Ventilation Testing for New Homes: What Building Control Needs

Ventilation Testing for New Homes: What Building Control Needs

Every new home with mechanical ventilation needs its air flow rates measured before sign-off. Building control wants the results on a commissioning sheet, sent within five days of the final test. If the sheet is late, or a fan is below its design rate, the completion certificate waits.

Why the test is required

Regulation 42 of the Building Regulations 2010 says that where a new dwelling is created by building work, the air flow rates of its mechanical ventilation must be tested using an approved procedure. Notice of the results must go to building control no later than five days after the final test.

Approved Document F Volume 1 (2021 edition) sets out that procedure in Section 4 and the commissioning sheet in Appendix C. Most new homes have at least kitchen and bathroom extract, so most new homes need the test.

What gets tested

• Intermittent extract fans in kitchens, bathrooms, utility rooms and WCs
• Cooker hoods that extract to outside
• Continuous mechanical extract (MEV) fans and terminals
• Mechanical ventilation with heat recovery (MVHR), supply and extract terminals

Each fan or terminal is measured against the design rate in Approved Document F. For intermittent extract the minimum rates are:

• Kitchen with a cooker hood extracting to outside: 30 l/s
• Kitchen without one: 60 l/s
• Utility room: 30 l/s
• Bathroom: 15 l/s
• WC: 6 l/s

For continuous systems the minimum high rates are 13 l/s in the kitchen, 8 l/s in a utility room or bathroom and 6 l/s in a WC. The total continuous extract must also reach the whole dwelling ventilation rate, which goes up with the number of bedrooms.

How the test is done

The tester places a calibrated air flow meter with a proprietary hood over each fan or terminal and records the flow in litres per second. The meter must be accurate to ±5% and calibrated within the last 12 months at a UKAS-accredited calibration centre. During the test all trickle vents and other background ventilators are open, and all internal and external doors and windows are closed.

Continuous and MVHR systems are balanced to the design rate at each terminal first. A copy of the completed commissioning sheet should also go to the homeowner.

Get the site ready first

Most wasted visits are homes that were not ready, not failed fans. Before the test:

• Fans wired, powered and working, with the controls set up
• Ductwork complete and connected, with nothing crushed or kinked in ceiling voids
• Grilles, valves and terminals fitted
• Trickle vents fitted in the windows
• Internal doors hung, with their undercuts
• For MVHR, the unit set up so the system can be balanced on the day

When a fan falls short

A fan below its design rate normally has to be fixed and retested before building control will accept the sheet. The usual causes are long duct runs, too many bends, squashed flexible duct or a fan too small for its run. We tell you which fan, what we measured and the likely cause, then retest once it is fixed. On continuous systems the fix is often rebalancing, or a higher fan speed.

What changes on 24 March 2027

The 2026 edition of Approved Document F Volume 1 takes effect on 24 March 2027, and on 24 September 2027 for higher-risk buildings. Work where the building notice, initial notice or full plans went in before 24 March 2027 stays on the current rules, as long as it starts before 24 March 2028. For testing, the new edition is more specific:

• Flow rates are measured and recorded in both background ventilation mode and high rate mode.
• Continuous extract and supply fans are measured with a powered flow hood. A vane anemometer is still allowed for intermittent extract fans.
• The meter and its hood are calibrated together, across a range from at least 4 l/s up to the system's maximum design rate.
• MVHR total supply and extract should balance within 10% in background ventilation mode.
• Whoever commissions and tests the system should belong to an organisation that regularly and independently checks their competence, such as a relevant competent person scheme.

If testing falls after March 2027, check which rules the scheme was submitted under.

Ventilation and the as-built SAP

The as-built SAP has to show the ventilation that was actually installed: the system type and the fan or MVHR unit models. A late swap of unit can change the SAP result. Send us the installed models with the test results and we will update the SAP at the same time.

What we need from you

Floor plans showing the wet rooms, the ventilation system type and fan models, the number of homes, and the date they will be ready. We can test ventilation on the same visit as the air tightness and sound tests, which cuts the cost. The report is issued within 5 working days of the visit.

Questions we get asked

Does every new home need a ventilation test? Every new home with mechanical ventilation does. That includes intermittent extract fans and cooker hoods, not just MEV and MVHR.

How quickly must the results go to building control? No later than five days after the final test, under regulation 42. Book the test early enough that the notice is in before your completion inspection.

Can a vane anemometer still be used after March 2027? For intermittent extract fans, yes. Under the 2026 edition of Approved Document F, continuous extract and supply fans must be measured with a powered flow hood.

Can you do the air test and sound test on the same visit? Yes. We can cover air tightness, sound and ventilation testing in one visit, which cuts the cost. Tell us when the homes will be ready.

More: Ventilation testing, air tightness testing, sound insulation testing, SAP calculations and EPCs, Why new homes fail Part O, industry updates

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