What Is Fire Compartmentation? A Building Owner's Guide

Fire compartmentation is the practice of dividing a building into separate fire-resisting compartments — using walls, floors and doors built to resist fire for a defined period — so that a fire starting in one part of the building is contained long enough for occupants to escape and firefighters to respond. Alongside detection and means of escape, compartmentation in fire safety is one of the three pillars of passive fire protection in every UK commercial building.

This guide explains what compartmentation is, what the regulations require of building owners, how compartment walls and floors actually work, and the single most common point of failure: service penetrations through concrete walls and floors.

What Is Fire Compartmentation?

A fire compartment is an enclosed space within a building — a floor, a flat, a stairwell, a plant room — bounded on all sides by construction that achieves a specified fire resistance, typically 30, 60, 90 or 120 minutes. Compartmentation works on a simple principle: a fire that cannot spread is a fire that can be survived and extinguished.

Building compartmentation is achieved through a combination of elements working together:

Why Compartmentation Matters in Fire Safety

Compartmentation buys time. It protects escape routes so occupants can reach safety, it limits fire and smoke damage to a fraction of the building, and it gives the fire service a fighting chance of controlling the blaze. In buildings where people sleep — flats, hotels, care homes, hospitals — compartmentation is the backbone of the "stay put" strategy: it is only safe to remain in an unaffected flat if the compartment walls and floors genuinely hold.

The legal framework is equally clear. Approved Document B of the Building Regulations sets out when compartment walls and floors are required and what fire resistance they must achieve. The Regulatory Reform (Fire Safety) Order 2005 makes a designated Responsible Person legally accountable for fire safety in occupied non-domestic buildings — and the Fire Safety Act 2021 clarified that this duty extends to the structure, external walls and flat entrance doors of multi-occupied residential buildings. A fire risk assessment that ignores the condition of compartmentation is not a complete fire risk assessment.

Fire Resistance Ratings Explained

Compartment elements are rated in minutes against standard fire test criteria. A wall rated EI 60 maintains its integrity (no flames or hot gases passing through) and its insulation (the unexposed face stays below a temperature that could ignite materials on the other side) for at least 60 minutes. Typical requirements range from 30 minutes in small, low-rise buildings to 120 minutes for basements, high-rise floors and buildings with sleeping risk. Crucially, every element in the compartment line must achieve the same rating — a 60-minute wall with an unsealed 100mm pipe hole through it is not a 60-minute wall.

Where Compartmentation Fails: Service Penetrations

Compartmentation surveys across the UK find the same defect over and over again: unsealed or badly sealed service penetrations. Every building's compartment walls and floors are pierced dozens or hundreds of times by soil pipes, water mains, electrical containment, data cabling, ductwork and sprinkler pipework. Each of those penetrations is a potential chimney for fire and smoke unless it is properly fire-stopped.

Common failures include penetrations packed with ordinary mineral wool or expanding foam that carries no fire rating, plastic pipes passed through walls without intumescent collars (the pipe melts in minutes, leaving an open hole), new cabling pulled through existing seals and never made good, and voids above suspended ceilings where compartment walls were never carried up to the structural slab.

Correct firestopping matches a tested system to each penetration type: intumescent collars and wraps for plastic pipes, fire-rated sealants and mortars for gaps around metal services, fire batts and ablative coatings for larger openings and mixed-service penetrations. The same penetrations frequently need to keep water out as well as fire in — particularly in basements and floor slabs — which is why penetration sealing is best specified as a single, coordinated package. Our guide to sealing pipes and services through concrete covers the waterproofing side in detail, and our penetration sealing service delivers both.

Compartmentation Surveys: What Good Looks Like

A compartmentation survey walks the compartment lines shown on the building's fire strategy drawings and verifies them against reality — above ceilings, inside risers, in plant rooms and service voids. A competent survey will:

Maintaining Compartmentation Over a Building's Life

Compartmentation is not a one-off construction feature; it degrades every time a contractor drills through a wall to run a new cable. The buildings that stay compliant are the ones that treat the compartment lines as controlled assets: permits to penetrate, mandatory fire-stopping of new penetrations by competent installers, and periodic re-survey — annually for higher-risk buildings, and after any significant fit-out or services work.

MPS Concrete Solutions seals service penetrations through concrete walls and floors across the UK — combining fire-stopping with waterproofing where penetrations pass through basements, podium decks and external structures. If a survey has identified unsealed penetrations in your building, or you need penetrations made good as part of a refurbishment, contact us for a free site survey and itemised quotation.