Summary
- Approved Document B Volume 1 governs fire safety in dwellings — means of escape, fire spread, cavity barriers and access for fire services. Loft conversions and open-plan ground floors are the two highest-risk domestic scenarios.
- The BSA Principal Designer must be able to show the escape strategy was designed and coordinated, not improvised — protected stair enclosures, fire doors, escape windows and interlinked alarms all need a written trail.
- Cavity barrier positions and fire-stopping are design decisions: record them on drawings at Stage 4 so contemporaneous site evidence can be checked against something.
What the Building Safety Act requires for Part B on non-HRB domestic jobs
Requirements B1–B5 apply to every dwelling regardless of height. A two-storey house becoming three storeys through a loft conversion is the classic trigger: the stair must become a protected route with FD20/FD30 fire doors (or a compliant sprinkler/alternative approach), and escape windows alone no longer suffice from the new storey.
As Principal Designer (BSA) you must coordinate the fire strategy across designers — the architect's plans, the manufacturer's fire door certification, the M&E designer's alarm layout — and keep evidence that the strategy holds together. "The builder fitted fire doors" is not evidence; the doorset certification and the drawing showing where FD30s were required is.
Open-plan ground-floor extensions are the second trap: removing the hall lobby can invalidate the means of escape from upper floors, forcing sprinklers, a fire-resisting partition or a re-planned stair. That judgement must be made and recorded at design stage, not discovered by Building Control at plan check.
Key design risks and evidence needed (RIBA Stages 2–4)
- Stage 2: establish the escape strategy — storey count after conversion, protected stair versus alternatives, open-plan implications. Record the chosen strategy and its rationale.
- Stage 3: coordinate compartment lines, cavity barrier positions at junctions and around openings, and alarm coverage (BS 5839-6 grade and category) with the layout.
- Stage 4: specify fire doorsets with test evidence (BS 476-22 or BS EN 1634-1), cavity barrier products and locations on drawings, escape window sizes (0.33 m², 450 mm minimum dimension), and the alarm specification. This drawing set is what contemporaneous site photos get checked against.
Standards and references you should be citing
- Approved Document B Volume 1 (2019 edition incorporating the 2020 and 2022 amendments) — the current baseline for dwellings.
- BS 9991 — the alternative code-based route for residential fire safety design where AD B guidance is departed from.
- BS EN 13501-1 — reaction-to-fire classification for linings and insulation products; record the declared class, not the marketing name.
- BS 5839-6 — fire detection and alarm systems in dwellings; specify grade and category (typically Grade D1, Category LD2 for conversions).
- BS 476-22 / BS EN 1634-1 — fire resistance test evidence for doorsets.
Loft conversion escape: what changes when a house gains a storey
| Situation | Escape approach | Evidence to log |
|---|---|---|
| Two-storey house (before) | Escape windows to first-floor habitable rooms | Window schedule showing clear openable areas |
| Three-storey after loft conversion | Protected stair to final exit with FD30/FD20 doors, or sprinkler alternative | Fire door schedule with certification, stair enclosure drawing, alarm upgrade spec |
| Open-plan ground floor + loft | Usually sprinklers to open-plan area plus fire-resisting construction, or re-planned layout | Fire strategy note recording the option chosen and why |
Common pitfalls that catch out sole practitioners
- Signing off a loft conversion escape strategy that relies on doors the client later replaces with non-fire-rated glazed doors — record the strategy in the handover pack so the client knows what must stay.
- Cavity barriers shown nowhere on drawings, making site evidence impossible to verify.
- Interlinked alarms specified as "smoke detection" with no BS 5839-6 grade/category, leaving the electrician to guess.
- Forgetting B4 external fire spread when cladding a boundary-hugging extension — unprotected areas near boundaries still need checking on small jobs.
Frequently asked questions
Does a loft conversion always need fire doors throughout the stair enclosure?
Where a house becomes three storeys or more, Approved Document B expects the stair to be a protected enclosure with fire doors to habitable rooms, or a recognised alternative such as a sprinkler-protected open-plan approach designed under BS 9991. The chosen strategy should be recorded by the Principal Designer at design stage.
Are sprinklers required in non-HRB houses?
Not normally in England for ordinary houses. They become one of the options where the standard protected-stair guidance cannot be met — commonly open-plan ground floors combined with loft conversions. In Wales, sprinklers are required in new dwellings, but that is a separate regime.
What fire evidence should be in my golden-thread record for a domestic job?
The fire strategy note, fire door schedule with test certification, cavity barrier locations on drawings, alarm specification to BS 5839-6, escape window schedule, and contemporaneous site photos of fire-stopping before it is covered up.
Track this natively instead of in Word templates
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