The odour and flue section of a kitchen extraction statement
The odour control part of a Ventilation and Extraction Statement turns on three numbers: extract volume, odour risk band and termination height. Here is how each is derived and evidenced.
The odour control part of a kitchen extraction odour statement is where most takeaway and restaurant applications are won or lost, and it comes down to three numbers: the extract volume, the odour risk band, and the height at which the plume leaves the building. Get those agreed with the environmental health officer early and the rest of the submission is drawings. Get them wrong and you are looking at a refusal on amenity grounds, or a condition you cannot physically comply with in the unit you have signed a lease on.
This is the section-by-section reasoning behind that part of a Ventilation and Extraction Statement, written for an operator rather than an engineer.
Sizing the extract for the menu, not the floor area
Extract rate follows the cooking appliances, not the size of the room. Two methods are in general use. The canopy face velocity method takes the open face area of the canopy and applies a design velocity, commonly in the range of 0.25 to 0.5 metres per second depending on the appliance duty beneath it. The thermal convection method calculates the buoyant plume rising off each appliance and sizes the canopy to capture it, which gives a more defensible answer for heavy-duty ranges, chargrills and tandoors.
The BS EN 16282 series is the current reference for kitchen ventilation design in the UK, replacing the older ductwork specification most caterers still name. Whichever method the designer uses, the statement should show the appliance schedule, the duty of each item, the calculated volume in litres per second or cubic metres per second, and the resulting duct velocity.
An undersized extract fails twice over. It lets grease-laden vapour escape into the dining room, and it pushes odour out through the front door and windows at street level, which is exactly the complaint route that generates objections from the flats above.
Odour risk banding and the level of control it demands
The banding approach from the Defra and EMAQ guidance on odour and noise from commercial kitchen exhaust is the framework almost every environmental health officer in England works from. It scores two things: the odour potential of the cooking, and the sensitivity of the surroundings.
Odour potential rises from low for a sandwich bar or a coffee shop with no frying, through medium for a general restaurant, to high for continuous deep frying, chargrilling, and cuisines with strong spice or fish profiles. Sensitivity rises with the number of residential receptors, how close they are, whether they have openable windows facing the discharge, and whether the discharge point sits below their eaves.
The two scores combine into a required control level.
| Odour risk band | Typical control package | Where it usually applies |
|---|---|---|
| Low | Grease filters at the canopy, good dispersion | Sandwich bars, bakeries, coffee shops with no frying |
| Medium | Grease filters plus secondary filtration or electrostatic precipitation | General restaurants and cafes with some frying |
| High | Grease filters, electrostatic precipitation or UV, then activated carbon | Takeaways, chargrill and tandoor kitchens, sites with flats above |
State the band you have landed on and show the working. An officer who can see the scoring can agree it. An officer handed a bare assertion that odour will be "adequately controlled" will ask for an Odour Assessment instead, and that is a slower and more expensive route.
Filtration stages and the maintenance nobody budgets for
Grease filtration comes first, always. Baffle filters at the canopy capture the bulk of the aerosol and protect everything downstream. Mesh filters cost less and perform worse. Beyond that, secondary filtration in the form of bag or panel filters takes out finer particulate, an electrostatic precipitator charges and collects the remainder, and ultraviolet or ozone systems break down odorous compounds by oxidation.
Activated carbon is the final polish and the stage operators neglect. Carbon adsorbs until it is saturated, at which point it does nothing at all while looking exactly the same. Replacement intervals depend on the cooking load and the carbon volume, and a system running twelve hours a day on a chargrill will exhaust its carbon far sooner than a lunchtime cafe.
Write the maintenance regime into the statement. Baffle filters cleaned weekly or more often, secondary filters changed to the manufacturer's schedule, precipitator cells washed on a set cycle, carbon replaced against a logged date rather than a guess. Councils increasingly attach a condition requiring a maintenance log to be kept and made available on request, and a statement that already commits to one is easier to approve.
Duct routes through a building you do not own
The duct has to get from the kitchen to the discharge point, and in a terraced high street unit that usually means going up the back of the building or through a riser owned by the landlord. Three problems appear in that order.
Consent comes first: a lease rarely grants an automatic right to fix a 500 millimetre duct to the rear elevation, and the freeholder's agreement is a separate negotiation from the planning application. Fire protection comes second. Grease-laden extract ductwork cannot be protected with fire dampers because grease deposits stop them closing, so where the duct passes through other fire compartments it needs a fire-rated enclosure or fire-rated duct construction, tested to the relevant standard and detailed in the Building Regulations submission under Approved Document B. Access comes third, because a duct that cannot be cleaned will not stay compliant, and access panels need to be reachable without scaffolding every time.
