From 30 September 2026, changes to Approved Document B (ADB) take effect in England, introducing guidance for more than one common staircase in new blocks of flats with a top storey of 18 metres or more.
For developers and contractors, the implications extend beyond finding space for another staircase. The changes affect core layouts, escape routes, design coordination and project programmes.
They also require careful interpretation when assessing existing buildings. The amendments do not introduce a blanket retrospective requirement to add a second staircase to every existing single-stair residential building at or above 18 metres.
Here’s what has changed, why it matters and what project teams should consider.
What has changed?
More than one common staircase at 18 metres or more
The updated guidance states that flats should be served by more than one common stair where the building has a top storey of 18 metres or more, measured in accordance with ADB.
That includes buildings at exactly 18 metres – the threshold is not limited to those exceeding it.
The guidance also makes clear that interlocked stairs count as a single escape route and do not provide an alternative means of escape. Simply placing two flights within an interlocked arrangement will therefore not satisfy this provision.
ADB provides statutory guidance on meeting the Building Regulations. The legal obligation is to satisfy the relevant regulatory requirements; following the approved document is an established way of demonstrating compliance.
Updated provisions for evacuation lifts
The amendments introduce design provisions supporting evacuation lifts, including the relationship between the lift, protected staircase, refuge area and evacuation lift lobby.
Where provided, an evacuation lift should sit within an evacuation shaft. Its lobby should provide a refuge area, connect directly to a protected stairway and have no direct access from flats, maisonettes, storage rooms or electrical equipment rooms.
These amendments do not, by themselves, introduce a universal requirement for evacuation lifts in every block at or above 18 metres. Their provision must be considered against the project’s applicable requirements and fire strategy.
Revised escape route layouts
The guidance updates provisions for horizontal and vertical escape, including corridor arrangements, access to alternative stairs and protection against smoke affecting multiple escape routes.
The practical message is clear: an additional staircase must form part of a coordinated escape strategy. Its location, protection and accessibility matter as much as its presence on a drawing.
Why does a second staircase matter?
A second staircase adds resilience by providing an alternative escape route if one becomes unavailable. It can also increase evacuation capacity, reduce congestion and support access for firefighting and rescue.
The government has described the change as an evolution of safety standards for future construction, building on the wider measures already introduced for residential buildings.
What does this mean for developers?
For developers, the priority is to establish the correct design basis before layouts and commercial assumptions become fixed.
An additional staircase can affect the building footprint, usable floor area, apartment layouts and development viability. Addressing those implications early gives the design team more opportunity to coordinate a workable solution.
Project teams should review:
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- Whether the building reaches the 18-metre top-storey threshold.
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- Which edition of ADB applies and whether transitional arrangements are available.
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- How the staircase arrangement affects layouts, circulation and usable space.
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- How escape routes, smoke control and firefighting access work together.
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- Whether evacuation lifts are needed under the wider project requirements.
Early fire engineering input can help identify conflicts before they become redesign, additional cost or programme pressure.
What does this mean for contractors?
For contractors, the key issue is translating the fire strategy into a coordinated, buildable package.
Tender information should clearly identify the intended staircase and lobby arrangements, fire resisting construction, doorsets, smoke control interfaces and any evacuation lift provisions.
These elements should be reviewed together. A change to a lobby, corridor or service location can affect the assumptions underpinning the escape strategy.
For higher-risk building projects, resolving these interfaces before the Gateway Two submission can help reduce the risk of inconsistencies between the fire strategy, drawings and specifications.
Do the changes apply to projects already underway?
The amendments take effect on 30 September 2026, but qualifying projects can continue under the previous guidance.
The transitional arrangements apply where the relevant building notice or initial notice was given, or a building control approval application with full plans was made, before 30 September 2026, and the work is sufficiently progressed either before that date or within the following 18 months.
For new construction, sufficient progress means the start of pouring concrete for permanent trench, pad or raft foundations, or the start of permanent piling placement.
Planning permission alone does not establish eligibility. Project teams should check the relevant building control submission and construction milestones before relying on the transition.
Does every existing single-stair building now need a second staircase?
No. These changes do not suddenly create a retrospective requirement to install a second staircase in every existing single-stair residential building over 18 metres.
That distinction is particularly important for anyone carrying out fire risk assessments on existing buildings.
The fact that current design guidance would produce a different building today does not automatically mean an existing building is unsafe. The government has expressly recognised that single-stair buildings are not inherently unsafe where they have been built to the relevant standards, maintained appropriately and properly managed.
An existing building must still be assessed on its actual circumstances. That includes its construction, compartmentation, fire doors, smoke control, escape arrangements, residents’ needs and management procedures.
The assessment should identify the risks present and the measures needed to address them. A difference from current new-build guidance should inform professional judgement rather than automatically trigger a conclusion that a second staircase must be retrofitted.
Equally, the absence of a blanket retrospective requirement does not remove existing fire safety duties or mean that every single-stair building is safe. Proposed alterations, extensions or changes of use may also bring Building Regulations considerations into play.
Make the right decisions before the design becomes fixed
For developers and contractors, the September 2026 amendments reinforce the value of considering fire safety at the earliest design stages.
Establishing the applicable guidance, coordinating escape arrangements and resolving interfaces early can help protect both the fire strategy and the project programme.
FDS Consult UK helps project teams understand what changing guidance means for their development and turn those requirements into a coordinated fire strategy.
Contact our team to discuss the implications for your new development or existing building.