What Is Fire Compartmentation and How Should It Be Maintained?

Summary

Fire compartmentation is one of the foundational principles of passive fire protection. By constructing physical barriers from fire-resisting materials, a building is divided into compartments that contain a fire for a defined period — typically 30, 60, 90, or 120 minutes. This containment limits fire and smoke spread, protects means of escape, and gives the fire and rescue service a stable structure to work in.

Every opening or penetration in a compartment wall or floor — for pipes, cables, ducts, structural beams, or doors — is a potential breach point. The integrity of the compartmentation system depends entirely on every penetration being properly sealed with appropriate fire-stopping products. A single unsealed cable penetration can undermine the protection of an entire floor in minutes.

Compartmentation surveys have become an important part of the fire safety landscape since the Grenfell Tower fire in 2017. Many buildings that were considered compliant have subsequently been found to have significant hidden breaches — often introduced during maintenance, refurbishment, or M&E installation work by contractors who either did not know or did not care about the fire-stopping implications of their work.

Key Facts

• Legal basis — Building Regulations 2010 (England), Approved Document B (ADB); BS 9999:2017; RRO 2005 for ongoing maintenance
• Purpose — Contain fire and smoke within a compartment for a defined period to allow safe evacuation and firefighting
• Fire resistance ratings — Expressed in minutes: 30, 60, 90, 120 (e.g., REI 60 = 30 minutes load-bearing, 60 minutes integrity, 60 minutes insulation)
• REI notation — R = load-bearing capacity, E = integrity (no passage of flame/hot gas), I = insulation (temperature rise on unexposed face)
• Maximum compartment size — Varies by purpose group; ADB Table 8 sets maximum floor areas for different occupancy types
• Protected shafts — Vertical elements (stairwells, lift shafts, service ducts) that pass through compartment floors must be enclosed within a protected shaft
• Cavity barriers — Required in concealed spaces (voids, cavities, ceiling voids) to restrict cavity fire spread; typically at junctions and at specified intervals
• Fire-stopping products — Intumescent mastics, pipe collars, fire batts, composite sheet, ablative coatings — all must be third-party certified
• Critical installer competency — Fire stopping must be installed by competent persons; FIRAS or IFC certification schemes are relevant
• Compartmentation surveys — Intrusive surveys needed to verify hidden penetrations; visual-only surveys can miss most breaches
• Common breach causes — M&E contractors, IT cable installations, plumbing modifications, and previous maintenance work
• Retrospective remediation — Required wherever breaches are found; cannot be deferred for occupied buildings
• ADB 2019 revision — Updated guidance on sprinkler systems, wayfinding, balconies, and compartment sizes

Quick Reference Table

Floor areas are for a single storey compartment. Multi-storey buildings have different volume limits. Always verify against current ADB and structural engineer's specification.

Detailed Guidance

Fire-Resisting Elements

Compartment walls separate adjacent compartments on the same floor. They must run full height from floor slab to the underside of the floor or roof slab above — not just to the suspended ceiling. A common (and critical) error is fire-rated walls that stop at the ceiling tile level, leaving the ceiling void open above. The void above a suspended ceiling is part of the compartment and must also be protected.

Compartment floors separate compartments on different storeys. In residential buildings, each flat is typically treated as its own fire compartment, with the floor and ceiling construction providing the separation. This is why the ceiling of a flat below must be maintained with the same fire resistance as the compartment floor — it is part of the system.

Protected shafts enclose services, stairs, and lifts that pass through compartment floors. The enclosing walls of a protected shaft must match or exceed the fire resistance of the floors they penetrate, and every opening into the shaft (doorways, access panels, service entries) must be fire-resisting and self-closing.

Cavity Barriers

Concealed spaces — the voids above suspended ceilings, within wall cavities, between the inner lining and the external cladding — provide channels through which fire and smoke can bypass compartment walls. Cavity barriers are used to subdivide these spaces and prevent this bypass.

ADB requires cavity barriers:

• At every compartment wall and floor junction with a cavity or void
• At the boundary with a protected shaft
• At specified horizontal intervals in ceiling voids (typically 20m maximum)
• At the top of external wall cavities where they meet the roof

Cavity barriers must achieve at least 30 minutes' fire resistance (integrity) and must be mechanically fixed and abutted tightly to all adjacent construction elements. In practice, cavity barriers are frequently found to be unsealed at junctions, compressed out of shape, or missing entirely where ducts and pipes pass through them.

Sealing Service Penetrations

Every penetration through a compartment wall or floor — a water pipe, gas pipe, electrical cable bundle, mechanical duct, or structural element — must be sealed with an appropriate fire-stopping product. The choice of product depends on:

• The type of penetration (rigid metal pipe, plastic pipe, flexible cable, duct)
• The fire resistance period required (30, 60, 90 min)
• Whether the gap is wide or narrow
• Whether the element is within a wall cavity or a floor/ceiling junction

Common fire-stopping products:

All products must be used in accordance with their third-party test evidence. Using a product outside its tested application (e.g., a collar rated for 100mm pipes on a 160mm pipe) renders the installation non-compliant regardless of how well it is fitted.

