Approved Document B, NHBC Chapters 6.1, 6.9 and 8.1

Fire Stopping Inspection Checklist

Cavity barriers, compartment line penetrations, service seals, fire collars, socket boxes and loft party wall detail — the work that is invisible once boarded and impossible to prove later.

22 checks · Reviewed 27 August 2026 by the ProPlot site team · How we write these guides

In short

The fire stopping inspection checks that every breach of a fire-resisting wall, floor or cavity is sealed with a tested system installed to the manufacturer’s detail: cavity barriers at compartment lines and around openings, collars on plastic pipes, sealed service penetrations, protected socket boxes and a continuous separating wall through into the loft.

Use it on site

Fire stopping is the least glamorous and most consequential work on a plot. It takes minutes to do, it is hidden within days, and if it is wrong nobody finds out until it matters. It is also the item that has moved furthest up the regulatory agenda since the Building Safety Act, and the item most likely to be asked about years after handover.

The rule that catches most sites out is that the product and the detail have to match. A tested sealing system is only tested in the configuration it was tested in: the right depth, the right substrate, the right annular gap, the right pipe material. Substituting a generic mastic or a can of foam for the specified product means the seal has no evidence behind it, whatever it looks like.

Treat evidence as part of the work, not a task afterwards. A dated photograph of each barrier and each penetration, filed against the plot, is what turns a compliant installation into a provably compliant one.

What happens at this visit

When it happens

Continuously through the build — at cavity closing, at each floor and compartment penetration during first fix, and finally in the roof void before the loft is closed. Checked formally before boarding.

Who inspects

Site manager, warranty inspector and building control, with a specialist installer’s sign-off where a tested system requires one.

If it fails

Missed fire stopping found after boarding means opening up finished construction. Found after handover it becomes a warranty and, on some buildings, a regulatory matter.

How this visit is booked and recorded

Inspection type: Inspected as part of the pre-plaster key stage visit, and on apartments as a dedicated fire safety inspection per plot and per compartment.
Notice required: Run your own check before boarding. Once a compartment line is closed up, the only proof it was ever right is the photograph you took.
What it signs off: Feeds the Part B compliance evidence, the building control completion certificate, and on higher-risk buildings the golden thread record.

What the inspector will ask for

Fire strategy drawing showing compartment lines and required resistance periods
Cavity barrier specification and manufacturer installation detail
Tested system data sheets for each penetration seal, collar and sealant used
Robust Details or tested detail for separating walls and floors
Register of penetrations, if the project runs one

Photograph these moments in time

Every cavity barrier in position before the cavity is closed
Each service penetration sealed, with the product visible in the photograph
Fire collars on plastic pipes at floor and compartment wall penetrations
Separating wall built tight to the underside of the roof covering
Socket and switch boxes on compartment walls, showing the protection used

Concealed work cannot be re-photographed later. Take these before the element is covered and file them against the plot.

Reportable Item hotspots at this stage

A Reportable Item (RI) is a defect the inspector records against the plot. NHBC weigh each one by its Damage Potential, and the score feeds your site's Construction Quality Review. These are the ones raised most often here:

Cavity barriers missing around window and door openings
Service penetrations sealed with expanding foam instead of a tested system
Separating wall not continued fully into the loft void

How Reportable Items and Quality Common Scoring work

The fire stopping checklist

0 of 22 ticked — saved on this device

Cavity barriers

Check cavity barriers are installed at the edges of cavities, around openings and at compartment lines (AD B)
AD B
Verify barriers are the specified product, correctly sized to the cavity and tightly fitted with no gaps (AD B)
AD B
Confirm barriers are mechanically fixed as the manufacturer requires, not just wedged into place (AD B)
AD B
Check horizontal barriers at floor levels are continuous across the full length of the cavity (AD B)
AD B
Verify barriers around window and door openings are continuous on all four sides where required (AD B)
AD B
Confirm barriers at eaves and verges close the cavity to the roof line (AD B)
AD B

Compartment walls and floors

Verify separating walls are continuous to the underside of the roof covering with no gaps at the junction (AD B)
AD B
Check the compartment floor detail is complete at the perimeter, including the junction with the external wall (AD B)
AD B
Confirm the wall construction matches the Robust Detail or tested detail specified, with no substitutions (AD E)
AD E
Check no service run, chase or recess has reduced the wall below its tested thickness (AD B)
AD B

Service penetrations

Verify every penetration through a fire-resisting element is sealed with a tested system, not general purpose foam (AD B)
AD B
Check plastic pipes through compartment walls and floors have the correct fire collar or sleeve fitted (AD B)
AD B
Confirm cable and cable tray penetrations are sealed to the tested detail including annular gaps (AD B)
AD B
Verify ductwork through compartment lines has the required damper or fire-rated ducting (AD B)
AD B
Check the seal depth and substrate match the manufacturer’s tested configuration (AD B)
AD B

