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Fire Escape Route Calculator — Check Compliance with Approved Document B
Check whether your escape route distances, corridor widths, and number of exits comply with UK fire safety regulations. For dwellings, flats and HMOs.
Total number of floors in the building
People served by the escape route on the busiest storey. Drives the AD B Vol 2 width and exit tables (assessed per storey, not whole building).
Longest actual travel distance (measured along the route, not straight-line). For a flat this is the common-corridor distance from the flat entrance door to the stair (AD B Vol 1 Table 3.1: 7.5 m one-way / 30 m two-way); the separate within-flat 9 m limit is shown in the guidance. Not used for a single dwellinghouse — houses are judged on storey height.
Clear width of the common escape corridor (flats/HMOs). Checked against AD B Vol 2 — not applicable inside a single house.
Two-way escape — applies the alternative-directions travel-distance limit (more permissive)
How We Calculate This
This calculator checks an escape-route design against Approved Document B (Fire Safety) and BS 9991 for residential buildings. It is a planning aid — not a substitute for a fire-risk assessment or Building Control sign-off — and covers travel distances, common escape-route widths, the number of exits, and fire-door provisions.
Travel distances
- Dwellinghouse: no horizontal travel-distance limit in Approved Document B Volume 1 — escape is governed by storey height (protected stairway where a floor is more than 4.5 m above ground; escape windows to first-floor rooms in a two-storey house up to 7.5 m).
- Flat: two separate limits — within the flat, 9 m from any habitable room to the flat entrance door (Diagram 3.3, a single maximum with no alternative-directions variant); in the common corridor, 7.5 m where escape is in one direction (dead-end) and 30 m where escape is possible in more than one direction (Table 3.1). This tool checks the common-corridor figure and reports the within-flat 9 m as guidance.
- HMO: 9 m single direction is a LACORS risk benchmark (18 m with alternative directions), not a hard pass/fail limit.
Escape-route width (Approved Document B Volume 2, Table 2.3)
These apply to common escape routes in buildings other than dwellings (flats and HMOs), not inside a single house. Width is set by the number of people served:
- up to 60 people: 750 mm
- up to 110 people: 850 mm
- up to 220 people: 1050 mm
- over 220 people: 5 mm × number of people (the 5 mm/person rule applies only above 220 people; never below 1050 mm)
Number of exits (Approved Document B Volume 2, Table 2.2)
Assessed per room, tier or storey occupancy, not by whole-building total. Table 2.2 has three bands:
- up to 60 people: 1 escape route
- up to 600 people: 2 escape routes
- more than 600 people: 3 escape routes
References
- Approved Document B — Fire safety, Volume 1: Dwellings (2019 edition, incorporating 2020 and 2022 amendments)
- Approved Document B — Fire safety, Volume 2: Buildings other than dwellings (same edition)
- BS 9991:2024 — Fire safety in the design, management and use of residential buildings (supersedes BS 9991:2015)
- LACORS Housing — Fire Safety Guidance (2008), for HMOs
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Last updated: February 2026
Verified against UK standards · estimates only, confirm with your supplier.