Third-Party Certification

Fire-stopping products must have credible evidence of performance. The most robust route is third-party certification — products and installation systems tested and assessed by independent bodies to:

• BS EN 1366 series — Fire resistance of service installations (pipes, ducts, cable trays)
• BS 476 Part 20 — Fire resistance of elements of building construction (older UK standard, still referenced)
• LPCB (Loss Prevention Certification Board) — Independent product certification
• BBA (British Board of Agrément) — Product approval certificates including fire-stopping products
• FIRAS — Installer certification scheme for passive fire protection contractors
• IFC Certification — Passive fire protection installer accreditation

Using FIRAS or IFC-certified contractors provides documented evidence of competency and is increasingly required by building owners, insurers, and enforcement authorities.

Common Breaches Found During Surveys

Compartmentation surveys — particularly intrusive surveys that open up ceiling voids and wall cavities — routinely find:

1. Unsealed cable penetrations — the single most common finding; IT and electrical contractors drilling through compartment walls without fire-stopping
2. Missing or displaced cavity barriers — particularly at compartment wall junctions with ceiling voids
3. Compartment walls that stop at suspended ceiling level — leaving the ceiling void open
4. Incorrect pipe collars — wrong size, wrong product, or not clipped correctly
5. Redundant penetrations — old pipe or cable runs abandoned but gaps not sealed
6. Mechanical duct penetrations without fire dampers — particularly in older buildings
7. Fire-stopping applied over previous fire-stopping — successive remediation attempts without clearing the original failed products
8. Fire-resisting walls and floors with unrated access panels — access hatches and inspection covers that are not fire-rated

Carrying Out a Compartmentation Survey

A visual compartmentation survey (walking the building) will identify obvious issues — propped fire doors, missing intumescent strips, visible gaps around pipes. However, the most serious breaches are typically hidden within ceiling voids and wall cavities. A thorough compartmentation survey requires:

• Access to ceiling voids (tile removal or borescope inspection)
• Inspection of all penetrations above suspended ceilings
• Checking cavity barriers at all compartment wall junctions
• Reviewing fire door condition (separate to compartmentation but part of the overall assessment)
• Documenting all findings with photographs and location plans

For higher-risk buildings, a Type 4 Housing Health and Safety Rating System (HHSRS) inspection or a fully intrusive compartmentation survey (involving some destructive investigation) may be required to give confidence in the findings.

Frequently Asked Questions

Does compartmentation apply to existing buildings or only new ones?

Building Regulations apply at the point of construction or material change of use. However, the RRO places an ongoing duty on the responsible person to maintain fire precautions in an effective state — and compartmentation is a fire precaution. Where a fire risk assessment identifies breaches in compartmentation, those breaches must be remediated regardless of when the building was built. There is no grandfather clause for legacy defects once they have been identified.

Who is responsible for maintaining compartmentation in a block of flats?

The responsible person for the common parts (typically the freeholder or managing agent) is responsible for the compartmentation of common areas and the structure. Individual flat owners or tenants are responsible for not breaching compartmentation within or from their flat — for example, by drilling holes in walls for cables without fire-stopping. In practice, this means managing agents must educate residents and conduct periodic surveys.

Can I use any intumescent mastic to seal a pipe penetration?

No. Intumescent mastic products are tested for specific applications — particular gap sizes, substrate types, and penetration types. A product tested for sealing 32mm plastic pipe penetrations in a 100mm block wall may not be valid for a 110mm soil pipe in a drywall partition. Always check the product's third-party test evidence or BBA certificate against the specific application. If in doubt, contact the manufacturer's technical team.

How do I know if a fire batt is correctly installed?

Fire batts (mineral wool or intumescent batts) must completely fill the annular gap around a penetration, be cut to the correct dimensions (no more than 25mm compression as a general guide — check manufacturer guidance), and be secured in position. The batt must sit flush with both faces of the wall or floor element, with any intumescent mastic applied to the exposed face. The surrounding structure must be intact — batts installed into crumbling plasterboard will not perform.

Regulations & Standards

• Building Regulations 2010 (SI 2010/2214) — Regulation 38 requires fire safety information to be handed over on completion

• Approved Document B (ADB) Volume 1 and 2 (2019 edition) — Guidance on fire safety in dwellings and other buildings

• BS 9999:2017 — Code of practice for fire safety in design, management and use of buildings; detailed compartment size and specification guidance

• BS EN 1366 series — Fire resistance of service installations; test methods for penetration seals, fire dampers, cable trays

• BS 476 Part 20 — Method for determination of the fire resistance of elements of building construction

• PAS 79-1:2020 — Fire risk assessments including compartmentation defects

• Regulatory Reform (Fire Safety) Order 2005 — Ongoing maintenance obligations

• Fire Safety (England) Regulations 2022 — Additional duties for higher-risk residential buildings

• Approved Document B — Fire Safety — MHCLG/DLUHC official guidance

• ASFP (Association for Specialist Fire Protection) — Technical guidance on passive fire protection and compartmentation

• FIRAS installer certification — Passive fire protection installer scheme

• BBA (British Board of Agrément) — Fire-stopping product certificates

• NFCC Compartmentation Guidance — National Fire Chiefs Council guidance

• passive fire protection — Overview of passive fire protection systems and products

• fire door installation — Fire door requirements and installation standards

• fire risk assessment — When and how to carry out a fire risk assessment

• cladding fire safety — External wall fire safety and cladding requirements