Building Regulations Approved Document F (Ventilation) Explained

What is Approved Document Part F of Building Regulations?

In June 2022, there was an update to Building Regulations Document F to address improving ventilation in homes.

F1(1): “There shall be adequate means of ventilation provided for people in the building.”

With a drive towards more energy efficiency, homes are now designed to be insulated and as airtight as possible to reduce draughts and avoid heat loss. The result of this is an increase in the retention of moisture in the home with a lack of air circulation and a need to maintain healthy air quality.

To balance any lack of natural ventilation, mechanical ventilation and/or background ventilation are requirements under Building Regulations.

Regulations also state that any renovations or home improvements made should be done without making the ventilation worse than it was before.

When replacing windows, this means that any existing trickle vents must be replaced, and new windows must install trickle vents, or demonstrate that sufficient background ventilation is provided by other means.

Read more: Why ventilation is so important in your home...

What is the purpose of Part F?

The main focus of Part F is to improve air quality and avoid the growth of mould, which is highly toxic and damaging to health.

1.1: “The aim of requirement F1(1) is to protect the health of occupants of the building by providing adequate ventilation. Without adequate ventilation, mould and internal air pollution might become hazardous to health.”

What Are the Different Types of Ventilation Covered in Part F?

There are three main types of ventilation that contribute to removing pollutants and maintaining air quality inside a home. A combination of all of these types of ventilation can be used via means of natural and mechanical ventilation.

• Extract
• Whole Dwelling
• Purge

Extract

Extract ventilation is required in rooms where excessive moisture is produced.

• Kitchens
• Utility rooms
• Bathrooms
• Toilets

Ventilation is required to remove as much moisture and odour as possible to minimise spreading to other parts of the house.

Extraction can be intermittent or continuous.

Note that toilets can use just purge only ventilation if there is an opening window of the required size.

Whole Dwelling

Apart from on-demand purge and extraction, there should be a minimum flow of ventilation for rooms, dependent on floor area and how many stories in the building.

Whole dwelling ventilation should distribute fresh air throughout the house without opening a window to disperse moisture and pollutants such as VOCs and carbon dioxide.

The distribution of air can be provided by a continuous supply fan or background ventilators depending on how airtight the property is:

• Natural background ventilators for less airtight houses, including trickle vents for windows, air bricks and passive stack ventilation.
• Continuous supply for airtight houses includes Mechanical Ventilation with Heat Recovery (MVHR).

As a note, internal doors are required to have space underneath for airflow through the home.

Note that the whole dwelling ventilation rates have increased considerably since the previous version.

Requirements for Trickle Vents in Windows

To explain what size trickle vents should be for a window or a room, you first have to understand that trickle vents are not measured in physical size. They are measured in the industry standard of equivalent area.

Equivalent area means the amount of air that can pass through the vent.

“Equivalent area is a measure of the aerodynamic performance of a ventilator. It is the area of a sharp edged circular orifice through which air would pass at the same volume flow rate, under an identical applied pressure difference, as through the opening under consideration.” Building Regulations Part F.

The number of ventilators installed in living spaces and kitchens should be no less than five (four in one-bedroom houses). For houses with continuous mechanical extract ventilation, the number of trickle vents must be the number of bedrooms plus two (E.g. Three for a one-bedroom house and five for a four-bedroom).

The table above also applies to ‘habitable rooms’ which is defined as ‘a room used for dwelling purposes'. Hallways and landings do not fall into this category.

There are exceptions to the table above for houses that only have one exposed elevation (e.g. back-to-back terraced houses). For houses with 70% of the windows on one side of the house (e.g. end back-to-back terraced houses), for kitchens with no external window or facade (e.g. in a basement), or for open plan kitchens/living rooms. Please refer to the full Approved Document Part F.

Trickle vents should be positioned 1.7m above the floor to help prevent draughts.

Less Airtight Houses

Houses that are considered ‘less airtight’ means they have:

• A design air permeability higher than 5m3/(h·m2) at 50Pa.
• An as-built air permeability higher than 3m3 /(h·m2) at 50Pa.

In houses that are defined above, they have the option of natural background ventilation.

Purge

Purge ventilation is the ability to open a window or door that can allow enough fresh air directly from the outside. The minimum rate for purge ventilation is four air changes per hour in an internal space.

Purge ventilation is required to quickly remove odours and fumes from cooking, cleaning or DIY jobs. Purge is also used to remove excess heat from a room to quickly cool the room down.

All habitable rooms must provide the ability to purge and where an outside window is not installed, a mechanical extract ventilation system can be used. Windows must have a minimum opening size.

Other Considerations

The ventilation must also achieve the following where reasonably practicable:

• Low noise
• Easy maintenance access
• Protection from cold draught

It should be noted that Part F also interacts with other Building Regulations and they may supersede in some instances:

• Part L Energy Efficiency and the control of infiltration must be factored in when choosing a ventilation system
• Part O Excess Heat should supersede Part F where the standards for purge ventilation in Part O are higher.

Building regulations are quite complex and not the easiest set of regulations to get your head around!

When buying new windows, make sure that you take advice from a registered supplier who can help you comply with regulations.

At Everest, we can advise you on what you need to ensure that all regulations are followed. We will provide you with a certificate that shows the work was completed by a registered supplier and that the windows meet Building Regulations.

The information above is provided as a guide only and correct at the time of publication: March 2023.

All data above is taken from here.

Building Regulations are subject to change. Always seek approval from your local planning authority before starting any building work.