Openings, boxes and small breaches

Check socket and switch boxes on compartment walls are protected with the specified fire-rated enclosure or putty pads (AD B)
AD B
Verify back-to-back boxes on either side of a separating wall are offset as required (AD E)
AD E
Confirm downlights in fire-resisting ceilings are fitted with tested fire hoods or are a tested rated fitting (AD B)
AD B
Check loft hatches in protected routes are the correct fire rating where the design requires it (AD B)
AD B

Evidence and records

Confirm each barrier and penetration has been photographed before it is concealed, with the date and location recorded (AD B)
AD B
Verify the products used match the fire strategy and the data sheets held on file (AD B)
AD B
Check specialist installer sign-off is on file where the tested system requires accredited installation (AD B)
AD B

Above and beyond: build the evidence as you build the seal

Compliance here is only half the job. The other half is being able to prove it in five years, to somebody who was never on site. No inspector will fail the visit on these — they are the difference between a plot that passes and a plot that hands over clean.

Photograph every penetration with the product packaging in shot
It proves not just that a seal exists but which tested system it is, which is the question that actually gets asked.
When: As each penetration is sealed.
Keep a penetration register per plot
A simple list of location, service, product and date turns a scattered set of photos into a document somebody can audit.
When: Running, through first fix.
Mark compartment lines on the structure in paint before first fix starts
Trades cannot avoid breaching a line they cannot see. Marked lines mean penetrations get planned rather than discovered.
When: Before services are installed.
Hold a single tested product range on site and remove everything else
Mixed products are how untested foam ends up in a compartment wall. If the only thing in the store is the specified system, that is what gets used.
When: At procurement.
Re-walk every compartment after the last trade leaves and before boarding
The final penetration is almost always made by the last person in, after the inspection.
When: The day boarding starts.
Photograph the loft party wall from both sides before the access is closed
The loft is the most common location for an incomplete separating wall and the hardest place to correct later.
When: Before the roof is finished.

Full inspection point register

14 inspection points that apply at the fire stopping stage, each written in our own words from openly published guidance, with how to check it on site and what counts as acceptable. Use the checklist above on the day and this register when you need to settle a detail.

Cavity barriers around openings
How to check
Check every window and door reveal, head and cill for a continuous barrier before the frame is fitted.
Acceptable when
Continuous around the full perimeter of the opening, tight to both faces of the cavity
See the measured value
Cavity subdivision spacing
How to check
Measure the unbroken cavity length on each elevation and in the roof void, and check barriers are fitted at the subdivision spacing.
Acceptable when
No unbroken cavity longer than 20 m, with barriers tight to both faces and mechanically fixed
See the measured value
Fire barrier at the party wall and roof junction
How to check
Inspect from the loft before insulation: the barrier must run tight to the underside of the roof covering with no gaps at the truss line.
Acceptable when
Continuous to the underside of the roof covering, dressed around trusses with no unfilled gaps
See the measured value
Fire Resistance of Timber Frame Walls
How to check
Confirm that the timber frame system installed aligns with the fire strategy design and has supporting certification.
Acceptable when
Timber frame walls must achieve adequate fire resistance in accordance with the Building Regulations. All timber frame systems, including their specific materials and construction details, require robust evidence demonstrating compliance with relevant fire safety standards.
Fire Resistance of Timber Walls and Panels
How to check
Check that fire resistance details match approved plans for timber elements and materials are certified for fire performance.
Acceptable when
Timber-framed walls and panels must be designed and constructed to effectively control and resist the spread of fire and smoke. All building elements are required to possess an adequate level of fire resistance, compliant with relevant Building Regulations.
Fire stopping at fire-resisting wall junctions
How to check
Verify that all junctions and service penetrations in fire-resisting walls are adequately fire-stopped.
Acceptable when
Fire-resisting walls must be effectively fire-stopped or constructed to prevent the passage of fire at their perimeters, at openings for services, and at all junctions with other fire-resisting elements such as walls, floors, and roofs. This ensures the integrity of the fire compartment.
Fire stopping at service penetrations
How to check
Photograph every penetration through a compartment element before it is covered, with a plot and location reference.
Acceptable when
Full fire resistance of the element reinstated using a tested system installed to the manufacturer's instructions
See the measured value
Fire stopping in boxed eaves
How to check
Check that fire-stopping within boxed eaves is tightly fitted, correctly positioned, and securely fixed as per manufacturer guidelines.
Acceptable when
Fire-stopping must be installed within boxed eaves to create a complete seal, effectively preventing fire spread into the roof space. This material should be accurately cut to fit the void between battens and above the underlay, and securely fixed according to the manufacturer's instructions.
Fire-resisting construction examples
How to check
Confirm the fire-resisting elements match the approved design and are installed without compromise.
Acceptable when
Various construction types, including masonry walls, timber-framed walls, and floor or ceiling assemblies, can be designed to provide required levels of fire resistance. These designs aim to compartmentalise fire and protect adjacent areas of a building.
Fire-stopping for services penetrating fire-rated walls
How to check
Check that all services penetrating fire-rated walls have suitable fire-stopping installed, noting that it should be neatly finished and fully sealed.
Acceptable when
All service penetrations, such as pipes, cables, and ductwork, passing through fire-resisting walls must be fire-stopped. The fire-stopping installation should conform to building regulations and the approved design. Workmanship must be of a high standard, ensuring a complete and neat seal.
Integral garage fire separation
How to check
Verify that all wall and floor constructions forming the separation between a garage and dwelling meet the specified fire resistance requirements.
Acceptable when
Walls and any floors separating an integral or attached garage from the rest of the dwelling must be designed and constructed to achieve the required fire resistance. These elements must work together as a system to prevent fire spread from the garage into the habitable parts of the building.
Moisture Protection for Lightweight Cavity Barriers
How to check
Visually verify that cavity barriers within lightweight cladding are correctly integrated with moisture protection elements like DPCs or trays.
Acceptable when
In lightweight cladding systems, horizontal cavity barriers must be protected from moisture ingress using appropriate cavity trays, DPCs, or flashings. This ensures the long-term integrity and performance of the barrier by preventing water from saturating or degrading the materials.
Pipe diameter through a compartment element
How to check
Measure the pipe diameter at each penetration and check the sleeve or collar used against the tested detail.
Acceptable when
40 mm maximum for an unprotected pipe, otherwise a tested sleeve or collar appropriate to the pipe material
See the measured value
Separating wall build-up
How to check
Check the wall build-up against the tested specification before boarding: board type, layers, joints staggered and perpends filled.
Acceptable when
60 minutes fire resistance achieved by the specified tested construction, with no missing layers or unfilled joints
See the measured value

