11 common fire stopping defects [And how to fix them]

Fire stopping defects are more common than they should be.

A review of 3,500 fire risk assessments carried out between October 2022 and September 2023 found that inadequate fire stopping accounted for around 20% of recommendations. The analysis also found that most of these recommendations related to missing or poorly maintained fire stopping.

And that’s just in residential buildings.

Given how important fire stopping is in preventing fire and smoke from spreading through a building, it’s crucial to catch problems early.

With this in mind, here are 11 common fire stopping defects and how to fix and prevent them.

Key takeaways

• Seal every service penetration
  Even small gaps can let fire and smoke spread.

• Use the right fire stopping products
  Check product evidence, compatibility, and application requirements.

• Install systems correctly
  Follow specified depths, compression, fixings, and movement limits.

• Protect and inspect completed work
  Check for damage, gaps, and missing seals before handover.

• Use fire stopping software to manage inspections
  Onetrace helps contractors capture evidence, track defects, and create client-ready reports.

11 common fire stopping defects at a glance

Category 1: Missing fire stopping defects

Fire stopping defects often start with something that should be there but isn’t.

1. Missing or incomplete fire stopping around service penetrations

Every pipe, cable, conduit, duct, or cable tray that passes through a fire-rated wall or floor needs a suitable firestop.

Yet, it’s common to find openings left completely unsealed, partially filled, or sealed on only one side when the specified system requires treatment on both. Redundant openings can also be overlooked after services are removed or rerouted.

These gaps often appear when services are added late, different trades work to separate schedules, or responsibility for sealing penetrations is unclear.

Whatever the cause, an unsealed opening can undermine the fire resistance of the compartment and allow flames, smoke, and hot gases to spread.

How to prevent or fix it

• Identify every service penetration and check it against the fire strategy and relevant drawings.

• Specify a tested fire stopping system that suits the service, opening, and supporting construction.

• Seal redundant openings using an appropriate system rather than leaving them exposed.

• Inspect completed work before it’s concealed, and record its location and installation.

Category 2: Wrong product defects

These defects involve using ordinary materials in place of fire stopping products, or choosing products that are unsuitable or incompatible with the application.

2. Ordinary expanding foam used instead of fire stopping products

General-purpose expanding foam is sometimes used to fill gaps around pipes, cables, and other services.

The mistake can happen when installers assume all expanding foam offers the same protection, or when a product is chosen because it’s readily available and easy to apply.

However, even foam marketed as fire-rated should only be used where its evidence covers the exact application.

RICS surveyor Christian Watkins reports finding both standard and “fire-rated” foam on service penetrations and says neither would last more than a few seconds in a fire.

How to prevent or fix it

• Select a fire stopping product with test evidence covering the actual application.

• Check the permitted services, opening sizes, substrates, and installation depth.

• Reject unapproved substitutions, even when the replacement product appears similar.

• Make sure installers understand the difference between general-purpose foam and specialist fire stopping products.

• Where foam has already been used, remove it and reinstall with a suitable system.

3. Incompatible or incorrectly specified fire stopping products

A fire stopping product can be unsuitable even when it’s designed for fire protection.

For example, a sealant may not be approved for the substrate, or a collar may not cover the pipe type or size. Mixing products from different manufacturers can also create a system that hasn’t been assessed as a whole.

Compatibility matters, too.

Some fire stopping products can be unsuitable for use with particular plastic pipes, including certain CPVC systems, because of potential chemical interactions.

These issues are easy to miss when products are selected by name or appearance rather than by checking the full system requirements.

How to prevent or fix it

• Ask for the test report, classification, or assessment, and confirm it covers the intended application.

• Match the product to the service type, substrate, opening size, and required fire performance.

• Confirm chemical compatibility with the pipe or service manufacturer where relevant.

• Combine products only as the manufacturer’s instructions allow.

• Replace unsuitable materials with a compatible system supported by the relevant evidence.

Category 3: Installation and after-installation defects

Even the right product can fail to provide the required protection if it’s installed incorrectly.

4. Insufficient fire stopping material or installation depth

Fire stopping systems rely on specific dimensions to achieve their stated performance. This means that a sealant can be applied too shallowly, a mortar seal may not fill the required depth, or mineral wool may be missing or too thin.

Mineral wool backing, in particular, is a frequent weak point. Systems specify its required density and compression, and a loose friction fit isn’t enough.

Typical causes of these defects include generic details, misread instructions, and shortcuts to save time.

