Extract systems for hot food premises: what officers ask
A hot food takeaway is sui generis, so the extract system is argued in full at application stage. Discharge height, abatement staging, fan noise and the maintenance plan officers condition.
A change of use to a hot food takeaway is sui generis, so there is no permitted development route and the application has to be made in full. The extract system is what the case officer and the environmental protection officer will actually argue about. Three things decide the outcome: where the duct terminates, what abatement is fitted to it, and how quiet the fan is at the nearest bedroom window. Everything else in a Ventilation and Extraction Statement supports those three answers.
Restaurants and cafés sit in Class E, which gives some flexibility. Hot food takeaways do not, and neither does a drinking establishment with expanded food service. Establish the use class position before you design the kitchen.
Why a change of use triggers the extract question
Cooking odour is a classic amenity issue and a classic statutory nuisance, and a council that grants permission without controlling it inherits the complaints. So the officer asks for the control to be designed, specified and conditioned at the application stage.
The trigger is not always a change of use. Installing or replacing an external duct on a building is usually development in its own right because of its effect on the external appearance, and in a conservation area or on a listed building consent is required. A new flue up the rear elevation of a Victorian parade is the commonest source of refusal on these schemes, not the cooking itself.
Residential above is what sharpens everything. A unit in a parade with flats over has a receptor a few metres from the discharge, and the design has to work for that geometry rather than for an ideal one.
Discharge height above the eaves and why it matters
The established approach in the Defra guidance on the control of odour and noise from commercial kitchen exhaust systems is to terminate the duct at high level, discharging vertically upwards, so the plume disperses above the building rather than across it. In practice that means the termination should sit at or above the eaves or ridge of the building it serves and of any adjoining building with a sensitive receptor, and clear of any openable window within a reasonable distance.
Three design points follow.
Discharge velocity matters as much as height. A plume leaving at low velocity falls back down the roof slope, so efflux velocities in the region of 10 to 15 metres per second are typically specified, which in turn sets the fan duty and the duct diameter.
A cowl or weather cap that deflects the plume sideways defeats the purpose. Use a design that sheds rain without turning the discharge horizontal.
Where a full height duct is not achievable, the alternative is heavier abatement at low level, and the officer will want the risk assessment that justifies it rather than an assertion that the duct could not be routed.
Odour control stages and when each is needed
The Defra guidance applies an odour risk assessment: the size and type of the kitchen, the food cooked, and the proximity and sensitivity of receptors give a risk band, and the band determines the level of abatement expected. Low risk may need nothing beyond grease filtration and a good discharge. High risk needs a multi-stage train.
| Stage | What it does | Typically specified when |
|---|---|---|
| Grease filters, baffle or mesh | Removes grease aerosol, protects downstream plant | Always, on any commercial kitchen |
| Electrostatic precipitator | Removes fine particulate and some odour | Medium and high risk, frying and grilling |
| Carbon filtration | Adsorbs odour compounds | Medium and high risk, close receptors |
| Ultraviolet or ozone treatment | Oxidises odour compounds | High risk, where carbon alone is insufficient |
| Odour neutralising dosing | Masks residual odour | Rarely accepted as a primary measure |
Specify the units by make, model and rated airflow, and show them on the drawings rather than listing them in a table alone. An officer who cannot see where the carbon cells sit will ask, and the answer usually reveals that the ceiling void cannot take them.
Carbon has a service life measured in months under heavy use, which is why the maintenance regime is part of the planning case rather than an afterthought.
Noise from the fan and the duct
Fan noise is assessed as commercial and industrial sound, normally against BS 4142:2014+A1:2019, comparing a rating level that includes any acoustic character correction with the measured background at the nearest noise sensitive facade. Night-time is the determining period for anything open in the evening.
The measures that work are unglamorous. Select a larger, slower fan rather than a small fast one. Fit attenuators on both the inlet and the discharge side, sized by the acoustic consultant rather than by the ductwork supplier's default. Mount the fan on anti-vibration mounts with flexible connections so the structure does not radiate. Avoid a straight duct run that acts as a speaking tube into a bedroom at second floor level.
Break-out noise through the duct wall is the failure people miss. A thin spiral-wound duct passing a bedroom window on the way up a rear elevation will transmit low frequency fan noise through its wall, and lagging it after installation is expensive. A Noise Impact Assessment covering the fan, the duct and the plant, with the specified attenuation shown in the calculation, settles the point before the condition is drafted.
