Compartmentation is a fundamental fire safety strategy that divides a building into separate fire-resistant sections, or compartments. These compartments are designed to contain fire and smoke for a specified period, giving occupants time to escape and the fire service time to respond.
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What is compartmentation?
Compartmentation is the use of fire-resistant walls, floors, and ceilings to divide a building into separate "fire compartments". Each compartment is designed to:
- Contain fire for a specified time (typically 30, 60, or 120 minutes)
- Prevent smoke spread to other parts of the building
- Protect escape routes so people can evacuate safely
- Limit fire damage to the compartment where it started
- Give the fire service time to arrive and tackle the blaze
Compartmentation is often called "passive fire protection" because it doesn't rely on activation or maintenance like alarms or sprinklers. It's built into the structure. But only if it remains intact.
Why compartmentation matters
In a building without effective compartmentation, fire and smoke can spread rapidly between floors and rooms. This is particularly dangerous in:
- Flats and apartment blocks — fire can spread from one flat to others and into escape routes
- Care homes and hospitals — where occupants cannot evacuate quickly
- Hotels and student accommodation — where people are asleep and unfamiliar with the building
- Multi-storey buildings — where escape takes longer
- Commercial buildings — where fire can spread between units or floors
Post-Grenfell, compartmentation has become a critical focus for enforcement. Fire services and building safety regulators are taking a much harder line on compartmentation breaches, especially in residential buildings.
The key elements of compartmentation
Effective compartmentation requires several interconnected elements:
1. Fire-resistant walls and floors
Compartment walls and floors are constructed (or upgraded) to resist fire for a specified period. This is measured in minutes:
- 30 minutes (FD30) — common for internal walls within flats
- 60 minutes (FD60) — typical for separating walls between flats or commercial units
- 120 minutes (FD120) — often required for walls separating different buildings or high-rise floors
The fire resistance rating refers to how long the structure can withstand fire before it:
- Loses structural integrity (collapse)
- Allows flames to pass through (integrity failure)
- Transfers excessive heat to the unexposed side (insulation failure)
2. Fire doors
Fire doors are essential components of compartmentation. They form openings in compartment walls and must:
- Be certified to the required fire rating (FD30, FD60, etc.)
- Close fully and latch correctly
- Have intumescent strips and smoke seals in good condition
- Not be propped open (unless on automatic release linked to the fire alarm)
- Have no gaps around the frame
A fire door is only as good as its installation and maintenance. A poorly fitted or damaged fire door can completely undermine the compartment it's supposed to protect.
3. Fire stopping
Fire stopping is the sealing of gaps, voids, and penetrations in compartment walls and floors to maintain their fire resistance. Common penetrations include:
- Pipes (water, heating, gas, drainage)
- Cables (power, data, telecoms)
- Ventilation ducts
- Service risers and shafts
- Conduits
Fire stopping materials include:
- Intumescent products (expand when heated to seal gaps)
- Fire-rated foam, sealant, and mastic
- Fire-rated boards and collars
- Fire barriers and cavity barriers
Every hole in a compartment wall or floor must be properly sealed with an appropriate fire stopping material. Even small gaps can allow fire and smoke to spread.
4. Cavity barriers
Cavity barriers prevent fire spreading through hidden voids such as:
- Above suspended ceilings
- Behind dry lining
- Within roof spaces
- Around window and door frames
Cavity barriers are especially important in modern construction where large voids are common.
Common compartmentation breaches
Compartmentation breaches are extremely common, often because building work has been carried out without proper fire stopping. Here are the most frequent issues:
Cable and pipe penetrations
The most common breach. Electricians, plumbers, and telecoms engineers make holes for cables and pipes, then fail to seal them properly (or at all).
What to look for:
- Visible gaps around cables passing through walls or floors
- No fire stopping material, or only filler or foam (not fire-rated)
- Multiple cables bundled through oversized holes
- Holes left from removed cables or pipes
Removed or damaged fire doors
Fire doors are sometimes removed, propped open, or damaged in ways that destroy their effectiveness:
- Doors wedged open
- Self-closers removed or broken
- Glass panels replaced with non-fire-rated glass
- Gaps around the frame or bottom edge
- Damaged intumescent strips
Altered or removed walls
Renovation work can inadvertently destroy compartmentation:
- Knocking through walls without understanding their fire-resistant role
- Installing new doors or hatches without fire-rated alternatives
- Creating new openings for pipework or ventilation
Ceiling and floor penetrations
Often invisible from normal viewing angles:
- Downlighters installed into fire-rated ceilings without fire hoods
- Loft hatches without fire resistance
- Underfloor heating or service ducts that breach compartment floors
- Access panels for services with no fire rating
Service risers and ducts
Vertical shafts (for lifts, stairs, services) are particularly critical:
- Missing fire stopping where services enter or leave the shaft
- Fire doors to risers left open or removed
- Ventilation grilles without fire dampers
Building work aftermath
Compartmentation is often compromised during:
- Loft conversions
- Kitchen and bathroom refits
- New boiler installations
- Data cabling and alarm installations
- Structural alterations
Fatal fire in converted building — compartmentation failures
A fire started in a ground-floor commercial unit in a converted building with flats above. The fire spread rapidly through breached compartmentation, reaching the residential floors within minutes.
