Start with what the law actually requires
The Building Regulations require the building to satisfy the functional requirements B1 to B5. They do not require you to follow Approved Document B, BS 9999 or anything else. Those documents are routes to compliance, recognised ways of demonstrating that the functional requirement is met.
This matters because it explains why departing from Approved Document B is not "non-compliance". It is a decision to demonstrate compliance a different way, and it puts the burden of demonstration on you.
The four documents at a glance
| Document | Status | Use it for |
|---|---|---|
| Approved Document B Vol 1: dwellings Vol 2: all other buildings |
Statutory guidance issued by government. Following it does not guarantee compliance, but a court will treat compliance with it as tending to show the requirement is met. | Most buildings, most of the time. The default. Prescriptive, table-driven, and the document a reviewer knows best. |
| BS 9991 Residential |
British Standard, code of practice. A recognised alternative route. | Residential buildings: blocks of flats, student accommodation, sheltered housing. More flexible than ADB Vol 1, with more design freedom in exchange for more justification. |
| BS 9999 Non-residential |
British Standard, code of practice. A recognised alternative route. | Non-residential buildings where ADB Vol 2 is too restrictive. Introduces risk profiles that can relax travel distances and widths where the occupancy and systems justify it. |
| BS 7974 + PD 7974 parts |
Framework for fire safety engineering, supported by published documents giving the methods. | Performance-based design. Not an alternative set of tables: a structured method for analysing a specific problem quantitatively when no code covers it. |
Approved Document B
ADB is prescriptive: look up the building use, read the number, apply it. That is a genuine strength. It is fast, it is predictable, everyone in the process understands it, and a design that follows it needs very little justification.
Its weakness is the same thing. It cannot flex for a building that does not resemble the buildings its tables were written around, and it gives you almost no credit for provisions that genuinely reduce risk. Install a sprinkler system in an office and ADB gives you very little back for it.
Use ADB when: the building is conventional in use and form, the layout works within the tables, and there is no commercial or architectural driver pushing you outside them. Which is most projects.
BS 9991
BS 9991 is the residential code of practice, and it is the natural route for blocks of flats where ADB Volume 1 does not fit: unusual layouts, mixed-use podiums, buildings where the evacuation strategy needs more thought than stay-put-by-default.
The 2024 edition, with its 2025 amendment, was a substantial revision. It reflects the post-Grenfell regulatory position, and it is materially more developed than its predecessor on evacuation of people who cannot use stairs, on evacuation alert systems, and on the interaction between the fire strategy and the higher-risk building regime.
Use BS 9991 when: the building is residential and ADB Volume 1 is constraining the design in a way you can justify relaxing, or the building's evacuation strategy is not the standard stay-put arrangement.
BS 9999
BS 9999 is the non-residential code of practice, and its distinctive mechanism is the risk profile. Instead of one set of travel distances for a building use, BS 9999 classifies the occupancy (how likely a fire is, how quickly people will respond, whether they are awake and familiar) and lets travel distances and widths vary with that classification and with the fire protection systems provided.
Done properly, this produces a design that is both less restrictive and better reasoned than the ADB equivalent. Done badly, it produces an optimistic risk profile with nothing supporting it, which is exactly what a reviewer will attack.
Use BS 9999 when: the building is non-residential, ADB Volume 2 is forcing a layout the design cannot accept, and you have the systems and occupancy characteristics to support a favourable risk profile, and the evidence to defend it.
BS 7974 and the PD 7974 series
BS 7974 is a different kind of document. It does not tell you what the answer is; it tells you how to structure an analysis that produces one. The supporting published documents carry the methods:
- PD 7974-1: initiation and development of fire within the enclosure of origin
- PD 7974-2: spread of smoke and toxic gases
- PD 7974-3: structural response and fire spread beyond the enclosure
- PD 7974-4: detection, activation and suppression
- PD 7974-5: fire service intervention
- PD 7974-6 (human factors: life safety strategies, occupant evacuation, behaviour and condition). This is the ASET/RSET part, and the one used most often.
- PD 7974-7: probabilistic risk assessment
Use BS 7974 when: the question genuinely cannot be answered from a code (an atrium, a large-volume space, a phased evacuation of an unusual population, a structural fire engineering assessment). It is expensive, it is slow, and it needs a competent person who can defend the assumptions. Use it because the building needs it, not because a table is inconvenient.
The rule that matters most. Do not mix. Each of these documents is an internally consistent package: its travel distances assume its exit widths, which assume its detection provisions. Taking the generous travel distance from BS 9999 and the simpler alarm provisions from ADB gives you a design that neither document supports, and a reviewer will find it. Pick one route, name it and its edition in the strategy, and treat anything outside it as a declared departure.
Where the other documents fit
- PAS 9980: appraisal of external walls on existing blocks of flats. Not a design code.
- The Regulatory Reform (Fire Safety) Order 2005: operational fire safety in buildings in use. Runs in parallel with the Building Regulations, not instead of them.
- The Building Safety Act 2022: the regulatory regime for higher-risk buildings. Changes who approves the design and when, not what the design has to achieve.
- Health Technical Memorandum 05 series, Building Bulletin 100: sector guidance for healthcare and schools respectively, which sit alongside the general documents.
- Scotland, Wales, Northern Ireland: the Technical Handbooks, the Welsh Approved Documents and the Technical Booklets. Building standards are devolved; do not assume transfer.
Last reviewed 25 July 2026 against the editions named above. Standards are revised; check the current published edition before relying on anything here in a design.