Fire Stopping & Compartmentation: A Trade's Guide to Passive Fire Protection (2026)

What Compartmentation Actually Means

Compartmentation is the principle of dividing a building into separate fire-resisting boxes — compartments — so that if a fire starts in one, it is contained there for a set period before it can spread. That period is measured in minutes of fire resistance: typically 30 or 60 minutes for domestic and small commercial work, and 90, 120 or more in larger and higher-risk buildings.

Those minutes are not arbitrary. They are the time the building's designer has decided occupants need to escape and the fire service needs to respond. A 60-minute compartment wall between flats, for example, is meant to hold the fire back for an hour. Every element of that wall — the blockwork, the plasterboard, the doors and crucially the seals around anything passing through it — has to deliver its share of that 60 minutes.

Why It Matters to Ordinary Trades

Here is the part that catches people out. The moment you run a cable, pipe, duct or even a single drill hole through a fire-rated wall or floor, you have created what the industry calls a service penetration. You have breached the compartment. The fire resistance the wall was designed to provide is now compromised at that point — fire and smoke will follow the path of least resistance, and an unsealed hole around a cable bundle is exactly that.

Reinstating the fire resistance is your responsibility as the person who made the breach. This is fire stopping: filling and sealing the penetration with a tested product or system so the wall performs as if the hole were never there. It is not a nicety or a finishing touch — it is part of completing the job to a compliant standard. A perfectly wired consumer unit or a flawless boiler install means nothing if the cables and flue pass through a compartment wall through an open gap.

The Standards and Drivers You Should Know

You do not need to memorise the regulations, but you should know what governs this work and why scrutiny has increased so sharply in recent years.

• Approved Document B (Building Regulations, fire safety): sets out compartmentation requirements and the principle that openings in fire-resisting elements must be sealed to maintain the rating. This is the design guidance building control checks against.
• The Regulatory Reform (Fire Safety) Order 2005 (the "RRO"): the legal duty on the "responsible person" to manage fire safety in non-domestic premises and common parts. Defective fire stopping is a recognised breach.
• The Building Safety Act 2022: the post-Grenfell legislation that introduced tougher accountability, the "golden thread" of information and the new regime for higher-risk buildings. It has put passive fire protection under a level of scrutiny it never had before.
• BS 476 and the EN test standards (such as BS EN 1366-3 for penetration seals and BS EN 13501-2 for classification): the fire test standards that products are tested and rated against. A product's fire rating is only valid for the way it was tested.

The Grenfell Tower fire and the subsequent inquiry fundamentally changed how this work is viewed. What was once treated as an afterthought is now a focus of inspection, insurance and prosecution. Treating fire stopping casually is no longer something you can get away with.

Common Fire Stopping Products and Where They're Used

There is no single product that does everything. The right material depends on what is passing through the wall, what the wall is made of, and the fire rating you need to achieve. Here are the staples you'll come across.

Intumescent Sealant and Mastic

A gun-applied sealant that swells when heated, closing the gap around cables and small penetrations. Used for sealing the annular gap around cable bundles, small pipes and the perimeter joints of fire boards. The word intumescent means it expands under heat — that expansion is what closes the void as a plastic component melts away.

Fire Collars and Wraps

Used for plastic pipes (waste, soil, push-fit). Plastic melts in a fire and leaves a clean hole, so a collar packed with intumescent material is fitted around the pipe; in a fire it crushes the softening pipe closed and seals the opening. Wraps do the same job where a collar cannot be fitted. Essential for plumbers and heating engineers running plastic pipework between compartments.

Fire Batt and Coated Batt

High-density mineral wool slab, usually faced with an ablative coating, cut to fill larger openings and service risers carrying multiple cables, trays and pipes. The coated batt forms a fire-resisting barrier that can be re-penetrated and patched as services change.

Fire Pillows (Bags)

Intumescent pillows packed into openings where services are likely to change frequently — comms rooms, risers, temporary or evolving cable routes. They give a re-openable seal, though they must be installed densely and to the tested arrangement, not just loosely stacked.

Putty Pads Behind Back Boxes

One of the most overlooked items in domestic and flat work. A recessed socket or switch box set into a compartment wall is a hole; an opposing box on the other side of the same stud creates a near through-path. Intumescent putty pads line the back and sides of the box to maintain the wall's rating and reduce sound transfer. Electricians and dryliners should treat these as standard on fire-rated partitions.

Cavity Barriers

Not a penetration seal as such, but related: barriers fitted within concealed cavities and voids to stop fire and smoke spreading unseen through the structure — for example within timber frame walls, behind cladding or above suspended ceilings at compartment lines.

