Kitchen extract filtration options in planning terms

Kitchen extract filtration is a planning issue because odour and fan noise are material considerations, and a council will decide your application on whether the system it can see on the drawings will keep both away from the nearest windows. The filtration itself is only half the answer. Where the duct terminates does more work than any filter you can buy, and an application that gets the discharge point wrong will not be rescued by adding carbon.

If you are fitting out a restaurant, takeaway or cafe in an existing unit, the practical sequence is: fix the termination point, size the fan, then select filtration to match the odour risk of the cooking you actually intend to do.

What the council is deciding

Two things, judged separately. Whether cooking odour will cause an unacceptable loss of amenity to residents and other occupiers nearby, and whether the mechanical plant will be audible enough to do the same.

Environmental health officers advise on both, and their comments usually determine the outcome. They work from the widely used Defra guidance on the control of odour and noise from commercial kitchen exhaust systems, which sets a risk banding based on the type of cooking, the size of the kitchen and the distance to the nearest sensitive receptor. High-risk cooking close to flats attracts the heaviest requirements. Low-risk cooking with a clear discharge above the roof may need very little beyond grease filtration.

Separately, the Environmental Protection Act 1990 gives the council statutory nuisance powers after you open. Planning conditions and nuisance law are different regimes, and satisfying one does not settle the other.

Discharge height does more than any filter

The default expectation is that the duct terminates at least one metre above the ridge of the building it serves and of any building close enough to be affected, discharging vertically at a velocity that carries the plume clear rather than dropping it onto a balcony.

Where that cannot be achieved, on a listed building, in a conservation area, or in a flat over a shop with no route to the roof, the case has to be made on filtration and dilution instead. That is a weaker position and it is the single most common reason a change of use to a hot food takeaway is refused.

Things that make a low-level or side-wall discharge harder to defend:

• Openable windows or balconies of dwellings within the plume path
• A discharge into a narrow lightwell, courtyard or covered service yard
• A cowl or rain cap that deflects the plume downwards
• No route for future maintenance access

A short Ventilation and Extraction Statement that shows the duct route, the termination height relative to surrounding roofs, and the exit velocity is the document that answers all four points at once.

The filtration stages and what each one removes

Systems are usually described as a train, and councils will want the train specified rather than a brand name.

Grease filtration is the baseline. Mesh or baffle filters in the canopy capture the coarse fraction, protect everything downstream and reduce fire risk. Nothing else works properly if these are missing or badly maintained.

Electrostatic precipitators charge and collect fine grease and smoke particles. They deal with visible plume and a share of the particulate, and they need a genuine cleaning regime because performance falls away quickly once the cells load up.

Activated carbon adsorbs the volatile compounds that carry smell. Performance depends on bed depth, face velocity and contact time, so a thin cassette in a high-velocity duct will do far less than the datasheet suggests. Carbon must be preceded by effective grease and particulate removal or it blinds within weeks.

Ultraviolet and ozone systems oxidise odorous compounds in the duct. They work, but they need designed residence time and a safe approach to ozone, and environmental health officers will ask how residual ozone is dealt with before discharge.

Odour neutralising sprays sit at the bottom of the hierarchy. Offering them as the primary control invites refusal.

Fan noise and the acoustic case

The plant case is normally made under BS 4142:2014+A1:2019, which compares a rating level, the specific sound of the plant with corrections for tonality, impulsivity and intermittency, against the representative background sound level at the nearest receptor. A rating level around ten decibels above background points to a substantial adverse impact and a rating level around background points to a low impact.

Mitigation is ordinary engineering: selecting a larger, slower fan, fitting attenuators either side of the fan, anti-vibration mounts and flexible connections, acoustic lagging on the duct where it passes bedrooms, and a plant enclosure. All of it is easier to design in than to retrofit after a condition is imposed.

Where the unit sits under or beside flats, expect the council to want a Noise Impact Assessment with a background survey covering the hours you intend to trade, including late evening. Background levels at 23:00 are what catch operators out, not daytime levels.

What to submit

For a straightforward fit-out in a commercial parade, a complete submission is usually:

1. A duct route drawing in section and elevation, showing termination height against neighbouring ridges.
2. A schedule of the extract system: canopy type, airflow rate, filtration stages with bed depths or cell counts, fan make and duty, and exit velocity.
3. An odour risk assessment placing the cooking type in a risk band and justifying the chosen filtration.
4. A noise assessment where residential receptors are close, or a plant noise schedule with sound power levels where they are not.
5. A maintenance schedule stating how often each filtration stage is cleaned or replaced.

Where cooking is high risk and receptors are very close, an Odour Assessment prepared or reviewed by a suitably qualified author carries more weight than a manufacturer's statement. On busy streets in an Air Quality Management Area, the council may also ask how combustion plant interacts with the wider air quality position, which is where an Air Quality Assessment comes in.

Illustrative example: a 60-cover Indian restaurant in a ground floor unit with two flats above and a rear courtyard. Charcoal and tandoor cooking puts it in the highest odour band. A rear courtyard discharge at first floor level is very hard to defend. Running the duct up the rear elevation to one metre above ridge, with baffle filters, an electrostatic stage, a deep carbon bed and an attenuated fan, is the version that gets consented.

The conditions that follow

Expect a condition requiring the system to be installed in accordance with the approved details before the use starts, another requiring it to be maintained in accordance with the submitted schedule for the life of the use, and often a restriction on cooking type or hours tied to the assessment you submitted. Conditions travel with the unit, so a later occupier switching from a cafe to a fried chicken shop inherits the restriction and usually needs a fresh application.

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.