- ✗Cable penetrations between floors not fire-stopped
- ✗Service riser doors missing or wedged open
- ✗Suspended ceiling voids lacked cavity barriers
- ✗Holes left from previous pipework installations unsealed
- ✗Fire doors on stairwell replaced with standard doors
Two residents died and several were seriously injured. The subsequent investigation revealed systematic compartmentation failures throughout the building. The owner and managing agent both faced prosecution.
Compartmentation breaches are not just technical defects — they can be fatal. All multi-occupancy and multi-storey buildings must have their compartmentation surveyed and maintained.
Compartmentation in flat blocks and high-rise buildings
Since the Grenfell Tower fire in 2017, compartmentation in residential buildings has been subject to intense scrutiny.
The "stay put" strategy
Many flat blocks are designed with a "stay put" policy in mind: if there's a fire in one flat, residents in other flats should remain in their own flats (which are designed as separate fire compartments) unless:
- The fire is in their flat
- There is smoke in the communal areas
- They are told to evacuate by the fire service
This strategy only works if compartmentation is intact.
If fire and smoke can spread from one flat to others, or into escape routes, the stay put policy fails — with potentially catastrophic results.
Post-Grenfell changes
The Fire Safety Act 2021 and Building Safety Act 2022 introduced significant changes:
- Landlords and building owners must actively check and maintain compartmentation
- External wall systems are now part of the fire risk assessment
- High-rise buildings (18m+) have additional requirements
- Enforcement action for breaches has increased dramatically
If you own or manage a residential building, particularly one with multiple flats or over 18 metres tall, you must have compartmentation surveyed by a competent fire safety professional. Failure to do so could result in enforcement action, prohibition notices, or prosecution.
How to inspect compartmentation
A proper compartmentation survey should be carried out by a qualified fire safety professional or fire engineer. They will:
- Review building records — original construction drawings, fire strategy, building control sign-off
- Physical inspection — walk through the building checking walls, floors, doors, and services
- Invasive investigation — if necessary, open up ceiling voids, check behind panels, inspect service risers
- Identify breaches — document every gap, penetration, or defect
- Assess risk — prioritise remedial works based on risk severity
- Produce a report — with photographs, locations, and recommended actions
What you can check yourself
While a professional survey is essential for multi-occupancy buildings, you can do basic checks:
- Fire doors — do they close fully and latch? Are seals intact? Any damage or gaps?
- Visible penetrations — are cables and pipes properly sealed where they pass through walls?
- Service cupboards and risers — are doors present and closing properly?
- Recent building work — has any work created new holes or removed fire stopping?
- Ceiling voids — if accessible, check for unsealed penetrations or missing cavity barriers
If you can see daylight, cables, or pipework through a gap in a wall or floor, it's almost certainly a compartmentation breach.
Remediation and repair
Once breaches are identified, they must be repaired using appropriate materials and methods:
Fire stopping products
Use only materials certified for fire stopping:
- Intumescent acrylic sealants (for small gaps around pipes and cables)
- Fire-rated expanding foam (for larger voids)
- Fire pillows and bags (for cable bundles and service penetrations)
- Intumescent wraps and collars (for plastic pipes)
- Fire-rated boards and batts (for large openings)
Who should do the work
Fire stopping must be carried out by someone competent. For large or complex buildings, use:
- Certified passive fire protection installers (e.g., FIRAS-accredited)
- Fire safety contractors with proven experience
- Contractors who provide certification of works completed
Certification
Remedial fire stopping work should be certified to confirm:
- The correct materials were used
- Installation was carried out correctly
- The fire resistance rating has been restored
This certification is essential for demonstrating compliance and for building safety case submissions (in high-rise buildings).
