Do You Need a Legionella Risk Assessment After Refurbishment?

If you have refurbished a building, altered the water system, or carried out works that touched pipework, tanks, outlets, or plant, the existing legionella risk assessment is almost certainly out of date. In most cases a legionella risk assessment after refurbishment is needed before reoccupation, and in some cases it is needed before the system is even put back into normal use.

That is not a blanket rule for the sake of it. The risk assessment is a snapshot of the system at a point in time. Once the system changes, the snapshot stops being reliable. ACOP L8 is clear that the assessment must be reviewed when there is reason to suspect it is no longer valid, and refurbishment is one of the most obvious triggers.

The practical question is not whether to reassess, but how far the reassessment needs to go. A new kitchen tap is not the same as a full plant room refit. The answer depends on what was disturbed, how the system was left, and whether the controls in your written scheme still match the building in front of you.

Why Refurbishment Changes Your Legionella Risk Profile

A legionella risk assessment describes a specific water system: where the cold storage sits, how hot water is generated and distributed, where the dead legs are, which outlets are infrequently used, and which assets sit on the monitoring schedule. Once any of those elements change, the assessment no longer describes the building.

Refurbishment introduces three problems at once. First, the system layout changes, often in ways that are not properly recorded. Second, the system is usually drained, stagnant, or partially isolated during the works, which creates ideal conditions for bacterial growth. Third, contractors and subcontractors make decisions on site that the original designer never saw, such as capping a redundant branch instead of removing it back to the main, or leaving a section isolated because a valve is seized.

By the time the building is handed back, you may have new fittings, altered flow patterns, materials that were not on the original specification, and sections of pipework that have sat full of warm static water for weeks. None of that is reflected in the assessment that was signed off before the works started.

There is also a commercial dimension. Lenders, insurers, and incoming tenants increasingly ask for evidence that the water system has been properly recommissioned after works. A legionella risk assessment that predates the refurbishment is not evidence. It is a document about a building that no longer exists in the same form.

What ACOP L8 and HSG274 Say About Reassessment After Water System Changes

The Approved Code of Practice L8 sets the baseline. The dutyholder must ensure the risk assessment is reviewed regularly and whenever there is reason to believe the original assessment may no longer be valid. ACOP L8 specifically lists changes to the water system or its use among the triggers for review. Refurbishment that alters pipework, tanks, calorifiers, outlets, or usage patterns falls squarely within that.

HSG274 then sets out the technical detail. Part 2 covers hot and cold water systems and is the document most relevant to refurbishment works. It deals with commissioning, disinfection, temperature control, materials in contact with water, and the management of dead legs and infrequently used outlets. Part 1 covers evaporative cooling systems, and Part 3 covers other risk systems such as spa pools, humidifiers and emergency showers. If your refurbishment touches any of these, the relevant part of HSG274 should sit alongside the reassessment.

It is worth being precise about what the law actually requires. The Health and Safety at Work Act and the Control of Substances Hazardous to Health Regulations require dutyholders to identify and control the risk from legionella. ACOP L8 has special status as the approved interpretation of those duties. HSG274 is guidance, not law, but a dutyholder who departs from it should be able to demonstrate they have controlled the risk to an equivalent standard. In practice, that means a written reassessment following refurbishment is the simplest way to demonstrate ACOP L8 compliance.

The Health and Safety Executive’s ACOP L8 guidance sets out the dutyholder’s responsibilities in full, and is the reference point any enforcing inspector will use if something goes wrong.

Which Refurbishment Works Trigger a Legionella Risk Assessment After Refurbishment

Not every change to a building requires a full reassessment. The trigger is whether the works affected the water system, the building usage, or the control measures recorded in the written scheme. Cosmetic works such as painting, flooring, or partition changes that do not touch services are not in scope on their own. But the moment pipework, outlets, tanks, or plant are involved, the position shifts.

The works that usually trigger a reassessment include:

• Alterations to incoming mains, cold water storage, or boosted cold systems
• Replacement or relocation of calorifiers, water heaters, or hot water generators
• Re-routing or extension of pipework, including riser changes
• Removal, capping, or addition of outlets such as taps, showers, drinking water points, or specialist fittings
• Changes to the layout of kitchens, bathrooms, washrooms, or wet areas
• Replacement of tanks, valves, expansion vessels, or thermostatic mixing valves
• Installation of new appliances such as ice machines, beverage units, or steam ovens
• Material changes to building occupancy or how the building is used
• Extended periods where parts of the system have been isolated or stagnant during works
• Any works in plant rooms, including pump replacement, sensor changes, or control upgrades

A useful test is to look at the schematic in the existing risk assessment and ask whether it still describes the building. If a competent person could not walk the system today with that schematic in hand and locate every asset and control point, the assessment needs to be revisited.

