Does an extension need building regulations for ventilation?

Yes. Ventilation for the new and altered parts of the home is covered by Part F and checked as part of the building control approval for the extension.

Can I add my extension to my existing MVHR?

Often yes, if the unit has spare capacity and the ducts can reach. Plan it into the extension design so the ducting goes in before the new structure is finished. The unit may need upgrading if it is near its limit.

Does a kitchen extension need extract ventilation?

Yes. A new kitchen needs extract at the Part F rate to deal with cooking moisture, either an extractor fan ducted to outside or a connection to a continuous system.

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Ventilation for extensions

An extension adds new space that needs ventilating, which brings Part F into play. Whether you extend an existing MVHR system, add extract ventilation, or fit something new depends on the extension and the home. This guide explains the options.

By VentRight Editorial · Last updated 2026-07-08 · Impartial · Sourced

Does an extension need ventilation under Part F?

Yes. An extension creates new space, and any new habitable rooms or wet rooms need ventilation under Part F, as for any building work. The work should also not make the existing home worse ventilated. Your building control body confirms what is needed for the specific extension.

Part F applies to the new and altered parts of a home, so a bedroom or living space in an extension needs a means of ventilation, and a new kitchen or bathroom needs extract ventilation at the Part F rate. It is handled as part of the building control approval for the extension.

Sources: GOV.UK

Do I need MVHR for an extension?

Not necessarily. If the home already has MVHR, the extension is usually added to the existing system if it has spare capacity. If it does not, an extension alone rarely justifies a whole-house MVHR system: extract ventilation for any new wet room plus background ventilation for the new rooms is often enough. It depends on the extension and the home.

MVHR makes sense across a whole airtight home, not as a bolt-on to one extension. For a typical extension on an otherwise conventional house, simpler compliant ventilation is usually more proportionate, unless you are doing a wider airtight renovation at the same time.

Can I extend my MVHR system into an extension?

Often yes, if the existing unit has enough spare capacity and the new ducting can reach the extension. It is best planned into the extension design so the ducts can be routed before the new structure is finished. If the unit is already near its limit, it may need upgrading to serve the extra rooms.

As with a loft conversion, the practical questions are unit capacity and duct routing. Designing the ventilation alongside the extension, rather than as an afterthought, keeps the runs short and tidy and avoids the duct routes competing for space with the new build.

What about a kitchen or bathroom in an extension?

A new kitchen or bathroom in an extension needs extract ventilation at the Part F rate, either an intermittent extractor fan or a connection to a continuous system. A kitchen extension in particular needs proper extract to deal with cooking moisture. This is a core Part F requirement, so it is checked as part of the building control approval.

Kitchen extensions are common and the extract is easy to overlook in the excitement of the new space. Whether it is a fan ducted to outside or an extension of an MVHR or MEV system, the moisture from cooking has to be removed at the required rate, or condensation and smells follow.

Questions

Does an extension need building regulations for ventilation?: Yes. Ventilation for the new and altered parts of the home is covered by Part F and checked as part of the building control approval for the extension.
Can I add my extension to my existing MVHR?: Often yes, if the unit has spare capacity and the ducts can reach. Plan it into the extension design so the ducting goes in before the new structure is finished. The unit may need upgrading if it is near its limit.
Does a kitchen extension need extract ventilation?: Yes. A new kitchen needs extract at the Part F rate to deal with cooking moisture, either an extractor fan ducted to outside or a connection to a continuous system.
Do I need MVHR for a single-storey extension?: Rarely on its own. An extension alone seldom justifies whole-house MVHR. Extract for any new wet room plus background ventilation for the new rooms is often enough, unless the home already has MVHR or is being deeply renovated.