Every fire-resisting wall and floor in a commercial building is only as strong as the holes cut through it. Cables, pipes and ducts all pass from one compartment to the next, and each opening they leave is a route for flame and smoke. Fire stopping is the work that closes those routes again.
This guide is written for facilities managers, estates teams and main contractors who need a working grasp of the subject. It covers what fire stopping is, the two main kinds of seal, how products are tested and classified, the rules in England and Scotland, and the questions worth asking before anyone picks up a gun of sealant. It is general information. Design decisions on your building sit with your designer, fire engineer and building control.
What fire stopping actually does
A commercial building is split into fire compartments. Walls and floors between them are built to resist fire for a set time, often 60 or 120 minutes. The idea is simple: a fire in one area stays there long enough for people to get out and for the fire service to act.
That only works if the barrier is continuous. Once a cable tray or a soil pipe passes through, the gap around it has to be sealed with a product that will hold back fire for the same period as the wall or floor itself. Fire stopping is the collective name for those seals.
It is easy to miss. Most of it sits above ceilings, inside risers and behind panels. Nobody sees it day to day, which is exactly why it gets damaged, forgotten or never done properly in the first place.
Penetration seals and linear joint seals
There are two broad families of seal, and the difference matters because they are tested separately.
- Penetration seals close the gap where a service passes through a wall or floor: a pipe, a bundle of cables, a small duct.
- Linear joint seals close long, narrow gaps: the head of a partition where it meets the slab, the gap where a blockwork wall meets a column, or any joint between two fire-resisting elements.
Both stop flame and smoke passing between compartments. But a product that works around a copper pipe will not automatically work along a deflection head, and the reverse is also true. Each needs evidence for its own use.
How seals are tested and classified
Fire-stopping products earn their rating through furnace tests. Penetration seals are tested to BS EN 1366-3, and linear joint seals to BS EN 1366-4. The results are then classified under BS EN 13501-2.
The classification uses letters and a time. E stands for integrity, meaning flame and hot gases don’t get through. I stands for insulation, meaning the cold side doesn’t get too hot. So EI 60 means integrity and insulation for 60 minutes, and EI 120 means the same for two hours.
A test result is narrow. It covers the product, the wall or floor type, the service type and size, the gap, the seal depth, any backing such as mineral wool, and the orientation (wall or floor). Change one of those and the evidence may no longer apply. That is why installers work to the manufacturer’s tested detail, not to habit.
The rules in England and Scotland
In England, Approved Document B gives guidance on fire stopping openings and penetrations in fire-resisting construction. References to the older BS 476 national fire-resistance classes are due to be removed from Approved Document B from 2 September 2029. After that, the European route under BS EN 13501-2 is the way to show performance, subject to the Government’s transitional arrangements. Socotec’s summary of the BS 476 change is a readable overview.
In Scotland, the rules sit in the Building Standards Technical Handbook. Clause 2.1.14 of the Scottish Technical Handbook (non-domestic), section 2.1 says service penetrations should be fire stopped to give at least the fire resistance duration of the wall or floor, and that proprietary fire-stopping products, intumescent ones included, should be tested for their end use.
For higher-risk buildings in England, the Building Safety Act 2022 has brought tighter oversight, and fire stopping records come up again and again. HSE’s building safety pages explain the regime.
Need the work done? Mastic Doctor covers South East England, London and all of Scotland, with a 12-month guarantee on our workmanship. Send details for a fixed quote.
Who designs it and who signs it off
This is the part people most often get wrong. Fire stopping is a design matter first and an installation matter second.
- The designer, principal designer or fire engineer decides which walls and floors are fire-resisting, to what period, and which systems are acceptable.
- The manufacturer supplies the tested details and installation guidance for each product.
- The installer fits the specified product to that tested detail.
- Building control (or the verifier in Scotland) checks the work against the regulations.
An installer who fits the seal is not the person who decides it is the right seal. If a contractor offers to do both without a designer involved, ask why.
Where sealant fits in
Fire-rated sealant is one fire-stopping product among several. Others include pipe collars, wraps, batts, pillows and boards. Each suits different services and gap sizes. A large cable tray through a wide opening, for example, might call for a batt system with sealant only at the edges.
Mastic Doctor installs fire-rated and intumescent sealant around service penetrations and linear gaps where it is specified, to the product’s tested detail. We work to the specification and the manufacturer’s installation guidance. If the detail calls for a collar or a batt rather than sealant, we’ll tell you so you can involve the right party. See our fire stopping page for the scope we cover, and our guide to fire-rated and intumescent sealant for how the sealant types differ.
Third-party schemes and what clients ask for
The ASFP (Association for Specialist Fire Protection) publishes guidance on fire stopping, including its “Red Book” on linear joint seals, penetration seals and cavity barriers. It recommends using installers who belong to UKAS-accredited third-party certification schemes.
Third-party installer certification is not a legal requirement. Even so, many clients and main contractors make it a condition of appointment, especially on larger or higher-risk projects. Check what your own contract, insurer or client requires before you appoint anyone, and ask each contractor plainly what they do and don’t hold.
A short checklist for owners and FMs
- Keep a set of drawings showing fire-resisting walls and floors.
- Hold the product data and tested details for every system used.
- Ask for a record of where seals were installed, with photos where practical.
- Check fire stopping after any M&E work, cabling or fit-out that cuts new holes.
- Include risers, ceiling voids and plant rooms in routine inspections.
- Don’t let trades “make good” with whatever product is in the van.
If new services have gone in since handover, read our guide to fire stopping after M&E and fit-out works. Then send details through our quote form or contact us, and tell us what records you need so we can confirm with the quote.
Quick answers
Is fire stopping the same as fire-rated sealant?
No. Fire-rated sealant is one kind of fire-stopping product. Collars, wraps, batts and boards are others. The specified system depends on the wall or floor, the services and the gap size.
What does EI 60 mean?
It is a classification under BS EN 13501-2. E means integrity and I means insulation, both held for 60 minutes in the fire test. The rating should match or exceed what the wall or floor requires.
Do installers need third-party certification?
It isn’t a legal requirement, but the ASFP recommends UKAS-accredited schemes and many clients ask for them. Check your contract and client requirements before appointing.
Who decides what fire stopping a building needs?
The designer, principal designer or fire engineer, with building control checking the result. The installer fits what has been specified, to the manufacturer’s tested detail.
Can Mastic Doctor sign off our fire stopping?
No. We install fire-rated and intumescent sealant where specified, to the tested detail, and we don’t certify or sign off fire stopping. That sits with your designer and building control.
Related services
More advice
- Fire-Rated vs Intumescent Sealant Explained
- Fire Stopping After M&E and Fit-Out Works
- Building Safety Act and Fire Stopping Records
- Fire Stopping and Scotland's Building Standards
- BS 476 to BS EN 13501: The 2029 Change
- All advice
This guide is general information about sealant work. It isn’t legal, fire-safety or structural advice; for those, speak to a qualified professional.