There is also a practical category that often gets missed: works that change the way water is used rather than the system itself. Converting an open-plan office floor into a multi-tenant layout with kitchenettes on each side, for example, may not require new mains pipework, but it changes outlet frequency, flow patterns, and the realistic flushing regime. That is enough to make the existing assessment unreliable.

Kitchen, Bathroom and Plant Room Refits: Practical Examples From Site

The clearest way to see how refurbishment affects legionella risk is to walk through three common scenarios.

Commercial Kitchen Refits

Kitchen refits are deceptively high risk. A full strip-out and refit usually involves new sinks, new dishwashers, new combi ovens with direct water feeds, and often a new mains-fed water filtration unit. Old equipment is disconnected, sometimes with the supply capped at the wall rather than removed back to the main. That leaves a short section of pipework with no flow, often in a warm kitchen environment, which is close to ideal for legionella proliferation.

We regularly see kitchens handed over with new equipment installed but the original cold feed still running to a redundant fitting behind the units. The risk assessment, which predates the refurbishment, shows the old layout. The contractor’s commissioning paperwork covers the new equipment. Nothing covers the gap in between, which is exactly where the dead leg now sits.

Bathroom and Washroom Refits

Washroom refurbishments often look straightforward but introduce specific issues. Showers are the highest-risk fittings in most buildings because they create aerosols, and any replacement programme needs to consider not just the new shower itself but the supply pipework, the thermostatic mixing valve, and the flushing regime after fitting. A shower that has been installed but not yet brought into regular use is a particularly common source of post-refurbishment problems.

Disabled or accessible washrooms add another layer because they often include emergency showers, low-use outlets, and TMVs that require specific servicing. If the assessment does not record these correctly, neither will the monitoring schedule.

Plant Room Refits

Plant room work is where the biggest changes usually happen. Replacing a calorifier, installing a new packaged water heater, changing pump sets, or reconfiguring the cold water booster all alter the hydraulic behaviour of the system. Temperatures shift. Return loops behave differently. Sentinel points may no longer be the right points to monitor.

A plant room refit also tends to reveal historical issues. Once panels come off and tanks are drained, you often find scale, sediment, or sections of pipework that were never on the original drawings. The reassessment after a plant room refit is rarely a quick update. It usually involves redrawing the schematic, reviewing temperature regimes against HSG274, and reconsidering the entire control strategy.

Dead Legs, Flushing Regimes and the Hidden Risks Left Behind by Contractors

The single most common issue we find after refurbishment is dead legs in pipework that should have been removed. A dead leg is any section of pipework with no flow or very low flow, such as a capped branch, a redundant fitting, or a length of pipe serving an outlet that is rarely used. HSG274 is specific about this: redundant pipework should be removed back to the main, not capped and left in place.

In practice, contractors under time pressure often take the quicker route. The fitting is removed, the supply is capped at the nearest accessible point, and the rest of the pipe is left in the wall, ceiling void, or service duct. From a plumbing perspective it works. From a legionella control perspective it is a future problem, because that section of warm static water will not be flushed, will not be monitored, and will not appear on any asset register.

Flushing regimes are the second common gap. After works, every outlet that has been disturbed, replaced, or left out of service should be flushed before the system is brought back into use, and then continue on a documented flushing regime if it remains low use. The regime should be specific: which outlets, how often, for how long, recorded by whom. A generic instruction to “flush low-use outlets weekly” without a list of which outlets and which days is not enough to demonstrate control.

Other recurring contractor-related issues include:

• New pipework installed but not chlorinated before commissioning
• Tanks refilled before they were properly cleaned and disinfected
• Insulation missing on cold pipework running through warm voids
• Hot water return loops not balanced, so distal legs do not reach control temperature
• TMVs fitted close to outlets without consideration of post-mix dead legs
• Sample points removed during works and not reinstated
• Materials used that are not approved under Regulation 4 of the Water Supply Regulations

These are not theoretical issues. They are the findings we see on site visits after refurbishment, and they are the reason a paper-based desktop review is not a substitute for a physical reassessment.

