Second staircase provision and planning layouts
Adding a second staircase turns an efficient point block into a different building. What changes in planning terms, which amendment route applies, and what the fire statement must say.
Approved Document B has been amended to require a second staircase in new residential buildings above 18 metres, with transitional arrangements for schemes already in the system. As at the time of writing, those transitional provisions are at or close to the end of their run, and the exact wording and dates should be checked against the current Approved Document B on gov.uk before any scheme is programmed around them.
The planning consequence is not the requirement itself, which is a Building Regulations matter. It is that a single stair core and a dual stair core produce different buildings, and a consented scheme designed around the first cannot simply be built with the second.
The policy position and its current status
The requirement sits in Building Regulations guidance rather than in planning policy. Height for this purpose is measured from ground level to the finished floor surface of the top storey, disregarding any storey consisting exclusively of roof-top plant, which is the same basis used for the higher-risk building definition under the Building Safety Act 2022.
Separately, the Building Safety Act framework defines a higher-risk building as one of at least 18 metres in height or at least seven storeys, containing two or more residential units, and brings it within the three gateway regime operated by the Building Safety Regulator within the Health and Safety Executive.
Those two thresholds broadly coincide, which is convenient, and they are not the same rule. One governs what you have to build. The other governs who approves it and when. Check both against the current published text rather than relying on a summary, including this one.
What a second stair does to a core
A single stair point block is efficient. One core, a short lobby, and units wrapping it on every side gives a high ratio of saleable area to gross area and allows dual aspect corners.
Adding a second stair takes that apart in one of three ways. Two stairs within a single enlarged core, sometimes as a scissor arrangement, keeps the plan compact and eats net area on every floor. Two separate cores served by a corridor turns a point block into a linear one, which changes the footprint, the elevation and often the site layout. Or the building comes down below the threshold, trading storeys for the stair.
Each route shows up in the planning drawings. The first changes the floorplate and the unit mix. The second changes the massing. The third changes the height, which is usually the parameter most carefully negotiated with the officer in the first place.
Corridor lengths matter as much as the stairs. Travel distance limits cap how far a unit door can be from a protected route, so a longer floorplate does not automatically absorb a second core without also adding a third.
Where a consented scheme has to be redesigned
Look first at the schemes consented before the amendment and not yet started. A permission granted for a 21 metre single stair block is still a valid permission, but it cannot lawfully be built if the building control route now requires a second stair.
The design work then produces one of two outcomes. Either the second stair is absorbed within the consented envelope by reducing the number or size of units, which is a viability question rather than a planning one. Or the envelope has to change, which is a planning question.
The honest test is whether the external appearance, the height, the footprint or the quantum changes. If none of them does, the amendment is a matter for building control and the planning permission stands. If any of them does, you are back in front of the local planning authority.
Amending a permission or starting again
Three routes, in ascending order of pain.
A non-material amendment under section 96A of the Town and Country Planning Act 1990 works for trivial changes only: an internal reconfiguration with no external effect, a door position, a minor plant relocation. Authorities apply it narrowly and they are right to.
A section 73 application to vary a condition covers minor material amendments, typically a change to the approved drawings condition. It is the usual route where the footprint grows slightly or an elevation changes, and it produces a new permission sitting alongside the original one. It cannot be used to change the description of development, so a scheme that drops from 96 units to 84 where the description names the number of units needs care.
A fresh full application is required where the change is fundamental: a different building form, a materially different height, or a reduction in units large enough to reopen the affordable housing and section 106 position. Budget for a full determination period and for the possibility that policy has moved since the original consent.
Interaction with the fire statement
For relevant buildings, article 9A of the Development Management Procedure Order 2015 requires a Fire Statement to accompany the planning application, and the Health and Safety Executive is a statutory consultee at that stage. This is Planning Gateway One.
The fire statement is a planning-stage document about how the site and building design address fire safety: access for fire service vehicles, water supplies, the evacuation strategy, the location of cores, and how the layout supports them. It is not the detailed fire engineering design, which sits in a Fire Safety Strategy to BS 9991 or BS 9999 and belongs to the Gateway Two submission.
Both are documents where fire engineering competence is legally expected, and an AI-assisted draft is a starting point for that professional rather than a substitute. Where a consented scheme is redesigned for a second stair, the fire statement has to be updated to match, and a statement describing a single stair evacuation strategy attached to a dual stair application will be noticed.
What happens after planning is covered in our note on what Gateway Two requires before construction starts, and on the information duties in the golden thread and what planning contributes.
Evidence to submit
Put the staircase strategy in front of the officer rather than leaving it to be inferred from a floor plan.
- Core plans at typical, ground and top floor levels, showing both stairs, the firefighting shaft and the lift arrangement including any evacuation lift.
- A section through the building with the 18 metre measurement marked from ground level to the top storey finished floor level, and roof plant identified.
- The evacuation strategy stated plainly, with the assumptions behind it.
- An updated fire statement reflecting the current design.
- Where this is an amendment, a comparison drawing set showing the consented and proposed arrangements side by side, with the areas scheduled.
- A revised accommodation schedule if the unit count or mix has changed, with the affordable housing position addressed.
That comparison set does more to speed up a section 73 than any amount of covering letter.
Programme and viability consequences
Three effects, and they compound.
The first is lost net area, which falls straight through to value. The second is the redesign and reapplication programme, which on a section 73 is months and on a fresh application longer. The third is the section 106 renegotiation that follows any material change in unit numbers or mix, which can take longer than the planning application it accompanies.
None of that is an argument against the requirement. Buildings with a single escape route above 18 metres were the subject of the Building Safety Act for reasons that do not need restating. But the cost lands on schemes that were designed lawfully under earlier guidance, and pretending otherwise in a viability discussion helps nobody.
Browse all 66 report types to see the full bundle a tall residential scheme needs. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. For specialist technical reports, qualified professional input may be required.
This is general guidance, not legal advice. The staircase requirement and its transitional arrangements sit in Building Regulations guidance that has been amended, so check the current Approved Document B and take advice from a competent fire engineer before relying on any date or threshold.
Frequently asked questions
How is the 18 metre height measured?
From ground level to the finished floor surface of the top storey, disregarding any storey consisting exclusively of roof-top plant or machinery. That is the same basis used for the higher-risk building definition under the Building Safety Act 2022. Mark the measurement on a section drawing and identify the plant level so the officer does not have to work it out.
Does a second staircase requirement invalidate an existing planning permission?
No. A permission granted for a single stair scheme remains valid. The question is whether the building can lawfully be constructed under current building control requirements and, if not, whether the redesign changes anything the planning permission controls. If height, footprint, elevations and quantum are unchanged, the permission stands.
Which amendment route applies when a scheme is redesigned for a second stair?
Section 96A for non-material internal changes with no external effect. Section 73 to vary the approved drawings condition where the footprint or elevations change slightly, producing a new permission alongside the original. A fresh full application where the form, height or unit numbers change materially enough to reopen the section 106 position.
What does the fire statement have to cover at planning stage?
Site and building design matters: fire service vehicle access, water supplies for firefighting, the evacuation strategy, core locations and how the layout supports them. It is required by article 9A of the Development Management Procedure Order 2015 for relevant buildings, with the Health and Safety Executive as statutory consultee. Detailed fire engineering belongs in the Gateway Two submission.
What does a second stair cost a scheme in floor area?
It depends on the chosen arrangement. Two stairs in one enlarged core eat net area on every floor while keeping the footprint. Two separate cores with a connecting corridor change the footprint and the massing. Dropping below the threshold trades storeys instead. Each route has a different effect on net to gross and unit mix, so test all three.
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.