Part F 2026: what changes for ventilation commissioning

There is a new edition of Part F of the Building Regulations (Approved Document F 2026). It changes how mechanical ventilation in homes is commissioned. This page is taken from the published text.

In short

England: it starts on 24 March 2027.
Wales: its own edition starts on 4 March 2027.
Continuous fans must be measured with a powered flow hood.
The hood and its meter are calibrated together, at a UKAS-accredited lab, in the last 12 months.
To commission most systems you need to be in a competent person scheme.
For one extract fan in an existing home, appropriate training is enough.
There is a new commissioning sheet.

When it starts

England: 24 March 2027.
Higher-risk buildings in England: 24 September 2027.
Already notified? If the building notice, initial notice or full plans went in before 24 March 2027, the old rules still apply. Work on that building must start before 24 March 2028. The regulations say what counts as starting.
Higher-risk buildings keep the old rules if a valid application went to the regulator before 24 September 2027 and was not rejected.
Wales has its own edition. It starts on 4 March 2027. Work notified before then keeps the old rules if it starts before 4 March 2028.

The rest of this page is about the England edition.

From Building Circular 01/2026 and Welsh Government circular WGC 006/2026.

Who can commission

One intermittent extract fan in an existing home: you need appropriate training.
Anything else: you need to be in a scheme that regularly checks your work, such as a competent person scheme.
This is new. The commissioning section of the 2021 edition had no such rule.
The work is signed off by a registered competent person or by building control. If you are not registered with a scheme, tell the local authority before work starts, or get a registered building control approver to oversee it. For a higher-risk building, tell the regulator.

From paragraphs 4.2, 4.6 and 4.10.

Measuring air flow

Continuous fans, extract or supply: use a powered flow hood.
Intermittent extract fans: a vane anemometer is still allowed.
Calibration: the meter and its hood are calibrated together, in the last 12 months, at a UKAS-accredited lab. It must cover at least 4 l/s up to the system’s top design flow.
Accuracy: within ±5%.
Take readings on background rate and on high rate. Background ventilators open. Doors and windows shut. Hood centred on the fan or terminal.
Each reading is the average over at least 10 seconds, in l/s.
Heat recovery: total supply and total extract must be within 10% of each other on background rate.

What is new: the 2021 edition did not ask for a powered hood, for the hood and meter to be calibrated together, for a calibration range or for a 10-second average.

From paragraphs 4.21 and 4.24, and 4.10 of the 2021 edition.

Which jobs need testing

New homes: test every fan. That includes cooker hoods, intermittent and continuous extract fans, and heat recovery fans and terminals.

Existing homes: test when you fit

a new central system, or make a big change to one
a new fan with more than 2m of duct
a new fan on duct with more than one 90 degree offset.

From paragraphs 4.23 and 4.26.

Paperwork

New homes: send the air flow results to building control within 5 days of the final test, on the Appendix C sheet. That is the same as now.
Send a commissioning notice too. For continuous systems, put the air flow readings on it. It goes in with your regulation 16(4) notice. If that does not apply, send it within 30 days of finishing.
Higher-risk buildings that need a completion certificate: the notice goes to the regulator with that application.
In a scheme? Within 30 days, you or your scheme give the occupier the Building Regulations compliance certificate. Building control gets the certificate or the details on it.
One document can be the commissioning notice for both Part F and Part L.
Give the owner a copy of the completed commissioning sheet.

From regulations 42 and 44, and paragraphs 4.5, 4.9, 4.12, 4.25 and 4.30.

The new commissioning sheet

Part 3 is split three ways: 3a for intermittent extract fans, 3b for decentralised continuous extract fans, 3c for central continuous systems.
Intermittent fan readings are listed by room.
It asks for the calibration certificate number.
The commissioning engineer’s details and scheme are always filled in.
Each of Parts 3a, 3b and 3c has its own declaration.
As before, one sheet per address, and a copy goes to building control.

Compare the 2021 and 2026 sheets line by line

Parts of the sheet

2021 edition: Part 1, Part 2a, Part 2b and one Part 3 for all air flow measurements.
2026 edition: Part 1, Part 2a, Part 2b, then Part 3a for intermittent extract fans, Part 3b for decentralised continuous extract fans and Part 3c for centralised continuous systems.

The least you must fill in

2021 edition: All the information in Part 3 (paragraph 4.3).
2026 edition: All the information in Parts 3a to 3c (paragraph 4.12).

Measuring equipment

2021 edition: Model and serial number, and the date of the last UKAS calibration.
2026 edition: Model and serial number, the date of the last UKAS calibration, and the calibration certificate number.

Commissioning engineer

2021 edition: Section 1.4, filled in only if different from the installer: name, company, address, phone and email.
2026 edition: Section 1.4 always, and it adds the engineer’s competent person scheme.

Fans installed

2021 edition: One manufacturer, model numbers and serial number, then up to seven fan locations.
2026 edition: One line per fan: location, manufacturer, model and serial number.

System classification

2021 edition: ‘Natural ventilation’, ‘mechanical extract ventilation’ or ‘as defined by Approved Document F’.
2026 edition: ‘Natural ventilation’, ‘continuous mechanical extract ventilation’ or ‘continuous mechanical extract and supply ventilation’.

Intermittent fan readings

2021 edition: Extract fan 1 to 4, against the fans listed in Part 1.
2026 edition: By room: cooker hood, kitchen, bathroom, en suite, utility and other.

Continuous rate to compare against

2021 edition: Table 1.3.
2026 edition: Paragraph 1.20.

Totals

2021 edition: No total rows.
2026 edition: Part 3c has a total extract row and a total supply row.

Background ventilators (Part 2b)

2021 edition: Asks for the total installed equivalent area in mm² and the dwelling’s floor area in m².
2026 edition: Asks yes or no: do the ventilators satisfy Table 1.7 or paragraph 1.57 (natural ventilation), or paragraph 1.64 (continuous mechanical extract)?

Declarations

2021 edition: One commissioning declaration, at 3.5.
2026 edition: One at the end of each of Parts 3a, 3b and 3c.

From Appendix C of both editions.

Also corrected in September

Flexible duct is allowed for the final connection to a fan, up to 200mm long, in any type of system. The corrected edition starts on the same dates.

From Circular 04/2026, paragraph 1.79.

Commissioning before then

CertBox’s ventilation commissioning certificate follows the 2021 edition, the one in force in England today. Ventilation commissioning certificate

Tell me when the 2026 sheet is ready in CertBox

When CertBox has a commissioning sheet set out to the 2026 edition, we will send you one email to say so.

Sources

Read on 26 October 2026.