For a dwellinghouse, Approved Document B describes an appropriate emergency escape window or external door, or a protected stairway leading to a final exit. That house guidance should not be copied indiscriminately into a block of flats. [1]
Decide the escape route before the layout
A direct external escape route and a protected internal stair can lead to different room arrangements. The fire design should identify how people reach safety from the basement and how the route is kept available. A lightwell that provides daylight is not automatically a suitable escape space. [1]
Ask the designer to mark the complete route on the plans, including its continuation outside. The drawings should show how someone reaches safety after passing through the opening. [1]
What makes an escape window suitable?
Approved Document B's dwellinghouse guidance specifies an unobstructed openable area of at least 0.33 square metres, with both its height and width at least 450 millimetres. The bottom of that opening should be no more than 1,100 millimetres above the floor. The opening must also remain open without being held. [1]
Those dimensions work together: a 450-by-450-millimetre opening does not achieve the required area. Escape must also lead to a place free from danger from fire; enclosed courtyards and inaccessible gardens need the additional consideration shown in the guidance. [1]
Stairs, doors and the existing house
A protected stair is a coordinated fire-resisting route, not simply a staircase with one new door at the bottom. The design needs to address the enclosure, openings and final exit as a whole. Structural and service alterations should not compromise the intended protection. [1]
The physical stair design also needs assessment under Approved Document K, including headroom and protection from falls. Fire safety and stair geometry are separate checks, so satisfying one does not establish compliance with the other. [2]
Discuss an open-plan basement and ground floor early. The responsible designer must establish an acceptable solution for the complete layout rather than treating alarms or suppression equipment as an automatic substitute for the guidance. [3] [4]
Coordinate the other design requirements
Lightwell guarding, ventilation equipment and new service routes should be reviewed against the escape design. A feature introduced for another purpose should not obstruct the opening or undermine the route on which the fire strategy depends. [2] [5]
Flood escape is a separate consideration. A route acceptable in the fire design may still need assessment against the site's flood conditions and safe access requirements. [6]
Published future change
The published Approved Document B amendments remove national fire-resistance classifications from the guidance from 2 September 2029, subject to transitional arrangements. This affects the evidence used for relevant fire-resisting construction; it is not a new universal requirement to add a second escape stair to an ordinary domestic basement. [7]
Agree the applicable guidance edition and the completed fire details before work is covered up. At completion, retain the design information and declarations rather than relying only on the visual appearance of the finished rooms. [8] [9]