Commercial kitchen ducts through residential buildings

Getting a kitchen duct through flats approved is a routing problem before it is an odour problem. The extract has to leave the kitchen, climb through a building full of homes, cross compartment walls and floors without compromising them, and discharge somewhere that does not blow cooking smells past a bedroom window. Solve that on a drawing before you sign the lease, because a unit with no viable duct route is a unit you cannot fit out as a restaurant, whatever the planning policy says about the high street.

Why the route decides the application

Councils refuse commercial kitchen applications in residential buildings for three linked reasons: odour, noise and the physical impact of the flue. All three are consequences of the route.

A duct that terminates at first-floor level next to a window will fail on odour no matter how good the filtration. A duct clipped to a rear elevation will draw an objection on appearance, and in a conservation area it may need consent in its own right. A duct running inside a residential riser raises fire compartmentation questions that the landlord's surveyor will ask before the council does.

So start with the section drawing, not the equipment schedule.

Internal riser or external flue

Two routes exist and each carries its own problems.

An internal riser keeps the duct out of sight and out of the weather. It needs a continuous vertical route from the kitchen to roof level, which in a converted building rarely exists. Where one does, the duct has to be fire-rated through its full height, it takes space at every floor, and it needs access panels for cleaning that somebody has to be able to reach.

An external flue is simpler to install and harder to get consented. It is visible, it needs fixing to a wall that may not be yours, and it changes the appearance of the building. On a listed building it will need listed building consent, and on many conservation area frontages it is a non-starter. Rear elevations are more likely to succeed than front ones.

Neither option works if the building has no route at all. That happens more often than agents admit, particularly in Victorian conversions with light wells and no service core.

Termination height and the rule of thumb

The established guidance on commercial kitchen exhaust is that the discharge should be vertical, at high velocity, and terminate at a height that carries the plume clear of nearby buildings, commonly expressed as at least a metre above the ridge or the eaves of the adjoining roofs.

Three details matter as much as the height.

• Discharge must be vertical. Cowls and hats that deflect the flow downwards defeat the dispersion and are a standing reason for refusal.
• Efflux velocity must be high enough to carry the plume upward, which means the fan and the duct diameter are a package rather than independent choices.
• Distance from openable windows, balconies and air intakes has to be checked in three dimensions, including windows on the building opposite.

Where the termination cannot reach the height the guidance indicates, the answer is not a taller argument. It is better abatement, a different route, or a different use for the unit. An Odour Assessment is the document that sets out how the plume behaves and what the abatement achieves, and councils expect a suitably qualified author for it.

Fire stopping and compartmentation

This is where inexperienced schemes come unstuck.

A kitchen extract duct passing through a compartment wall or floor breaches that compartment. In most services the answer is a fire damper. In kitchen extract ductwork it usually is not, because grease deposits stop dampers operating and because closing the damper traps a fire in the duct.

The accepted approach is fire-rated ductwork or a fire-resisting enclosure for the full run through other occupancies, designed so that the compartmentation is maintained without relying on a moving part. Access panels for cleaning have to be provided at intervals along the duct, and they have to be fire-rated too, and reachable.

Get the building control body and the fire engineer involved at design stage rather than at fit-out. A duct that has to be opened up and re-enclosed after installation is an expensive lesson, and a residential landlord whose compartmentation has been compromised will not be patient about it.

Noise breakout along the route

The fan is the obvious noise source. The duct is the one people forget.

Sound breaks out through duct walls along the whole run, so a duct passing a bedroom in a flat three storeys above the kitchen can be audible at night even when the fan is nowhere near. Lagging, acoustic enclosure and attenuators are the remedies, and all of them add dimensions that have to be allowed for in the riser.

Structural transmission is the second path. Fan and duct fixings transmit vibration into the building frame, which then radiates into rooms. Anti-vibration mounts and flexible connections are standard, and they need specifying rather than assuming.

The assessment goes in the Noise Impact Assessment alongside the plant noise, and the hours of operation usually end up in a condition. Where a condition is being proposed that the business cannot actually meet, say so during determination. The note on statutory nuisance and what a condition cannot fix explains why living with an unworkable condition is worse than negotiating it.

Landlord consent and the lease

Planning permission does not give you the right to run a duct through somebody else's building.

Check the lease for alterations clauses, for rights to use risers and common parts, and for any absolute prohibition on external alterations. Most work of this kind needs a licence for alterations, and the landlord's surveyor will want the fire strategy, the structural details and often a specification for cleaning and maintenance.

Where the building contains long leaseholders, their consent may also be needed, and the freeholder may be obliged to consult them. That process has its own timetable, which is frequently longer than the planning application.

Two practical points. Get the landlord's in-principle agreement in writing before you spend money on a planning application, because a permission you cannot implement is worth nothing. And make the lease conditional on both consents where you can, rather than signing and hoping.

Getting the design agreed before you commit

The sequence that works is short and it front-loads the risk.

1. Establish the duct route on a section drawing, from hood to termination.
2. Test it against the landlord's title, the lease and the fire strategy.
3. Have the odour and noise consultants confirm the route can perform.
4. Take it to pre-application advice with the council, with the section drawing.
5. Only then negotiate heads of terms.

A Ventilation/Extraction Statement prepared on that basis tells the officer what they need in one document: the route, the termination, the abatement, the cleaning regime and the noise control.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it.

Draft the ventilation and extraction documents for your unit on PlanScope, then have the design checked by your mechanical engineer.

PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.