What Is Passive Fire Compartmentation and Why Does It Matter in Multi-Occupancy Buildings?

TL;DR

• Passive fire compartmentation divides a building into fire-resistant zones to contain smoke and flames and allow safe evacuation.

• In multi-occupancy buildings such as flats, HMOs, student accommodation and care homes, compartmentation is a legal requirement under the Regulatory Reform (Fire Safety) Order 2005 and the Building Safety Act 2022.

• Breaches are common after refurbishments, maintenance works and building service penetrations.

• A professional compartmentation survey identifies breaches that are invisible during routine inspections.

• Responsible persons face legal liability for failure to maintain compartmentation integrity.

When a fire starts in a multi-occupancy building, the outcome is rarely determined by how the fire began. It is determined by how well the building contains it.

Passive fire compartmentation is the structural system that makes that containment possible. It is not a product you can buy or a system you can switch on. It is built into the fabric of the building itself, through fire-rated walls, floors, ceilings, doors and seals. When it works correctly, a fire in one flat or one room stays in that space long enough for occupants to escape and for emergency services to respond.

When compartmentation has been breached, a building that looks compliant on paper can fail within minutes of a fire starting.

This guide explains what passive fire compartmentation is, why it matters more in multi-occupancy buildings than anywhere else, what the law requires, and how to ensure your building is actually protected.

What Is Passive Fire Compartmentation?

Passive fire compartmentation is the process of dividing a building into separate fire-resistant zones, called compartments. Each compartment is designed to contain a fire for a minimum period, typically 30 or 60 minutes, giving occupants time to evacuate and limiting the spread of smoke and flames throughout the building.

The word "passive" distinguishes this from active fire protection systems such as sprinklers and fire alarms. Passive measures require no activation. They work through their physical construction, not through sensors, electronics or water supplies.

The Key Components of Compartmentation

Compartmentation relies on the integrity of several different elements working together:

Fire-rated walls and floors form the primary barriers. These are constructed or lined with materials tested to withstand fire for a defined period.

Fire stopping seals any gaps, joints or penetrations in those barriers. Wherever a pipe, cable, duct or building service passes through a fire-rated wall or floor, that penetration must be sealed with a tested, approved product to maintain the compartment's fire resistance.

Fire doors maintain compartment boundaries at every opening. A fire door is a tested assembly that includes the door leaf, frame, intumescent seals, smoke seals, hinges and hardware. Every component contributes to its fire resistance rating.

Cavity barriers prevent fire from spreading through concealed voids and cavities within the building structure.

Together, these elements form an integrated system. A single failure in any one component can compromise the entire compartment.

Why Multi-Occupancy Buildings Present a Higher Risk

Multi-occupancy buildings are more vulnerable to compartmentation failures than single-occupancy properties for several reasons.

Multiple Tenancies Mean More Penetration Points

In any multi-occupancy building, there are more occupants, more services, and more opportunities for the building fabric to be penetrated. Every time a tradesperson runs a cable, installs pipework or carries out a repair, there is a risk that a fire-rated barrier will be breached and not correctly reinstated.

These penetrations are often invisible after the work is completed. Cables pass through walls in ceiling voids. Pipes run between floors in service risers. Unless a surveyor physically inspects the concealed structure, breaches can go undetected for years.

Residents May Not Have Control Over Shared Spaces

In a block of flats or HMO, individual residents have no control over the common parts, corridors, service risers or structural fabric. Compartmentation in these areas is entirely the responsibility of the building owner or responsible person. If those areas are compromised, every resident is at risk.

Higher Overnight Occupancy

Multi-occupancy residential buildings typically have higher overnight occupancy than commercial premises. Fires at night are more dangerous because occupants may be asleep, evacuation takes longer, and the consequences of slow detection or contained spread are more severe.

Frequent Refurbishments and Maintenance Works

Buildings with multiple tenancies are refurbished and maintained more frequently than single-occupancy buildings. Each intervention creates a new opportunity for compartmentation to be compromised. A contractor who replaces a boiler, upgrades insulation or installs new electrical services may not be aware of their obligation to reinstate fire stopping after completing their works.

What the Law Requires

In England and Wales, the legal framework for passive fire compartmentation in multi-occupancy buildings is primarily set by two pieces of legislation.

The Regulatory Reform (Fire Safety) Order 2005 requires the responsible person for any non-domestic premises, and for the common parts of multi-occupancy residential buildings, to carry out a suitable and sufficient fire risk assessment and implement appropriate fire safety measures. Compartmentation is explicitly included within those measures.

The Building Safety Act 2022 introduced significantly strengthened requirements, particularly for higher-risk buildings (those over 18 metres or seven storeys with at least two residential units). The Act created new accountabilities for building owners and managers, with robust enforcement powers and serious consequences for non-compliance.

For buildings subject to the higher-risk regime, a Structural Safety Case Report is required, and building owners must demonstrate ongoing compliance with fire safety obligations.

Approved Document B (Building Regulations Part B) sets out the technical standards for compartmentation in new buildings and material alterations. Where existing buildings have been altered without regard to these standards, compartmentation may no longer be compliant.

Responsibility sits with the responsible person, which is typically the building owner, managing agent or employer. Failure to maintain compartmentation integrity is not a minor oversight. It can result in prosecution, unlimited fines, and in the event of a fire, criminal liability.

Our fire compartmentation service covers surveys, remedial works and ongoing compliance support for multi-occupancy buildings across the UK.

What a Compartmentation Survey Involves

A compartmentation survey is a systematic inspection of all fire-rated elements within a building to identify breaches, deficiencies and areas of concern.

