In short
- Second staircases are required in new residential buildings over 18m under Approved Document B.
- The transition ended on 30 September 2026 for schemes without a qualifying application.
- Schemes with an application in before then must be sufficiently progressed – for new builds, foundations or piling started – within the deadlines.
- The rule isn't retrospective, but it affects the value and perception of single-stair buildings.
The rule
On 29 March 2024, the government updated Approved Document B to require second staircases in new residential buildings over 18 metres in England. A transitional period was confirmed, and the requirement took full effect on 30 September 2026.
Who is caught
Any new residential building over 18m that doesn't benefit from the transitional arrangements must be designed with a second staircase. For higher-risk buildings, that design is assessed by the Building Safety Regulator at Gateway 2 – see Gateway 2 rejections.
Transitional arrangements
A building is exempt from the new requirement if, before 30 September 2026, a building notice, initial notice or full plans building control application was submitted, and the work either:
- had started and was sufficiently progressed before 30 September 2026, or
- starts and is sufficiently progressed within 18 months after that date.
What "sufficiently progressed" means
- New build: concrete has begun to be poured for the permanent foundations, or permanent piling has started
- Work to an existing building: that work has started
- Change of use: work to effect the change has started
A scheme with no qualifying application in before the deadline doesn't benefit from the transition. A scheme with one must get on site and reach "sufficiently progressed" within the window.
What it means for developers
- Redesign risk. Adding a second core can change unit numbers, mix and layouts, and is unlikely to be a non-material amendment – a section 73 variation is often needed, with fresh consultation and, in London, referral to the Mayor.
- Viability. A second stair reduces saleable area.
- Planning. In London, the Mayor and many boroughs were already expecting second staircases in tall residential schemes before the national rule took effect.
- Fire statements. The stair decision is made at planning, so the Planning Gateway One fire statement and the fire strategy need to agree from the start.
What about existing single-stair buildings?
The requirement isn't retrospective. Existing single-stair residential buildings aren't required to add a second staircase. But commentators note that dated single-core buildings may face questions from buyers, lenders and insurers, so it's worth having a clear, current fire strategy that explains how the building's fire safety measures work together – see retrospective fire strategies.
Getting the design right under the second staircase rules
- Fix the stair strategy at RIBA Stage 2, before planning
- Check the height properly – it's measured to the top storey, not the roof
- Coordinate the fire strategy, fire statement and drawings, so the regulator sees one consistent design
- Look at the whole package – evacuation alert systems, firefighting provisions and external walls – not just the stair count
What a second staircase changes in the fire strategy
A second stair isn't just an extra core. It affects the evacuation strategy, the firefighting approach, travel distances, smoke control and how the common corridors are protected. The fire strategy should explain how the two stairs work together – for example whether both are firefighting stairs, how they're separated, and how residents and firefighters use them.
Questions for your design team
- Have we measured the height correctly, to the top storey's floor surface?
- Does our scheme benefit from the transitional arrangements, and what's the deadline to be sufficiently progressed?
- If we're redesigning, does the change need a section 73 variation?
- Are the fire statement, the fire strategy and the drawings consistent?
- Have we considered evacuation alert systems, firefighting provisions and external walls at the same time?
Our fire strategy reports and Gateway One fire statements are prepared by fire engineers working alongside your design team.
How we can help
We match each project to a qualified specialist and confirm the scope, the named professional and a fixed fee before you commit.
Sources
- Forsters – Second staircases mandatory in residential buildings over 18m from 30 September 2026
- GOV.UK – Circular 04/2024: stairs
This guide is general information based on the law and guidance in England as at 8 November 2026. It isn't legal advice – for advice on a specific building, get in touch.