Firefighting shafts and how they shape a residential core
A firefighting shaft is a stair, lobby, fire main and lift working as one enclosure. How the triggers work and what the shaft does to core planning.
Firefighting shaft planning decisions are made at the massing stage, whether or not anybody realises it. Once a residential building has a storey with a floor more than 18 metres above fire service vehicle access level, Approved Document B expects a firefighting shaft, and a firefighting shaft is not a stair with a hose outlet bolted on. It is a protected assembly of stair, lobby, fire main and lift, and it reshapes the whole core.
Architects who treat it as a late technical adjustment end up losing a unit per floor. Architects who set the core out for it from the first sketch usually do not.
What the shaft contains
A firefighting shaft is a fire separated volume running the full height of the building. Inside it sit four things that have to work together.
The firefighting stair, protected and continuous, providing the route for crews carrying equipment upwards while occupants may still be coming down. The firefighting lobby at every storey, which is the space crews use to set up before opening the door to the accommodation. The fire main, with its landing valve located in the lobby rather than on the stair or in the corridor. And the firefighting lift, where the building height requires one, opening into the same lobby.
The lobby is the part that gets squeezed and the part that must not be. It needs enough floor area for a crew and their equipment, ventilation or pressurisation as part of the smoke control strategy, and a hose run from the landing valve to the furthest point of the storey within the stated distance. Approved Document B sets a minimum lobby area, and BS 9991 covers the same ground for residential buildings in more detail.
The heights that trigger one
Two numbers do most of the work.
| Condition | Consequence in Approved Document B terms |
|---|---|
| Topmost storey floor more than 18 m above fire service vehicle access level | Firefighting shaft expected, including a firefighting lift |
| Basement floor more than 10 m below fire service vehicle access level | Firefighting shaft expected serving the basement storeys |
| Floors more than 18 m above access level | Fire mains required, with the wet or dry question turning on height |
Note the datum. It is the level at which fire service vehicles can reach the building, not ground level, and on a sloping site or a podium scheme those are different by a useful margin. A building that reads as 18 metres on the section can be over or under the trigger depending on where the appliance stands.
The dry and wet main distinction is a separate height question, covered in our note on dry risers, wet risers and the height that separates them.
The 18 metre figure also appears elsewhere, which causes confusion. It is the height at which a building becomes higher risk under the Building Safety Act 2022 where it has at least seven storeys or is 18 metres or more and contains two or more dwellings. And it is the threshold for the second staircase expectation in residential buildings, a change with its own transitional arrangements set out in our piece on second staircases above 18 metres.
Three different regimes, one number, different consequences. Check each separately rather than assuming they move together.
What it does to lobby and corridor planning
The firefighting lobby sits between the stair and the accommodation, so the plan gains a room that every route has to pass through or around.
On a single core block the effect is direct. The common corridor narrows to serve the lobby rather than the stair, the refuse and service risers have to find a position that does not open into the lobby, and the flat entrance doors move away from the lobby wall. On a building requiring two stairs, the arrangement doubles and the question of whether both stairs are firefighting shafts, or only one, becomes the single biggest driver of core area.
Smoke control is the other coupling. The lobby forms part of the strategy for keeping the stair clear, so a pressurisation system, a smoke shaft or an openable vent has to land in or next to it, and the shaft it needs runs the full height. Leaving that shaft out of the early core diagram is the most common reason a core grows late in design development.
There is a knock on effect on unit mix. A core that has to contain two stairs, a firefighting lobby, a firefighting lift, a passenger lift, a smoke shaft and the services can leave a floorplate where single aspect units are unavoidable on one side, which then becomes a daylight and housing quality argument at planning.
The firefighting lift
The firefighting lift is a normal passenger lift with additional protection, controls and power supply, and it lands in the firefighting lobby. Its car has to be large enough for a crew with equipment and, in practice, for a stretcher, which sets a minimum car size that is larger than the cheapest standard lift a developer might otherwise specify.
Three points that matter at planning stage rather than at technical design.
- The lift needs a secondary power supply and a switching arrangement, which means plant space and a route for the supply that does not pass through the accommodation.
- Its shaft is within the firefighting shaft enclosure, so it cannot be moved to a convenient corner of the plan later.
