Basement Fire Escape Calculator

Approved Document B Volume 1 para 2.16 requires that where a basement storey contains any habitable room, it is provided with EITHER (a) an emergency escape window or external door providing escape from the basement (per para 2.10), OR (b) a protected stairway (para 2.5a) leading from the basement to a final exit. These are equivalent alternatives. In practice a basement bedroom is usually served by a protected stairway (REI 30 enclosure with minimum E 20 (FD20) fire doorsets, which in a single family house need no cold smoke seal and no self-closing device), with interlinked smoke detection on each level and fire separation between the basement and ground floor. An escape window/door via a lightwell can satisfy option (a) where the opening meets the para 2.10 dimensions.

A protected stairway is an enclosed staircase that provides a safe route from the basement to a final exit (external door). The enclosure must have 30-minute fire resistance (REI 30), with minimum E 20 (FD20) fire doorsets at each level. AD B Vol 1 Table C1 item 11(b) rates a door forming part of the enclosures to a protected stairway in a single family dwellinghouse at E 20, and the E 30 Sa (FD30S) line at item 4a expressly excepts that case, so no cold smoke seal is required; Appendix C para C5c also exempts fire doorsets within a dwellinghouse from self-closing devices. FD20 doorsets are no longer certified as products, so in practice an FD30 door is fitted to satisfy the E 20 minimum. No habitable room should open directly onto the protected stairway without a fire doorset. This is the primary means of escape for most basements.

Not necessarily. AD B Vol 1 para 2.16 gives two equivalent alternatives: an emergency escape window/external door from the basement, OR a protected stairway to a final exit. An escape window via a lightwell satisfies the window/door option only if it meets para 2.10: an unobstructed openable area of at least 0.33m², at least 450mm high and 450mm wide, with the bottom of the openable area no more than 1100mm above the floor, and the lightwell sized so a person can exit and reach safety. If you instead provide a protected stairway, an escape window is not separately required by para 2.16 — though a second means of escape from a basement bedroom is good practice.

In a single family house the minimum is E 20 (FD20) fire doorsets at: the head of the basement stairs, any opening from the basement stairway to habitable rooms, and between the basement and ground floor level. AD B Vol 1 Table C1 item 11(b) sets E 20 for doors forming part of the enclosures to a protected stairway in a single family dwellinghouse, and the E 30 Sa (FD30S) entry at item 4a expressly excepts that case, so a cold smoke seal is not required. Self-closing devices are not required on fire doorsets within a dwellinghouse (Appendix C para C5c), although some building control bodies still recommend a closer on a basement stair door. The door that does need FD30S with a self-closer is a door between the house and an integral garage (Table C1 item 11a). Because FD20 doorsets are no longer certified as products, an FD30 door fitted with intumescent strips is what you buy to meet the E 20 minimum.

The AD B Vol 1 minimum for a new dwelling is a Grade D2 Category LD3 system to BS 5839-6 — interlinked mains-powered alarms with a user-replaceable integral standby battery, covering the circulation spaces that form the escape routes on every level (e.g. basement, each landing). For a basement conversion or a basement bedroom, good practice is commonly to upgrade to Category LD2 (adding a detector in the principal habitable room and high-risk rooms) and to Grade D1, which uses a sealed, tamper-proof, non-user-replaceable (long-life) standby battery, with heat/multi-sensor detectors in kitchens. Detector positions are placement-based per BS 5839-6, not a fixed floor-area divisor.