In short
- Compartmentation limits fire and smoke spread – and stay put strategies depend on it.
- Much of it is hidden above ceilings, in risers and roof voids, so an FRA can only assume it's adequate.
- Surveys often find unsealed service penetrations, missing cavity barriers and incomplete walls above ceilings.
- The output is a prioritised defect schedule and marked-up plans – evidence for the FRA, fire strategy and safety case.
What compartmentation is
Compartmentation divides a building into fire-resisting compartments – usually each flat, the stairs and lift shafts, and service risers – so a fire is contained long enough for people to escape and firefighters to work. It's made up of:
- Compartment walls and floors with the required fire resistance
- Fire-stopping – the seals around pipes, cables and ducts passing through those walls and floors
- Cavity barriers that close off hidden voids, including in the external walls
- Fire doors and fire dampers where openings are needed
In a block of flats, a stay put strategy depends on compartmentation working. If it doesn't, the evacuation strategy may need to change.
Why compartmentation fails
- Poor original construction – walls stopping at the ceiling instead of continuing to the slab above
- Later alterations – new cables, pipes, data lines and extractor ducts punched through without being sealed
- The wrong products, or the right products installed wrongly
- Damage during maintenance, refurbishment or fit-out
- Conversions where the original building wasn't designed as flats
When you need a compartmentation survey
- Your fire risk assessment has recommended one, or keeps assuming compartmentation is adequate
- You're preparing a retrospective fire strategy or safety case report and need evidence
- You're buying or taking over the management of a building
- Works have been carried out through compartment lines
- There's doubt about whether stay put is still appropriate
A compartmentation survey is often commissioned instead of a Type 2 or Type 4 fire risk assessment – see FRA types 1–4.
What a survey inspects
- Service risers and shafts at each floor
- Ceiling voids above corridors and lobbies
- Roof voids and plant rooms
- Walls and floors between flats and common parts, including from inside a sample of flats where access allows
- Fire dampers, where present
- Cavity barriers in accessible locations
Inspection is mostly non-destructive – lifting ceiling tiles, opening access panels and risers – with small, made-good openings where needed.
What surveys usually find
- Unsealed or poorly sealed service penetrations – the most common defect by far
- Gaps above corridor walls where they stop at a suspended ceiling
- Missing or damaged cavity barriers
- Expanding foam used as fire-stopping without evidence that it's suitable
- Unprotected openings left from earlier works
What you get and what happens next
A good survey produces a schedule of defects with photos, locations on marked-up plans and a priority for each item. Remedial work should be carried out by third-party certificated installers, with records kept for the golden thread. Many clients follow up with a re-inspection to confirm the work was done correctly.
Compartmentation in different building types
- Purpose-built blocks of flats – focus on risers, corridor ceiling voids, bin stores and the junctions between flats and common parts
- Converted buildings – original floors and walls may not have been upgraded properly, so separation between flats needs closer inspection
- Mixed-use buildings – separation between commercial units and flats is critical
- Hotels and student accommodation – long corridors, many penetrations and frequent refurbishment
- Offices – compartment floors, protected stairs and service risers
How long a survey takes and what it costs
A survey of a typical block of flats usually takes one to a few days on site, depending on size, access to risers and voids, and how many flats can be entered. The fee depends on the building's size, the areas to be inspected and whether any opening-up is needed – see the cost guide.
Our compartmentation surveys cover risers, ceiling and roof voids, and flats where access allows, and link directly to fire door inspections and retrospective fire strategies.
How we can help
We match each project to a qualified specialist and confirm the scope, the named professional and a fixed fee before you commit.
Sources
- LEASE – Fire risk assessment (FRA) FAQ
- London Fire Brigade – Fires in communal areas (Guidance Note 84)
This guide is general information based on the law and guidance in England as at 8 November 2026. It isn't legal advice – for advice on a specific building, get in touch.