Quick Reference: Penetration Type and the Fire Stopping Method

Treat this as a guide to the right family of product, not a substitute for the manufacturer's tested detail. Always confirm the specific system against the wall type and rating you are working to.

Use a Tested System — Not Just "Any Sealant"

This is the single most important principle in the whole subject. A fire stopping product only carries a fire rating because it was tested in a specific configuration — a particular wall type, a particular thickness, a particular gap size, a particular depth and bead of sealant, a particular fixing pattern. That tested arrangement is the system. Change the configuration and the rating no longer applies, because nobody has proven it performs.

In practice this means you cannot simply grab a tube of "fire sealant" and fill a hole. You need to match the product to the substrate (masonry, plasterboard, concrete floor), the service type, the gap dimensions and the required rating, and install it exactly as the tested detail specifies — correct depth, correct backing, correct fixings. A pretty bead of the wrong product, or the right product installed the wrong way, gives a false sense of security and will fail under inspection or, far worse, in a real fire.

Keep the manufacturer's installation data and the relevant test or assessment reference for the systems you use. If you cannot point to the tested detail you followed, you cannot demonstrate the seal does what it is supposed to do.

Competent Installers and Third-Party Certification

Because fire stopping is hidden once boards and finishes go on, the only meaningful assurance of quality is the competence of the installer and independent verification of the work. This is why third-party certification has become so important.

Schemes such as FIRAS and IFC Certification certify installers and contractors for passive fire protection. A certificated installer has demonstrated they understand tested systems, install to the correct details and keep proper records. On larger and higher-risk projects, certificated installation is increasingly a contractual or building control requirement, not an optional extra. Even on smaller work, being able to say your fire stopping was done by a competent, certificated person is a strong protection for you and reassurance for the client.

If fire stopping is a regular part of your work, getting yourself or your firm certificated is worth serious consideration. If it is occasional, know your limits — and bring in a specialist where the rating, complexity or risk justifies it.

Document It — And Don't Cover Up Someone Else's Bad Work

Once the boards, plaster or screed go on, your fire stopping is invisible. The only way anyone can verify it later is your records. Photograph each penetration before and after sealing, note the product and system reference, the rating achieved and the date. This is exactly the kind of evidence the "golden thread" under the Building Safety Act expects, and it is your defence if the work is ever questioned.

Just as important: do not board over or conceal someone else's defective fire stopping. If you arrive to find unsealed penetrations, the wrong products or expanding foam stuffed into a fire-rated wall, do not hide it behind your finish. Raise it, record it and get it put right. If you cover it up, you can find yourself carrying the liability for a breach you did not create. Expanding foam in particular is not a fire stopping product unless it is a specifically tested fire-rated grade — ordinary builder's foam offers no fire resistance and is a classic site failure.

The Consequences of Getting It Wrong

Poor fire stopping has real costs beyond a redo. The immediate one is a failed building control or fire risk assessment inspection, which holds up handover and forces remedial work — often after finishes are complete, meaning everything has to come back off. Then there is liability: if a breach you created or concealed contributes to fire or smoke spread, you can be on the hook professionally, financially and potentially criminally under the RRO and the Building Safety Act.

And underneath all of that is the reason the regulations exist at all: danger to life. Compartmentation buys people the minutes they need to get out. A single unsealed penetration can let smoke fill an escape route long before the fire itself arrives. This is not paperwork for its own sake — it is the difference between a contained incident and a fatal one.

Frequently Asked Questions

Do I really have to fire stop a single small cable hole?

If that hole passes through a fire-rated wall or floor, yes. The rating applies to the whole element, and an unsealed gap around even one cable is a breach of it. The seal is small and quick — but it is not optional.

Can I use ordinary expanding foam?

No, unless it is a specifically tested fire-rated foam used within its tested system. Standard builder's foam has no fire resistance and is one of the most common reasons fire stopping fails inspection.

How do I know what fire rating the wall needs?

It comes from the building's design and Approved Document B — commonly 30 or 60 minutes in domestic and small commercial work, higher in larger buildings. Check the drawings, fire strategy or with building control rather than guessing.

Do I need to be certificated to do fire stopping?

Not always for occasional small seals, but you must be competent and use tested systems correctly. On larger and higher-risk projects, third-party certification such as FIRAS or IFC is increasingly required — and it is the clearest way to prove your work stands up.

Whose responsibility is the fire stopping — mine or the main contractor's?

As a general principle, the trade that creates the penetration is responsible for reinstating the fire resistance, unless the contract clearly assigns it to a dedicated fire stopping specialist. Agree this in writing before you start so nobody assumes someone else is doing it.