What is fire stopping?

Fire stopping is the sealing of gaps, holes, and service penetrations in fire-resisting elements (walls, floors, ceilings) to prevent fire and smoke from bypassing the fire-resisting construction. When a pipe, cable, duct, or beam passes through a fire compartment wall or floor, it creates a hole - without sealing, fire can travel through that hole and defeat the fire compartmentation. Fire stopping materials seal these holes to the same fire resistance rating as the surrounding construction. It is a form of passive fire protection that requires no activation or manual operation.

What materials are used for fire stopping?

Fire stopping materials include: mineral wool (rock wool or glass wool) tightly packed around rigid pipes and cables - the most commonly used domestic fire stopping material; intumescent mastic or sealant (applied in the annular gap around penetrations, expands on heat); intumescent pipe collars (clamps around plastic waste pipes that close when the pipe melts in a fire); intumescent boards or pillows (for larger service openings); gypsum-based mortars for filling structural penetrations; and fire-rated silicone sealant for cable bundles. The choice of material depends on the penetrating element (metal pipe, plastic pipe, cable, duct), the gap size, and the required fire resistance rating.

Where is fire stopping required in domestic properties?

Fire stopping is required wherever services (pipes, cables, ducts) pass through a fire-resisting element. In domestic houses, key locations include: pipes and cables passing through the floor between floors in a house of three or more storeys (where the floor has fire resistance); pipes and cables passing through the ceiling of an integral garage into the house above; any penetration through a separating wall between semi-detached or terraced houses (which must have 60-minute fire resistance); and any penetration through the fire-resisting ceiling of a loft conversion. Even in two-storey houses without loft conversions, the garage ceiling and party walls must be fire-stopped at service penetrations.

What is a cavity barrier?

A cavity barrier is a fire stopping measure installed within concealed cavities (roof spaces, wall cavities, floor voids) to restrict the spread of fire through the cavity. Without cavity barriers, a fire in one part of a building can spread rapidly through connected cavities without encountering any fire-resisting construction. Cavity barriers are required in roof spaces at party wall positions (to prevent fire spreading from one house's loft to an adjacent house's loft), at junctions between cavities, and at the edges of cavities around openings. They are typically formed from mineral wool, timber blocking, or proprietary intumescent strips fitted in the cavity.

Fire Safety noun / verb

Fire Stopping

/ faɪə ˈstɒpɪŋ /

Also known as: penetration seal, passive fire protection, cavity barrier, fire seal

Definition

Fire stopping is the sealing of gaps, holes, and service penetrations in fire-resisting walls, floors, and ceilings to prevent fire and smoke bypassing the fire compartmentation. It is a form of passive fire protection requiring no activation. Common materials include mineral wool packing, intumescent mastic, intumescent pipe collars (for plastic pipes), and gypsum-based mortars. Required wherever pipes, cables, or ducts pass through a fire-resisting element, and in roof voids at party wall positions as cavity barriers.

In practice

Fire stopping is one of the most commonly missed or poorly executed elements of domestic building work. Every pipe and cable that a plumber or electrician routes through a fire compartment wall or floor creates a penetration that must be sealed. Typical failures include: gaps left around plastic waste pipes through ceilings (plastic pipes burn away in a fire, leaving an open hole - intumescent pipe collars are required to close this hole); cables passing through walls without mineral wool filling the annular gap; and builder's foam used as a fire stop (standard polyurethane foam is combustible and unsuitable for fire stopping - only certified fire-rated foam is acceptable).

Fire stopping must be inspected before it is concealed - Building Control inspectors will look for fire stopping evidence as part of loft conversion, garage conversion, and new-build inspections. Evidence (photographs before closing up, together with product certification) should be kept in the building file. In multi-storey and multi-residential buildings (blocks of flats, HMOs), fire stopping is a critical life-safety issue - the Grenfell Tower Inquiry identified deficient cavity barriers and fire stopping as significant factors in fire spread.

Building Regulations

Part B requirementAll penetrations through fire-resisting elements must be sealed

Plastic pipesIntumescent pipe collar required through fire walls/floors

Cavity barriersRequired in roof voids at party wall positions

NOT suitableStandard PU foam - must use certified fire-rated products only

Approved Document B Section 9 (Concealed spaces) requires cavity barriers in concealed roof voids and wall cavities to restrict fire spread, and fire stopping at all service penetrations through fire-resisting elements. Materials used for fire stopping must be non-combustible or tested and certified for the specific application. BS EN 1366-3 covers testing of linear joint seals and penetration seals. Building Control must inspect fire stopping before it is concealed - do not close up walls or ceilings with service penetrations until they have been inspected and signed off.

Full Building Regulations guidance

Fire Stopping

Just so you know...