Second staircase rules and their planning consequences

Second staircase residential planning consequences reach further than the stair itself. A single additional protected stair changes the core area, the net to gross ratio, the unit mix, the daylight results for the units that move, and the viability case that the section 106 package was built on. Schemes consented on a single core and not yet started are the ones that feel it, because the planning permission describes a building that the fire guidance no longer supports.

Where the requirement applies and from when

The national position sits in Approved Document B, the fire safety guidance supporting the Building Regulations. Following consultation, the guidance was amended to expect a second staircase in new residential buildings above 18 metres in height.

Two points about that sentence matter. It is guidance rather than a regulation, so the legal duty is the functional requirement in the Building Regulations and the Approved Document describes one way of meeting it. And the threshold sits at 18 metres, which is the same figure used for relevant buildings in the planning fire statement regime and for higher-risk buildings under the Building Safety Act 2022 framework, though each of those definitions is drafted separately and should be read on its own terms.

Height measurement follows the convention used elsewhere in this area, taken to the floor surface of the top storey rather than to the parapet, so a building that looks taller than 18 metres on an elevation may not be, and vice versa. The measurement conventions are set out in counting storeys and measuring height.

In London, schemes referable to the Mayor were affected earlier through Greater London Authority guidance, so check the London position separately rather than assuming the national date governs.

Transitional arrangements and their effect

The amendment came with transitional provisions, which is where most of the commercial argument now sits.

The structure of those provisions is the familiar one for Approved Document changes: a cut-off date by which a building control application or initial notice has to be given, and a further requirement that work has begun and is sufficiently progressed within a defined period afterwards. Both elements have to be satisfied, and the second one is the trap, because a scheme that files in time and then sits unstarted loses the benefit.

Read the current published Approved Document for the dates and the test rather than relying on any summary, including this one. The dates in this area have moved more than once, and a scheme programmed against an out-of-date understanding of the transitional window is a scheme that will be redesigned at the worst possible moment.

Three practical checks are worth making now on any consented single-core scheme above 18 metres.

1. Whether a building control application or initial notice has been submitted, and on what date.
2. Whether the works have begun in the sense the transitional provision uses, which is not necessarily the same as the planning test for implementation.
3. Whether the programme will reach the required stage of progress within the period allowed.

Floorplate and core efficiency consequences

The area cost is geometric and it can be estimated early. A second protected stair with its associated lobby commonly takes somewhere in the region of 20 m² to 30 m² per floor, depending on the stair width, the lobby arrangement and whether a scissor stair or two separate enclosures are used. That range is illustrative and any particular scheme needs its own layout study.

On a 600 m² floorplate that is 3 to 5 per cent of the plate, taken from the most valuable part of it, because cores sit centrally and the area lost is often the area that would have been a room.

The knock-on effects compound. A larger core reduces the frontage available for units on each floor, which reduces the number of units, which raises the core area per unit, which reduces efficiency further. On a small plate the arithmetic can reach the point where the building no longer works with one core at all and needs either a different plan form or fewer, larger units.

Two responses are common. Accept fewer units per floor and adjust the mix upwards in size, or increase the plate by extending the footprint or the height, both of which are planning changes. There is no arrangement in which the stair is free.

Effect on unit mix and viability

The unit that disappears first is the small single-aspect flat at the end of a corridor, because that is the area the stair takes. So the mix shifts towards larger units, which changes several things the permission was based on.

Affordable housing contributions calculated on unit numbers or habitable rooms change. The mix policy compliance position changes, and a scheme consented as policy-compliant on mix may no longer be. The gross development value changes, and the cost of the additional core is added to the build cost, which is a double effect on the residual.

Where a section 106 package was agreed on a viability appraisal, expect the council to want the appraisal revisited rather than simply accepting a reduced offer. Bring the Viability Assessment forward with the revised scheme and be explicit that the driver is a change in the fire guidance rather than a change in market assumptions, because those two arguments are received very differently.

Be realistic about sequencing too. A viability review takes months, and the transitional window will not wait for it.

Redesigning a consented single core scheme

Start with the honest question: is the change a variation or a new building?

A second stair usually changes the core, the internal layout, the unit count and frequently the elevations and the massing. That is rarely a non-material amendment under section 96A, and a non-material amendment application refused on that basis wastes six weeks.

Section 73 of the Town and Country Planning Act 1990 allows conditions to be varied, including the condition listing the approved drawings, provided the result is not a fundamental change and the description of development is not altered. Where the unit numbers appear in the description of development, that constraint bites. The Levelling-up and Regeneration Act 2023 introduced a further variation power intended for changes that are not substantially different, and whether it is yet in force should be checked before relying on it.

Where the change is large, a fresh application is often faster than arguing about the boundaries of a variation power. The considerations are:

• Whether the description of development can survive the change unaltered.
• Whether daylight, overshadowing and townscape results change enough to need reassessment.
• Whether the section 106 needs a deed of variation or a new agreement.
• Whether the Health and Safety Executive has to be reconsulted, which it will be where the building remains a relevant building.
• Whether any conditions already discharged will need to be discharged again against new drawings.

Update the Fire Statement with the revised scheme rather than resubmitting the original, because the stair arrangement is one of the matters the Gateway One consultation looks at directly.

Section 73 or a fresh application

The choice turns on three tests, and it is worth setting them out before instructing anyone.

Does the description of development still describe the building? If the description says 120 flats and the revised scheme has 112, a section 73 application cannot fix that, because the description cannot be varied.

Is the change fundamental? A core rearrangement with the same footprint, height and unit count is arguably not. A taller building with a different footprint is.

What does the council prefer? Some authorities will take a section 73 application for a substantial internal reconfiguration and some will not, and a short pre-application discussion settles it faster than a legal opinion. Where the authority wants a fresh application, take that route, because a refused or invalid section 73 costs more time than the fresh application would have.

Evidencing the change to the council

Officers are receiving these applications in numbers and are generally sympathetic. What they need is a clear account of what changed and why.

Provide a comparison document: consented and proposed floor plans side by side at the same scale, with the core highlighted, a schedule of accommodation showing the change in unit numbers and mix, and elevations showing any change to the envelope. Add a short statement explaining the fire guidance driver, with the reference to the Approved Document, and confirming that the rest of the scheme is unchanged where it is.

Then deal with the consequential assessments honestly. Where the massing changes, update the daylight and overshadowing work rather than asserting the effect is neutral. Where the unit count falls, address the mix and affordable housing policies directly. And where the core arrangement affects the evacuation strategy, update the Fire Safety Strategy and say so, since the planning-stage account and the building control design need to describe the same building. The layout logic behind cores and shafts is set out in firefighting shafts and how they shape a residential core.

PlanScope drafts a Fire Statement, a Planning Statement and the supporting reports for a revised scheme from your project details, with "TO BE CONFIRMED" flags wherever a design decision is outstanding. A fire statement is one of the report types where a competent professional is legally required, and the PlanScope draft is a starting point for that professional rather than a substitute. 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. Check the current Approved Document and the position with your local planning authority or a qualified professional before relying on any date or threshold here. Browse the 66 report types to see what a revised tall residential scheme needs.