Which fire safety standard applies to my building?
Choosing the design route is the first real decision on a fire strategy, and it is the one that most often gets made by accident. Approved Document B is guidance, not law; the law is the functional requirements B1 to B5. BS 9991 and BS 9999 are alternative ways of showing you meet them, and BS 7974 is the framework for a fully fire-engineered solution.
Answer the questions below and this tool returns the route it points to, what that route commits you to, and where the traps are. You can always mix, but you cannot cherry-pick: you cannot take a relaxation from BS 9999 while keeping an Approved Document B baseline everywhere else without justifying the whole picture.
BS 9991:2024
State this route explicitly on the front sheet of the fire strategy, with the edition and date of every document you are relying on. Reviewers should never have to guess what you designed to.
Working
| Step | Value |
|---|---|
| UseResidential | Volume 1 / BS 9991 family |
| Building Safety Act21 m against 18 mBSA 2022 s.65 | Likely higher-risk building |
What this means
- This building is likely to be a higher-risk building, so Gateways 1, 2 and 3 apply. The design route you pick has to be stated in the Gateway 2 application and held to through change control. Confirm it properly first: the full test is 18 m or 7 storeys and at least two residential units, and this tool asks only for height.
Sources
- The Building Regulations 2010, Schedule 1, Requirements B1–B5The functional requirements the design must actually meet.
- Approved Document B (fire safety), Volumes 1 and 2Statutory guidance. Volume 1 covers dwellings; Volume 2 covers buildings other than dwellings.
- BS 9991:2024Fire safety in the design, management and use of residential buildings. Published November 2024, corrigendum A1 June 2025.
- BS 9999:2017Fire safety in the design, management and use of buildings. Risk-profile based, for buildings other than dwellings.
- BS 7974:2019Application of fire safety engineering principles to the design of buildings.
- PAS 9980:2022Fire risk appraisal of external wall construction and cladding of existing blocks of flats.
This is an engineering aid, not engineering advice. The result above is produced from the inputs you gave and the guidance cited. It does not account for everything a competent fire engineer would consider on a real building, and it is not a substitute for reading the current published standard. Check every number before it goes into a design.
Questions people ask
What is the difference between BS 9991 and BS 9999?
BS 9991 covers residential buildings: blocks of flats, student accommodation, sheltered housing. BS 9999 covers buildings other than dwellings and is structured around risk profiles that combine occupancy characteristic and fire growth rate. They are not interchangeable: pick the one that matches the use, and for a mixed-use building expect to use both, with a clear line between them.
Can I use BS 9999 instead of Approved Document B?
Yes. Approved Document B is guidance on how to meet requirements B1 to B5, not the only way. BS 9999 is an accepted alternative for buildings other than dwellings. What you cannot do is take a single relaxation from BS 9999 into an otherwise Approved Document B design without justifying the whole package: the standards are internally consistent, and their provisions are not portable.
When do you need a fire engineered approach under BS 7974?
When the building cannot be described by the prescriptive routes: large atria, deep basements, complex phased evacuation, buildings where smoke control has to be demonstrated by modelling, or where the client wants an outcome the tables will not give. BS 7974 sets the framework: a qualitative design review, sub-system analysis and acceptance criteria agreed with stakeholders before the analysis, not after.
Is BS 9991:2024 mandatory?
No British Standard is mandatory in itself. BS 9991:2024 was published in November 2024, with a corrigendum in June 2025, and superseded the 2015 edition without a transition period. If you are still designing to the 2015 edition, expect building control and the Building Safety Regulator to ask why.
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