Fire Compartmentation: A Guide to Building Safety

Fire compartmentation is a passive fire protection strategy that divides a building into sealed sections, or compartments, using fire-resistant walls, floors, doors and service penetration seals. Each compartment is designed to contain fire and smoke for a defined period, usually 30, 60, 90 or 120 minutes.
The purpose is twofold: to give occupants enough time to evacuate via protected escape routes, and to limit structural and property damage until the fire service can intervene. Compartmentation is a core requirement under Approved Document B of the Building Regulations in England and Wales, with equivalent provisions in Scotland, Northern Ireland and most international fire codes.
Effective compartmentation relies on every element performing together: fire-rated walls and floors provide the primary barrier, fire doors protect openings, cavity barriers close concealed voids, and fire stops seal service penetrations. A single unprotected cable tray or downlight cut-out can undermine the entire strategy. This is why compartmentation must be considered holistically at design stage, with every penetration, junction and cavity void accounted for in the fire strategy from the outset.

The Building Safety Act 2022 created the most significant change to UK building safety law in a generation. It established the Building Safety Regulator (BSR), brought residential buildings over 18 metres or 7 storeys within a new higher-risk building regime, and introduced three mandatory gateway stages: Gateway 1 (planning), Gateway 2 (pre-construction) and Gateway 3 (completion).

For fire compartmentation, Gateway 2 requires a full building safety case including a documented fire strategy before construction can begin. The golden thread requirement means every product in the compartment line must be traceable: the product selected, the test evidence it carries, and the installation detail on site must all be logged and accessible.

Under section 38 of the Building Safety Act, developers and principal contractors face potential liability if a building does not comply with building regulations, and the limitation period for civil claims has been extended. For specifiers, this substantially raises the importance of third-party certified products, competent installation and documented inspection records.

Tenmat cavity barrier systems are supported by third-party certification and clear product information intended to support robust specification and golden thread record-keeping.

Approved Document B is published in two volumes. Volume 1 covers dwellings; Volume 2 covers other buildings. Both were updated in 2022 following post-Grenfell review.

Volume 1 Section 3 sets out that concealed cavities must not undermine compartment lines. Section 9 adds requirements for external wall cavities: limited combustibility materials are required in buildings over 11 metres, and A2-s1,d0 or better classification in buildings over 18 metres. These classifications apply to every product installed within the external wall cavity, including cavity barriers.

Volume 2 Sections 8 and 9 repeat these requirements for non-residential buildings, with additional requirements for taller buildings. Both volumes require cavity barriers to be placed at compartment boundaries, at floor and party-wall junctions, around openings in external wall cavities, and at the edges of cavities. Correct positioning at each of these locations is essential to maintaining the integrity of the compartment line.

ADB Volume 1, Table 9.1 and Diagram 9.1 map directly to Tenmat products: the NVFB range (A1 stone mineral wool) and the VFB open state range (A2-s1,d0 or better classification).

BS EN 1363-1 is the foundational fire resistance testing standard. It defines the ISO 834 time-temperature curve, failure criteria (E for integrity, I for insulation, R for loadbearing capacity), and classification rules. All cavity barrier test reports in the UK and Europe reference this standard.

BS EN 1365 covers loadbearing elements. It is relevant to compartment wall and floor assessment in structural masonry and concrete-frame buildings where the fire-rated element also carries load.

For cavity barriers specifically, open state and ventilated barriers (including Tenmat VFB range) are tested in representative external wall build-ups to BS EN 1363-1, using the ASFP TGD19 protocol for open-state products. Tenmat non-ventilated cavity barriers are tested and classified in representative constructions in accordance with the standards and assessment routes stated in the applicable product evidence.

Performance ratings are expressed as E30, EI30, E60, EI60, E120 or EI120. The test report records the exact wall build-up, cavity width and fixing details. Any variation from the tested or assessed field of application must be reviewed by a competent party and supported by appropriate evidence before specification or installation. Where available and applicable, an extended application or third-party technical assessment may be required.

Cavity barriers and fire stops are both passive fire protection components, but they address different weaknesses in the compartment line.

A cavity barrier is installed inside a concealed void, typically the gap behind external cladding, inside a timber frame or in a roof space, to block fire and smoke spread through that continuous cavity. Barriers are placed at compartment boundaries, at floor junctions and at building envelope edges. The ventilated cavity fire barriers hub covers the full Tenmat product range for this application.

A fire stop seals a specific hole where a pipe, cable, duct or conduit passes through a fire-rated wall or floor. That penetration creates a direct path for fire to bypass the compartment line. Pipe fire sleeves, intumescent seals and fire collars close individual penetrations to the same fire resistance period as the host element.

