Second staircases in new blocks of flats: what the 18 metre rule means now it applies
Since 30 September 2026, new blocks of flats with a storey 18 metres or more above ground should have more than one common stair. What changed, which schemes the transitional rules protect, and what it means for existing single-stair buildings.
Since 30 September 2026, Approved Document B expects new blocks of flats with a storey 18 metres or more above ground level to be served by more than one common stair. The government published the change in March 2024 with a two and a half year lead-in, and it applies in England.
What has changed
The amended guidance sets a new height threshold for a second staircase in blocks of flats. The same update restructures the means of escape section of Approved Document B to separate horizontal and vertical escape, and introduces evacuation shafts to support evacuation lifts, with new terms including evacuation lift lobby, interlocked stair and storey exit.
Which schemes the transitional rules protect
The previous edition of Approved Document B still applies where a building notice, an initial notice or a full plans application reached building control before 30 September 2026, and the work either was sufficiently progressed before that day or is sufficiently progressed within 18 months of it.
For a new building, work counts as sufficiently progressed once concrete is being poured for the permanent trench, pad or raft foundations, or permanent piling has started. Planning permission alone does not count. Writing in PBC Today, Dan Quinn, director of fire at Frankham Risk Management Services, puts it plainly: a consented scheme without a building control application in by 30 September is designed to the new guidance.
Three questions for schemes near 18 metres
Quinn suggests three checks for any residential scheme close to the threshold.
Where does the scheme stand against the transitional test? The trigger is the building control submission and progress on site.
Can it realistically be sufficiently progressed within 18 months? If funding, procurement or approvals could push the foundations beyond that window, plan for the second stair now rather than redesigning later.
What does a second stair do to the rest of the design? The core layout, net to gross, smoke control, firefighting access and the fire strategy all move with it.
In Quinn’s reading, the change is not retrospective. An existing single-stair block built to the relevant standards, and well maintained and properly managed, is not made unsafe by it, and 30 September created no new legal duty for its owners. Residents, boards, lenders and insurers may still ask questions. His answer is a suitable and sufficient fire risk assessment that reflects the building as it really is: the evacuation strategy, the condition of compartmentation and fire doors, smoke control, and how the fire and rescue service would fight a fire there.
What comes next
Remaining references to BS 476 for fire resistance are due to be removed from Approved Document B on 2 September 2029, and a wider review of the guidance continues.
Practical takeaways
Check every residential scheme near 18 metres against the transitional test now, using the building control submission date and the likely start of the foundations.
If a scheme may miss the 18 month window, design in the second stair now.
For existing single-stair blocks, make sure the fire risk assessment can answer clearly, with evidence, whether the building is safe.
