Phoenix Journal · Ductwork
When flats and a working kitchen share one structure, the extract system has to protect residents from fire, odour and noise while still moving enough air for the cooks. Here is how mixed commercial and residential ventilation is designed, tested and kept clean.
Mixed-use buildings
When a restaurant, takeaway or cafe sits underneath flats, the ductwork is doing two jobs at once - and the two occupants want opposite things from it.
A commercial kitchen needs a strong, steady pull of air to clear heat, steam, combustion gases and grease-laden vapour away from the cooking line. The homes above want quiet, clean, odour-free air and, above all, the confidence that a fire in the kitchen cannot travel up to where people sleep. A single vertical route often carries the kitchen extract past bedrooms, landings and shared escape stairs on its way to the roof, so the same duct that keeps the chefs comfortable also runs through the part of the building where the fire risk matters most.
That overlap is what sets a mixed-use property apart from a standalone unit. You are not simply cleaning a greasy duct - you are managing fire risk, indoor air quality, odour, noise and legal compliance for two groups of people who never meet. Get the design and the maintenance right and nobody upstairs ever notices the business below. Get it wrong and you invite grease fires, statutory nuisance complaints and invalidated insurance, all at the same time.
In practice the duty is shared. The kitchen operator is the responsible person for the extract system they use, but the building owner or managing agent usually owns the shared riser, the roof discharge and the compartmentation that protects the residents. Both need to know where the boundaries of their system sit, because a gap in ownership is where maintenance quietly stops happening.
The rules that apply
The legal framework is not a single document - it is a stack of overlapping duties, and a mixed-use building triggers more of them than a lone kitchen ever would.
None of these are optional extras. TR19 is a standard rather than a law, but insurers and fire risk assessors treat compliance as the evidence that you are discharging your legal duties - and in a building full of residents, an insurer that finds an uncleaned, undocumented extract has an easy reason to decline a claim.
Route, fire and discharge
In a standalone unit the duct simply needs to get grease-laden air out of the building. In a mixed-use property, every metre of that route is passing through, or beside, space that people live in - so three things become critical.
Where the extract duct crosses a compartment wall or floor - which it almost always does on the way from the kitchen to the roof - the fire separation between the business and the homes has to be maintained. That usually means fire-rated ductwork or correctly specified fire dampers tested to standards such as BS 9999, so that a fire in the kitchen cannot use the duct as a chimney into the residential floors or the protected escape stair. A build-up of grease inside that same duct is exactly what turns a small flare-up into a fire that spreads, which is why cleaning frequency and fire protection are two halves of the same problem here.
The second issue is where the air comes out. DW172, the industry specification for commercial kitchen ventilation, guides discharge design, and the general principle is high-level dispersal - typically discharging vertically, unhindered, around a metre above the roof ridge - so that cooking smells are thrown clear rather than dropping straight back into open bedroom windows. Odour control such as an appropriately maintained filtration stage often sits alongside this. Local environmental health teams can restrict or modify a system that causes an odour nuisance under statutory nuisance powers, and in a residential setting complaints arrive quickly.
The third is noise. A fan that is inaudible during a busy service in the kitchen can be a persistent low hum in a flat three floors up, especially late at night. Anti-vibration mounts, correct fan sizing and attenuation keep the system within acceptable limits and out of the complaints book. Because these three demands pull against each other - more airflow can mean more noise, a longer duct run means more places for grease to settle - the whole system has to be considered together rather than component by component. That is the essence of balancing ventilation across a mixed-use building, where supply, extract and pressure are tuned so no single zone loses out.
Planning, testing and cleaning
The answer is a maintenance regime that treats the whole route as one system and proves, in writing, that each part has been dealt with. TR19® Air classifies systems as high, medium or low based on the spaces they serve, and that classification drives how often they are inspected and the point at which cleaning becomes mandatory. A greasy kitchen extract running through occupied residential floors will sit at the demanding end of that scale.
A sound approach for a mixed building looks like this:
If the terminology in a specification or a report leaves you second-guessing, our plain-English glossary of commercial kitchen ventilation terms explains the standards, classes and test methods referenced above.
Questions
There is no single fixed interval - it depends on how many hours a day the kitchen cooks and the type of cooking, which TR19 Grease uses to set frequency. Heavy use such as frying or char-grilling can warrant cleaning every three months, while lighter use may extend the interval. In a mixed-use building with residents overhead the safe approach is to err towards more frequent cleaning, because the fire risk is a life-safety risk, and to keep dated post-clean reports as evidence for your insurer.
Usually both, across different parts of the route. The kitchen operator is the responsible person for the extract serving their cooking line and is accountable for keeping it clean under the Fire Safety Order. The building owner or managing agent typically owns the shared riser, the fire compartmentation and the roof discharge that protect the residents. The key is to agree in writing where one party's responsibility ends and the other's begins, so no section of duct is left unmaintained in the gap between them.
Phoenix Duct Clean · by the numbers
Phoenix surveys and cleans kitchen and building ductwork to the TR19 standard - measured, cleaned and certificated, UK-wide.