Fire Compartmentation in HMOs Explained: 30 vs 60 Minute Fire Resistance

Picture a council environmental health officer standing in your HMO hallway, torch on the ceiling, marking down every recessed spotlight and every gap around a soil pipe. If the fire-resisting construction meant to hold a fire back has been quietly wrecked by DIY, the officer can serve an improvement notice under the Housing Act 2004, and the fire service can serve a prohibition notice under the Regulatory Reform (Fire Safety) Order 2005 that stops you letting rooms. Poor compartmentation in an HMO, with walls that no longer deliver even 30 minute fire resistance, is one of the fastest ways to fail an inspection.

The good news is this is fixable, and most of it is visible once you know what to look at. This guide explains 30 and 60 minute fire resistance in plain English, why converted houses are the highest-risk category, and the everyday breaches that turn a compliant layout into a paper compliance failure.

What compartmentation in an HMO actually does

Compartmentation is the principle of dividing a building into pockets so that a fire starting in one room is boxed in for a set period of time. The walls, floors, ceilings and doors around that pocket are built or upgraded to resist fire and to hold back smoke, which is what actually kills most people in a house fire.

The point is time. Nobody expects a partition wall to stop a fire forever. The job is to buy your tenants enough minutes to get out of their room, along the escape route and out the front door before heat and smoke reach them. In a shared house where people sleep behind different doors and may not know each other, that bought time is the whole safety case.

Fire-resisting construction is measured by how long an element holds up under test conditions. A wall rated for 30 minutes should keep fire and smoke on one side for half an hour. That rating only counts if the wall is intact. Drill a hole through it, drop a light fitting into it or leave a pipe running through an open gap, and you have handed the fire a shortcut.

30 minute versus 60 minute fire resistance

The two numbers you will see again and again are 30 and 60 minutes. Which one applies depends on the building and which part of it you are looking at.

For a typical shared house or bedsit HMO, the escape route is usually protected to a 30 minute standard. That means the walls between habitable rooms and the hallway or staircase, plus the doors onto that route, are expected to give 30 minutes of protection. The LACORS housing fire safety guidance, which most councils and fire services still work from, treats 30 minute fire-resisting construction as the benchmark for the partitions and doors around the protected route in most low-rise shared houses.

Sixty minutes comes into play in higher-risk situations. Where a house has been converted into self-contained flats, or where the residential floors sit above a shop or other commercial premises, you generally need 60 minutes of separation between those separate premises. Taller buildings and purpose-built blocks also tend to demand the higher standard between each flat and the common escape route. If your HMO is above a takeaway or a retail unit, assume the floor between you and the business below needs to perform for a full hour, and get that checked.

Protected routes: the spine of the system

A protected route is the corridor, hallway and staircase that everyone uses to get out. The whole idea is that a tenant can leave their room and walk through a space that is shielded from fire on all sides until they reach the open air. That is why the walls lining it and the doors opening onto it carry the fire-resisting job.

Two things make or break a protected route. The first is the doors. Habitable rooms opening onto the escape route should have fire doors, correctly fitted with the right seals and closers, which is a big enough topic that we cover it separately in our guide to HMO fire door regulations. The second is the route itself staying clear and enclosed, which we set out in detail in the guide to fire escape routes in HMOs.

Fire-stopping: where compartmentation is won or lost

Fire-stopping is the sealing of every hole that passes through a fire-resisting wall, floor or ceiling. Every time a cable, pipe, duct or vent crosses a compartment line, it leaves a gap, and an unsealed gap lets fire and smoke straight through. Proper fire-stopping fills those gaps with tested materials such as intumescent sealant, fire collars around plastic pipes, or fire batt around larger openings.

This is the part landlords most often miss, because it is hidden. A wall can look solid from the room while the void behind the plasterboard is wide open to the next compartment. When a plumber reroutes a waste pipe or an electrician pulls new cables through, they punch through compartment walls and floors, and unless someone reinstates the seal with the right product, the barrier is gone.

Why converted houses are the biggest risk

Houses converted into HMOs and flats carry the worst compartmentation record of any building type. Fire safety audits routinely find that converted properties fall short far more often than purpose-built blocks, and a large share of the conversions inspected turn out not to comply.

The reason is history. A house built as a single family home was never divided into fire compartments. When it becomes an HMO, someone has to build that protection in after the fact: upgrade the floors, line the staircase, fit fire doors and seal the penetrations. Older conversions were often done to a lighter standard, or the protection has been eroded by decades of rewiring, replumbing and tenants propping doors open. Purpose-built blocks start life with the compartmentation designed in, which is why they tend to hold up better.

If you own a Victorian or Edwardian terrace running as a shared house, treat the compartmentation as guilty until proven innocent. The layout that feels safe because it looks like a normal home is exactly the layout most likely to have hidden gaps.

Common compartmentation breaches to check today

Most breaches are cheap to find and cheap to fix once spotted. Walk the property with these in mind:

• Recessed downlighters. Every spotlight cut into a fire-resisting ceiling is a hole in the barrier. Standard downlights leave the ceiling open to the void above. They need fire-rated fittings or intumescent fire hoods fitted over them to restore the rating.
• Unsealed service penetrations. Holes where pipes, cables, waste stacks and extractor ducts pass through compartment walls and floors. Each one needs the correct collar, sleeve or sealant, not expanding foam, which is not a fire-stopping product.
• Unrated loft hatches. In many houses the loft is a single open space running above every room. If the hatch on the escape route is a thin plywood board with no rating and no seals, fire can get into the roof void and spread across the whole top floor. It should be a fire-rated, sealed hatch.
• Gaps around pipes and behind boxing. The gap where a radiator pipe or soil stack disappears into the floor, or the void behind a boxed-in pipe run, is a classic smoke path between storeys.
• Damaged or missing plasterboard. Old lath-and-plaster ceilings, holes knocked through for access and never patched, or partition walls that stop short above a suspended ceiling all break the line.
• Meter cupboards and risers. Electricity meters and cupboards opening onto the escape route are ignition points and should be enclosed to hold fire back for at least 30 minutes.

Who enforces this and what it can cost

Two regimes bear down on HMO compartmentation at once. The local housing authority enforces the physical condition of the dwelling through the Housing Health and Safety Rating System under the Housing Act 2004, and can serve improvement notices or prohibition orders. The fire service enforces the common parts and the wider building under the RRO 2005 across England and Wales, and is generally consulted by the council before it acts on a fire hazard in an HMO. In practice the two often inspect together.

Penalties are not trivial. Councils can issue civil penalties running to tens of thousands of pounds, and serious RRO 2005 breaches can carry unlimited fines and, in the worst cases, imprisonment. A prohibition notice can force rooms out of use and cut your income overnight. Scotland runs a separate regime under the Fire (Scotland) Act 2005 and its own housing standards, so the exact duties differ if your property is north of the border, though the compartmentation principles are the same.

There is an insurance angle too: if a fire spreads because compartmentation had been breached and you had no assessment flagging it, an insurer may question the claim.

Next steps

Start with a walk-through today using the breach list above, and note anything that looks wrong for a competent person to check closely. Then get it recorded properly. A written assessment is what an inspector, a fire officer and an insurer all want to see, and it is the document that turns a pile of observations into a defensible position. If you are weighing up a self-assessment against hiring someone, our guide to LACORS fire safety guidance for HMOs explains the standard your assessment is measured against.

FRASafe guides you through a BS 9792:2025-aligned fire risk assessment, free to complete, with a council-ready PDF for £45. It prompts you room by room on the compartmentation, fire doors and escape route points covered here, so nothing hidden in a loft void or behind a downlight gets missed.