Is Approved Document B law?

No, but it carries legal weight. Approved Document B is statutory guidance issued under section 6 of the Building Act 1984. Following it is not mandatory and does not guarantee compliance; section 7 of the Act says failure to follow it can be relied on in court as tending to establish liability, and following it as tending to disprove liability. The courts have confirmed it is guidance to be applied with judgement, not legislation to be parsed like a statute.

What does the law actually require for smoke ventilation?

At design stage, the Building Regulations 2010 require the building to meet functional requirements B1 to B5, which include appropriate means of escape and access for the fire service; smoke control is one of the established ways of achieving them. For higher-risk buildings (at least 18 metres or 7 storeys with 2 or more residential units, with care homes and hospitals at that height also caught at the design and construction stage), the Building Safety Act 2022 adds building control approval from the Building Safety Regulator before work starts and a completion certificate before occupation. In occupied buildings, the Fire Safety Order 2005 requires smoke control systems to be maintained in efficient working order, and the Fire Safety (England) Regulations 2022 add monthly checks of smoke control systems in high-rise residential buildings, with faults that cannot be fixed within 24 hours reported to the fire and rescue authority.

Which edition of BS 9991 should I use?

BS 9991:2024 was published in November 2024 and superseded the 2015 edition, but Approved Document B still lists the 2015 edition among its referenced documents. The Construction Leadership Council's advisory note, developed with the Building Safety Regulator, confirms there is no legal requirement to comply with BS 9991, and sets the expectation that new building control applications for higher-risk buildings adopting BS 9991 should use the 2024 edition from 30 September 2026. For any live project, the fire strategy should state the edition it is designed to, and that is the edition the building must be built and maintained against.

23 Aug 2026 11 min read

Is BS 9991 a Legal Requirement? Law vs Guidance in Smoke Ventilation

Q: Is BS 9991 a legal requirement?

No. BS 9991:2024 is a British Standard code of practice, which is voluntary guidance. It becomes binding only when a contract specifies it or the building's fire strategy adopts it, and at that point departing from it without justification is a contractual and professional problem. The legal requirements are the functional requirements of the Building Regulations 2010 (B1 to B5), the Building Safety Act 2022 for higher-risk buildings, and the Fire Safety Order 2005 in occupied buildings. BS 9991 is one recognised way of demonstrating that a residential design meets them.

The Building Safety Act is law. BS 9991 is guidance. What that distinction actually means for smoke ventilation projects, and where it catches people out.

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Two sentences get repeated on smoke ventilation projects, and both are wrong. The first: “it’s in BS 9991, so it’s a legal requirement.” The second: “BS 9991 is only guidance, so we don’t have to follow it.” The first confuses a voluntary code of practice with legislation. The second ignores how guidance actually behaves once a fire strategy, a contract, or a court gets hold of it.

The distinction matters more than it used to. The Building Safety Act has put criminal offences, named dutyholders, and a regulator with approval powers around work that used to be waved through. Knowing which documents bind you, and how, is now part of doing the job. Here’s the hierarchy, top to bottom.

The Hierarchy in One View

England’s fire safety documents sit in five tiers, and each tier binds differently:

Acts of Parliament: the Building Safety Act 2022 and the Building Act 1984. Law.
Secondary legislation: the Building Regulations 2010 (made under the Building Act 1984), the Fire Safety Order 2005, and the Fire Safety (England) Regulations 2022. Also law, and where most of the enforceable detail lives.
Statutory guidance: Approved Document B. Not law, though it has a defined legal effect.
British Standards: BS 9991:2024 and BS 9999:2017, voluntary codes binding only by adoption. The BS EN 12101 product standards sit differently: they are designated standards, and a manufacturer placing a covered product on the GB market must declare its performance against them.
Manufacturer literature: brochures and datasheets. No status at all beyond the test evidence behind them.

Everything below tier 2 exists to help you meet tier 2. That’s the whole structure.

What Is Actually Law

The Building Regulations 2010 are where fire safety becomes legally enforceable for building work. Schedule 1 sets functional requirements B1 to B5: means of warning and escape, internal fire spread (linings and structure), external fire spread, and access and facilities for the fire service. They’re deliberately broad. B1 requires “appropriate means of escape in case of fire from the building to a place of safety outside the building capable of being safely and effectively used at all material times”, and says nothing about how. Smoke ventilation is one of the established ways of making a design satisfy B1 and B5. The regulations also carry regulation 38, requiring fire safety information to be handed to the Responsible Person by completion of the work (or first occupation of a new building, if earlier), and, since October 2023, the dutyholder and competence regime: clients with named legal duties on all building work, plus principal designers and principal contractors wherever more than one contractor is involved, not just high-rise.

The Building Safety Act 2022 adds a second layer for higher-risk buildings, defined for the occupation regime as at least 18 metres or at least 7 storeys with at least 2 residential units. For design and construction the definition is slightly wider: care homes and hospitals meeting the height threshold also count. Work on these buildings needs building control approval from the Building Safety Regulator before it starts (the stage everyone, including the regulator, calls Gateway 2) and a completion certificate before occupation (Gateway 3). Starting without approval is an offence. The Act also created the golden thread duty to keep prescribed building information current, and the Accountable Person regime in occupation. We’ve covered what that means for smoke ventilation records in The Golden Thread and Smoke Ventilation.

