Building Regulations Part F – Ventilation

Volume 1 - Domestic

Introduction

In 2022 a new version of Approved Document Part F relating to ventilation is coming into force. The 2022 changes to Part F will cover all building work;

• Volume 1 is the dwellings

• Volume 2 is for buildings other than dwellings.

This video looks at volume 1 for domestic buildings. Note that volume 2 covers buildings containing rooms used for non-dwelling residential purposes. For example, hotels, hostels, halls of residence and boarding houses.

Both volumes have been updated in response to the significant changes within the 2022 edition of Part L conservation of energy.

Mechanical Ventilation

Mechanical ventilation will be required in kitchens, utility rooms, bathrooms and windowless sanitary accommodations. Minimum extract rates are detailed in Table 1.1 of the new approved document, as shown below:

• 30 l/s – Kitchen (cooker hood extracting externally)

• 60 l/s – Kitchen (no cooker hood or does not extract externally)

• 30 l/s – Utility room

• 15 l/s – Bathroom

• 6 l/s – Sanitary Accommodation

There is now clear guidance that recirculating cooker hoods require an additional mechanical extract fan to external air within the room.

Whole Dwelling Ventilation

Supply air for the dwelling should be delivered through either

• A continuous supply fan

• Background ventilation

The performance requirement is specified in litres per second per meter square of floor area or litres per second per bedroom.

Internal doors should also allow air to flow through the dwelling. To achieve this, doors should be undercut by one of the following:

• Where the floor finish is fitted 10mm above the floor finish

• Where the floor finish is not fitted 20mm above the floor surface

Purge Ventilation

A system of purge ventilation should be provided. Purge ventilation is manually controlled ventilation that allows for a relatively large change of air in a short period of time e.g. opening windows or a mechanical fan.

If this is provided through openings in a habitable room these openings should be of a minimum area shown in table 1.4 or be otherwise demonstrated to provide four air changes per hour. Hinged or pivot windows with an opening angle of less than 15 degrees are not suitable for purge ventilation.

Reference is also made to Part O of the build regulations which is likely to require higher purge ventilation rates and larger opening windows than detailed in table 1.4.

System Guidance

For whole-house ventilation, the choice of system is restricted for buildings with low air permeability rates. Part L of the build of regulations is driving lower air leakage rates, when buildings are designed with air permeability rates that are less than 5 meters cubed per meter square per hour at 50 pascals, trickle ventilators are not deemed acceptable.

In this case, continuous mechanical extract ventilation (CMEV) or whole house mechanical ventilation with heat recovery (MVHR) should be installed in place of or to supplement the trickle ventilators. Continuous mechanical extract ventilation can even be a centralized system or a series of individual continuous extract fans in place of intermittent extract fans.

Natural Ventilation

For less airtight dwellings, whole-house ventilation can be achieved using trickle ventilators rather than continuous mechanical extract ventilation.

Purge ventilation can be provided by openable windows. Intermittent extract fans should be provided to wet rooms, utility rooms, bathrooms, kitchens and sanitary accommodations. Wet rooms with no external walls should have fans that extract four air changes per hour to provide purge ventilation. Windowless rooms should have a 50-minute overrun to the mechanical extract ventilation system.

Openable windows can be used as an alternative to intermittent extract fans to WC’S. However, shower and bathrooms still require mechanical extra fans.

For whole-house ventilation in dwellings with single ventilated facade mechanical systems are expected. Expert advice is required if you want to use trickle ventilation in these situations.

If fans and background ventilators are close to main roads or areas of sustained loud noise then noise attenuating trickle vents are required.

Background Ventilation

Background ventilation should be provided following the guidance in Table 1.7.

Figures are provided for minimum equivalent areas of background ventilation for single-story dwellings and dwellings with multiple floors.

Performance Testing

All mechanical extract systems installed within new dwellings or dwellings formed by material change of use should be performance tested at completion of the building work. The test report should be provided to build control prior to sign-off.

Transitional Provisions

Transitional provisions apply to this document. To use the old version of Part F, an application must be received before the 15th of June 2022 and work must start on site before 15th of June 2023.

For multiple dwellings or buildings on an application work on each unit must have commenced for the transitional provisions to apply. So on an application for 100 dwellings, the application must be submitted by the 15th of June 2022 and the work on all 100 units must be commenced by the 15th of June 2023. If only 10 dwellings have started only these can be built to the old standard and the remainder must be the new 2022 Part F. Foundations for blocks of flats are considered a start on site for all the units within the block.