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In the past few weeks, we’ve taken a look at a number of the UK’s building regulations; those that relate directly to installations. Here, we’re going to explore another key regulation: Part F.

What’s the purpose of Part F?

Put simply, Part F requires that a ventilation system capable of limiting the accumulation of moisture be installed, in order to remove any potential health hazards and to stop the growth of mould and prevent pollutants from filling the area.

(In this case, ventilation is classed as the removal of stale air from the environment and its replacement with fresh outside air).

Why is ventilation necessary?

Ventilation is a necessary provision for four main reasons:

  • The provision of outside air for breathing
  • The dilution and removal of airbourne pollutants (including odours)
  • The control of excess humidity
  • The provision of air for fuel-burning appliances, as covered in building regulations Part J.

How can the Part F Building Regulations requirements be met?

There are a number of techniques for ensuring that any building achieve the necessary criteria. Typically, a ventilation system capable of meeting the regulations should be able to:

  • Extract water vapour from areas in which it is created in large volumes (bathrooms and kitchens, for example).
  • Extract pollutants from any rooms in which they are produced.
  • Rapidly dilute – if needed – the presence of any water vapour or pollutants that spread into habitable or occupied rooms.
  • Supply occupants with outside air over long periods whilst minimising draughts and providing protection against rain penetration.
  • Perform and operate in a way which doesn’t hinder the health of the building occupants
  • Be installed in a way which facilitates any necessary maintenance

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The two main types of ventilation

Typically, modern buildings will use a combination of infiltration and purpose-provided ventilation:

  • Infiltration is the uncontrollable air exchange between the inside and outside of the building through the natural range of air leakage paths inherent in any structure (the gap between doors and frames, for example).
  • Purpose-provided ventilation, such as that found in skylights or mechanical structures such as kitchen extractor fans.

Section 4.12 of Part F states that, where possible, it is always preferable to minimise uncontrollable infiltration and emphasise sufficient purpose-provided ventilation.

A reasonably high level of air tightness should be achieved in the building - a level significantly higher than the minimum standards recommended in Building Regulations Part L.

(All new buildings are expected to better the target values for air tightness).

The approved ventilation strategy

Within Part F, a three-pronged strategy is recommended as the approved method. The focus of any design should be as follows:

  • To extract ventilation from any rooms where the most water vapour and pollutants are released.
  • To provide fresh air ventilation throughout the whole building, with the aim of removing any additional water vapour and providing a nominally continuous air exchange. (The ventilation rate may be reduced or ceased if the building is unoccupied, though it may be necessary to re-purge the area once it becomes occupied again).
  • To provide purge ventilation options in the event of accidental pollutant releases such as in the case of burnt food or water spillage. (Purge ventilation is only intermittent; it occurs when such an incident happens, but it must still be planned for).

The above strategy can be delivered by either a natural or mechanical ventilation system (or a combination of both) but any installation that will aid the process is encouraged.

(Our electric-operated opening skylights, for instance, can play a key part in aiding the ventilation process).


It’s recommended that any ventilation systems installed in both new and existing dwellings be installed in keeping with the 2010 edition of the Domestic Ventilation Appliance Guide. It’s also necessary where ducting passes through a fire-resisting wall, floor or fire compartment, that the required measures remain in-keeping with Part B of the Building Regulations.

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