What is a fire compartmentation survey?

Compartmentation is one of the least visible parts of a building's fire strategy and one of the most important. Most of it sits inside walls, above ceilings and behind risers, which is exactly why it's so often found to have been quietly compromised by the time anyone looks properly. A fire compartmentation survey is how you find out whether it's actually doing its job — not just whether the walls are in the right place, but whether every penetration, joint and door within them still holds the fire resistance the building's strategy depends on.

What fire compartmentation is

Compartmentation is the principle of dividing a building into separate fire-resisting cells — compartments — using construction that's designed and tested to hold back fire and smoke for a defined period. That construction typically includes fire-resisting walls and floors, fire doors at compartment boundaries, and fire stopping around anything that has to pass through them: pipes, cables, ductwork and structural elements.

The purpose isn't to stop a fire indefinitely. It's to contain a fire to the compartment where it starts for long enough that occupants elsewhere in the building have time to escape, and the fire and rescue service has time to arrive and intervene. In a block of flats operating a stay put strategy, compartmentation is doing most of the work: residents in other flats are only safe to remain in place because the walls, floor and front door of the flat of origin are relied upon to hold the fire back. Where that reliance turns out to be misplaced, the consequences can be severe — which is exactly why compartmentation has had so much regulatory attention in recent years, including from the Independent Review of Building Regulations and Fire Safety that followed the Grenfell Tower fire.

Why it matters

Compartmentation is only as good as its weakest point, and a single unsealed penetration or wedged-open fire door can undermine an otherwise well-built compartment line. Unlike active systems such as alarms or sprinklers, passive fire protection doesn't announce when it's failed — a badly fire-stopped cable penetration looks exactly like a properly sealed one from a distance, and a fire door with the wrong seals still looks like a normal door until it's tested or inspected. That's what makes compartmentation defects so persistent: they accumulate silently, through years of cabling upgrades, plumbing works, tenant alterations and general wear, with nobody responsible for checking that each one was properly reinstated.

For any building where the fire strategy depends on containment — which is most multi-occupied buildings — an unverified assumption about compartmentation is a genuine risk, not a technicality. It affects how much time occupants have to escape, whether an evacuation strategy based on stay put or simultaneous evacuation actually holds up in practice, and what a fire risk assessment can honestly conclude about the building's overall fire safety.

What a compartmentation survey is

A compartmentation survey is a focused technical inspection of a building's passive fire protection — the walls, floors, doors and service penetrations that form its compartment lines — carried out to establish whether that construction is actually providing the fire resistance it's meant to. It's a different exercise to a fire risk assessment. A fire risk assessment considers the building's fire safety as a whole, including management arrangements, means of escape and fire detection, and it may recommend a compartmentation survey where compartmentation can't be adequately verified by visual inspection alone. The survey itself goes further: it's specifically about the physical integrity of the compartment lines, often involving access into voids, risers and ceiling spaces that a general assessment wouldn't open up.

The output is a detailed record of what was found — compartment by compartment, defect by defect — rather than a general commentary on fire safety. That record is what allows genuine defects to be distinguished from routine wear, and what turns "we think the compartmentation is probably fine" into a documented, evidenced position.

Which buildings may require one

Compartmentation surveys are most commonly commissioned for multi-occupancy residential buildings — blocks of flats, HMOs and converted properties — where compartmentation between separate households is central to the fire strategy and where a fire risk assessment has identified that it can't be verified without further investigation. They're also a standard part of due diligence when a residential or mixed-use building changes hands, since a buyer or funder typically wants documented assurance about passive fire protection before completion, not an assumption carried over from the seller.

Higher-risk buildings under the Building Safety Act 2022 — broadly, residential buildings of 18 metres or seven storeys or more — have a particular need for this evidence, since compartmentation forms part of the safety case and golden thread of information that the Act requires the accountable person to maintain. Older buildings with a long history of refurbishment, re-servicing or tenant fit-out are also higher priority, since each round of works is a further opportunity for compartment lines to have been breached and not properly reinstated. A single-let residential property with no shared compartment lines is a different picture — its compartmentation needs are usually addressed through the ordinary fire risk assessment rather than a standalone survey.

