.5 and Diagram 2.3 ask for either cavity barriers or a fire resisting ceiling of at least EI 30, so fire can't travel over the top of the stair walls through a void. Where the new stair rises into the roof space, ask how the top of the enclosure is closed off.

How long does all of this need to hold? Table B2 note 5 gives 30 minutes as the minimum for a three-storey house. The longer period in that note is for compartment walls separating one building from another, and the stair inside your house isn't one.

Where the stair goes and how much headroom it gets are part of this same decision. Loft conversion stairs covers the Part K side.