Small vs Large HMOs: Do Fire Safety Requirements Change With Size?

Fire and rescue authorities can serve a prohibition notice on a modest three-bedroom shared house just as readily as on a ten-bed block, and a prosecution under the Regulatory Reform (Fire Safety) Order 2005 (the RRO 2005) carries an unlimited fine. Plenty of landlords assume small HMO fire safety is a lighter-touch affair, something you can cut corners on because the property is small. That assumption is exactly how people end up with an enforcement notice, an invalidated insurance policy, or a court date.

The confusion comes from mixing up two separate things: licensing and fire safety law. Whether your HMO needs a licence depends heavily on its size. Whether it needs proper fire precautions does not. Getting clear on where large HMO requirements genuinely differ from small ones, and where they are word-for-word identical, is the line between a compliant let and a prohibition notice pinned to your front door.

What counts as an HMO, and what "small" and "large" really mean

An HMO (house in multiple occupation) is a property let to three or more people who form more than one household and share facilities such as a kitchen, bathroom or toilet. A household is a single person or members of one family living together. So three unrelated tenants sharing a kitchen make an HMO, while a couple and their two children do not.

Notice what that definition leaves out. It says nothing about storeys, floor area, or rent. The moment you have unrelated occupiers sharing amenities, you have an HMO, and the fire safety duties arrive with it. This is worth spelling out because so much landlord folklore treats "HMO" as a label reserved for big licensed houses.

Where licensing comes in

Mandatory HMO licensing under the Housing Act 2004 applies in England where five or more people from two or more households share one property. The old rule that the building had to be three or more storeys was scrapped in October 2018, so a single-storey flat let to five sharers now needs a licence. Many councils also run additional licensing schemes that pull in smaller HMOs, which is why you must check the rules for your specific local authority rather than rely on the national baseline. Our guide to HMO licence FRA requirements by council sets out how much this varies from one town hall to the next.

Landlords still use "small HMO" and "large HMO" as everyday shorthand. A large HMO usually means five or more occupants, often spread across three or more storeys, and it is the group that attracts mandatory licensing and the heaviest large HMO requirements. A small HMO tends to mean three or four sharers sitting below the licensing threshold. Handy shorthand, but it smuggles in a dangerous idea: that the small ones are somehow off the hook. They are not.

The myth: a small HMO does not need less fire safety

Here is the firm position. The RRO 2005 applies to the common parts of every HMO in England and Wales, from a two-up two-down let to three students right up to a large licensed block. There is no small-property exemption. If your building has a shared hallway, staircase, landing or communal kitchen used by more than one household, you are the "responsible person" and you owe a legal duty to assess and manage fire risk.

That duty is triggered by the arrangement, not the address. A licence is a separate permission you may or may not need. The written fire risk assessment is not optional either way: it is the mechanism the law uses to prove you have identified the hazards and put proportionate precautions in place. If you are still unsure whether the rule reaches your property, read whether your HMO needs a fire risk assessment, because the answer for shared housing is almost always yes.

So small HMO fire safety is not a watered-down version of the real thing. The law is the same law. What changes is not whether you must act, but how much you must do to reach the same outcome: everyone gets out safely.

What actually scales with the size of the building

Fire precautions are meant to be proportionate to the risk, and risk rises with the number of storeys, the number of occupants, and the complexity of the escape route. This is the genuine difference between a small shared house and a larger one. Three things scale in particular.

Escape strategy

In a single-storey flat, everyone is on the same level as the exit, travel distances are short, and a simple simultaneous evacuation works. Add storeys and the escape route becomes the weak point. Occupants on the top floor of a three-storey house have to pass the most likely seat of a fire (the kitchen, on the ground floor) to get out.

That is why taller HMOs need a protected escape route: a stairway and hallway enclosed in fire-resisting construction with fire doors, so the way out stays usable while a fire develops. The strategy itself is still simultaneous evacuation in almost all HMOs, but the physical protection it depends on gets more demanding as you go up.

Alarm grade

The alarm system is where scaling is most visible. LACORS guidance, still the reference point most councils and assessors use, generally accepts a Grade D system (mains-powered, interlinked detectors with battery backup) in a lower-risk two-storey shared house. Step up to a three-storey shared house and the guidance typically points to a Grade A system: a proper fire alarm installation with a control panel, designed and certified to BS 5839-6. The jump in cost and specification is real, and it catches landlords out when they convert a two-storey let into a three-storey one. We break down the practical difference in Grade A versus Grade D fire alarms for HMOs.

Compartmentation and fire doors

Compartmentation is the fire-resisting fabric that boxes a fire into the room where it starts and keeps the escape route clear. In most HMOs this means 30 minutes of fire resistance (FD30 fire doors, fire-rated walls and ceilings) between rooms and the escape route. Larger, taller or higher-risk buildings can require 60 minutes. A small shared house still needs proper fire doors on habitable rooms opening onto the escape route: "small" does not translate to a stripped-out standard here either.

The 3-storey HMO: where the requirements step up

The 3 storey HMO is the property type where all of this converges, and it is worth singling out. Historically the third storey was the trigger for mandatory licensing, and although the storey test was removed from the licensing rules in 2018, three storeys remains the point at which fire precautions clearly step up under LACORS guidance.

At three storeys you are typically looking at a protected staircase from top to bottom, FD30 fire doors on every room that opens onto that staircase, and a Grade A alarm system rather than domestic-style interlinked detectors. Emergency lighting on the escape route becomes far more likely to be needed, because a stairwell that loses power in a fire is a stairwell people fall down. None of this is optional generosity: it is the proportionate response to the fact that occupants now have further to travel and more hazards to pass.

The trap is the landlord who converts a loft or adds a storey and treats it as a cosmetic change. Adding that third floor can reclassify the risk, tip you into mandatory licensing, and require a materially different fire safety specification. Do the fire risk assessment before, not after, the works, so the upgrades are designed in rather than bolted on.

Next steps

Stop asking whether your HMO is too small to bother. Every HMO carries the same legal duty under the RRO 2005, and the size of the property changes the scale of the precautions, not the existence of the obligation. Work out how many storeys and occupants you have, identify your escape route, alarm grade and compartmentation, and record it all in a written assessment you can hand to a council officer.

FRASafe guides you through a BS 9792:2025-aligned fire risk assessment, free to complete, with a council-ready PDF for £45. It walks you through the storey count, escape strategy, alarm grade and fire door checks in plain English, so a small shared house and a three-storey licensed HMO both come out with a document that stands up to inspection. Start yours today and get the paperwork off your to-do list.