Phoenix Journal · Ductwork
Building Regulations Part F sets the rules for getting fresh air in and stale, greasy air out - and for a commercial kitchen the wording matters. Here it is in plain English, with the routes to compliance laid side by side.
Part F, decoded
Part F of the Building Regulations is the bit that says a building must have enough ventilation for the people using it - fresh air in, moisture and pollutants out - and it is written in the careful, hedged language that makes most operators glaze over.
The current version is the 2021 edition of Approved Document F, which came into force on 15 June 2022. It comes in two volumes: Volume 1 covers dwellings, and Volume 2 covers everything else - so if you run a restaurant, a pub kitchen, a care home servery or a staff canteen, Volume 2 is your document. It sits alongside Part L (energy) and the newer Part O (overheating), because the tighter you make a building for heat loss, the harder you have to work to keep the air moving.
Part F itself does not hand you a single kitchen design. It sets the outcome - adequate ventilation - and points you at the numbers and at supporting standards such as CIBSE Guide B and BESA's DW/172, the specification for commercial kitchen ventilation. The practical question every operator ends up facing is the same one Part F frames from the start: do you meet the requirement with natural ventilation, or with a mechanical system? So let's put the two routes side by side.
Natural ventilation means using openings - windows, louvres, vents, the stack effect of warm air rising - to move air without a fan. Part F recognises it as a legitimate strategy for occupiable rooms, and Volume 2 gives you a sizing rule of thumb: openable area of at least one fiftieth (1/50th) of the floor area it serves, provided that area is reasonably split high and low so air can actually circulate.
For anything beyond very light cooking, natural ventilation on its own leaves you exposed - both to a failed Part F assessment and to a hot, smoky, grease-laden kitchen that nobody wants to work in.
Mechanical ventilation uses fans to move a known, controlled volume of air - typically a canopy over the cook line extracting grease-laden air through filters, matched by a supply (make-up) system bringing tempered fresh air back in. This is the route Part F effectively steers commercial kitchens towards, and it is what CIBSE Guide B and DW/172 are written around.
Part F reads like prose, but compliance comes down to a handful of figures. For a commercial kitchen the extract requirement scales with the cooking: a space with only a microwave can sit around 15 l/s, while a cook line runs to 30 or 60 l/s at the appliance depending on where the extract sits relative to it - and in practice the canopy design under DW/172 and CIBSE Guide B is what governs a real hot line. Here are the three worth committing to memory.
The catch most operators miss is that meeting Part F on paper at handover is not the end of it. A mechanical system only keeps delivering its certified airflow if the ductwork stays clear - and in a kitchen, that means grease. As deposits build, extract volume drops, the kitchen drifts back below the rates Part F assumed, and you quietly acquire a fire hazard at the same time. Compliance and cleaning are the same conversation. If you want the vocabulary that sits behind the standards - the difference between grease extract and general air ductwork - our TR19 Grease vs TR19 Air glossary unpacks it in the same plain-English spirit as this page.
In short: for anything more than the lightest cooking, Part F points you at a properly designed, tested and maintained mechanical system - and the maintenance half of that promise is where most kitchens slip. Keeping the extract clean is what keeps you compliant, not just what keeps you safe.
Questions
Part F is triggered by building work - a new build, an extension, a material change of use or a system replacement - rather than applying retrospectively to a kitchen that has run unchanged for years. That said, if you refit the kitchen or replace the ventilation, the current 2021 Approved Document F applies to that work. And regardless of Part F, your existing extract system still has to be maintained and cleaned for fire safety under separate law.
Part F is the legal Building Regulation - it sets the outcome, that a building must have adequate ventilation, and gives baseline rates. DW/172 is BESA's technical specification for how you actually design and build a commercial kitchen ventilation system to achieve that, covering canopies, duct construction, access for cleaning and airflow. In practice you use Part F and CIBSE Guide B to set the targets and DW/172 to engineer the system that meets them.
For non-domestic spaces, Approved Document F Volume 2 sets a fresh-air supply of 10 litres per second per person, or 1 litre per second per square metre of floor area, whichever is the greater. On top of that, the kitchen itself needs dedicated extract - scaling from around 15 l/s for a microwave-only area up to 30 or 60 l/s at a cook line - with CIBSE Guide B pointing to roughly 30 air changes per hour for a busy kitchen.
Phoenix Duct Clean · by the numbers
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