When to get a specialist survey
You should arrange a professional compartmentation survey if:
- You own or manage a multi-occupancy residential building (flats, HMOs)
- Your building is over 18 metres tall
- You operate a care home, hospital, hotel, or other premises where people sleep
- Your building has had significant refurbishment or alteration
- Your fire risk assessment identified concerns about compartmentation
- You're purchasing a building and need to understand fire safety liabilities
- The fire service has raised concerns during an inspection
Basic Inspection vs Specialist Survey
Basic Visual Check
- •Check fire doors close properly
- •Look for obvious gaps around pipes/cables
- •Inspect service cupboards and risers
- •Review recent building work
- •Can be done by competent person in-house
- •Good for ongoing maintenance
Full Compartmentation Survey
Recommended- •Detailed inspection of all compartment lines
- •Invasive investigation (opening up voids)
- •Review of construction drawings and fire strategy
- •Prioritised remediation schedule
- •Certification and evidence for compliance
- •Typically costs £1,000-5,000+ depending on building size
Bottom line: For multi-occupancy residential buildings, a full specialist survey is strongly recommended. For simple commercial premises, a visual check as part of your fire risk assessment may be sufficient.
Legal duties and enforcement
Under the Regulatory Reform (Fire Safety) Order 2005 (as amended by the Fire Safety Act 2021), the "responsible person" must ensure that:
- Compartmentation is adequate and maintained
- Breaches are identified and remediated
- Building work does not compromise compartmentation
- Records are kept of surveys and remedial works
Enforcement action
Fire and rescue services can take action if compartmentation is inadequate:
- Informal notices — warning letters requiring action
- Enforcement notices — legal requirement to remediate within a specified time
- Prohibition notices — immediate closure of the building or restriction on use
- Prosecution — unlimited fines and up to 2 years imprisonment for serious breaches
Since Grenfell, fire services have significantly increased enforcement activity around compartmentation. This is no longer seen as a technical detail — it's a life-safety critical issue.
Compartmentation and building insurance
Insurance companies are increasingly asking questions about compartmentation:
- Has the building been surveyed?
- Are there any known breaches?
- Have remedial works been carried out?
Failure to disclose compartmentation issues could invalidate your insurance. Some insurers now require evidence of compartmentation surveys for multi-occupancy buildings.
Frequently asked questions
Most buildings constructed or refurbished to modern standards have some level of compartmentation, especially multi-storey or multi-occupancy buildings. Check your building control completion certificate, fire strategy document, or building regulations approval. If in doubt, a fire safety professional can assess it.
Simple fire stopping (like sealing a small cable penetration with fire-rated sealant) can be done yourself if you use the correct materials. However, complex or large-scale work should be done by certified fire stopping contractors. Always check that materials are tested and certified for the application.
For a small block of flats (10-20 units), expect £1,000-3,000. Larger or more complex buildings can cost £5,000-15,000+. Invasive surveys (where voids need to be opened up) cost more. Get quotes from specialists with proven experience in your building type.
Document them, assess the risk, and arrange remediation. High-risk breaches (e.g., on escape routes or between residential units) should be addressed urgently. Keep records of what you found and what you did. Update your fire risk assessment and consider notifying your insurer.
There's no fixed legal requirement, but you should inspect compartmentation as part of your annual fire risk assessment review. Any time building work is done, you must check that compartmentation hasn't been compromised. High-risk buildings (care homes, high-rise) should have more frequent checks.
Yes, but they must seal them properly with fire-rated materials. In practice, many contractors don't understand fire stopping requirements. Make it a contractual requirement that any penetrations are fire-stopped, and inspect the work before signing off.
Fire doors are part of compartmentation. Compartmentation is the overall strategy of dividing the building into fire-resistant sections. Fire doors are the openings in those sections that allow people and goods to pass through while maintaining fire resistance (when closed).
Many do, though standards have evolved over time. Older buildings may have compartmentation that doesn't meet current standards, or it may have been compromised by decades of alterations. A survey can establish the current state and what improvements are needed.
Next steps
If you're responsible for a building with multiple occupants or multiple floors, compartmentation should be a priority:
- Review your fire risk assessment — does it adequately cover compartmentation?
- Commission a compartmentation survey if you haven't already (essential for flats, care homes, high-rise)
- Inspect after building work — make sure contractors haven't created breaches
- Remediate any breaches identified, prioritising high-risk areas
- Keep records of surveys, remedial works, and ongoing inspections
Not sure if your compartmentation is adequate? A qualified fire safety professional can survey your building, identify any breaches, and help you prioritise remediation work.
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