Part F Domestic Ventilation Guidance

As can be seen with the targets in Table 5.1a, a single fan is required in every wet room including any Utility room where there is provision for sinks, washing machine or dryers.

Where there is no cooker hood, an extractor can be fitted adjacent to the cooker which achieves 30l/s, or an extractor anywhere in the kitchen which reaches 60l/s.

There is a requirement from Building Regulations Part F for background ventilators such as trickle vents or passive ventilation sized appropriately for the size of the plots. This can be derived from table in section 5.2a of Building Regulations Part F. In most cases, trickle vents installed into each window frame will suffice.

Specifically, Decentralised Continuous mechanical extracts can be installed in a similar manner to System 1 fans, with the exception that they run continuously. These are more common in plots where the air tightness result is expected to be below 3m3/h/m2. 

As shown by cross referencing Tables 5.1a and 5.1b taken from Building Regulations Part F, compliance is achieved by each individual fan reaching its “Minimum high rate”, and for the total of the low rates to be greater than the “whole dwelling ventilation rate”, which must be calculated prior to installation to ensure compliance can be reached by the fans. 

Ventilation Testing and commissioning requires that the low and high rates of each fan be taken, then adjustments to be made to ensure that the flow rates are reached. This process can often lead to excessive noise from fans in situations where insufficient fans have been installed, requiring that a number of fans need to be run at higher speeds continuously.

Cooker hoods may be installed but cannot be ducted externally, instead made to recirculate the air back into the kitchen allowing a System 3 extract installed in the kitchen to remove the polluted air.

For any design air permeability, controllable background ventilators having a minimum equivalent area of 2500mm2 should be installed in each room, except wet rooms, from which air is extracted. As an alternative, where the design air permeability is leakier than 5m3/h/m2 at 50Pa, background ventilators are not necessary but see precautionary advice in paragraph 5.10 of Building Regulations Part F as this approach can lead to long term issues.