Cart is emptyBS 9991:2024 is a published amendment to BS 9991:2021 that updates the code of practice for fire safety in the design, management and use of residential buildings. Key changes include revised guidance on smoke ventilation system design, updated requirements for higher-risk buildings under the Building Safety Act 2022, and amended provisions for single-stair buildings.
Background: What Is BS 9991?
BS 9991 is the British Standard code of practice for fire safety in residential buildings. It covers new-build and existing buildings of all heights and provides detailed design guidance that goes beyond the minimum performance-based requirements of Approved Document B (ADB). Fire engineers, building control bodies, and the Building Safety Regulator use BS 9991 as a key reference document.
The standard was substantially revised in 2021 to reflect post-Grenfell lessons. The 2024 amendment builds on that revision.
What Changed in the 2024 Amendment
1. Single-Stair Buildings
The 2024 amendment includes revised guidance on smoke ventilation in single-stair buildings — a major concern following investigations into evacuation failures. The updated standard provides clearer design criteria for the interaction between the stairwell, lobbies, and AOV systems in buildings served by a single means of escape.
2. Higher-Risk Buildings
Buildings over 18 m in height are now subject to more prescriptive requirements reflecting the Building Safety Act 2022 regime. The 2024 amendment aligns BS 9991 more closely with the Regulator’s requirements, covering the competence of those designing and installing AOV systems and the documentation required as part of the Golden Thread.
3. AOV System Design Criteria
The amendment updates the section on smoke ventilation design to include refined guidance on vent sizing, the calculation of free area relative to corridor and lobby geometry, and the treatment of wind pressure on natural AOV installations. Buildings in exposed locations may need larger vents or mechanical extract to compensate for wind-driven smoke re-entry.
4. Testing and Commissioning
BS 9991:2024 strengthens requirements for system testing on completion and at regular intervals thereafter. AOV systems must be tested to confirm that all vents open fully, that the control panel triggers correctly on smoke detection, that battery backup operates as specified, and that fire service override switches function correctly.
5. Interaction With Sprinkler Systems
Where a building has sprinkler protection, the 2024 amendment provides updated guidance on how this affects the smoke ventilation strategy. Sprinklers can reduce smoke production, which may allow modified AOV designs in some configurations — but the standard is clear that this requires case-by-case fire engineering assessment.
How BS 9991:2024 Relates to Approved Document B
Approved Document B sets the minimum statutory requirements. BS 9991 is a non-statutory standard that provides detailed guidance on how to meet and exceed those requirements. Building control bodies and the Building Safety Regulator will generally accept a design that follows BS 9991 as demonstrating compliance with ADB — but the two documents must be read together, not as alternatives.
Where BS 9991:2024 is more demanding than ADB (for example on single-stair buildings or higher-risk buildings), the standard’s approach is increasingly expected by building control bodies and fire engineers.
Implications for AOV System Specification
The 2024 amendment reinforces that AOV systems must be specified, installed, and maintained by competent persons. Key implications for specifiers include:
- Vent free areas must be calculated to the updated methodology, not simply selected from tables
- Battery backup must meet BS EN 12101-10 and provide sufficient capacity for the specified hold-open duration
- Control panels must be capable of interfacing with the building’s fire detection and alarm system
- Commissioning records and operation and maintenance manuals form part of the Golden Thread for higher-risk buildings
AOV Direct supplies products — including smoke control panels and battery backup units — that are compatible with BS EN 12101-compliant system designs. All products are supplied with full technical documentation.
Frequently Asked Questions
Is BS 9991:2024 mandatory?
BS 9991 is not directly mandatory under statute, but it is the primary reference standard used by fire engineers and building control bodies. Departure from its guidance requires justification. For higher-risk buildings, the Building Safety Regulator expects designers to follow it.
Does the 2024 amendment apply to existing buildings?
The standard applies primarily to new-build design. For existing buildings undergoing material alteration or where a fire risk assessment identifies deficiencies, the updated guidance will inform remediation design. The Responsible Person should take advice from a competent fire engineer.
Where can I get a copy of BS 9991:2024?
BS 9991:2024 is available from the British Standards Institution (BSI). It can be purchased at shop.bsigroup.com. The 2024 document is an amendment to BS 9991:2021 and should be read in conjunction with it.