Having already addressed the importance of indoor air quality and the role of ventilation in improving IAQ, this article will focus on the closely related subject of air flow. We will first consider the importance of air flow in maintaining indoor air quality, before examining the requirements and regulations regarding air flow in UK-based residential properties. Finally, we will look at ways to achieve optimal air flow when designing and constructing a new build property.

What do we mean when we talk about optimal air flow?

Air flow refers to the movement of air in and out of a building, and from one room to another, typically through a building's ventilation system. This can affect indoor air quality, thermal comfort, and energy efficiency. Achieving optimal air flow involves striking a balance between energy-efficient design (avoiding unnecessary heat loss) and effective ventilation and air exchange.

Going with the flow: the importance of air flow in domestic dwellings

In response to the government’s Future Homes and Building Standard having raised the bar in terms of the energy efficiency of new buildings from 2025 onwards, new constructions are becoming increasingly airtight. Without adequate ventilation and a suitable flow or air passing in and out of the building, this can result in the build-up of pollutants such as volatile organic compounds (VOCs), carbon dioxide, and particulate matter (dust, pollen, other allergens).

This naturally has a major adverse effect on the health of building inhabitants. Symptoms and conditions resulting from poor indoor air quality and stale air can include respiratory issues, allergies, headaches, and fatigue. It therefore goes without saying that, when it comes to future-proofing building design, ensuring adequate ventilation and optimal air flow are of vital significance. In addition to alleviating potential health concerns, good air flow can improve temperature and humidity control within a building, considerably improving occupant comfort.

While, as a building developer, you may not be directly affected by the health and comfort-related impact of poor ventilation, the subject is of primary concern when it comes to producing a saleable product that is compliant with current and future regulations and requirements.

Overview of regulations and requirements concerning air flow in residential properties

As already discussed extensively in previous articles, the key piece of legislation governing ventilation and air flow in domestic dwellings is volume one of Approved Document F. An amendment first announced in 2021, and which came into effect in June 2022, tightened the requirements regarding design air flow rates and their documentation. Measured in litres per second and metres cubed per hour, the Approved Document specifies air flow rates for various types of ventilation system, and for various rooms within a dwelling. Whole property ventilation rates are also specified based on the number of bedrooms within a property. Finally, the use of trickle vents is also regulated, with stipulations regarding the number of vents installed, as well as the size of vents.

When using mechanical ventilation solutions, such as an MVHR system, intermittent extractor fans, cooker hoods, or continuous extract fans, air flow rates and the direction of flow are required to be measured at each room terminal. Appropriate equipment must be used to this end. Air flow measurement devices are required to have:

A proprietary hood attachment
An accuracy of ±5%
Been calibrated within the past 12 months.

Furthermore, air flow measurements are required to be recorded on the commissioning sheet, for submission to building control.

How to achieve optimal air flow in a residential dwelling

So how can you, as a house builder, ensure optimal air flow within your residential projects? If you are already building highly airtight and energy-efficient homes, then under the new legislation a mechanical ventilation system is a requirement rather than an option. There are a number of options available. The table below outlines the characteristics of the various systems.

Type of system	Type of installation	Advantages	Disadvantages
Extractor fans	Targeted – primarily in bathrooms & kitchens	- Inexpensive - No major renovation/construction work required	- Installed in specific rooms, meaning the benefits are not as apparent throughout the entire building. - Heat loss
PIV (Positive Input Ventilation)	Whole house	- Can be retrofitted without significant renovation - Improves air quality throughout the house - “Fit & forget” – limited maintenance/management	- Some additional enhancement measures may be needed, dependent on building shape and layout.
MEV (Mechanical Extract Ventilation)	Whole house/decentralised	- Improves air quality throughout the house - Removes stale, moist air from all wet rooms in the property. - Decentralised options available.	- Centralised option only suitable in case of major renovations or in new builds - Does not offset heating costs in the same way as an MVHR system
MVHR (Mechanical Ventilation with Heat Recovery)	Whole house	- Improves air quality throughout the house - Can be configured and adjusted to suit conditions in and around the property, number of occupants etc. - Provides a supply of filtered, warmed air back into the property, thus offsetting heating costs - Creation of an air-tight home reduces the ingress of pollution and external noise	- Only suitable in case of major renovations or in new builds - Requires significant installation planning and expertise - Higher installation cost

These mechanical solutions can also be complemented with passive solutions such as trickle vents in windows, or through-wall vents. Our team of experts at EnviroVent is available should you require advice on which solution is best suited to your build, or recommendations regarding air flow measurement, reporting and compliance.

If you are interested in further reading on related topics, why not check out our articles on heat loss through ventilation.

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Air Flow Requirements for Residential Indoor Air Quality