The result may be a firestop that can’t provide the required fire resistance.

How to prevent or fix it

• Read the system’s required depth, backing material, and compression before work starts.

• Fit backing materials carefully, avoiding gaps and loose sections.

• Compress mineral wool to the density and compression the system calls for.

• Install the full system to the manufacturer’s stated dimensions.

• Use depth gauges or other checks where they help confirm the finished installation.

• Remove and reinstall seals that are too shallow or incomplete; don’t just add a surface layer.

5. Gaps around fire stopping materials and services

A firestop needs to form a continuous seal between the service and the surrounding construction.

That’s why small voids around pipes and cables, gaps between sealant and the substrate, and cracks where materials have separated count as defects.

Poor surface preparation is a common cause.

Dust, debris, or moisture can affect adhesion, and uneven openings can leave spaces that are difficult to fill. Sealant also needs tooling, which means pressing it firmly into the gap so it bonds to both the service and the substrate.

Untooled sealant can look finished but be loose or unevenly distributed. If the chosen system isn’t suitable for the opening’s shape, gaps may also develop after installation.

How to prevent or fix it

• Clean the opening and prepare the surfaces as required by the product instructions.

• Tool sealant firmly into the gap so it bonds to the service and the substrate.

• Apply sealant or mortar continuously, without voids, so it contacts the required surfaces.

• Examine the full perimeter of the seal, not just the visible front face.

• Replace defective sections using an approved detail rather than covering gaps with an unapproved material.

6. Incorrectly installed fire collars or wraps

Fire collars and wraps are used in specific systems to protect combustible pipes where they pass through fire-rated walls and floors.

They may be labelled as defective when they’re missing, fitted in the wrong position, secured with the wrong fixings, or installed with an incorrect number of wrap layers. A collar or wrap may also be unsuitable for the pipe diameter, material, and wall or floor construction.

Collars and wraps work by expanding when heated, which closes the gap left by a melting plastic pipe. The wrong position, fixings, or wrap count stops them from doing that.

How to prevent or fix it

• Position collars and wraps on the correct side of the wall or floor, as specified by the system.

• Secure collars with the required mechanical fixings into the supporting construction.

• Apply the specified number of wrap turns, overlap, and depth.

• Have completed collars and wraps checked before they’re concealed.

7. Inadequately supported penetrating services

Pipes, cables, cable trays, and ducts need suitable support on both sides of a fire-rated wall or floor.

If supports are missing, too far apart, or poorly fixed, services can sag or move. The firestop may then be left carrying loads it was never designed to support.

Support is often planned separately from fire stopping, and later changes add weight or movement.

In a fire, a failing service or support can pull on the seal and damage the penetration, creating a route for fire and smoke.

How to prevent or fix it

• Support services independently on both sides of the penetration.

• Keep supports within the spacing and fixing requirements for the service and system.

• Use fixings suitable for the supporting construction and expected conditions.

• Keep the weight of pipes, trays, and other services off the firestop.

• Recheck supports whenever services are added, altered, or rerouted.

8. Damaged or deteriorated fire stopping

Fire stopping can be damaged after it’s been correctly installed.

For example, follow-on trades may drill through a seal, remove material to add services, or knock a collar out of position. Over time, movement, maintenance work, or deterioration can also leave cracks and holes.

The defect may be small, but the effect is the same: The compartment boundary no longer has a complete firestop.

This defect is particularly easy to overlook during refurbishment, when existing seals are hidden behind finishes or disturbed as new services are installed.

How to prevent or fix it

• Protect completed fire stopping from damage during follow-on works.

• Share fire stopping locations with contractors carrying out maintenance or service alterations.

• Require approval before existing seals are disturbed or removed.

• Inspect affected areas after any work that could’ve damaged the firestop.

• Reinstate damaged systems using a suitable, approved detail and update the installation records.

Category 4: Design and detailing defects

Some fire stopping problems are built into the opening or junction before installation begins.

9. Unsuitable fire stopping at movement joints and deflection gaps

Movement joints and deflection gaps are designed to open, close, or flex, so the fire stopping has to move with them.

Rigid mortar or sealant that’s suitable for a static penetration can crack or pull away once the structure moves. Other defects include missing backing material, incorrect compression, and seals that have separated from the surrounding construction.

Every system also has a limit.

Movement capability is stated as a percentage of joint width, and some stuffed-and-sealed systems allow only around 10–25%, so check the system’s own figure.

Problems often begin when expected movement isn’t established or a standard penetration seal is specified for a linear joint.

