Cooking odour and the flats above a food business

Cooking odour reaching flats above a restaurant is an extraction design problem long before it is a planning problem. The controls that work are a duct routed to discharge above roof level, at a high enough efflux velocity, with filtration matched to the type of cooking and a maintenance regime somebody is contractually obliged to follow. Where a scheme cannot achieve a roof-level discharge, the abatement has to do far more work, and councils are right to be sceptical of a low-level discharge next to an openable window.

Why flats above food uses generate complaints

Odour behaves unlike noise. It is intermittent, it varies with the menu and the shift, and the same concentration will be tolerated by one household and reported by another. Sensitivity rises sharply where the receptor is a bedroom or a private balcony rather than a street.

Mixed buildings concentrate the problem. A ground-floor unit with flats above shares a structure, a rear elevation and often a light well, and the light well is the worst place a duct can terminate. Sound and smell both collect there, and a resident with a bedroom window three metres from the outlet will notice both.

Odour from trade or business premises can amount to a statutory nuisance under section 79 of the Environmental Protection Act 1990, which sits alongside the planning system rather than inside it. A permission does not license a nuisance, and an abatement notice can follow a lawful consent. That is why environmental health officers ask hard questions at application stage rather than after. Their colleagues in development management will usually adopt the answer without revisiting it, so the first response sets the condition wording for the life of the permission.

Assessing the odour risk before designing

The approach most environmental health teams use is a risk assessment rather than a model. Three things drive it: the type and scale of cooking, the sensitivity of the receptors, and the separation between the discharge point and those receptors.

Frying, grilling, tandoor and charcoal cooking sit at the high end. Reheating, steaming and cold preparation sit at the low end. A high-risk kitchen discharging four metres from a bedroom window needs a different system from a low-risk one discharging above a ridge with no receptors within 20 metres.

Work the assessment before the layout is fixed. Where the duct route is decided after the kitchen is designed, the riser is usually too small and the only remaining option is more abatement in less space. An Odour Assessment done early costs far less than a redesign, and it gives the case officer something to condition against. It also settles the argument about whether the use is high risk before the applicant has committed to a menu and a fit-out.

Duct routes, termination and discharge

Vertical discharge at high level is the design that works. The standard aim is a termination at least a metre above the eaves or ridge of the building and of any adjacent building within the affected zone, discharging vertically upwards with nothing on top of the stack.

Two details matter more than they look.

The first is the cowl. A conical rain cap directly above the outlet deflects the plume downwards and destroys the dispersion the height was meant to provide. Use a rain defeating design that keeps the discharge vertical.

The second is efflux velocity. A plume needs enough momentum to clear the building's wake, and a fan sized for pressure drop alone will often deliver too little. Where the designer reduces velocity to cut fan noise, odour performance goes with it, and the two have to be solved together rather than in sequence.

Where the duct must run externally on a rear elevation, remember the planning consequences. On a listed building the duct is likely to need listed building consent, and in a conservation area the visual impact of a stack running past three storeys of windows is a refusal reason in its own right.

Filtration and who maintains it

Grease filtration comes first, because grease carries odour and clogs everything downstream. Beyond that the usual steps are electrostatic precipitation, activated carbon, and in some systems ultraviolet or ozone treatment, with odour neutralisation as a final stage on higher-risk installations.

Carbon is the element that fails quietly. It has a finite adsorption capacity, it is exhausted long before anything looks wrong, and a system with spent carbon performs roughly as though the carbon were not there. Replacement intervals depend on the hours of use and the cooking type, so the maintenance schedule has to be specific to the installation rather than generic. A schedule copied from a supplier's brochure tells an officer nothing about this kitchen.

Councils increasingly condition a maintenance regime and a log. That is sensible and enforceable, provided the condition names the frequency and requires records to be produced on request. Conditions of that shape survive scrutiny in the same way that well-drafted obscure glazing conditions do, because compliance can be checked by inspection.

Write the obligation into the lease as well as the decision notice. A tenant who changes the menu from sandwiches to grilled meat has changed the odour risk without touching the planning permission, and the landlord is the one the neighbours will contact.

Noise from the same system

The extraction fan, the ductwork and the condensers usually arrive as one package and get assessed as three separate documents. That is how the conflicts get missed.

Larger ducts and lower velocities reduce regenerated noise but reduce plume rise. Attenuators add pressure drop, which pushes the fan harder. Anti-vibration mounts and flexible connections stop structure-borne transmission into the flats above, which is the complaint that is hardest to cure later because it is felt rather than heard.

Assess the whole installation together in a Noise Impact Assessment using the background at the nearest residential facade, including night-time where the kitchen operates late. And specify the fan once, with both the acoustic and the odour requirement in the same specification.

Conditions, and retrofitting an existing installation

For a new consent, the workable condition set is short: no use of the premises for cooking until the extraction system has been installed in accordance with approved details, a maintenance schedule with records, an hours restriction where late operation is in issue, and a noise limit at a defined position with post-installation verification.

Retrofitting is harder, because the building is occupied and the complaints have already started. Work in this order.

1. Establish what is installed, including filter type, last service and actual fan duty against the design duty.
2. Check the termination height and the presence of a cowl before spending anything on filtration.
3. Service or replace the grease and carbon stages, then reassess.
4. Extend the stack where the discharge is below roof level and the structure allows.
5. Only then consider additional abatement, which is the most expensive step and the least effective if the discharge point is wrong.

Document the works in a Ventilation and Extraction Statement whether or not a fresh application is needed, because it is the document the environmental health officer will ask for. Enter your postcode on PlanScope to see which reports a food use at your address is likely to need.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it. Councils usually expect a suitably qualified author for odour and acoustic work, and professional review is strongly advised. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.