Approved Document F · Approved Document G
Extractor fan flow rate testing
Airflow measured at every fan against the rates in Approved Document F, with the certificate issued within 24 hours of the visit. Site attendance typically within two working days across Kent and the South East.
Flow hood in use at an extract terminal
Services
Approved Document F
Extractor fan flow rate testing
Airflow measured at every extract point and recorded against the minimum rates for each room type. A certificate suitable for building control is issued within 24 hours. Where a fan fails, the cause is identified on site and the retest is included.
£60 minimum charge · £20 per fan on developments
Approved Document G
Water efficiency calculations
Consumption calculated from the schedule of fittings and returned within 24 hours of receiving the information. No site visit is required, so the service is available anywhere in England and Wales.
£40 per dwelling type · not per plot
Why the test is required
Building control require evidence that the extract ventilation installed in a new or converted dwelling achieves the airflow the design specifies. Without that evidence, the plot is not signed off.
In practice, fans frequently do not perform to their rated figure. Ductwork is run too long or pulled around tight bends, terminals are restricted, and units are occasionally faulty from new. Measurement is the only way to establish whether a system complies.
A failed test at the point of completion is expensive because it stops handover. Testing early, once the fans are wired and running, leaves time to correct anything that does not pass.
Recent work
Book a test
Give the site postcode and the number of fans and you will have a price the same day.
Approved Document F
Extractor fan flow rate testing
Airflow tested at every fan, certificate issued within 24 hours, retest included where a fan fails.
Building control require evidence that the extract ventilation in a new or converted dwelling achieves the airflow specified. That means measuring the rate at each extract point and issuing a certificate recording the results.
Approximately 800 fan tests completed over the past ten years, principally for small developers, self builders and architects across Kent and the South East.
The required rates
Approved Document F, 2021 edition, in force since 15 June 2022. Table 1.1 sets the following minimum extract rates for intermittent systems in dwellings.
| Room | Minimum extract rate |
|---|---|
| Kitchen, cooker hood extracting to outside | 30 l/s |
| Kitchen, no cooker hood or not extracting outside | 60 l/s |
| Utility room | 30 l/s |
| Bathroom | 15 l/s |
| WC or sanitary accommodation | 6 l/s |
A fan that does not achieve the rate for its room type fails, and building control will require it to be corrected and retested before the plot is signed off.
The test procedure
QuotationProvide the site postcode and the number of fans. A firm price is given at the point of enquiry, before any travel is committed.
Site attendanceTypically within two working days, and within a week at the outside.
MeasurementAirflow is recorded at each extract point. Allow approximately 30 minutes for the first fan and less thereafter. A four fan dwelling takes around an hour and a half from arrival to departure.
FailuresWhere a fan does not achieve its rate, the cause is identified and the remedy explained. If it can be corrected while on site, up to an hour is allowed and the retest is included at no additional charge.
CertificationThe certificate is issued by email within 24 hours of the visit.
How a result is judged
Testing is carried out under the minimum benchmark method, which is the method building control most commonly accept for dwellings. It applies a lower acceptance threshold than the design rate.
| Design extract rate | Benchmark acceptance |
|---|---|
| 60 l/s | 35 l/s |
| 30 l/s | 24 l/s |
| 15 l/s | 12 l/s |
| 6 l/s | 6 l/s |
A bathroom fan measuring 13 l/s against a 15 l/s design rate has not failed. Under the benchmark method the acceptance figure is 12 l/s, so it passes and the certificate records both numbers. Assuming otherwise leads to fans being replaced that did not need replacing.
Site requirements
A test cannot proceed unless the following are in place. Confirming them before the visit avoids an abortive attendance.
- Power on to the dwelling
- Fans installed, wired and running
- Clear access to the face of every extract point
- Someone on site to provide access
A test cannot be carried out until the fans are installed and running. Where the installation is not complete, call to provisionally hold a date and the visit can be confirmed once the units are in.