Most common reasons this visit fails

Expanding foam used as a fire seal

Standard polyurethane foam has no fire performance. Unless it is a tested fire-rated product installed to the tested detail, the penetration is unsealed.

Reportable Item and a common cause of building control refusal.

Cavity barriers missing around openings

Barriers get installed at floor levels and forgotten around windows and doors, where the cavity is most likely to be open.

Reportable Item; requires opening the reveal to correct.

Separating wall stopped at ceiling level

The wall looks complete from inside the plot but the loft void is continuous between dwellings. Fails both fire and sound.

Reportable Item and a sound test failure.

Penetration made after the inspection

A late satellite cable, boiler flue or waste run goes through a sealed compartment line and nobody re-seals it.

No record of what was installed

The work is correct but there is no photograph, no product reference and no register — so there is nothing to show when it is questioned.

Fire Stopping inspection FAQs

Fire stopping is the sealing of any gap or penetration through a fire-resisting wall, floor or cavity so that fire and smoke cannot pass through it for the required period. It includes cavity barriers, collars around plastic pipes, sealed cable and duct penetrations, and protection around socket boxes.

Not unless it is a fire-rated product tested in that exact configuration and installed to the manufacturer’s detail. Standard expanding foam offers no fire resistance, and a penetration filled with it is treated as unsealed.

At the edges of cavities, at compartment wall and floor lines, around openings such as windows and doors, and at junctions such as eaves and verges. The exact positions come from the fire strategy for the building.

Yes. A separating wall between dwellings must be continuous to the underside of the roof covering, with the junction sealed. Stopping the wall at ceiling level is one of the most common and most serious fire stopping failures.

A dated photograph of every barrier and penetration before concealment, the product reference or packaging visible where possible, the manufacturer data sheets, a penetration register, and any specialist installer sign-off the tested system requires.

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Where this sits in the build

The key stage inspection sequence on a typical UK housing plot.

Other inspection stage checklists

Excavation & foundations

21 checks →

Drainage

20 checks →

Basement / lower ground

28 checks →

Ground Floor & Slab

19 checks →

Superstructure

22 checks →

Timber Frame Erection

21 checks →

Roof

22 checks →

Windows and External Doors

24 checks →

Insulation & Airtightness

23 checks →

First Fix

28 checks →

Pre-Plaster

21 checks →

Second Fix

31 checks →

External Works & Pre-Handover

23 checks →

Pre-handover

22 checks →

General Quality

20 checks →

All key stage checklists

Related guides

Snag lists with GPS photo evidence

How to record and close out defects with evidence that stands up at handover.

NHBC stage inspections on site

Running key stage inspections and keeping the paperwork straight.

Build programme scheduling

Generating and maintaining plot-by-plot build programmes.

BREL report photo requirements

What Part L photographic evidence has to show, and when.

Go deeper: Quality Intelligence

Our free, cited reference library — critical dimensions, build stage guidance, common defects and plain-English guides.

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