The Fire Safety Order 2005 takes over once a building is occupied. Article 17 requires fire safety equipment, smoke control systems included, to be “maintained in an efficient state, in efficient working order and in good repair” under a suitable system of maintenance. And for high-rise residential buildings in England, the Fire Safety (England) Regulations 2022 name smoke control systems explicitly: regulation 7 requires monthly routine checks of essential firefighting equipment, the definition of which includes smoke control systems twice over, once as key firefighting equipment and once via detection linked to ancillary equipment. A fault that can’t be fixed within 24 hours must be reported to the local fire and rescue authority. If you manage a high-rise block and the AOV panel has been showing a fault light for three months, with nothing reported and no repair in hand, that’s not a housekeeping issue. It’s a breach.

Approved Document B: Guidance With Teeth

Approved Document B is statutory guidance issued under section 6 of the Building Act 1984, and its legal effect is defined by section 7: failing to follow it does not of itself make you liable for anything, but in proceedings about a breach of the Building Regulations, failure to comply with it “may be relied upon as tending to establish liability”, and compliance with it as tending to establish the opposite. The courts have put it plainly enough; in the leading post-Grenfell cladding case, Martlet Homes v Mulalley, the court treated Approved Document B as statutory guidance to be applied with judgement, not legislation to be construed like a statute.

ADB says the same about itself. Its own introduction states that complying with the guidance “does not guarantee” compliance with the regulations, and that “there may be other ways to comply with the requirements than those described in an approved document.”

So the practical position: follow ADB and you have a strong evidential presumption of compliance. Depart from it and the burden of demonstrating compliance is yours. Neither of those is “ADB is mandatory”, and neither is “ADB is optional”. One more thing to watch: ADB is a moving target. The 2025 amendments took effect in March 2025, the second-staircase provisions for blocks of flats with a storey 18 metres or more arrive on 30 September 2026, and a further amendment package lands in 2029. Our guide to Changes to Approved Document B covers the revision history.

Where BS 9991 Actually Sits

BS 9991:2024 is a code of practice published by BSI. It is not legislation, it is not statutory guidance, and the Construction Leadership Council’s advisory note, developed with the Building Safety Regulator, confirms there is no legal requirement to comply with it: design teams choose their design code and must justify the choice. BSI’s own front matter says a code of practice is not to be quoted as if it were a specification, and that compliance with a British Standard cannot confer immunity from legal obligations.

Then how does it end up binding almost everyone? Three routes:

The fire strategy adopts it. Once the strategy says the smoke control design follows BS 9991:2024, every damper, vent, and panel on the job is measured against it. The standard’s own front matter expects anyone claiming compliance to be able to justify any deviation from its recommendations.
The contract specifies it. A specification clause invoking BS 9991 makes it contractually enforceable, with none of the “it’s only guidance” softness.
It’s used to demonstrate compliance. ADB’s alternative-approaches paragraph allows other guidance to be used to meet B1 to B5, provided the overall level of safety is not lower and the publication’s recommendations are followed in their entirety. In residential work, BS 9991 is the obvious candidate, and “in their entirety” is the phrase people forget: you can’t cherry-pick the convenient halves of ADB and BS 9991 and call the result compliant.

There’s an edition trap here too. ADB’s referenced-documents list still cites BS 9991:2015, the edition the 2024 revision withdrew, and the CLC advisory note expects new higher-risk building applications adopting BS 9991 to use the 2024 edition from 30 September 2026. Until the documents catch up with each other, say which edition you mean. A spec that just says “BS 9991” is an argument waiting to happen, and the 2024 changes are not cosmetic: smoke shaft requirements, damper performance expectations, and height thresholds all moved.

The Bottom Rung: Brochure Claims

Below the standards sits the layer where the real trouble starts: manufacturer literature quoting fragments of standards as sales claims. “Tested to BS EN 1366-10” on a brochure tells you a test happened, not what the product achieved, in which orientation, or whether it covers multi-compartment use. The legal vehicle for a performance claim is the Declaration of Performance against the designated product standard, with CE or UKCA marking (both currently accepted in Great Britain, with no end date set for CE recognition). If the classification isn’t on the DoP, the product hasn’t demonstrated it, whatever the brochure implies. We’ve broken down how to read those classification strings in Smoke Control Damper Classifications: What E, S and I Actually Mean.

The discipline is the same one the Building Safety Act now expects of dutyholders: claims need evidence. Ask for the DoP and the classification report. A supplier who can’t produce them has answered your question.

What This Means for Your Project

Knowing the hierarchy turns several recurring site arguments into short conversations. “Is BS 9991 mandatory?” No, but the fire strategy adopted it, so it governs this job. “Can we deviate from ADB?” Yes, if you can demonstrate the functional requirements are still met, and the demonstration is your responsibility, in writing. “The brochure says it complies.” The DoP decides, not the brochure. “It passed building control, so it must be legal.” Building control approval is not immunity; the functional requirements and, in occupation, the Fire Safety Order keep applying for the life of the building.

And one closing caution for anyone working across borders: most of the detail above is England-specific. Wales has its own approved documents, its own higher-risk building definitions, and its own building safety legislation arriving through the Building Safety (Wales) Act 2026. The hierarchy is the same shape; the documents in it are not. Scotland’s system, built on the Building (Scotland) Regulations and its Technical Handbooks, is separate again.

Sources

Official legislation, guidance, and standards referenced in this article:

Specifying to BS 9991:2024?

We supply certified smoke ventilation products with the Declarations of Performance and classification evidence to stand behind them: AOVs, smoke control dampers, and control panels, held in UK stock in Poole with next-working-day despatch on most lines. If a spec or a fire strategy has you unsure what the law actually requires of a product, our technical team will give you a straight answer.

Call 01202 725 689 or email info@vent-trade.co.uk.

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