The 30 September Second Staircase Deadline: What It Means If Your Scheme Is Still in Design

Most of what has been written about the second staircase deadline describes a single test: get building regulations approval before 30 September 2026 and you are safe. That is half the rule, and the half that is easier to satisfy. The other half has a date eighteen months further out, a definition drawn tight enough to catch schemes that genuinely believe they have commenced, and no discretion in it at all.

With 27 days to go, it is worth being precise about what the deadline does, who it still catches, and which of the two dates you should actually have in your programme.

What the requirement is

Approved Document B was amended and published on 29 March 2024 to require a second staircase in new residential buildings over 18 metres in England. It was originally proposed at 30 metres in December 2022 and reduced to 18 metres following consultation — a change that, on the industry’s own estimates, held up something in the region of 38,000 homes in London alone while designers waited to find out which threshold would land.

The requirement applies to new residential buildings. Government has been explicit that existing single-staircase buildings are inherently safe where they were built and are maintained to standard, so this is not a retrofit obligation on standing stock. It is a design rule for what comes next.

Because 18 metres is also the height threshold for a higher-risk building — 18 metres or seven storeys, with two or more residential units — almost everything caught by this rule is also caught by the Gateway regime. That matters more than it first appears, and we will come back to it.

The transitional test has two limbs

To rely on the transitional arrangements and build a single-staircase scheme over 18 metres, you need both of the following. Not either.

Limb one. Building regulations approval for the single-staircase scheme must be obtained before 30 September 2026.

Limb two. Work must be sufficiently progressed within 18 months of that date — so by the end of March 2028.

Satisfy limb one and fail limb two, and the transitional relief falls away entirely. You need fresh building regulations approval, on a two-staircase design.

What “sufficiently progressed” actually means

This is where schemes get caught, because the definition is narrower than the ordinary meaning of the words.

Work is sufficiently progressed when the pouring of concrete has started, for either the permanent placement of trench, pad or raft foundations, or for the permanent placement of piling.

That is the whole test. Which means the following do not count, however much they cost you or however convincingly they look like a construction site:

• Site clearance and demolition
• Earthworks and bulk excavation
• Hoarding, welfare and site set-up
• Utility diversions
• Piling mats, temporary works and enabling works
• Archaeological investigation or remediation

It is the same commencement definition used in the Building (Higher-Risk Buildings Procedures) (England) Regulations 2023, so if you are already working to that test for Gateway purposes you have the logic in hand. If you are used to the planning definition of commencement, which a trench and a few metres of drainage will satisfy, this is a materially harder bar.

The uncomfortable arithmetic on limb one

Here is the part that is not being said clearly enough.

If your 18-metre-plus residential scheme does not already have a building control application in and progressing, limb one is closed to you.

Higher-risk buildings go to the Building Safety Regulator for building control approval, and the published data for May to July 2026 puts the median time to approve a new build or conversion Gateway 2 application at 22 weeks. The statutory target is 12. The regulator’s own target, which it is aiming to hit by March 2027, is 18 weeks for non-complex cases. None of those numbers fit inside 27 days.

So for most readers the honest position is this: either your approval is already in the bag or all but in the bag, or the transitional route is not available and you are designing to two staircases. There is no version of the next four weeks that produces an approval from a standing start.

That is not a counsel of despair. It is a reason to stop spending money testing whether a single-staircase layout can be rescued, and to redirect it into the two-staircase design you are now going to need.

Which means the live risk is limb two

If you do hold, or are about to hold, approval for a single-staircase scheme, your exposure is no longer 30 September. It is the end of March 2028, and it is a date that will not be in most programmes because it does not correspond to any contractual milestone.

Put it in. Explicitly, by name, as a hard constraint on the substructure package:

• Identify the specific building. The test is applied per building, so a phased scheme with three cores has three separate dates to satisfy, not one.
• Work backwards from end March 2028 through piling or foundation concrete, through the substructure design and its own approvals, through procurement of the piling or groundworks package, and through whatever enabling works have to happen before a rig can stand on the site.
• Then ask honestly what float is left. On a scheme with a live land assembly, an unresolved utilities diversion, or funding that is not yet drawn, eighteen months is not the comfortable runway it sounds like.
• Write the constraint into the contract. If a delay to substructure costs you the transitional relief, that is a consequence worth naming in the risk register and worth allocating in the contract, rather than discovering after the event that nobody owned it.

What it costs to miss

Retrofitting a second core into a designed scheme is not a stair. It is:

• Net-to-gross loss. A second core and its associated lobbies take saleable or lettable area out of every floor, on a scheme whose appraisal was built on the original figure.
• A re-run fire strategy. Evacuation approach, compartmentation, smoke control and firefighting provision all reopen, and the fire engineer’s advice on one floor plate rarely survives the change unaltered.
• Structural and MEP redesign. A new core changes the frame, the stability strategy, the riser layout and the plant distribution. It is rarely a local change.
• A planning question you may not like. Whether the revised scheme can proceed on a section 73 variation or needs a fresh application is a judgement about whether the change is material. A second core that alters massing, elevations or unit numbers frequently pushes it over the line — and a fresh application reopens affordable housing, contributions and viability under the August 2026 NPPF, which is not the same document your consent was granted under.

The scheme that is genuinely dangerous is the one where the appraisal was set on the single-staircase layout, the land price reflects it, and nobody has tested what the two-staircase version does to the residual. Test it now, while it is a modelling exercise rather than a crisis.

And what is coming after

The Building Safety Regulator consulted on a wider review of Approved Document B between 25 March and 1 July 2026, with a target implementation date of 2 September 2029. Nothing in it is binding yet, but two proposals are worth designing with in view if your scheme completes toward the end of the decade:

• Two staircases and two evacuation lifts in new residential buildings above 18 metres, with firefighting lifts able to double up.
• An 11-metre threshold above which Approved Document B could not be used where combustible structural elements, including timber, are present — which has significant implications for mass timber and for a good deal of modern methods of construction.

Also proposed: enhanced fire stopping at compartment wall junctions, new provisions for roof-mounted PV, and increased fire resistance for open-sided multi-storey car parks. If you are working on anything with a 2029 or later completion, these are the assumptions to be testing against, not today’s guidance.

What to do this month

1. Establish which limb you are relying on. If you do not have building regulations approval in hand or imminent, you are on a two-staircase design. Confirm it in writing and stop paying for the alternative.
2. If you do have approval, diarise end March 2028 per building and drive it back through the substructure programme.
3. Check that “commencement” means the same thing to everyone on the project. The planning definition, the contract definition and this one are not the same, and the gap between them is where the relief gets lost.
4. Re-run the appraisal on the two-staircase layout if you have not already, so that the number is known before it is urgent.
5. Record the decision and its basis. Which limb, which building, which date, who owns the milestone. This is precisely the kind of design decision the Building Safety Regulator will expect to see evidenced, and precisely the kind that is reconstructed badly two years later if it was never written down.

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The deadline itself is straightforward. What causes the damage is a project team that satisfied limb one, told itself the risk was closed, and then let eighteen months go by without anyone owning the foundations milestone.

If you are carrying an 18-metre-plus scheme and you are not certain which limb you are on — or you have approval and no clear line of sight to concrete before March 2028 — that is a programme and design management problem before it is a legal one. Get in touch and we will work through where your scheme actually sits.

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Related reading

• RIBA Stages Explained — A Guide for SME Clients
• Design Freeze: What It Is, When to Call It, and What Happens When You Don't
• Gateway 2 Is Delaying Your Project — Who Bears the Risk, and How to Protect Your Programme