Single staircase residential buildings and the height limit
The second staircase threshold sits at 18 metres, the same height that triggers the fire statement duty and the building safety gateways. Redesigning a consented single stair scheme is usually a section 73 application, not a minor amendment.
A second staircase is now expected in new residential buildings above 18 metres in England, following the government's decision to set the threshold there rather than at the 30 metres originally consulted on, and the amendment of Approved Document B that followed. For a developer, a single staircase residential building above that height is no longer a design preference. It is a question about whether the scheme as consented can still be built, and the answer usually depends on whether the transitional arrangements can be met.
Why staircase provision reached the planning stage
Means of escape has always been a building regulations matter. It reached planning because the core is the single element of a residential building that cannot be changed later without redesigning everything around it.
A second stair takes floor area on every storey. It changes the position of the lift lobby, the corridor layout, the number of units that can be served per core and often the footprint of the building. Those are planning matters, since they alter the massing, the unit mix and the elevations.
Planning Gateway One reinforced the link. Since August 2021 an application for a relevant high-rise residential building has had to be accompanied by a fire statement, and the Health and Safety Executive comments on it as a statutory consultee. The core strategy is exactly the kind of decision that consultation is designed to surface while it can still be changed.
The threshold and what it applies to
The expectation attaches to new residential buildings at or above 18 metres in height, measured under the definitions used in the guidance rather than by eye. Measure to the floor surface of the top storey and record the measurement on a drawing, because schemes sitting within a metre of the threshold need certainty rather than an assumption.
Two points are frequently misunderstood.
The requirement concerns new buildings. Existing single stair buildings are not required to gain a second stair, though the fire safety regime around occupied higher-risk buildings applies to them in other ways.
And 18 metres is not the only relevant number. It coincides with the higher-risk building threshold used for the building safety gateways, which means a scheme crossing it acquires the second stair expectation, the Gateway One fire statement duty and the Gateway Two hard stop at the same moment. Design decisions near that height carry more consequence than the single metre suggests.
What it does to core efficiency and yield
The commercial effect is straightforward and it is not small.
A second stair and its associated lobby consume floor area on every residential storey, and the area is taken from the most valuable part of the plan. Net to gross falls, which reduces saleable or lettable area for the same envelope.
Corridor arrangements change too. A single core serving a compact plan may need to become a longer corridor with different escape distances, which can push habitable rooms into positions with poorer aspect.
And on a small footprint the effect compounds, because the fixed area of the core is a larger proportion of a small floor plate. Tall buildings on tight urban sites are the schemes most affected.
Three responses are worth testing before concluding that the scheme is undeliverable. Reducing the building below the threshold and adding the lost units elsewhere on the site. Consolidating two smaller cores into one better-arranged core. Or reconfiguring the unit mix so that the remaining area is used for the mix that performs best on the plot.
Redesigning a consented scheme
Where permission exists for a single stair building above the threshold, the practical route depends on how far the change goes.
- Establish whether the transitional arrangements are available to the scheme, since that determines whether a redesign is needed at all.
- Test the second stair against the approved parameters, including any maximum heights and building footprints fixed by condition or by an outline permission.
- Decide whether the change is non-material, in which case a section 96A application may serve, or material, which means a section 73 application or a fresh application.
- Check whether the amended scheme crosses any threshold it did not cross before, such as an affordable housing trigger or a change in floorspace that affects the levy position.
- Re-engage on the fire statement, because a changed core strategy means the Fire Statement submitted with the original application no longer describes the building.
Point three is where schemes get stuck. A second stair rarely reads as non-material, because it alters internal layout, unit numbers and often the elevations. Assume a section 73 application and be pleasantly surprised.
Transitional arrangements and how to check them
Transitional provisions attached to the Approved Document amendment allow schemes at a defined stage of progress to continue under the previous position, subject to conditions about when the relevant building control application was made and how far work has progressed by a stated date.
Those provisions are time-limited and the cut-off has been widely discussed in the industry. Verify the current wording and dates on gov.uk before relying on them, and record the date on which you checked, because a scheme depending on transitional relief needs documentary evidence that it met the conditions at the time.
Three pieces of evidence are worth assembling now for any scheme in this position: the date and reference of the building control application, the record of what work had started and when, and the correspondence with the building control body confirming the position.
Where the transitional route is not available, the redesign has to happen and the programme should assume it.
Evidence to submit with the application
An application for a residential building near or above the threshold should make the fire strategy legible to a planning officer without requiring them to be a fire engineer.
Show the core arrangement on every floor plan, with escape routes marked. State the building height with the measurement point identified. Provide the fire statement on the published form, cross-referenced to the drawing numbers. And where the strategy is anything other than conventional, a Fire Safety Strategy prepared by someone with the relevant fire engineering competence should sit behind it.
Both documents are ones where qualified professional input is legally required under the Building Safety Act 2022 framework and Article 9A of the Development Management Procedure Order 2015, so an AI-assisted draft is a starting point for that professional rather than a substitute for their judgement.
The viability conversation, handled properly
Lost net area affects the appraisal, and where a scheme carries affordable housing or infrastructure obligations, developers will want to reopen them. That conversation goes better when it is evidenced.
A Viability Assessment prepared to the RICS approach, showing the change in net developable area between the consented and revised schemes and its effect on residual land value, is the document councils will engage with. Councils normally expect a suitably qualified author, and most authorities appoint their own reviewer at the applicant's cost.
Two cautions from experience. Reopening viability on a consented scheme invites the authority to re-examine the whole appraisal, including inputs that were previously accepted. And an argument that rests only on the second stair, without showing what else was tested, tends to be met with a request to test more.
Be candid about the trade-off. A scheme that delivers fewer units with a safer core is still a scheme worth building, and framing the change as an unavoidable regulatory cost is more persuasive than presenting it as an injustice.
Enter your postcode on PlanScope to see which reports your scheme is likely to need. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. This is general guidance rather than legal advice, and the guidance and its transitional provisions are subject to change, so verify the current position on gov.uk before relying on any of it.
Frequently asked questions
At what height is a second staircase expected?
At or above 18 metres for new residential buildings in England, following the government's decision to set the threshold there rather than at the 30 metres originally consulted on, with Approved Document B amended accordingly. Measure to the floor surface of the top storey under the definitions used in the guidance and record the measurement on a drawing.
Do existing single stair buildings have to add a second staircase?
The requirement concerns new buildings. Existing single stair residential buildings are not required to gain a second staircase, although the wider fire safety regime applying to occupied higher-risk buildings continues to apply to them. Any major works to an existing building should be discussed with the building control body early.
Is adding a second staircase a non-material amendment?
Rarely. A second stair alters internal layout, unit numbers, corridor arrangements and frequently the elevations, which is more than a section 96A application is designed for. Assume a section 73 application or a fresh application, and check whether the amended scheme crosses any threshold the original did not.
How do I know whether transitional arrangements apply?
Check the current wording and dates on gov.uk and record when you checked. The provisions turn on when the relevant building control application was made and how far work had progressed by a stated date. Assemble the application reference, evidence of the work already carried out and the building control body's confirmation of the position.
Can I reopen affordable housing obligations because of the change?
You can ask, with evidence. A viability assessment prepared to the RICS approach, showing the change in net developable area and its effect on residual land value, is what councils engage with. Expect the authority to appoint its own reviewer at your cost and to re-examine inputs that were previously agreed.
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.