Approved Document B: The Second Staircase Rule Is Now in Force (From 30 September 2026)

Most of the fire safety changes we've covered this year — BS 8214:2026, the Building Safety Regulator's move out of the HSE — have been about standards and oversight rather than the underlying Building Regulations themselves. That changed on 30 September 2026, when the amended Approved Document B (ADB) came into force, with direct implications for how new residential blocks are designed.

What it is

Approved Document B sets out how to comply with Part B (Fire Safety) of the Building Regulations. The amendments were published in 2024 with a transition period that ended on 30 September 2026. The headline change is a requirement for more than one common staircase in new residential buildings with a storey 18 metres or more in height. Separately, the Building Safety Regulator is running a wider review of ADB, so further changes are likely over the next year or two.

What's changing

The headline change: new blocks of flats with a storey 18 metres or more in height must now provide more than one common staircase, rather than relying on a single stair as the primary means of escape. Alongside this, the amendments also cover:

• Escape routes — the guidance on means of escape from flats has been restructured to separate horizontal and vertical escape, with new terms such as “storey exit” and “interlocked stair”.
• Evacuation lifts — new design provisions where evacuation lifts are provided (they aren't mandated), including protecting evacuation lift shafts to the same standard as the stair.
• Fire doors — guidance that dovetails with the BS 8214:2026 code of practice we covered last month, reinforcing the shift toward evidence-based, whole-door-set verification.

Transitional arrangements

Not every project is caught straight away. The previous version of ADB still applies where a building control application was made before 30 September 2026 and the work is “sufficiently progressed” within 18 months of that date — by 30 March 2028. Single-staircase schemes that miss that window will need fresh approval with a two-staircase design.

Does this apply to you?

This is squarely about residential buildings — if you don't own, manage or advise on blocks of flats, this one isn't for you. If you do, the 18m threshold is the number to check first: it's the same height trigger used elsewhere in building safety regulation (including the Building Safety Act's "higher-risk building" definition), so if you're already tracking that threshold for other purposes, this sits alongside it rather than introducing a new one to learn.

New-build and major refurbishment schemes are directly affected, since staircase and evacuation route provision is largely a design-stage decision. Building Regulations don't apply retrospectively to existing buildings, but if you manage a single-staircase block over 18m it's good practice to make sure your fire risk assessment and evacuation strategy reflect current guidance.

What to do now

1. Check whether any of your buildings meet the 18m threshold — if you're already tracking this for Building Safety Act purposes, cross-reference the same list.
2. Review current staircase and evacuation route provision against the updated guidance, particularly for buildings with a single common staircase.
3. Flag any live design or refurbishment projects to your architect or fire engineer and confirm whether they fall within the transitional arrangements — and if so, what has to happen by 30 March 2028.
4. Fold the review into your existing fire risk assessment and Golden Thread documentation, rather than treating it as a standalone exercise.
5. Check your fire door specifications against BS 8214:2026 at the same time — the two updates are closely linked.

If you'd like help working out whether any of your buildings fall within the 18m threshold, or want a second opinion on how the updated guidance affects a live project, get in touch for a free 30-minute consultation.

This article is general guidance, not legal advice. For a definitive view on how the updated Approved Document B applies to a specific building or project, consult the official guidance or a suitably qualified fire engineer.