Who is competent to design a commercial kitchen extract system

Kitchen extract system designer competence is the thing councils are really asking about when they refuse a takeaway or restaurant application on odour grounds. The refusal reason says the proposal fails to demonstrate that odour can be adequately controlled. What it means is that nobody with the right training sized the system, chose the abatement or set the discharge point, so the environmental health officer could not check the arithmetic.

The recognised reference is the specification for kitchen ventilation systems published by the Building Engineering Services Association, usually called DW/172, read alongside the Defra-funded guidance on the control of odour and noise from commercial kitchen exhaust systems. Between them they cover capture, ductwork, abatement, discharge and the risk-based approach an officer will apply. Neither is a legal requirement. Both are what the officer will measure your submission against.

Why installer knowledge is not design competence

An installer who has fitted a hundred canopies knows what fits through a riser and what the fan sounds like at full speed. That is useful. It is not the same as calculating the extract volume from the cooking appliance duty, sizing the make-up air so the kitchen does not go into negative pressure and pull air from the dining room, selecting an abatement train against an assessed odour risk, and working out a discharge height that gets the plume above the building's recirculation zone.

The division that matters in practice is between the person who specifies the system and the person who installs it. One produces calculations, a drawing and a performance specification. The other builds to that specification and commissions it. Councils are increasingly explicit that they expect the first of those to exist as a document, with a named author.

What the recognised specification actually requires

A design that follows the specification will have settled, on paper and before submission:

1. Extract volumes derived from the appliance schedule, not from a rule of thumb per square metre.
2. Capture velocities at the canopy edge, with canopy overhang and height above the appliance stated.
3. Grease filtration in stages, with access for cleaning at every change of direction.
4. Make-up air provision and the resulting pressure regime in the kitchen and dining areas.
5. Duct material, gauge, jointing and fire rating, with access panels at the intervals the specification sets.
6. Odour abatement selected against the assessed risk, which may be filtration alone, carbon, electrostatic precipitation, ultraviolet or ozone, or a combination.
7. A discharge point, usually at or above ridge level and clear of openable windows, with efflux velocity stated.
8. Fan selection with duty, static pressure and sound power levels at octave band centre frequencies.

If a supplier quotation gives you a canopy size, a fan model and a price, it is a quotation and not a design. Ask for the calculations.

Fire, grease and cleaning access built into the design

Grease-laden ductwork is a fire risk, and the design has to anticipate cleaning rather than leaving it to be solved later. Access panels at bends and at regular intervals along straight runs, a route for the cleaning contractor, and a documented cleaning frequency based on hours of use are all design decisions. The fire strategy for the building has to deal with duct penetrations through compartment walls and floors, with fire-rated ductwork or fire dampers depending on the arrangement.

That interface is where the planning submission and the building control submission diverge. Planning deals with the external effects, meaning odour, noise, the appearance of the flue and its position. Fire-stopping and duct fire resistance are Building Regulations matters. Say so in the planning documents rather than filling them with Approved Document references the case officer cannot act on.

How the odour and noise authors depend on the design

The odour assessment and the noise assessment are not independent of the extract design. They are downstream of it.

The risk-based approach in the Defra-funded guidance works by scoring the sensitivity of the surroundings and the size and type of the cooking operation, then setting the level of abatement that follows. An Odour Assessment that applies that approach without an appliance schedule and an extract volume is doing arithmetic on invented inputs, and an experienced officer will say so. Councils usually expect a suitably qualified author for odour and acoustic work, and professional review is strongly advised.

The same applies to the acoustic side. A Noise Impact Assessment for a kitchen extract needs the fan manufacturer's sound power data, not a single overall figure, because attenuator selection is a frequency-by-frequency exercise. And a terminal discharging two metres from a bedroom window will fail on noise even where the odour case is sound.

Who signs the design for the planning submission

For planning purposes, the document that carries the design is the Ventilation and Extraction Statement. It should name the designer, state their qualifications or professional membership, and identify which parts of the submission are their work. Where an AI-assisted draft has been used to set out the structure, the policy context and the management regime, the technical content still has to be checked and adopted by the designer who is prepared to stand behind it. The question of where responsibility sits between a lead consultant and a specialist is dealt with in the guide to sub-consultants and where liability sits.

Membership of a relevant institution is the shorthand officers use, but the better test is whether the author can produce the calculations when asked. Ask a prospective designer for a redacted example of a previous system design with the extract volume derivation shown. The ones who have done this work will send it the same day.

Commissioning evidence and what to retain

Approval is normally conditioned, and the condition usually requires the approved scheme to be installed before the use starts and retained thereafter. Discharging it needs evidence, so keep:

• The as-installed drawings, where they differ from the approved scheme.
• Commissioning records with measured air volumes against design volumes.
• The operation and maintenance manual, including filter change and abatement servicing intervals.
• The cleaning contract and the first cleaning certificate.

Authorities that have been burned before sometimes add a condition requiring a post-installation verification report from an independent assessor. Agree the scope of that at the condition drafting stage rather than after installation.

Checking a supplier proposal against the standard

Six questions that separate a design from a sales sheet. What is the extract volume and how was it derived from the appliance duty. Where does the make-up air come from and what is the resulting pressure in the kitchen. What odour risk level has been assumed and what abatement does that require. Where is the discharge point relative to the ridge and to the nearest openable window. What is the fan sound power by octave band. What access is provided for cleaning, and at what intervals.

If the answers to those come back as a model number and a reassurance, go elsewhere. The professional directory is the route for finding a reviewer to check a design and a draft statement before submission.

This is general guidance, not legal advice. Standards, guidance editions and local validation requirements change, so confirm the scope with the environmental health officer before you commission anything. For specialist technical reports, qualified professional input may be required.

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