Means of escape and layout at planning stage

Escape travel distances decide how many flats a core can serve, and that decides the efficiency of the whole floor plate. In a dead end condition, where residents can only go one way from their front door to the stair, Approved Document B Volume 1 works to a maximum travel distance of 7.5m, rising to 30m where there is an alternative escape route. On a typical plan that 7.5m limit means a single core serves a handful of flats per floor, and a scheme drawn without it tends to lose units at technical design stage or gain a second core it was not costed for.

Fire engineering is not a planning matter in the ordinary sense. Layout is. So the fire logic has to be in the plan before the application, not after.

Why escape distances shape a floor plate

Three dimensions do most of the work: the distance from each flat entrance door to the stair, whether residents can turn either way when they leave the flat, and the position of the firefighting access.

Measure travel distance along the route people would actually walk, around corners and through lobbies, not as a straight line on plan. That is where optimistic early drawings fail. A corridor that looks 7m long on a sketch becomes 9m once the lobby door, the riser cupboard and the dog leg around the lift are drawn.

The consequence is geometric. Flats cluster around cores, cores sit at intervals set by the travel distance, and a long thin block needs either multiple cores or a corridor arrangement giving escape in two directions. Deep plan blocks with a single central core run out of compliant corridor before they run out of floor area.

Travel distances and the number of cores

Work the arithmetic the other way round and the layout almost designs itself.

Take the limits and their conditions from the current Approved Document rather than from a table in an article, because they come with qualifications about lobbies, ventilation and sprinklers that change the answer.

The commercial consequence is worth stating plainly. Adding a second core costs net saleable area on every floor, so the difference between a compliant six flat core and a non compliant eight flat core is the difference between two viable schemes and one.

Protected corridors, lobbies and smoke control

Common corridors serving flats are protected routes, and the detail of how they are protected shapes the plan.

A single stair building normally needs a ventilated lobby or a protected corridor arrangement between the flats and the stair, with a smoke shaft or an automatic opening vent to clear smoke. Those shafts occupy plan area at every level and need a route to the roof, which has to be coordinated with the structure and the risers rather than added at the end.

Riser cupboards, dry or wet risers, firefighting lobbies and the firefighting shaft all take space adjacent to the core. On a tight urban plot that cluster of requirements is often what determines the core position, with the saleable accommodation fitted around it.

Dead ends, unit counts and single stair buildings

The second staircase question has moved. Following consultation, the government confirmed a requirement for a second staircase in new residential buildings above 18m in height, with transitional arrangements for schemes already designed or submitted. Check the current Approved Document B and the transitional provisions, because the threshold, the height measurement and the transitional dates are the details that decide whether a particular scheme is caught.

For buildings below the threshold, single stair design remains possible and the dead end limit governs the unit count. For buildings above it, a second stair changes the core strategy entirely, and a scheme designed around one stair cannot usually absorb a second without losing units or gaining a storey.

That is a planning risk as much as a technical one. A permission granted for a single stair scheme that then requires a second stair at detailed design produces a material change needing a section 73 application or a fresh permission.

Where a building sits just under the threshold, the margin needs checking carefully against the measurement convention, and our note on fire evidence for a building just below the threshold deals with the evidence that goes with it.

Dual aspect units and escape

Dual aspect units help with ventilation, daylight and overheating, and they interact with escape in a way worth understanding.

Escape from a flat above ground floor is through the front door into the protected route, not through a window, so dual aspect does not provide an alternative escape route. What it does provide is cross ventilation, better smoke clearance within the flat, and a plan arrangement that tends to produce shorter internal travel distances to the flat entrance door.

Single aspect flats push the plan deeper and increase the length of internal corridors within each flat, which has its own travel distance consideration within the dwelling and makes the internal layout harder. North facing single aspect units attract objection on amenity grounds in many authorities regardless of fire.

Where a layout cannot be made to work

Some plans cannot be rescued, and recognising that early saves months.

The classic cases are a deep plan block with one core and eight flats per floor, a long corridor with a stair at one end only, a core position that cannot accommodate the smoke shaft and firefighting lobby, and a scheme where fire appliance access cannot reach within the required distance of the dry riser inlet because of the site boundary or a level difference.

In each case the answer is a layout change rather than an engineering justification. A fire engineer can sometimes support a departure through a performance based approach, but doing so at planning stage, on a residential scheme, with the Building Safety Regulator as a Gateway One consultee, is a difficult route and it needs committing to early rather than discovering late.

Showing escape intent on planning drawings

Planning drawings are not fire drawings, and officers are not assessing compliance. What the submission should do is demonstrate that the layout can comply, so that a condition or a later approval does not force a redesign.

1. Mark core positions, stair widths and lift positions on every floor plan.
2. Annotate the dead end and total travel distances along the actual route, with the measured line shown.
3. Show the smoke shaft or vent, the firefighting lobby and the riser positions, with a note of the route to roof level.
4. Show fire appliance access, hardstanding and hydrant or riser inlet positions on the site plan, with distances.
5. Identify which units are single aspect and which are dual aspect, since that connects to the amenity and overheating case in the Design and Access Statement.
6. Where the building is a relevant building for Gateway One, submit the Fire Statement on the prescribed form as required by Article 9A of the Development Management Procedure Order 2015.

A Fire Statement and a Fire Safety Strategy both require a competent professional: the Gateway One statement has to be prepared by someone with the necessary fire engineering competence under the Building Safety Act 2022 framework, and a BS 9991 strategy is a fire engineering document. A PlanScope draft gives the structure and the policy framing, and it is a starting point for that professional rather than a substitute for them. Reports are AI-assisted, should be reviewed before submission, and we do not guarantee planning approval.

Basement and lower ground accommodation raises separate egress questions, covered in our note on safe egress from habitable basement rooms.

This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it.