Grease and odour control in an extraction statement

Grease and odour control is the part of an extraction statement that decides whether a commercial kitchen gets permission, and it is the part most often written as a product brochure instead of an assessment. The council's environmental health officer wants two things from it: a reasoned judgement of how much odour the cooking will produce, and a filtration and discharge design matched to that judgement. A statement that lists equipment without connecting it to the cooking process and the nearest window will come back with a request for more information.

The document itself is short. A Ventilation and Extraction Statement for a restaurant or takeaway usually runs to a few pages plus drawings, and it accompanies either a change of use application or a planning application for the flue.

What the statement has to prove

Three findings, in this order.

First, that the odour risk has been assessed rather than assumed. Second, that the chosen filtration stages are capable of handling that level of risk. Third, that the discharge point releases the cleaned air where it will disperse instead of arriving at a neighbour's bedroom window.

Add a fourth in practice: that someone will maintain the system. Grease filters left uncleaned stop working within weeks, and an odour complaint two months after opening is an enforcement problem rather than a design one.

Where the plant is on a wall or roof near residential windows, the same application will also need sound levels for the fans and any external condensers. That is a separate assessment under BS 4142, and it belongs in a Noise Impact Assessment rather than being buried in a paragraph about the flue.

Reading the odour risk from the cooking

Odour potential comes from the process, the ingredients and the scale, not from the name over the door. Charcoal grilling, deep frying, tandoor cooking, wok frying and roasting release far more odorous compounds than steaming, boiling or reheating. A 40-cover Italian restaurant serving pasta and pizza from a deck oven is a different problem from a 20-cover grill house.

Set out in the statement:

• the cooking appliances by type and rated input, because that drives extract volume
• the menu categories and the proportion of the covers they account for
• the number of covers and the hours of operation, including late-night trading
• the distance and direction to the nearest sensitive receptor, measured to the nearest openable window rather than to the site boundary
• whether that receptor is above the discharge, level with it or below it

The risk category that comes out of those inputs determines the control package. High-risk cooking within a few metres of a residential window needs more stages than the same kitchen 30m away across a service yard. State the reasoning in a sentence rather than leaving the officer to infer it. Where the proposal is borderline, a quantified odour assessment using an accepted methodology is the way to settle it, and a standalone Odour Assessment is the place for that work.

The filtration stages and what each one does

Each stage removes a different fraction, and they work in sequence.

Carbon is the stage that does the odour work, and it is also the stage most often undersized. Adsorption depends on the air spending long enough in contact with the carbon bed, so a thin cassette in a high-velocity duct will not deliver what a datasheet implies. Give the carbon mass or bed depth, the design face velocity and the replacement interval.

Odour neutralising sprays and masking agents are not a substitute for filtration, and presenting them as the primary control is the fastest way to lose the officer's confidence.

Grease removal does more than control odour. It is also a fire measure, which is why duct cleanliness standards and access provision sit alongside the filtration schedule.

Where the duct ends

Discharge geometry does more for odour than an extra filter stage. The default expectation is a vertical discharge at high level, terminating at least 1m above the ridge of the building and above the eaves of taller adjoining buildings, with an efflux velocity high enough to carry the plume clear of the roof and away from the pressure zone around the structure.

Low-level discharge through a wall grille, at head height into a courtyard or under a balcony, is the arrangement that produces complaints. So is a cowl or a bend that turns the plume downward. If a cowl is proposed, say why it does not defeat the vertical discharge.

Common traps worth checking on the section drawing:

1. A neighbouring window, air intake or balcony within the plume's likely path.
2. A flue that stops below the ridge because the applicant wanted to avoid a conspicuous duct on a listed or conservation area frontage. That is a real tension, and the answer is usually an internal riser or a rear routing rather than a shorter flue.
3. Recirculation into the building's own fresh air intake.
4. A terminal that a cherry picker cannot reach for maintenance.

Routing through a building in multiple occupation

In a terrace with flats above, the duct route is often the deciding constraint. Running a new riser through a residential flat is rarely possible without that owner's agreement, and the alternative external route up the rear elevation raises appearance, fire compartmentation and noise transfer questions at the same time.

Deal with them together in the statement. Say where the duct crosses compartment walls and floors and how compartmentation is restored, note the acoustic treatment where the duct passes bedrooms, and show the fixing arrangement on the elevation drawing. Where the kitchen shares a bin store or yard with flats above, the waste arrangements will be asked about too, and the storage and collection detail sits close enough to this work that it pays to read the waste strategy section guide alongside it.

Illustrative example: a hot food takeaway in the ground floor of a three-storey Victorian terrace, with flats on the first and second floors held by a separate freeholder. No internal riser is available. The workable scheme runs a stainless duct up the rear elevation to 1m above the ridge, set in from the party boundary, with an acoustic enclosure at the fan and a cleaning hatch at each bend. The alternative that fails is a wall grille into the rear yard at first-floor window level.

Maintenance, access and the conditions that follow

Councils grant these permissions on the strength of continued maintenance, so the statement should give the regime rather than promise one. Filter cleaning and replacement intervals, duct cleaning frequency and the standard it follows, carbon replacement triggers, and who holds the records.

Expect conditions requiring the approved extraction scheme to be installed before the use begins and retained and maintained for the life of the use, sometimes with a requirement to keep a maintenance log available for inspection. Some authorities add a restriction on cooking types, which is why a statement written around a specific menu can constrain a later change of operator.

Statutory nuisance powers under Part III of the Environmental Protection Act 1990 sit behind all of this, independently of the planning permission, so an underperforming system remains a live risk to the business even after the condition is discharged.

Write the maintenance section as though you will have to comply with it. That is the test the environmental health officer is applying.

Enter your postcode on PlanScope to see which reports a kitchen extraction proposal is likely to need before you commission the ductwork design.

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. For specialist technical reports, qualified professional input may be required.