Building Regulation Part F

Building Reg.s for ventilation

Ventilation is most effective when air is extracted close to the vapour source; bathroom, kitchen, drying clothes and occupied rooms.

Modern life and the drive to conserve energy means properties should comply with Building Regulation 2010 Part F requirements to stay dry and mould free. This is best achieved with mechanical extractor fans. 

 See specifically P39 and P19:

  1. Bathroom 15 l/s with a 30-minute overrun.
  2. Kitchen 30 l/s adjacent to hob; or 60 l/s elsewhere in kitchen.

Building Reg.s part F failure

A majority of ventilation systems are not properly tested and fail to comply with Building Reg.s. Part F


Vent reg.s typically fail because;

  • Flexible ducting is used too much, dramatically reducing flow rates over manufacturers published data, compared to rigid ducting.
  • Most ventilation installers don’t change factory settings, such as for overruns (which should be set to 30 minutes in bathrooms).
  • It is rare that the airflow exiting a property is tested, as should be the case, so leaks and other errors will go unnoticed.

Top tips

  1. Always test ventilation outflow for all bathroom and kitchen extractors with an anemometer (Testo make the best known).
  2. If you can’t reach the outflow, then test at the extractor side, but look for reasons why there could a leak in the ducting.
  3. Check the overrun setting is 20 minutes or more (ideally 30 minutes), if not note the overrun setting and consider the effect.
  4. Consider if the occupants typically leave the bathroom door closed or open.
  5. Consider whether the kitchen extractor fan is used and is effective such kitchen’s open plan to another room.

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