How to prevent or fix it

• Establish the joint type, width, and expected movement before choosing a product.

• Specify a tested or assessed linear joint seal whose movement capability exceeds that movement.

• Compare backing material, compression, and installation depth with the system details.

• Install the seal exactly as the joint detail and manufacturer’s instructions show.

• Reinstate cracked or separated seals with a suitable system, not a rigid surface patch.

10. Oversized or incorrectly formed service openings

Service openings should be large enough for the planned installation, but no larger than necessary.

That’s because oversized or irregular apertures can fall outside what the system’s collars, wraps, and seals are tested to cover, while crowded or undersized ones leave no room to install them properly.

This defect can happen when openings are formed before service routes are finalised, or when drilling and core cutting aren’t coordinated with the fire strategy. Installers may then try to fill the extra space with more sealant or an improvised material.

However, this approach doesn’t make the installation compliant if the opening falls outside the system’s tested or assessed limits.

How to prevent or fix it

• Coordinate service routes and opening sizes before drilling or forming apertures.

• Keep openings as small as practicable while allowing enough space for the services and firestop.

• Check the permitted aperture dimensions and service arrangements for the chosen system.

• Allow enough room for collars, wraps, fixings, and access during installation.

• Seek an appropriately supported detail where an existing opening falls outside the system’s scope.

11. Open or poorly sealed junctions between walls, floors, and roofs

Compartment walls rarely meet the structure around them perfectly.

Gaps are typically left where the wall meets the profiled metal deck or soffit at the head, where it meets the floor at the base, and where it joins an external wall.

In addition, mineral wool may be fitted but not fill the profile above, leaving voids that fire and smoke can pass through.

Gaps between fire door frames and the surrounding structure are another frequent miss.

According to Watkins, it’s extremely common in older buildings to find no fire stopping between riser door frames and the surrounding structure, which he calls a tell-tale for how the building’s other fire doors have been detailed. 

How to prevent or fix it

• Mark every compartment wall and floor junction on the construction drawings, not just the fire strategy.

• Choose a system suited to the substrate, including profiled decks, and the required fire performance.

• Make sure backing and insulation fully fill the profile or gap, as the detail shows.

• Include the gap between fire door frames and the structure in the fire stopping scope.

• Sign off junctions before finishes close them in, and correct gaps with an approved system.

How fire stopping software helps contractors manage inspections and surveys

Finding and fixing fire stopping defects is only part of the job. Contractors and subcontractors also need to record their work, show that the correct materials and methods were used, and give clients verifiable evidence of what has been completed.

Fire stopping software like Onetrace brings these tasks together in one platform.

You can create custom forms for fire stopping surveys, inspections, and installations, making sure operatives capture the right information every time. Mandatory fields, checklists, and photo uploads help prevent important details from being missed, while before-and-after photos provide a traceable record of remedial work.

You can also pin inspections and completed work to digital site drawings, organised by blocks, levels and zones, so every defect or installation is linked to its exact location. Record the materials used, track variations when additional defects or work are identified, and set up approval stages so supervisors and clients can review completed work and request changes where needed.

When it’s time to hand over, generate professional PDF or Excel reports with the relevant job details, photos, and records.

With Onetrace, fire stopping contractors can spend less time managing paperwork and more time delivering quality work, while giving clients the evidence and visibility they need. Book a tailored demo with the team to learn more.

FAQ

Who is responsible for fire stopping?

Responsibility for fire stopping is shared across different parties throughout a building’s lifecycle, with the responsible person, such as the employer, building owner, or landlord, holding ultimate legal accountability for occupied premises.

How do you check fire stopping?

Checking fire stopping requires a detailed visual and physical inspection of all service penetrations and structural joints to ensure they match tested manufacturer specifications.

How often should fire stopping be inspected?

Inspect fire stopping on completion and after any alterations or new service installations. Ongoing checks should follow the building’s fire risk assessment. Many owners schedule them annually.

Does fire stopping training for site managers reduce snagging at handover?

It can help. By training site managers to identify compliance issues early, construction teams can avoid the costly, disruptive cycle of opening up finished spaces for late-stage remedial work.

How do we scope remedial works in construction when fire stopping defects show up at snagging?

Start by recording each defect, including its exact location, photographs, opening dimensions, and affected services. Next, check the original fire stopping specification and identify a suitable repair system for the opening and surrounding construction. Finally, define the work required, materials to be used, and evidence needed for sign-off before issuing the scope to the contractor.