BS 9991 June 2025 amendments - corrigendum A1

Last year in November, the final version of BS 9991:2024 Fire Safety in the Design, Management and Use of Residential Building – Code of Practice was published after three years of anticipation. We shared a summary and reflection breaking down the changes made since the 2021 version and now.

As of 26 June, BS 9991 has now been updated with corrigendum A1. This has resulted in some minor amendments to the text in the standard, a few of which do have significant implications on how residential buildings are designed. Below are laid out the most important changes throughout the document and how they will make a difference to your projects.

New clarity on the design of escape staircases and doorways  

Staircases

References to the use of BS 5395-1 have now been removed from the document, meaning that it will be permissible to design common staircases using Approved Document K in England, and similar local design requirements in Wales, Scotland and Northern Ireland.  

This will also mean that common staircases are permitted to use winder steps, where they are not fire-fighting staircases.  

BS 9991 does require that stair width should still be measured as per BS 5395-1, ie between handrails as opposed to the full tread width, meaning that where a staircase is a fire-fighting stair, it should achieve 1,100mm between handrails rather than simply the full tread width. Designers should bear this in mind when designing buildings over 18m in height.  

The standard provides a method of calculating the capacity of a staircase for escape when designing a building for simultaneous evacuation. This allows a greater degree of confidence in the design of staircases when using simultaneous evacuation by providing a clear method for calculating capacity that can be referred back to.    

Doorways

Clarified wording is provided regarding the sizing of final exits which removes ambiguity present in the previous version. BS 9991 now clarifies that if an exit is only serving as the exit from a communal space, it should be sized based on 4.1mm / person, but that if the exit is serving from both an escape staircase and a communal space then the final exit width will need to be further increased to account for merging flows.  

Clarified common escape routes at ground floor level  

New wording has been added to Section 11.2.3 explaining the requirement for imperforate construction between the escape routes at final exit level. This applies to the exit passageways leading from adjacent lobbies of two or more stairs / evacuation lifts.  

The implication of this change is that the restriction on having doors between the final exit routes at ground floor level now applies to the passageway from the lobby, and no longer strictly prohibits a door or similar connection between the two lobbies. However, the routes from the lobby to a final exit should still remain fully segregated and, where practicable, Cundall recommends these should be arranged to escape in alternative directions.  

Additionally, when the staircase lobbies are not adjoining and are in separate locations at ground floor level, there is no restriction on doors between the lobbies and exit passageways.  

It is also clarified that where a building has multiple evacuation lifts present, these should terminate in separate enclosures at ground floor level (ie not a shared lobby) – with the exception of evacuation lifts which are provided to give additional capacity rather than as a required second means of escape.  

Clarifications on smoke control and escape within common escape corridors  

In buildings using multi-stair escape design, where there is a dead-end section of corridor which is provided with a smoke control system to protect the staircase, the travel distance within this section of corridor to the staircase lobby is limited to 7.5 m. This cannot be increased unless the staircase is provided with a protected lobby and smoke control systems are provided to both the lobby and corridor.  

Where extending the travel distance within a common corridor by the provision of sprinkler protection and smoke ventilation in the corridor, the new BS 9991 clarifies that the smoke control should be in accordance with Annex F, F.3.2.2. This annex describes the use of a two-shaft system, typically with two mechanical shafts running in a push/pull arrangement which is designed to rapidly return the corridor to tenable conditions. Therefore, a standard extract-only smoke ventilation system is no longer suitable to permit extended corridors.  

Note that these above two requirements only apply to multi-staircase design.  When using single-stair design in buildings less than 18m in height, it is still acceptable to have a 15m single-direction travel distance in a corridor that provides direct access to the staircase.

Additionally, when designing mechanical smoke ventilation systems (MSVS’s) in buildings >60m in height, the system design should consider the effect of seasonal climactic effects on the building as outlined in BS EN 12101-13.  

Rooms and spaces requiring fire-resisting construction  

The document specifies that requirements for fire resisting enclosures for electric wheelchair / mobility scooter charging stations only apply to common areas and are not strictly required within individual apartments.  

Utility cupboards are also only required to be 30-minute fire resisting enclosures where they open onto the internal protected hallway of an apartment.  

Where there is an external wall within 1.8 m of a required escape route, this wall must now provide at least 30 minutes fire resistance for both integrity and insulation, where previously it only required integrity.  

Guidance on fire service access  

The previous recommendation that protection from falling debris should be provided has been amended to a note that recommends designers consider the risk of falling debris when selecting the positions of access roads, fire main inlets and fire service entry points. This will allow designers to take a more holistic view of the external fire service access provisions and envelope of the building and choose measures that are appropriate to the design of the building.  

The guidance and diagrams showing the dimensions and clearances of roads for high-reach fire appliances have been removed, which acknowledges the variation in vehicle fleets across different local fire services. Designers must still ensure that overhead obstruction to high-reach appliances should be avoided. This highlights the importance of engagement with local fire services to seek their guidance on the access provisions needed.  

Other quick-fire changes

In addition to the points discussed, there are also a number of smaller additional changes that, while minor on their own, should also be taken into consideration:

• Open-plan flats are considered unsuitable for use where occupants require assistance to escape.
• The construction of balcony floors should be designed as compartment floors.  
• All emergency luminaires now need to be fitted with an automatic test system to BS EN 60234.
• Use of products classified under BS EN 13501-1: 2007 is no longer allowed and all products must be classified to the latest edition of BS EN 13501-1.  
• Low-mounted guidance systems, required in buildings >50m in height, do not need to be electrically powered – and the use of photoluminescent systems would also be acceptable.
• Smoke shafts serving basement levels are clarified to be allowed to discharge at ground floor level or any level above ground as well.  
• Controls within the lift car for an evacuation lift may now be 400 mm from the nearest adjacent wall in the car, down from 600 mm.  

This updated standard has brought some welcome clarifications to areas of ambiguity stemming from BS 9991: 2024’s initial release, which will allow for improved and rational fire safety design in buildings. That said, there is a near endless variety in building scenarios and there are still many situations where BS 9991 either does not provide specific guidance or does not provide guidance that is appropriate for the situation at hand. 

As such it is always important to ensure your building’s fire strategy is developed by a competent fire engineer who has the skills and knowledge to apply such standards, and to develop appropriate engineering solutions where the standards do not provide relevant advice. One example is timber structures over 11m in height, which BS 9991 still excludes from its scope, and which require a specialist engineering strategy.

If you would like to discuss any queries or engineering needs relating to fire strategy, please feel get in touch with Cundall engineers who will be happy to help.