What the 30 September 2026 Approved Document B change actually requires, and why it doesn't end at construction

There is a date most people in building safety and compliance have had circled for a while now: 30 September 2026. From that point, new residential blocks in England over 18 metres need two staircases, not one. It has been talked about for long enough that it risks sounding like old news by the time it actually lands. It is not old news. It is the point where a policy that has existed on paper since 2024 becomes something building control will actually enforce, and where the gap between "planning for it" and "living with it" closes.

At a glance

• Takes effect: 30 September 2026
• Applies to: new residential blocks of flats in England where the top storey is 18 metres or more above ground level
• Does not apply to: existing occupied buildings, or schemes with foundations already poured or piling already started before the deadline (up to 18 months' grace)
• Also changes: minimum clear width for common stairs (1,100mm), and new guidance on protected lobbies and evacuation lift shafts

The 18m threshold matches the Building Safety Act's definition of a higher-risk building, which is not a coincidence.

Why 18 metres, and why this is a construction rule, not a retrofit one

It is worth being precise about scope, because it is easy to read "second staircase rule" and assume it applies to every tall block already standing. It does not. This is a change to Approved Document B, the fire safety guidance that sits under the Building Regulations, and it governs new building control applications and new construction. A block built in 2015 does not gain a staircase overnight. What changes is what gets built from here.

The 18 metre threshold is not arbitrary. It is the same height used to define a higher-risk building under the Building Safety Act, the same threshold that already triggers duties around the Golden Thread of information, the accountable person, and the safety case regime. The government could have kept the original 30 metre proposal. Settling on 18 metres instead lines fire safety guidance up with the regime that already treats these buildings differently for everything else.

What this means once the building is occupied

The construction industry will feel this first, and there is a real cost to it. A second staircase core eats into net-to-gross floor area, which affects unit numbers and viability on schemes already at an advanced design stage. Some projects will need a section 73 amendment or a fresh planning application. The transitional protection is narrower than it sounds too: "sufficiently progressed" means foundations poured or piling started before 30 September, not a submitted application or an agreed design.

But the part that matters to the people running these buildings long after the contractors have left is what happens to the information. A second staircase, the protected lobbies around it, the evacuation strategy it supports, all of that is exactly the kind of safety-critical decision the Golden Thread exists to capture and never let go missing. For a higher-risk building, that record has to travel from design through construction and into occupation, available to the accountable person and the Building Safety Regulator on request.

This is where I'd gently push back on treating 30 September as a construction industry date and nothing more. Every one of these new blocks becomes, from handover, a building where FM and compliance teams inherit a live obligation to keep that safety information current and evidenced. The staircase gets built once. The record about it has to be maintained for as long as the building stands.

The genuine upside, and the honest limit of this change

The case for the rule itself is straightforward. One staircase is a single point of failure. Bringing England in line with how most of the world already builds tall residential blocks, before rather than after the next serious incident, is the right call.

The honest limit is that it only touches what gets built next. The existing stock of tall residential buildings with a single staircase stays exactly as it is. Those buildings remain higher-risk buildings under the Building Safety Act regardless, still carrying full Golden Thread and safety case duties, just without a second means of escape to show for it. That is a much harder, slower and more expensive conversation, and 30 September 2026 does not touch it.

For anyone managing higher-risk buildings, new or existing, the practical takeaway is the same either way. The design decisions get made once, but the evidence that they were made, why, and what changed afterwards has to survive for decades, across contractors, ownership changes and staff turnover. Whether that lives in a system built for it or in a collection of PDFs nobody can find quickly says a lot about how a building would hold up if the Building Safety Regulator ever came asking.