On a listed building or in a conservation area, the external duct is a separate consent question, and a vertical stainless steel riser on a rear elevation facing a churchyard will be resisted. Plan the route before you commit to the unit.
Termination height and dispersion
Vertical discharge at high level, clear of the building and any structure that could trap the plume. The standard expectation is a termination at least one metre above the ridge of the building the kitchen sits in, and above the ridge of buildings close enough to interfere with dispersion, with the current guidance setting the method for deciding how far that reaches.
Efflux velocity matters as much as height. A discharge leaving at 10 to 15 metres per second punches the plume up into the wind stream. A lazy discharge at 3 metres per second falls back down the elevation and into the nearest open window. Do not fit a rain cowl or a deflector cap, because both turn a vertical plume into a horizontal one. Use a tapered outlet and a drain point instead.
Where the ridge-height discharge is impossible, because the building above is in separate ownership or the roof is listed, the fallback is a high control package with dispersion modelling to show the exposure at each receptor. That is an Air Quality Assessment style exercise and it is the point at which a specialist becomes necessary rather than helpful.
Fan noise and the plant in the yard
The fan that moves that volume of air makes noise, and it usually runs into the evening when background sound levels have fallen. Plant noise is assessed against BS 4142:2014+A1:2019, comparing the rating level of the plant with the background sound level at the nearest noise-sensitive facade, with penalties added for tonality, impulsivity and intermittency.
Attenuation is straightforward if it is designed in. Acoustic louvres, in-line attenuators, anti-vibration mounts under the fan, and an acoustic enclosure for a roof-mounted unit will usually bring the rating level down to something an officer can accept. Retrofitting the same measures into a duct that is already installed costs several times as much. A Noise Impact Assessment is normally expected wherever residential windows sit within earshot, and the same environmental health team that reviews it will also look at external lighting in a service yard, which follows the environmental zone framework for obtrusive light.
The drawings and schedules to submit
A submission that officers can approve without a further information request usually contains the appliance schedule with duties, the extract calculation and method, the odour risk scoring, a schedule of the filtration stages with the maintenance intervals, a duct route drawing in plan and section, an elevation showing the termination point against the ridge line, the fan performance data with sound power levels, and the acoustic assessment.
Add a short commitment on commissioning. Say who will verify the installed system against the design, and offer the commissioning certificate to the council before first use. That single sentence removes the officer's main worry, which is that the drawings show one system and the unit ends up with another.
Draft your Ventilation and Extraction Statement in minutes, then send it for professional review through the PlanScope professional directory before it goes to the council.
This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
How high does a kitchen extract flue have to terminate?
The usual expectation is vertical discharge at least one metre above the ridge of the building the kitchen occupies, and clear of nearby buildings that would disturb dispersion. Efflux velocity matters too, with 10 to 15 metres per second giving good plume rise. Rain cowls and deflector caps should be avoided because they turn the plume sideways.
What decides the odour risk band for a restaurant?
Two things combine. The odour potential of the cooking rises from a coffee shop with no frying, through a general restaurant, to continuous deep frying, chargrilling and strongly spiced or fish-heavy menus. The sensitivity of the surroundings rises with the number of nearby homes, their distance and whether their windows face the discharge. The combination sets the control level.
How often does activated carbon need replacing?
It depends on the cooking load and the volume of carbon fitted, so no single interval applies. A chargrill running twelve hours a day exhausts carbon far faster than a lunchtime cafe. The practical answer is to log installation dates and replace to the manufacturer's stated capacity, because saturated carbon looks identical to fresh carbon and stops working entirely.
Can I put fire dampers in a kitchen extract duct?
No. Grease deposits prevent dampers closing reliably, so grease-laden extract ductwork is not protected that way. Where the duct crosses other fire compartments it needs fire-rated duct construction or a fire-rated enclosure, detailed in the Building Regulations submission. Cleaning access panels must also remain reachable along the full route.
Do I need planning permission for an external extract flue?
Often yes, particularly where the flue is visible on a front or side elevation, on a listed building, or in a conservation area. A change of use to a hot food takeaway is a separate question again. Ask the local planning authority before signing a lease, because a unit with no lawful flue route is very hard to fix later.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.