- Evacuation lift provision, where the strategy includes it, may use the same lift or a separate one, and the decision changes the core area.
Where the building includes accessible dwellings above the ground storey, the evacuation strategy and the lift provision have to be settled together rather than sequentially.
Showing the shaft on planning drawings
Planning is not building control, and a case officer is not checking compliance with Approved Document B. But the drawings submitted for planning fix the envelope, the floorplate and the core, and a scheme that has to grow its core after permission needs an amendment.
Put the following on the submitted general arrangement plans: the stair or stairs with their enclosure, the firefighting lobby shown at a realistic size and labelled, the firefighting lift, the smoke shaft or pressurisation duct, and the riser positions. Show the fire service vehicle access position on the site plan with the standing point marked, because that is the datum the height is measured from.
A section through the core with the 18 metre and 10 metre datums annotated saves an enormous amount of correspondence later. The area the shaft takes out of the floorplate is worth quantifying early, as our note on what firefighting shafts take from the floor plate sets out.
Coordinating with the fire statement
For relevant buildings, Article 9A of the Development Management Procedure Order 2015 requires a fire statement with the planning application, and the Health and Safety Executive is a statutory consultee at that stage under the arrangement known as Planning Gateway One. A Fire Statement has to be prepared by someone with the necessary fire engineering competence. That is a legal requirement rather than a preference, and an AI-assisted draft is a starting point for that person rather than a substitute for them.
The statement and the drawings must say the same thing. Where the statement describes a firefighting shaft and the plans show a single stair with no lobby, the consultee response writes itself. The fuller technical document, a Fire Safety Strategy to BS 9991 or BS 9999, is also a fire engineering document and is prepared by a competent professional.
Engage that person before the core is fixed. The cost of an hour of advice at concept stage is trivial against the cost of a revised planning permission.
Layout mistakes that surface late
The recurring ones, roughly in order of how often they appear:
- A lobby drawn at the minimum with no allowance for the door swings, so the usable area falls below the requirement.
- The landing valve positioned in the corridor rather than the lobby, which then forces a redesign of the door arrangement.
- Hose run distances to the far corner of an L shaped or deep plan floorplate exceeding the permitted length, discovered after the massing is fixed.
- Refuse chutes and service risers opening into the firefighting lobby.
- A basement more than 10 metres below access level treated as though the trigger applied only to height above ground.
- Fire service access assumed along a route that the landscape design later turns into a pedestrian area, moving the datum.
That last one is worth a specific check on any scheme with generous public space. Appliance access is a hard constraint with defined widths, turning and standing positions, and a landscape architect who has not been told will design it out.
Browse all 66 PlanScope report types to see which documents your scheme is likely to need.
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
When does a block of flats need a firefighting shaft?
Approved Document B expects a firefighting shaft where the floor of the topmost storey is more than 18 metres above fire service vehicle access level, or where a basement floor is more than 10 metres below that level. The datum is the level where appliances can stand, which on a sloping or podium site differs from ground level.
What is inside a firefighting shaft?
A protected firefighting stair running the full height, a firefighting lobby at every storey, the fire main with its landing valve located in the lobby, and a firefighting lift where the height requires one. Smoke control provision serving the lobby and stair usually runs within or immediately next to the same enclosure.
Is the 18 metre trigger the same as the higher risk building threshold?
No, although the number is the same. Approved Document B uses 18 metres above fire service access level for the firefighting shaft. The Building Safety Act 2022 defines higher risk buildings at 18 metres or at least seven storeys containing two or more dwellings. The second staircase expectation uses 18 metres again with its own transitional arrangements.
Does the firefighting lift have to be separate from the passenger lift?
Not necessarily, but it must sit within the firefighting shaft enclosure, land in the firefighting lobby, have a secondary power supply and a car large enough for a crew with equipment. Where the evacuation strategy relies on lifts, whether the same lift serves both purposes is a decision that changes the core area.
What should planning drawings show about the shaft?
The stair enclosure, the firefighting lobby at realistic size and labelled, the firefighting lift, the smoke shaft or pressurisation duct, riser positions, and the fire service vehicle standing point on the site plan. A section through the core annotated with the 18 metre and 10 metre datums prevents most later correspondence.
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.