Common compartmentation defects

The same handful of defects turn up repeatedly, wherever compartmentation is properly investigated. The most frequent is unsealed or poorly sealed service penetrations: gaps left around pipes, cables and ductwork where they pass through a fire-resisting wall or floor, often because whoever cut the opening for a later cabling or plumbing job never reinstated the fire stopping afterwards. Missing or damaged cavity barriers in voids and roof spaces are another common finding, particularly in older or converted buildings where the void wasn't fully compartmented in the first place. Fire doors are a recurring source of defects in their own right — incorrect seals, disconnected closers, doors wedged open, or hardware that was never fire-rated to begin with.

Beyond these, surveys regularly turn up downgraded partitions — a wall that was originally fire-resisting but has since had a section removed or altered without matching fire-resisting materials — and undocumented alterations from tenant fit-outs or previous works that were never checked against the building's compartmentation strategy. None of these are usually deliberate. They're the accumulated result of ordinary building use and maintenance carried out without anyone responsible for protecting the compartment lines specifically.

Fire stopping and service penetrations

Fire stopping is the general term for sealing a gap or penetration in a fire-resisting element so that the element's fire resistance is maintained across the whole of its area, not just where it's solid construction. Service penetrations — the points where pipes, cables, cable trays and ductwork pass through a compartment wall or floor — are where fire stopping matters most, because every one of them is a deliberate hole in what would otherwise be a continuous fire-resisting barrier.

Properly done, fire stopping uses products and systems tested and certified to match the fire resistance period of the element being penetrated: intumescent sealants and collars that expand under heat to close around a plastic pipe as it softens, fire-rated foam and mineral wool for smaller gaps, and proprietary systems for larger or more complex penetrations. What a survey is specifically checking for is whether that match has actually been achieved — a generic silicone sealant or an unrated foam filling a gap will often look similar to a proper fire-stopping product, but provides none of the fire resistance the compartment line depends on. Because service penetrations tend to be added to throughout a building's life — a new cable run here, a replacement pipe there — fire stopping is one of the areas most exposed to being undone by routine maintenance carried out without fire safety in mind.

Fire doors and compartmentation

Wherever a compartment line has an opening in it for a door, the door itself becomes part of that compartment line, and it only provides the intended protection if every component of the door assembly — the leaf, frame, seals, hinges, glazing and self-closing device — is correct and properly maintained. A fire door inspection and a compartmentation survey are closely related but not the same thing: a fire door inspection is a dedicated, detailed check of the door sets themselves, while a compartmentation survey considers doors as one part of the wider compartment line alongside walls, floors and service penetrations.

In practice, the two are often commissioned together, since a compartmentation survey will always need to record the condition of the doors sitting within the compartment lines it's assessing. If you want the full detail on what a fire door inspection specifically covers, our guide to fire door inspections sets out what's checked and why each element matters.

How surveys are carried out

A compartmentation survey typically begins with a review of whatever building information is available — construction drawings, previous fire risk assessments, any record of past alterations — to identify where the compartment lines are meant to be before anyone goes on site. On site, the surveyor carries out a visual inspection of accessible compartment lines, doors and service penetrations, and where compartmentation can't be verified from what's visible — inside a riser cupboard, above a suspended ceiling, within a roof void — the survey typically needs some level of intrusive or invasive investigation, opening up sections of construction to inspect what's actually there rather than relying on assumption.

On larger buildings or portfolios, this is often carried out on a risk-based sample rather than every single compartment line, with common parts, risers and shared voids treated as priority areas since a defect there can affect multiple compartments at once. Every finding is recorded with its location, a description of the defect, supporting photographs, and an assessment of its significance, so that the eventual report reflects exactly what was found rather than a general impression.