Common causes of failure
Frequently the case on plots where the electrical second fix is incomplete at the time of testing.
Flexible duct drawn around a tight radius, or compressed within a ceiling void, will reduce the measured rate regardless of the fan specification.
A proportion of fans do not achieve their rated output in installed conditions and require replacement.
Pricing
£20 per fan on developments
Developments of 15 fans or more, typically four plots and upwards, are priced at £20 per fan.
Smaller instructions, including single dwellings, are priced individually against the postcode and the number of fans. A minimum charge of £60 applies to any attendance.
Either way a firm price is given when you call, before any travel is committed.
Instrumentation
UKAS accredited calibration
Testing is carried out with a Testo 417 vane anemometer, used with a Testo 445/400 flow hood.
The anemometer is calibrated annually by BSRIA under their UKAS accredited scheme. The current certificate is provided on request, which is what building control ask for where a result is queried.
Approved Document G
Water efficiency calculations
Returned within 24 hours of receiving the drawings and schedule of fittings. No site visit required, so the service is available anywhere in England and Wales.
A twenty plot development with three house types requires three calculations, so £120. The calculation is determined by the fittings specified, and identical dwellings share a result.
New dwellings must demonstrate a maximum water consumption figure under Part G of the Building Regulations. The calculation totals the flow rates and capacities of every water using fitting in the property and establishes the consumption per person per day.
Approximately 200 calculations completed to date.
The standard
| Requirement | Limit |
|---|---|
| Mandatory, all new dwellings | 125 l/person/day |
| Where imposed as a planning condition | 110 l/person/day |
If the planning consent for the site carries the tighter condition, say so when sending the details. It materially affects which fittings can be specified.
What the calculation covers
Fittings assessed
- WCs, single or dual flush
- Basin and other taps
- Kitchen and utility room taps
- Bath and shower
- Washing machine and dishwasher
- Waste disposal unit and water softener, where fitted
Method
Each fitting is assigned a flow rate or capacity, a use factor and a fixed use allowance. Any contribution from greywater or rainwater harvesting is deducted, a normalisation factor of approximately 0.9 is applied to the total, and a fixed allowance for external use is added to produce the final figure.
Information required
- Drawings
- Schedule of fittings and appliances
- Quantities
The calculation is returned within 24 hours of receiving these.
Coverage
Where testing is carried out
Based in Maidstone, covering Kent as standard and the wider South East for larger instructions.
Standard coverage
Any size of instruction, including single dwellings.
Wider South East
Attended for multi plot instructions where the travel is proportionate to the work. Call to discuss a specific site.
No site visit is required for a Part G calculation, so it can be produced for a development anywhere in England and Wales at the same price and the same turnaround.
About
Roy Salmon
Thirty years in building testing, the last ten of them on extract ventilation and water efficiency.
I worked in air permeability testing for eighteen years and have spent the last ten carrying out extractor fan flow rate testing and water efficiency calculations for building control sign off. Before that, twenty years in technical support to the communications industry.
That amounts to approximately 800 fan tests and 200 water efficiency calculations.
Around half the work is for small developers and a third for self builders. The remainder is architects, electrical contractors and private clients.
A single assessor carries out every test. The person who quotes the job is the person who attends site and issues the certificate.
Instrumentation
Testo 417 and 445/400
A Testo 417 vane anemometer used with a Testo 445/400 flow hood. The anemometer is calibrated annually by BSRIA under their UKAS accredited scheme, and the current certificate is provided on request.
Approach
Diagnosis, not just a result
Where a fan fails, the cause is identified and the remedy explained rather than simply recorded. Where the fault can be corrected during the visit, the retest is included.
Scope
Two services, done properly
Air testing, sound testing, SAP calculations and EPCs are not offered. Contacts for each can be provided, which is usually quicker than sourcing them independently.
Contact
Request a quote
Calling is quickest and a price can usually be given on the spot. Otherwise send the details below and a quotation will follow the same day.