A professional survey will typically include:

• Inspection of all fire-rated walls, floors and ceilings

• Identification of all service penetrations through fire-rated elements

• Assessment of fire stopping products used and their suitability and condition

• Review of fire door assemblies, including frames, seals and hardware

• Inspection of cavity barriers where accessible

• A detailed written report with photographic evidence of findings

• Remedial recommendations with priority ratings

Surveys should be carried out by a competent specialist. For high-risk buildings, BM TRADA Q-mark certification and third-party accreditation are markers of a qualified contractor.

Our passive fire protection services team carries out compartmentation surveys and remedial works to a third-party accredited standard.

Common Causes of Compartmentation Failure in Multi-Occupancy Buildings

Understanding how compartmentation fails is essential to preventing it. The most common causes are:

Service penetrations left unsealed. This is the most frequent finding in compartmentation surveys. Wherever a cable, pipe or duct passes through a fire-rated element, it must be sealed with a tested fire stopping product. In practice, these penetrations are routinely left open, or filled with non-rated materials that will fail in a fire.

Our fire stopping service covers penetration sealing with BM TRADA-certified products and methods.

Fire doors that no longer meet their rating. Fire doors are complex assemblies. Over time, seals deteriorate, frames become damaged and hinges fail. A fire door with a broken smoke seal or a gap above the door leaf is no longer providing its rated protection. Our fire door inspection service identifies defects and remedial requirements.

Missing or incorrectly installed cavity barriers. In older buildings, cavity barriers may never have been installed. In refurbished buildings, they may have been removed or displaced during works and not reinstated.

Poor quality or non-compliant fire stopping products. Not all products sold as fire stopping are tested or rated. The use of the wrong product in the wrong application can result in a seal that looks intact but will fail quickly under fire conditions.

Building work carried out without fire safety awareness. Many compartmentation failures result from works carried out by contractors who were not aware of fire safety obligations, or who prioritised speed over compliance.

Who Is Responsible for Compartmentation in Multi-Occupancy Buildings?

Responsibility is clear in law, even if it is not always clear in practice.

In a block of flats or an HMO, the responsible person is typically the building owner, the management company or the principal accountable person under the Building Safety Act. That person is legally responsible for ensuring fire safety measures, including compartmentation, are adequate and maintained.

Leaseholders and tenants have responsibilities within their own demised areas in some circumstances, but the structure, common parts and shared services remain the responsibility of the building's responsible person.

Where managing agents are appointed, they may take on delegated responsibilities, but ultimate accountability cannot be outsourced. If compartmentation fails and a fire spreads, the enforcement action and any resulting prosecution will focus on the responsible person.

A current and thorough fire risk assessment is the starting point for identifying compartmentation obligations and gaps. However, a fire risk assessment alone is not sufficient to identify compartmentation breaches. A dedicated compartmentation survey is required for that purpose.

Frequently Asked Questions

What is the difference between fire stopping and fire compartmentation?

Fire compartmentation is the overall system of dividing a building into fire-resistant zones using rated walls, floors, doors and seals. Fire stopping is a specific component of compartmentation. It refers to the materials and methods used to seal penetrations through fire-rated elements, such as where cables, pipes and ducts pass through walls or floors. Both are essential to maintaining the integrity of the compartment.

How often should a compartmentation survey be carried out?

There is no single prescribed frequency set out in UK legislation, but compartmentation surveys should be carried out following any refurbishment or building works, after a change of use, when a fire risk assessment identifies concerns, and as part of a regular compliance programme. For higher-risk buildings under the Building Safety Act 2022, more frequent formal inspections are generally expected. Many responsible persons commission surveys every three to five years as a minimum.

Are HMOs subject to fire compartmentation requirements?

Yes. Houses in multiple occupation are subject to fire safety requirements under the Housing Act 2004, the Regulatory Reform (Fire Safety) Order 2005 and additional mandatory HMO licensing conditions. Compartmentation requirements apply to the structural elements of HMOs, including walls, floors, ceilings and fire doors between bedrooms and shared areas. Local authorities can and do enforce these requirements through licensing conditions.

What happens if compartmentation is found to be inadequate?

If a compartmentation survey identifies breaches, remedial works should be carried out as a priority. The urgency depends on the severity of the breach. An unsealed penetration in a high-risk area may require immediate action. A deteriorating fire door seal may allow a short period for planned replacement. The survey report should include a priority rating for each finding. Leaving known compartmentation failures unaddressed creates significant legal exposure for the responsible person.

Does a fire risk assessment cover compartmentation?

A fire risk assessment should consider compartmentation as part of a wider review of passive fire protection. However, most fire risk assessors are not specialist passive fire protection surveyors. A fire risk assessment can flag compartmentation concerns, but it does not substitute for a dedicated compartmentation survey. For detailed identification of penetration failures, cavity barrier issues and fire stopping defects, a specialist survey by a competent passive fire contractor is required.

What is a higher-risk building under the Building Safety Act 2022?

Under the Building Safety Act 2022, a higher-risk building in England is defined as a building that is at least 18 metres or seven storeys high and contains at least two residential units. These buildings are subject to the higher-risk building regime, regulated by the Building Safety Regulator. Responsible persons for these buildings have additional duties, including registration, a structural safety case report and an ongoing resident engagement strategy. Compartmentation requirements are among the most significant elements of compliance for these buildings.

Can I rely on original building records to confirm compartmentation compliance?

Original building records, such as as-built drawings and fire strategies, provide useful context but do not confirm that compartmentation is currently intact. Buildings change over time through maintenance, refurbishment and building services works. Compartmentation that was correct at original construction may have been compromised many times since. The only way to establish current compartmentation integrity is through a physical inspection by a qualified specialist.