Legionella Risk Assessment for HMOs: What's Different

A House in Multiple Occupation (HMO) has the same legal framework for legionella compliance as any other residential property — ACoP L8, the Health and Safety at Work etc. Act 1974, and COSHH 2002. But in practice, HMOs present a higher legionella risk than single lets, and the Management of Houses in Multiple Occupation (England) Regulations 2006 explicitly require landlords to maintain water systems in good repair under regulation 5.

This guide explains what is different about legionella compliance in an HMO, what the assessment must cover, and who is responsible.

Why HMOs carry higher legionella risk

HMOs typically present more legionella risk than a standard single let for several reasons:

More water outlets and longer pipe runs. A 6-bed HMO has at least 6 en-suites or shared bathrooms, a communal kitchen, and potentially utility rooms. Longer pipe runs increase the chance of temperature loss. More outlets mean more potential points of stagnation.

Shared hot water systems. Many HMO conversions have a single central hot water system serving multiple floors. If the system is undersized or poorly configured, not all outlets may reach the required 50°C delivery temperature.

Occupancy patterns create stagnation. In shared houses, rooms may be vacant between tenancies, and occupants have no reason to flag an unused bathroom or a toilet that hasn't been flushed this week. Stagnation builds undetected.

Conversion pipework creates dead legs. HMO conversions often involve plumbing changes — adding en-suites, moving kitchens, splitting facilities. These changes frequently create dead legs: capped-off sections of pipework where water sits stagnant. Dead legs that were not removed at conversion remain a risk for the building's lifespan.

Frequent tenant turnover. Void periods between individual room lets are common. During vacancies, specific rooms can have outlets that go unused for weeks.

Legal basis: what the law requires

The core legionella obligations come from:

• Health and Safety at Work etc. Act 1974 — duty to ensure the health and safety of persons not in your employment (including tenants)
• COSHH Regulations 2002 — legionella bacteria are a biological hazard within COSHH scope; you must assess and control the risk
• ACoP L8 — approved code of practice. Following L8 demonstrates compliance with the above. Departing from L8 requires demonstrating an equally effective alternative

For licensed HMOs, the Management of Houses in Multiple Occupation (England) Regulations 2006 add a further layer: regulation 5 requires the manager to maintain the water supply and drainage systems in good working order and repair. This does not create a separate legionella obligation, but it means HMO licensing inspectors may check whether legionella compliance forms part of the water system management programme.

Similar provisions apply in Wales under the Management of Houses in Multiple Occupation (Wales) Regulations 2006. Scotland has separate housing regulation under the Repairing Standard.

What a compliant HMO risk assessment must cover

A legionella risk assessment for an HMO must meet the same seven-section standard as any ACoP L8 assessment — but the content of each section is necessarily more complex:

1. Water system inventory

For an HMO, this means:

• Every room's hot and cold water outlets (tap by tap, shower by shower)
• The central hot water system — cylinder size, thermostat setting, distribution pipework layout
• Any cold water storage tanks — typically in the loft, serving the whole building
• All showers and their connection to the hot and cold circuits
• Any dead legs from conversion work — these must be identified and listed

2. Hazard identification

Specific HMO hazards to identify:

• Any outlet with a measured hot water delivery temperature below 50°C within one minute
• Any cold water outlet above 20°C within two minutes of running
• Dead legs — documented, with a note on whether they are active, dormant, or scheduled for removal
• Shared bathrooms or en-suites in rooms that may be vacant between tenancies
• Long hot water pipe runs from the cylinder to the top floor where temperature loss is most likely

3. People at risk

HMOs house a general adult population, usually without the specific vulnerability groups that elevate risk in care homes. However, the density of occupants and the aerosol exposure from shared showers means the risk exposure is higher per person than in a single let.

4. Control measures

For an HMO, control measures typically include:

• Hot water cylinder set to 60°C or above
• Monthly temperature checks at sentinel outlets — the nearest and furthest outlets from the cylinder, plus any outlets where temperature failures have previously been found
• Weekly flushing schedule covering rooms known to have lower occupancy
• Quarterly showerhead descaling for all en-suites and shared bathrooms
• A void room procedure — when a room is between tenants, a flushing check before the new tenant moves in

5. Monitoring schedule

More outlets mean more to monitor. The monitoring schedule must be realistic for the size of the building and documented clearly enough that you (or a managing agent) can demonstrate what was checked and when.

6. Named responsible person

For an HMO, the responsible person should be named. If you use a managing agent, the contractual arrangement should specify who holds the legionella compliance responsibility — landlord or agent — because ambiguity about this has been the basis of enforcement actions.

7. Review arrangements

ACoP L8 requires the assessment to be reviewed regularly and whenever there is reason to believe it is no longer valid — in an HMO that means reviewing it whenever any of the following occur: room conversion work, plumbing changes, new tenant type (e.g., the property becomes occupied by elderly tenants for the first time), or a temperature failure at monitoring. Many landlords also carry out a full review at least every two years as good practice, but this is a practical convention rather than an ACoP L8 interval.

Can HMO landlords self-assess?

For a small HMO (up to ~6 beds, simple plumbing, no converted dead legs), a landlord can carry out a competent self-assessment if they understand the water system thoroughly. HSE confirms that landlords do not need to be professionally trained or accredited for residential properties.

For larger or more complex HMOs — particularly converted properties with multiple pipe circuits, dead legs from previous plumbing, or a complex shared hot water system — a professional assessment is the practical standard. Not because the law mandates it, but because the technical complexity genuinely exceeds what most non-specialists can reliably assess.

As a rough guide:

HMO type	Self-assess?
Up to 6 beds, simple conversion, standard cylinder	Yes — if you understand the pipework
7+ beds or multiple floors	Consider professional
Complex conversion with dead legs or modified plumbing	Professional recommended
Purpose-built or large HMO (10+ rooms)	Professional standard

Practical takeaway

HMOs require the same legal framework as single lets — but the practical complexity is higher. More outlets, more pipe runs, more potential dead legs, and more variable occupancy patterns all increase risk relative to a standard residential let.

The assessment must be specific to the building — a generic one-page form does not meet ACoP L8 for an HMO with complex pipework. For licensing purposes, being able to demonstrate a compliant written assessment, a named responsible person, and evidence of ongoing monitoring (temperature logs, flushing records) is the standard an HMO licensing inspection expects.

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This guide covers legionella risk assessment requirements for HMOs in England under ACoP L8 and the HMO Management Regulations 2006. This is general compliance guidance, not legal or professional advice — for complex systems or licensing compliance queries, consult a competent person and your local licensing authority.

Sources

• HSE — ACoP L8: Legionnaires' disease
• HSE — Legionella and landlords' responsibilities
• Management of Houses in Multiple Occupation (England) Regulations 2006