What is fire stopping?

Fire stopping is any approved material or system used to seal gaps, penetrations, and joints in fire-resisting elements of a building — walls, floors, and ceilings — to prevent the passage of fire and smoke. Every pipe, cable, duct, and beam that passes through a fire-resisting wall or floor creates a potential breach in the fire barrier. Fire stopping reinstates the required fire resistance at that point. Without it, compartmentation fails at the point of penetration.

Where is fire stopping legally required?

In the UK, Approved Document B to the Building Regulations requires that all penetrations through fire-resisting elements are fire stopped. This applies to: pipes and cables passing through party walls or floors; ductwork penetrations; structural elements where the fire resistance must be maintained; and junctions between fire-resisting walls and floors. In HMOs and flats, fire stopping between dwelling units is often found to be absent or breached by subsequent building works. For compartmentation context, see our fire compartmentation glossary entry.

What happens if fire stopping fails?

If fire stopping is absent or failed at a penetration, fire and smoke pass through the opening and breach the compartment. The effect is that the fire spreads to the next floor or adjacent flat without the delay intended by the compartment design. In a multi-storey building, a single failed fire stop can allow a fire starting on one floor to reach a sleeping floor above within minutes — bypassing the protected staircase entirely. This is why fire stopping is a life-safety defect, not merely a compliance note.

How do I identify fire stopping failures?

Common visible signs include: visible gaps around pipes or cables where they pass through walls or ceilings; missing or damaged intumescent collars on plastic pipes; fire-rated sealant that has cracked, shrunk, or been disturbed by subsequent works; and open cable ducts or service voids that communicate between floors. A fire risk assessment should include a check of all visible penetrations. In older buildings, fire stopping was often not installed at all — any penetration that is not sealed and has no visible intumescent product should be assumed to be unprotected until confirmed otherwise.

⚠ Emergency: If fire spreads rapidly through a building with a fire stopping deficiency — evacuate immediately and call 999. Do not re-enter.

Glossary — Passive Fire Protection

Fire Stopping

Fire stopping seals the gaps that building services — pipes, cables, and ducts — create in fire-resisting elements. Without it, compartmentation is theoretical. Every unstopped penetration is a direct fire and smoke path between compartments.

Definition

Fire stopping — materials and systems used to seal penetrations, gaps, and joints in fire-resisting elements so that the required fire resistance (typically 30 or 60 minutes) is maintained across the entire element, including at service penetrations. Required under Approved Document B (Building Regulations) and enforced under the RRO 2005 as part of the fire risk assessment.

Common fire stopping materials and applications

Material	Application	Standard
Intumescent sealant	Sealing cable and pipe penetrations through fire-resisting walls; expands on heat to block opening	BS EN 1366-3
Intumescent collars	Around plastic pipes — the collar crushes the pipe as it expands when heated	BS EN 1366-3
Mineral wool / rockwool board	Filling larger voids; duct penetration packing; between joists at party walls	BS EN 1363-1
Fire-rated board (calcium silicate, etc.)	Capping service voids; fire-rated boxing around ductwork	Tested to EI classifications
Intumescent pillows / bags	Cable tray bundles passing through walls; flexible bundled cables	Site-applied; BS EN 1366

The relationship with compartmentation

Fire stopping is the implementation detail that makes fire compartmentation work in practice. A compartment can be perfectly designed — fire-resisting walls, floors, and fire doors — and still fail at the first penetration if fire stopping is absent. In high-rise residential buildings, the building safety investigations triggered by the Grenfell Tower fire identified fire stopping deficiencies as among the most common active remediation requirements.

Intumescent products: how they work

Intumescent materials expand dramatically when exposed to heat — typically beginning at around 150–200°C. An intumescent sealant around a plastic pipe will remain flexible at ambient temperature; when fire heats the surrounding area, the sealant expands to fill the void left as the plastic pipe melts. Without an intumescent product, the melted pipe leaves an open hole. The test standards (BS EN 1366 series) verify that products maintain integrity for their rated period after the pipe has been destroyed.

Common inspection failures

Penetrations cut for cables or pipes and never sealed
Intumescent collars missing from plastic pipes in ceilings of lower floors
Fire stopping disturbed by subsequent maintenance works and not reinstated
Rockwool packing that has compressed or been removed
Open service voids communicating between floors, visible through inspection hatches

For high-rise and flat fire safety context where fire stopping is most critical, see our fire safety for flats guide and our high-rise fire safety 2026 article.

Frequently asked questions

FAQ

Fire Stopping

Common fire stopping materials and applications

The relationship with compartmentation

Intumescent products: how they work

Common inspection failures

Related terms and guides

Frequently asked questions

Frequently asked questions