Conditions requiring a limit at a facade are only as good as their enforceability, and the same weaknesses apply here as to noise limiter conditions on entertainment venues.
Routing a duct on a listed or conservation area building
On a listed building, an external duct on a principal elevation is rarely acceptable, and consent turns on finding an internal route. Existing flues, redundant chimney stacks, service risers and rear closet wings are the places to look. Where an external run is unavoidable, a position on a secondary elevation, in a dark matt finish, fixed into mortar joints rather than masonry, with a reversible fixing detail, is the proposition that has the best chance.
In a conservation area the test is the effect on character and appearance, so an unlisted building in a terrace may still be refused a prominent duct. A rear elevation visible from a public footpath counts as prominent.
Either way the application needs a heritage case made properly rather than a sentence. Set out the significance of the building, the harm the duct causes, the alternatives tested and the reason the proposed route is the least harmful. Where a listed building is involved, listed building consent is a separate application and runs alongside the planning permission rather than inside it.
Maintenance and the management plan
Officers condition maintenance because an unmaintained system is an odour complaint waiting to happen, and because they have no other control once the use is operating.
A management plan that satisfies them covers the cleaning frequency for grease filters and ductwork against the recognised ductwork hygiene standard, the replacement interval for carbon media with the basis for it, who holds the service contract, where the records are kept, and the response procedure if a complaint is received. Add the hours of operation of the extract system, because a fan running at 02:00 for cleaning is itself a complaint.
Keep it short and specific. A two page plan with intervals and responsibilities is more likely to be complied with than a twenty page document, and the officer knows that.
What to submit with the application
For a straightforward unit in a parade, the package is modest.
- Floor plans showing the kitchen layout, the hood positions, the canopy extent and the route of the duct through the building.
- Elevations showing the duct and the termination, with heights dimensioned against the eaves and ridge and against the nearest openable windows.
- An odour risk assessment following the Defra approach, with the risk band and the abatement selected.
- Equipment schedules with make, model, airflow, efflux velocity and sound power levels.
- A noise assessment where there are sensitive receptors nearby, with background measurements and the predicted rating level.
- The maintenance and management plan.
- A heritage statement where the building is listed or in a conservation area.
An Odour Assessment is the right document where the risk band is high, the receptors are close or the local authority has asked for one specifically. For a small café conversion with no residential above, the risk assessment inside the extraction statement usually covers it.
One honest point. Odour prediction for commercial kitchens is not precise, and two competent assessors can reach different risk bands for the same unit. That is why the design margin, the maintenance regime and the willingness to return and adjust matter more than the decimal places in the assessment.
This is general guidance, not legal advice. Check the position with your local planning authority and its environmental protection team, and have the design reviewed by a qualified ventilation or acoustics professional before submission.
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Frequently asked questions
Does a hot food takeaway need planning permission?
Yes. A hot food takeaway is sui generis under the Use Classes Order as amended, so it sits outside Class E and there is no permitted development route into it from a shop or a café. The change of use needs a full planning application, and the extract system is normally assessed as part of it.
How high does a kitchen extract duct have to terminate?
The established approach is to discharge vertically upwards at or above the eaves or ridge of the building served and of any adjoining building with a sensitive receptor, clear of openable windows. Discharge velocity matters too, since a slow plume falls back down the roof slope rather than dispersing above it.
When is carbon filtration required?
When the odour risk assessment puts the kitchen in a medium or high band, which is driven by the size and type of kitchen, the food cooked and the proximity and sensitivity of receptors. Grease filtration is always needed. Electrostatic precipitation, carbon and ultraviolet treatment are added as the risk band rises.
Can I put the duct up the front of a listed building?
Almost never. Consent turns on finding an internal route through existing flues, redundant stacks or service risers. Where an external run is unavoidable, a secondary elevation with a dark matt finish and reversible fixings into mortar joints is the proposition most likely to succeed, supported by a proper heritage case.
What maintenance conditions should I expect?
Expect a condition securing a management plan covering grease filter and ductwork cleaning frequencies against the recognised hygiene standard, carbon media replacement intervals, who holds the service contract, where records are kept and how complaints are handled. Also expect the operating hours of the extract system itself to be controlled.
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.