Phoenix Journal · Extraction
School kitchens in old or listed buildings must meet the same fire safety standard as any commercial kitchen - while protecting historic fabric that cannot be replaced. Here is how that balance is managed in practice.
A school kitchen tucked inside an old or listed building carries two duties at once - the same fire safety standard as any commercial kitchen, and a legal obligation to protect historic fabric. Getting both right takes planning, not improvisation.
Many school kitchens sit in buildings that were never designed to house a modern extract canopy, let alone a run of grease ductwork threading through solid walls and up past protected features. Yet the cooking is real, the volumes are real, and the grease that settles inside the system is exactly the same as it would be in a new-build. The challenge is meeting the standard without damaging the very thing that makes the building special - and doing it in a way a conservation officer, an insurer and a fire risk assessor would all recognise as sound.
This is a working guide to how that balance is struck, what the rules actually require, and where the awkward compromises usually appear in older estates.
Grease does not care how old the walls are. Every time a burner fires under a busy canopy, a fine aerosol of fat and oil is drawn up into the extract system, where it cools and settles on the inside of the ductwork. Over a term of service that film builds into a continuous, combustible lining. If it ignites - and a stray flame or a chip-pan flare is all it takes - fire can travel the length of the duct in seconds, carried through cavities and voids that were never meant to have a fire in them.
In an old or listed building that risk is sharper, not softer. Historic structures often have concealed timber, lath and plaster, and irregular voids running alongside the duct route. A duct fire in that setting can reach parts of the fabric that would be impossible to replace. So the cleaning standard is not a bureaucratic nicety - it is the single measure that keeps a hidden lining of fuel from accumulating next to irreplaceable structure.
The recognised benchmark in the UK is TR19 Grease, the specification published by BESA (the Building Engineering Services Association) that governs the cleanliness of kitchen extract systems. It sets out how a system should be cleaned, how the result is measured, and how it is verified. A properly cleaned system should be left with less than 50 microns of residual grease - roughly half the thickness of a human hair - and grease should be controlled so it does not exceed a mean average of 200 microns between scheduled cleans. Those are not opinions about how clean something looks; they are measured thresholds, recorded with a certificate, before-and-after photographs and thickness readings.
The other half of the picture is legal. Under the Regulatory Reform (Fire Safety) Order 2005, the responsible person for the premises - in a school, typically the trust, the governing body or the local authority - must assess and manage fire risk, and that explicitly includes the condition of the extract system. A grease-laden duct that has not been cleaned to standard is a finding an assessor and an insurer will both act on, and cover can be affected where the system is not maintained to a recognised specification.
TR19 Grease ties frequency to how hard the kitchen works. Heavy, continuous frying justifies cleaning every few months; moderate use, quarterly to twice a year; and light use - the category most school and care catering falls into - is generally cleaned every twelve months. School kitchens are a genuine light-use case for much of the year, running to term-time service patterns rather than all-day heavy frying. That said, frequency should follow the evidence, not the label. A kitchen doing a lot of fried service, or one with a long, complex duct route through an old building where grease is harder to shift, may need more frequent attention. The honest answer comes from measuring grease depth, not from assuming the calendar is enough.
The numbers that matter
These are the figures a fire risk assessor and an insurer will look for on a compliant school kitchen extract system.
Behind every one of those numbers sits a verification record. A clean is only worth what the certificate can prove, and in a listed setting that documentation does double duty - it satisfies fire compliance and it provides a clear paper trail of exactly what was accessed and how, which matters if a conservation officer ever asks.
The difficulty in an old or listed school building is almost never the cleaning method itself. It is access. TR19 Grease expects the whole system to be reachable and inspectable, and that relies on properly positioned access panels - openings in the ductwork that let a technician get to every internal surface. The relevant guidance points to access at regular intervals along the run and at every point where grease tends to collect, such as bends and the base of vertical risers. In a modern kitchen those panels are designed in from the start. In a building that predates the extract system, they often are not there at all, or they are in the wrong place, or the duct is buried in a wall where no panel can reasonably go.
That is where heritage law enters. Cutting a new access panel into an external elevation, adding a flue or vent, or re-routing ductwork on a listed building can require Listed Building Consent from the local planning authority - and standard listed building conditions frequently state that no new pipes, flues, vents or ductwork may be fixed to external faces beyond what has been formally approved. Making an unauthorised alteration to a listed building is a criminal offence, so this is not a corner anyone should cut to save a cleaning visit. The sensible route is to design access thoughtfully, use internal panel positions wherever possible, and engage the conservation officer early with a documented case when an external change genuinely cannot be avoided. Our guidance on managing ventilation in listed heritage buildings goes further into how those consents and constraints tend to play out in practice.
A few things make the whole exercise far smoother when the building is protected:
None of this makes an old building harder to keep safe than a new one. It simply means the work has to be surveyed, planned and recorded with more care, by people who understand both the fire standard and the fabric they are working around. Done properly, a listed school kitchen can be just as compliant as any modern one - and the historic structure is protected in the process.
Questions
Yes. The age or protected status of the building has no bearing on the fire risk inside the extract system, so the same TR19 Grease standard applies. Under the Regulatory Reform (Fire Safety) Order 2005 the responsible person - usually the trust, governing body or local authority - must manage that risk, and insurers expect the system to be maintained to a recognised specification. The building's heritage status changes how the work is accessed, not whether it must be done.
School catering usually falls into the light-use category, which TR19 Grease generally cleans every twelve months. Frequency should follow measured grease levels rather than the label alone, so a kitchen doing heavier fried service or one with a long, awkward duct route may need more frequent attention. The reliable way to set the interval is to measure residual grease depth against the standard's thresholds.
You may. Cutting new panels, flues or vents into external elevations of a listed building, or re-routing ductwork on it, can require Listed Building Consent from the local planning authority, and standard conditions often prohibit new external fixings beyond what has been approved. Unauthorised alteration of a listed building is a criminal offence. The best approach is to place access on internal faces and concealed runs where possible, and to engage the conservation officer early with a documented case if an external change is genuinely unavoidable.
A clean is verified, not just declared. Under TR19 Grease a technician records before-and-after photographs, grease thickness readings and a certificate summarising the work, leaving the system with less than 50 microns of residual grease. In a listed building that record does double duty - it evidences fire compliance and provides a clear account of exactly what was accessed, which is useful if a conservation officer ever asks.
Phoenix Duct Clean · by the numbers
The right kit only helps if the system stays clean. Phoenix degreases canopies, filters and ductwork to TR19 Grease - UK-wide, overnight.