Firefighting shafts and their effect on core planning
A firefighting shaft is a stair, lobbies at every level and a firefighting lift. How that assembly reshapes a residential core, the plan and the unit mix.
In a residential building tall enough to need a firefighting shaft, the shaft sets the core, and the core sets the plan. Above 18 m to the top storey floor level, Approved Document B requires a firefighting shaft containing a firefighting stair, firefighting lobbies at each level and a firefighting lift, and once that assembly is drawn properly the core has usually grown by more than the architect assumed at concept stage. The consequence at planning stage is a lower net to gross ratio, a different unit mix, and in tight plans a fundamental change to the building footprint.
Draw the shaft early. It costs less to lose a unit on paper than to discover the core at technical design and go back for a fresh permission.
Why the shaft drives the core
A firefighting shaft is not a stair with a lift beside it. It is a protected enclosure containing the stair, a lobby at every storey served, the firefighting lift and its machinery arrangements, with a route for hose and a rising main. The lobby is the element that surprises people: it has to be large enough for firefighters to work in, it sits between the accommodation and both the stair and the lift, and it cannot double as a corridor to flats without meeting the separation requirements.
Stack that against the other things the core has to contain. Smoke control shaft, risers, refuse chute, the second stair where one is required, and the lobby depths that make the doors swing properly. Cores in this building type are commonly a third larger than a concept sketch allows.
One live matter to check rather than assume: the requirement for a second staircase in new residential buildings above 18 m was confirmed in 2024 with transitional arrangements, and it changes core area substantially. Check the current Approved Document B and the transitional dates before you rely on a single-stair layout, because this has moved recently and the design consequence is large.
Lobby, lift and stair relationships
The geometry that works is well established and there is less freedom than it looks.
- the firefighting lobby is entered from the accommodation side and gives access to both stair and lift
- the firefighting lift opens into the lobby, not into a common corridor
- the rising main outlet sits in the lobby where a firefighter can reach it with the door closed
- the firefighting lift car is dimensioned and rated for a firefighting crew and a stretcher, so it is larger than a standard passenger lift
- the stair width and the lobby area have to work together, because a firefighter in full kit is wider than a resident
That last point is the design reality behind the dimensions. Where the lobby is squeezed to gain a square metre in a flat, the drawing stops working and a fire engineer will say so.
Effect on net to gross
Net to gross is the number the appraisal turns on, and the shaft affects it in three ways: the area of the shaft itself, the area of the lobbies at every storey, and the loss of usable frontage where the core meets the external wall.
| Element | Typical planning stage effect |
|---|---|
| Firefighting stair and lift | Fixed core area on every floor |
| Firefighting lobby at each level | Additional area per storey, often the largest single loss |
| Second stair, where required | A further fixed area on every floor |
| Smoke shaft and risers | Small but inflexible |
| Corridor length to reach units | Grows as the core grows, cutting efficiency further |
The temptation is to put more units on each floor to recover the ratio, which lengthens the corridor and can push you past travel distance limits. On tight sites the honest answer is often a taller building or fewer, larger units rather than a more efficient core.
Where the shaft conflicts with unit layouts
Three conflicts recur.
Corner units. The core wants to sit where the plan is deepest, which is often the corner, and corner units are the dual-aspect homes that carry the design case for daylight and outlook. Moving the core inboard fixes the units and creates an internal lobby with no natural light, which is acceptable technically and weaker in planning terms.
Single-aspect north-facing units. Where the core takes the south frontage, the remaining units face the wrong way, and the daylight and overheating cases both get harder. Test that before the core position is fixed.
Podium and ground floor. At the base, the shaft has to come out somewhere accessible to the fire service, which competes with the commercial frontage, the residential entrance and the servicing bay.
Showing the arrangement at planning stage
You are not submitting a fire engineering design with a planning application, and you should not pretend to. What the drawings should show is that the strategy works spatially: the shaft in position on every floor plan, lobbies drawn to a workable size, the firefighting lift identified, the fire service access route shown on the site plan with the appliance position, and the rising main location noted.
For relevant buildings, a Fire Statement is a national requirement on the application under the Development Management Procedure Order, and the Health and Safety Executive is a statutory consultee at Planning Gateway One. That statement has to be prepared by someone with the necessary fire engineering competence, and the report is a starting point for that professional rather than a substitute for their judgement. The fuller Fire Safety Strategy to the relevant British Standard follows at technical design.
Where sign-off by a competent person is needed, the professional directory is the route to a reviewer.
Changes that trigger a fresh submission
The changes that cause problems after permission are the ones that alter the external envelope or the approved plans. Enlarging the core to accommodate a second stair changes the floor plans, usually changes the elevations, and often changes the unit count, which is beyond what a non-material amendment can carry. A section 96A amendment deals with changes that are non-material in substance. A section 73 application deals with changes to conditions, including approved drawings, where the development remains substantially the same.
Two practical protections. Draw the core to the size a fire engineer signs off before you submit, even if the detailed design comes later. And avoid conditioning the internal layout more tightly than the planning issues require, since a condition listing every internal drawing turns a technical change into a planning application.
Our note on disproportionate collapse and building class covers the structural consequence of the same height thresholds, which often lands on the same drawings.
Coordinating with the access strategy
The fire service access route, the hard standing for the appliance, the distance from the appliance to the dry or wet riser inlet, and the turning provision all sit on the landscape drawing, which is usually produced by a different team from the one drawing the core. Coordinate them before submission, because a landscape design with a tree in the appliance position is an easy objection from the consultee and a costly redesign.
Accessible approach requirements and the evacuation strategy for residents who cannot use stairs also affect the core, and the planning-stage answer is to show the lift arrangement and the refuge or evacuation lift provision on the plans rather than to leave it to the technical stage.
Draft your fire statement in minutes on PlanScope, then send it for review by a fire engineer before submission.
This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
At what height is a firefighting shaft required?
Approved Document B requires firefighting shafts in buildings where the top storey is more than 18 m above fire service access level, and in buildings with deep basements. The shaft contains the firefighting stair, a firefighting lobby at each level served and a firefighting lift. Check the current Approved Document, because the residential provisions have been amended recently.
Does a firefighting lobby have to be separate from the corridor?
It has to function as a protected space from which firefighters work, entered from the accommodation side and giving access to both the stair and the firefighting lift. It cannot simply be the common corridor unless the separation requirements are met. Squeezing the lobby to gain flat area is the change a fire engineer will refuse to sign.
How much does the shaft cost me in net to gross?
Three ways: the shaft area on every floor, the lobby area at each storey, which is often the largest single loss, and the longer corridors needed as the core grows. Adding units to recover the ratio lengthens travel distances, so on tight sites fewer larger units or a taller building is usually the better answer.
What fire information does a planning application need?
For relevant buildings a fire statement is a national requirement under the Development Management Procedure Order, and the Health and Safety Executive is a statutory consultee at Planning Gateway One. It must be prepared by someone with fire engineering competence. The detailed fire safety strategy to the relevant British Standard comes later, at technical design.
Can a core enlargement be handled as a minor amendment?
Rarely. Enlarging the core to add a second stair changes floor plans, usually changes elevations and often changes unit numbers, which goes beyond a non-material amendment under section 96A. A section 73 application to vary the approved drawings is the usual route, provided the development remains substantially the same.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.