Second staircases above 18 metres: the current expectation

A second staircase is now expected in new residential buildings above 18 metres in England, and the number to design to is 18 rather than the 30 metres that was originally consulted on. The expectation sits in Approved Document B, which is building regulations guidance rather than planning policy, so no planning officer will refuse an application for having one stair. The problem arrives later, at Gateway Two, when a consented scheme turns out not to work with a second core. Design for it at planning stage or redesign it afterwards.

Where the expectation comes from

The sequence was a consultation proposing a 30 metre threshold, a written ministerial statement in July 2023 confirming that the threshold would instead be 18 metres, and then an amendment to Approved Document B published in March 2024 setting out the guidance and its transitional arrangements.

Approved Document B is statutory guidance supporting Part B of the Building Regulations 2010. Compliance with the Regulations is the legal requirement, and following the Approved Document is the accepted route to demonstrating it. A fire engineered alternative remains possible in principle, and on a residential building above 18 metres it is a difficult argument to run and an expensive one to lose.

The wider legal frame is the Building Safety Act 2022, which defines higher-risk buildings and creates the three gateways. The staircase guidance and the higher-risk building definition both use 18 metres, which is not a coincidence, and they are separate instruments with separate wording.

How the height is measured

Get this right before anything else, because a scheme designed to sit just under the threshold usually turns out to be over it.

For higher-risk building purposes, height is measured from ground level to the floor surface of the top storey, and a storey consisting only of roof-top plant or machinery is left out of the count. So it is not the height to the parapet, not the height to the top of the lift overrun, and not the height to the roof of the uppermost flat.

Ground level itself needs care on a sloping site, and the regulations and the Approved Document each set out how to treat it. Where a building sits on a slope steep enough that the answer changes depending on which elevation you measure from, take advice early and record the assumption on the drawings. That single dimension drives the fire statement, the staircase provision, the firefighting shaft design and whether the Building Safety Regulator is a statutory consultee at planning stage.

Confirm the definitions in the current published documents rather than working from a summary, because the staircase guidance and the higher-risk building regulations do not use identical wording.

The transitional arrangements, and what they protect

The March 2024 amendment came with a transitional period rather than immediate effect, and that period has a defined end date after which the guidance applies in full.

Transitional provisions in Approved Documents usually turn on two things: the date a building control application or initial notice was given, and whether work on the building has sufficiently progressed within a further defined period. Both limbs matter. A building control application lodged in time does not preserve the old position indefinitely if the site then sits still.

Two practical consequences for an architect. A planning permission granted before the transition ends confers nothing at all in building control terms, because the two regimes are separate. And a scheme with an old building control application, a long lead-in and a funding delay is the classic case where the transitional protection lapses and a single-stair design has to be reworked.

Read the published transitional wording for your specific project rather than relying on the headline date.

What a second core does to the floorplate

This is the part that lands on the architect, and it is rarely just a stair.

On a tight urban site the honest answer is sometimes that the building goes below 18 metres instead. That is a legitimate design response, and it is a much better conversation to have at concept stage than after a planning committee.

Where the massing does change, the neighbour effects change with it, and a revised Daylight and Sunlight Assessment will be needed rather than an annotation to the old one.

Planning Gateway One runs alongside

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, acting as the Building Safety Regulator, is a statutory consultee. That is Gateway One, and it happens at planning stage rather than at building control.

The fire statement is a planning stage document about how fire safety has influenced the design: site layout, access for fire appliances, water supplies, the location of cores, and the evacuation strategy in principle. It is not the detailed fire strategy. A Fire Statement for a relevant building must be prepared by someone with the necessary fire engineering competence, because the Building Safety Act framework and article 9A require it, and an AI-assisted draft is a starting point for that professional rather than a substitute. The same is true of a Fire Safety Strategy to BS 9991 or BS 9999, which belongs to Gateway Two.

How the three gateways interact, and what each one asks for, is set out in more detail under Building Safety Regulator gateways for planning teams.

What to submit with the planning application

For a residential building above 18 metres, the pack should include:

1. A fire statement on the published form, completed by a competent author
2. Floor plans showing both cores, the lobbies and the stair enclosures, at a scale the consultee can read
3. A site plan showing fire appliance access, hardstanding, turning and hydrant positions
4. A section showing the height to the floor surface of the top storey, with the measurement annotated and ground level defined
5. A short design statement on the evacuation strategy in principle, including any evacuation lift provision
6. Consistency between the fire statement and every other document, particularly the design and access statement

Point six sounds trivial and is where consultee comments most often come from. A fire statement describing two stairs alongside plans showing one, or a section that does not agree with the stated height, produces a request for further information that costs weeks.

Checking the current published guidance

Approved Document B has been amended repeatedly, and the second staircase guidance has moved from a consultation position to a ministerial statement to published guidance with transitional arrangements. Treat any summary, including this one, as a pointer to the published document rather than a substitute for it.

Check three things on the government publications page for the Approved Document before you fix a design: the current threshold, the transitional wording and its dates, and the accompanying provisions on evacuation lifts and smoke control. Then check whether the London Plan or a local policy adds anything, because fire safety requirements for tall buildings in London have their own layer. Reform news is tracked on the planning law timeline.

This is general guidance, not legal advice. Building regulations and fire safety requirements change, so verify the current position in the published Approved Document and with a competent fire engineer before relying on anything here. 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.