The Building Regulations (Part F)

The Approved Document F: Ventilation is a government publication in the UK that provides guidance on the minimum requirements for ventilation in buildings. It is split into Volume 1 for dwellings, and Volume 2 for non dwellings, and sets out the standards for ventilation in different parts of a building including the kitchen, bathroom, and living spaces, within the following methods:

Natural Ventilation

Previously known as System 1
  • Suitable for less airtight dwellings.
  • Requires correctly sized and fitted trickle vents to be installed.
  • Intermittent extract fans should be fitted in all wet rooms and their extract rates comply with the below table.
intermittent house
Table 1.1 Minimum extract ventilation rates for intermittent extract systems (REFERENCED FROM PART F VOLUME 1)
Room Intermittent extract rate (l/s)
Kitchen (cooker hood extracting to the outside)(1) 30
Kitchen (no cooker hood or cooker hood does not extract to the outside)(2) 60
Utility room 30
Bathroom 15
Sanitary accommodation(3) 6

NOTES: 1. See Diagram 1.1.   2. See Diagram 1.2.   3. As an alternative for sanitary accommodation, the purge ventilation guidance may be used.

Continuous Mechanical Extract

Previously known as System 3

These systems operate by running continuously with an adjustable trickle rate and then boost their speed when a room is occupied, when humidity rises, or when it’s manually overridden.

There are two types of continuous mechanical extract:

    • dMEV (decentralised mechanical extract ventilation) – for individual rooms.
    • MEV (Mechanical Extract Ventilation) A central extract system used for the entire dwelling.
  • Both systems require correctly sized and fitted trickle vents to be installed.
  • Requirements for ventilation rates are measured in both continuous and boost rates as seen in the tables below.
Table 1.2 Minimum extract ventilation rates for continuous extract systems (referenced from Part F Volume 1)
Room High rate (l/s)
Kitchen 19
Utility Room 8
Bathroom 8
Sanitary Accommodation 6

Continuous Rate – The sum of all extract ventilation in the dwelling on its continuous rate should be at least the whole dwelling ventilation rate given in Table 1.3

NOTE: 1. If the continuous rate of ventilation provided in a room is equal to or higher than the minimum high rate specified in the table, no extra ventilation is needed.

Table 1.3 Minimum extract ventilation rates for continuous extract systems (referenced from Part F Volume 1)
Number of bedrooms Minimum ventilation rate by number of bedrooms (l/s)
1 19
2 25
3 31
4 37
5 43

NOTES: 1. If the dwelling only has one habitable room, a minimum ventilation rate of 13l/s should be used. 2. For each additional bedroom, add 6l/s to the values in Table 1.3.

Mechanical Extract with Heat Recovery (MVHR)

Previously known as System 4
MVHR systems utilise the whole house by extracting air from wet rooms, recovering the heat and then supplying fresh, filtered air into habitable rooms.
  • MVHR systems must meet the whole dwelling ventilation rates set out in Table 1.3 (above).
  • Have a minimum heat recovery efficiency of 73%.
  • The Extract air flow must match the supply air flow in order to create a balanced system.
  • Must be installed by a competent person.
  • The system should be designed to minimise the overall length of ducting, the number of bends and also ensure the appropriately sized duct for the air flow rate.

Positive Input Ventilation (PIV)

Positive Input Ventilation (PIV) units work by drawing fresh air from outside a building, filtering it, and then supplying it to the living spaces.

PIV units create a positive pressure in the building, which helps to prevent the ingress of polluted air from outside. This positive pressure also helps to reduce the risk of condensation and mold growth in the building.

PIV units typically include a fan that is located in the loft space of the building, which draws in the fresh air through a filter. The fan then delivers the filtered air to the living spaces via ducts that are connected to ceiling diffusers or wall vents.

In the context of the Approved Document F: ventilation, Positive Input Ventilation (PIV) units are a type of mechanical ventilation system that can be used to provide whole-house ventilation.

PIV units are not specifically mentioned in the Approved Document F, but they are a valid option for providing whole-house ventilation and can be used in conjunction with other ventilation systems such as extract-only or balanced mechanical ventilation, as well as natural ventilation. The document provides guidance on the minimum ventilation rates required for different spaces within a building, and PIV units can be designed to deliver the required rates.

However, it’s important to note that the design and installation of PIV units must be carried out by a qualified professional to ensure that they are effective and safe. The document provides guidance on how to design and install ventilation systems, including PIV units, to ensure that they meet the required standards.


As of 15th June 2022 testing and commissioning is compulsory with the air flow rates of all mechanical ventilation fans should be tested.

This includes:

  • Intermittent Extract Fans
  • Cooker Hoods
  • Continuous extract fans
  • MEV systems
  • MVHR Systems
  • PIV Systems

All extraction readings need to be submitted to the local building control authority and a certificate stating the recorded rates mustbe left with the property owner.

Ventilation rates should be tested using the correct UCAS accredited flow test instrument in accordance with Building Regs Part F.

Appendix C of Part F features an example form that can be downloaded and used to submit the information.

While we have tried to summarise Part F above, we advise you read the full document here to ensure correct compliance for your application:

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