Typical survey outputs

The core output of a compartmentation survey is a written report setting out the compartment lines surveyed, the survey methodology and any limitations on access, and a schedule of defects identified — each one located, described, photographed and given a clear priority for remediation. Where drawings or as-built information exist, the report may also mark up the compartment lines against them, giving a visual record of what was inspected and what wasn't.

That report is meant to be used, not filed. Its findings should feed directly into the building's fire risk assessment, inform a prioritised programme of remedial works, and — for higher-risk buildings — form part of the evidence base for the safety case and golden thread of information required under the Building Safety Act 2022. A survey that identifies defects without giving you a way to act on them in order of genuine priority isn't doing its job.

Relevant UK legislation, guidance and standards

The Regulatory Reform (Fire Safety) Order 2005 places a general duty on the responsible person to ensure that a premises' general fire precautions — which include the structural and passive fire protection measures that make up compartmentation — are adequate and properly maintained. The Fire Safety Act 2021 put beyond doubt that this duty extends to a building's structure, external walls and flat entrance doors in multi-occupied residential buildings, closing a point of uncertainty about how far the Order's scope reached. The Fire Safety (England) Regulations 2022 add more specific duties for high-rise residential buildings, including requirements around checking fire doors in the common parts.

For buildings meeting the higher-risk threshold, the Building Safety Act 2022 introduces the accountable person's duty to manage building safety risks — including those arising from compartmentation — and to maintain a golden thread of information and a safety case that can demonstrate it. On the technical side, BS 9999 and BS 9991 provide the recognised guidance on fire safety design, compartmentation strategy and ongoing management for general and residential buildings respectively, and Approved Document B sets out the Building Regulations guidance on compartmentation requirements for new work and material alterations. None of these documents replace a competent survey — they set the standard a survey is checking the building against.

Frequently asked questions

How is a compartmentation survey different from a fire risk assessment?

A fire risk assessment looks at a building's fire safety as a whole, including management arrangements, means of escape and detection, and it identifies where compartmentation needs closer investigation. A compartmentation survey is that closer investigation — a focused, often more intrusive check of the physical construction forming the compartment lines themselves.

How often should compartmentation be surveyed?

There's no single statutory interval that applies to every building. The right frequency depends on the building's construction, occupancy, history of alterations and what your fire risk assessment recommends — a building with a long history of tenant fit-outs and re-servicing generally warrants more frequent review than one with a stable, well-documented history.

Is a compartmentation survey the same as a fire door inspection?

No, though they're closely related. A fire door inspection is specifically about the condition of the door sets. A compartmentation survey covers doors as part of a wider check of walls, floors and service penetrations, and the two are often commissioned together for that reason.

Do I need a compartmentation survey for a single let property?

Usually not as a standalone exercise. Compartmentation matters most where fire needs to be contained between separate occupancies, so a single-let property's fire safety is typically addressed adequately through its fire risk assessment rather than a dedicated survey.

What happens after defects are found?

You should receive a prioritised schedule of remedial works, ranked by the significance of each defect, so that the most serious breaches — particularly in risers, common parts and shared voids — can be addressed first rather than everything being treated as equally urgent.

Will a survey involve opening up finishes or decoration?

Where compartmentation can't be verified visually, some intrusive investigation is often necessary — for example opening a small section of ceiling or riser access panel. A competent surveyor will explain in advance where this is likely to be needed and keep any disturbance to a minimum.

When to seek professional advice

A compartmentation survey is worth commissioning wherever a fire risk assessment has flagged compartmentation as something that can't be verified without further investigation, wherever a multi-occupied building is changing hands and passive fire protection needs to be evidenced rather than assumed, and wherever significant refurbishment, re-servicing or recladding works are planned that could affect existing compartment lines. For higher-risk buildings, it's also a practical starting point for building the evidence a safety case depends on.

If you're not sure whether your building needs a dedicated survey or whether existing compartmentation records are good enough to rely on, that's a reasonable thing to ask before committing to anything — a proper fire risk assessment is often the right first step, and where it identifies genuine compartmentation risk, we can advise on what a survey should cover for your specific building. Get in touch if you'd like to discuss your building's compartmentation or arrange a survey.