Commissioning, Disinfection and Sampling Before Reoccupation

Before the building goes back into use, the new or altered water system should be properly commissioned. For most refurbishments this means chlorination disinfection of the affected sections, followed by post-disinfection sampling for total viable counts and, where appropriate, legionella.

The sequence matters. The system should be cleaned and flushed, disinfected to the standard set out in BS 8558 and HSG274, neutralised, refilled, and brought up to operating temperatures. Sampling should then take place once the system is in a steady operational state, not immediately after disinfection when chlorine residuals are still elevated and results will not reflect normal conditions.

Legionella sampling after refurbishment is not always mandatory, but it is sensible in higher-risk situations. These include healthcare premises, care homes, buildings with vulnerable occupants, hot and cold systems that have been substantially altered, and any system where there is doubt about whether stagnant water remained in place during the works. Sampling provides defensible evidence that the system is fit to be reoccupied.

One point that often gets missed: the commissioning records, disinfection certificates, and sample results are not the same as the risk assessment. They are inputs to it. The reassessment should reference and rely on those records, but it remains a separate document that describes the system as it now stands and the control measures that will apply going forward.

Updating Your Written Scheme, Schematics and Asset Register

ACOP L8 requires a written scheme of control where the risk assessment identifies a reasonably foreseeable risk. The written scheme sets out how the system will be managed: what is monitored, by whom, how often, against what control limits, and what happens when something goes out of specification. After refurbishment, the written scheme almost always needs updating, even if the assessment itself only requires minor amendment.

Three things usually need attention.

The schematic should be redrawn to reflect the system as built. Original design drawings are rarely accurate by the end of a refurbishment, and a schematic that does not match the building is worse than no schematic at all, because it gives false confidence. The redrawn schematic should show pipework runs, tanks, calorifiers, sentinel points, sample points, and any thermostatic mixing valves.

The asset register should be reviewed and updated. New outlets, new TMVs, new water heaters, and new sample points need to be added. Removed assets need to be taken off. Every asset on the register should have a clear location, an inspection frequency, and a responsible person.

The monitoring schedule should be reset where necessary. Sentinel outlets may have moved. Temperature monitoring points may need to change to reflect the new hot water distribution. Flushing schedules need to reflect actual low-use outlets, not historical ones. If the monitoring contractor is using a schedule that was set before the works, they will be monitoring the wrong things.

This is also a good moment to check that the responsible person and deputy are still correctly identified in the written scheme, that training records are current, and that the management arrangements still match the way the building is actually being run. Refurbishment often coincides with changes in tenancy, management, or facilities arrangements, and the documentation should catch up.

When to Bring in a Specialist and What Good Looks Like

For minor works, an in-house responsible person with adequate training can usually update the assessment and written scheme themselves. For anything beyond a simple like-for-like replacement, specialist input is normally needed. The threshold is not the cost of the refurbishment. It is the complexity of the water system and the consequence of getting it wrong.

Specialist input is particularly important where:

• Plant rooms have been altered or reconfigured
• The building serves vulnerable occupants such as in healthcare, care, or residential settings
• The system includes cooling towers, evaporative condensers, or other Part 1 assets
• The works were extensive and the as-built layout differs significantly from the original
• The previous risk assessment was old, incomplete, or carried out to a low standard
• There has been a change of dutyholder, managing agent, or occupier alongside the works
• The building is being sold, refinanced, or relet and evidence of compliance is required

A good post-refurbishment reassessment includes a physical site survey, a review of the contractor’s commissioning and disinfection records, an updated schematic, a revised asset register, a clear monitoring schedule aligned with HSG274, and an action plan with reasonable timescales for any remedial work. It should be specific to the building, not a template with the address changed.

It should also be honest about uncertainty. If sections of the system could not be inspected, if records from the works are incomplete, or if there is reasonable doubt about how a particular area was left, the report should say so and recommend what is needed to close the gap. A reassessment that quietly glosses over missing information is a liability, not an asset.

For dutyholders who want to understand the full regulatory picture, our overview of legionella regulations and guidance covers how ACOP L8, HSG274 and related legislation fit together. Examples of how post-works reviews play out in practice are set out in our legionella case studies.

If you have completed refurbishment works and need a competent reassessment before reoccupation, Acorn Safety Services (Legionella) can survey the system as built, review the contractor’s commissioning records, update your written scheme and schematics, and provide clear evidence that the building is ready to return to normal use. Contact us to discuss your project.