For a full comparison of both product families, including specification guidance and regulatory references, see the guide to the 5 key differences between cavity barriers and fire stops.

Approved Document B requires compartmentation in virtually every multi-storey or multi-occupancy building in England and Wales.

For dwellings, Volume 1 requires compartment walls and floors between every dwelling unit and between dwellings and common areas. In blocks of flats over 11 metres, external wall cavities must carry limited combustibility cavity barriers. Over 18 metres, A2-s1,d0 or better classification is required for all external wall products. These height thresholds were reinforced following the post-Grenfell review of the 2022 edition.

For non-residential buildings, Volume 2 sets maximum compartment sizes by use class, with requirements varying according to the purpose group of the building. Hospitals, care homes and educational buildings carry additional requirements under HTM 05-02 and BS 9999, which sit alongside and extend the baseline ADB provisions.

Higher-risk buildings under the Building Safety Act 2022, defined as residential buildings of 18 metres or 7 storeys, trigger the full BSR gateway regime, requiring a documented fire strategy at each stage. Beyond legal minimums, compartmentation is also required by insurer mandates on commercial and industrial buildings, and by developer standards on mixed-use schemes.

When a pipe passes through a fire-rated wall or floor, the annular gap around the pipe, and in the case of plastic pipes the pipe bore itself, must be sealed to maintain the compartment line.

Pipe fire sleeves fit around plastic pipes at the penetration point. When the pipe melts in a fire, the sleeve’s intumescent lining expands to fill the void and maintain integrity. They suit PE, PVC and CPVC pipes across a range of diameters.

Intumescent pipe wraps perform the same function but are wrapped around the pipe at installation rather than pre-formed. They suit larger diameters and retrofit applications.

For metal pipes, the annular gap is typically sealed with intumescent sealant or fire-rated mortar. All penetration seal systems must carry test evidence to BS EN 1366-3 in the specific host element and pipe configuration on the project. The intumescent materials range covers the most common penetration applications with traceable IFC certificates.

The golden thread was introduced by Dame Judith Hackitt’s 2018 review and given legal force through the Building Safety Act 2022. It requires a continuous, accurate digital record of information about a building’s design, construction and occupation.

For fire compartmentation, this means: every product in the compartment line must be documented (manufacturer, product reference, test certificate number, field of application); every deviation from the tested build-up must be assessed and the assessment recorded via an EXAP report; installation must be documented by a competent installer.

For higher-risk buildings, this information must be available to the BSR at gateway submissions and kept current by the Accountable Person post-occupation. Products supported by third-party certification and clearly defined fields of application can simplify specification, verification and record-keeping requirements.

Tenmat’s IFC Certification and CCPI-verified products are specifically designed to meet this standard. The comprehensive guide to cavity fire barriers explains the documentation requirements in detail for external wall cavity barrier installations.

Healthcare fire compartmentation follows the progressive horizontal evacuation strategy defined in HTM 05-01 and referenced in BS 9999. Because many patients cannot self-evacuate, the strategy moves them sideways into an adjacent safe zone on the same floor rather than down stairs.

The compartment boundaries between adjacent zones must maintain integrity and insulation for the transfer period, typically 30 to 60 minutes minimum. The same period applies to every element in the compartment line: walls, floors, fire doors, cavity barriers and every service penetration through the boundary.

Healthcare buildings run continuous refurbishment works alongside live occupation. Every break in the compartment line during works must be documented and temporarily sealed. This is where competent contractor certification (FIRAS, IFC Certification) and regular inspection are particularly important.

For new healthcare builds, the fire compartmentation strategy is developed across all RIBA stages. Cavity barriers behind rainscreen cladding and curtain walling are increasingly reviewed separately from general compartmentation because of the post-Grenfell regulatory changes to external wall product standards.

Intumescent materials expand significantly when exposed to heat, typically activating at 120 to 200 degrees Celsius depending on the product. This expansion closes gaps, crushes burning pipes and seals penetrations when a fire reaches the compartment line.

In fire compartmentation, intumescent materials serve several distinct functions. Fire door strips expand on heating to seal the gap between door and frame. Pipe fire sleeves, collars and wraps rely on intumescent linings to close the bore of a plastic pipe as it melts. Open state cavity barriers, including Tenmat’s VFB range, contain intumescent layers that expand to seal the ventilated cavity automatically in a fire.

Intumescent sealants are used around the annular gaps of metal pipe and cable penetrations, in expansion joints and at compartment wall junctions where movement must be accommodated.

All intumescent products must be tested in the specific configuration they will be used in. Substituting one intumescent product for another in an existing tested assembly invalidates the test evidence. The intumescent materials range on tenmat.com covers the most common penetration and barrier applications with traceable test certificates.