Cavity barriers and fire stopping around openings and services
Cavity barriers are required continuously around the full perimeter of every opening in a cavity wall, at the edges of cavities, and at every compartment junction. Where a service passes through a fire-resisting element, the fire stopping has to reinstate the full fire resistance of that element using a system tested in that substrate.
The figures on one page
| Item | Limit | Figure |
|---|---|---|
| Cavity barriers around openings in a cavity wallIncludes windows, doors, and any duct or vent passing through the cavity | Minimum | Continuous around the full perimeter of the opening |
| Cavity barriers at timber frame panel junctionsBarriers tight to both faces of the cavity, fixed and continuous | Maximum | At every compartment junction and opening edge |
| Fire stopping at a service penetrationSealed with a system tested for that substrate, aperture size and service type | Minimum | Reinstate the full fire resistance of the element |
| Cavity subdivision in a roof voidMaximum distance between cavity barriers in a concealed roof space | Maximum | 20 m |
| Door Clearances and Fire Door InstallationInternal doors, including fire doors, must be installed with sufficient clearance from the finished floor level to accommodate flooring, typically around 10mm for non-fire doors | exact | 10 mm |
| Fire resistance of a compartment floor between flatsIncludes the ceiling line, service voids and any penetrations through it | Minimum | 60 minutes |
| Maximum pipe diameter through a compartment wall or floorNominal internal diameter for a non-fire-rated pipe; larger pipes need a tested sleeve, collar or non-combustible material | Maximum | 40 mm |
What this means on site
The most common cause of a failed fire stopping inspection is not the missing barrier but the wrong product: a sealant tested in blockwork used in plasterboard, or a collar sized for a different pipe diameter.
Barriers must be tightly fitted with no gaps at joints, and fixed so they cannot slump into the cavity over time.
What actually gets picked up
- Barrier stopped short at the head or sill of an opening, leaving a clear path up the cavity.
- Expanding foam used as fire stopping where a tested system is required.
- Penetrations formed after the barrier was installed and never made good.
- No evidence retained — no photographs of the barrier before it was closed in.
Questions we get asked
- Where are cavity barriers required?
- Around the full perimeter of every opening, at the edges of cavities, at compartment junctions, and subdividing large cavities including roof voids.
- What counts as acceptable fire stopping?
- A system tested in the same substrate and configuration that reinstates the full fire resistance of the element being penetrated.
- How is fire stopping evidenced at inspection?
- Photographs before close-in, product data for the tested system, and a record of the location — this is normally requested at pre-plaster.
Where this is inspected
This is ProPlot's editorial summary of publicly available UK regulation and good practice. It is not building control approval or a warranty determination, and the designer's or manufacturer's tighter figure always takes precedence.