What is fire stopping?
Fire stopping is the material or system used to seal a gap in fire-resisting construction: around pipes, cables, cable trays and ducts that pass through a compartment wall or floor, and along linear joints such as the head of a wall. Penetration seals are tested to BS EN 1366-3:2021 and classified to BS EN 13501-2:2023; older products may have been tested to BS 476-20:1987 and BS 476-22:1987.
You find fire stopping wherever a service crosses a compartment line: risers, plant rooms, service cupboards and above suspended ceilings.
What is a cavity barrier?
A cavity barrier is a barrier installed inside a concealed space to stop fire and smoke travelling through it. Without one, a fire that gets into a roof void or ceiling void can spread across the building out of sight, bypassing the fire-resisting walls below.
Approved Document B (2019 edition incorporating 2026 amendments) sets out where cavity barriers are expected in new buildings in England, such as where a compartment wall meets a roof void or a ceiling void.
Where is each one found?
- Fire stopping: at penetrations and joints in fire-resisting walls and floors.
- Cavity barriers: in concealed spaces such as roof voids, ceiling voids, floor voids and wall cavities, often in line with the compartment walls below.
The two often meet. Where a compartment wall stops at a suspended ceiling, the line may need to continue up to the slab, or be closed by a cavity barrier, depending on the design.
How do they commonly fail?
Fire stopping usually fails when later works make new holes, or remove services and leave the hole behind. It also fails when unsuitable materials are used, such as general-purpose foam.
Cavity barriers are more often missing altogether, never installed or removed during later works. They can also be damaged by services pushed through them, gaps at their edges, or barriers that do not meet the roof or structure above.
How does a survey check both?
A compartmentation survey follows each compartment line, through risers and plant rooms and up into ceiling and roof voids where access is provided. It records penetrations and their seals, and where cavity barriers would be expected, whether one is present and its condition, with photographs and locations.
Some concealed spaces cannot be seen without opening up. Those limits are recorded in the report. See compartmentation survey types for intrusive options.
Frequently asked questions
Is a cavity barrier the same as fire stopping?
No. Fire stopping seals penetrations through fire-resisting construction; a cavity barrier closes a concealed space.
Do you check roof voids?
Yes, where safe access is provided.
Can a missing cavity barrier be seen without opening up?
Often, where the void can be reached through a hatch or tile. Where it cannot, the report says so.
Which standard covers cavity barriers in new buildings in England?
Approved Document B (2019 edition incorporating 2026 amendments) sets out where they are expected.
Do you install cavity barriers?
Ask us about remedial works. Any work is quoted separately after the scope has been verified on site.