Air Bricks And Underfloor Ventilation Building Regulations by Fastbuild Supplies

Ventilation is one of the most important parts of any building work. While it may not be the most complex part of a project, ensuring correct underfloor ventilation is essential for meeting UK building regulations and preventing long-term issues such as damp, mould, and timber rot.

This article looks at regulations around venting for subfloors, including when to use airbricks and cavity wall vents. Remember that the following information only provides general guidance, so before starting on your project, make sure you’ve received relevant instruction from a qualified architect or structural engineer.

What are the Requirements for Underfloor Ventilation in the UK?

Similar to requirements in other areas of construction, such as cavity closer building regulations, there are various documents related to building standards in which underfloor venting plays a role.

Some of the most notable regulations and standards relating to underfloor venting in the UK include:

All these documents outline that buildings which have a subfloor – a suspended floor creating a void before the ground foundation – need to have some form of adequate ventilation. Ventilation is required because, otherwise, the air trapped in the void will eventually cause problems with moisture build-up, including mould and rot.

A common solution for underfloor ventilation is airbricks and cavity wall vents, which allow a managed airflow to pass through a building’s subfloor. The main considerations when installing these are:

  1. How much ventilation is required? (This comes down to the size of the external walls or floor.)
  2. Ensuring the void is of an adequate size, and that ventilation points are placed around the building to encourage airflow.
  3. Ensuring external ventilation is placed high enough to avoid obstructions such as overgrowth or flooding.

You should always speak to a structural engineer or architect to understand in detail how much ventilation is required on your project.

Airbricks & Cavity Wall Vents Explained

An air brick is a type of brick, commonly made from clay or plastic, designed with holes in it that allow air to flow through. They are installed in much the same way as regular bricks and will usually be found around the ground level of a building.

Cavity vents, meanwhile, are plastic or metal fittings designed to provide air flow between or through a building’s cavity walls. They come in many different shapes and sizes for different requirements, but when it comes to underfloor ventilation, telescopic underfloor vents are a common feature.

A telescopic underfloor vent allows air to flow from an external cavity down through a vent and into the underfloor void, which ensures airbricks are high enough to avoid obstructions while still providing adequate airflow to the subfloor.

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How Many Airbricks Do You Need for Adequate Ventilation?

To know how many airbricks you need, you need to calculate based on either the length of the external wall or the floor size. NHBC 5.2.10 states that:

“Void ventilation should be provided to whichever gives the greater opening area: 1500mm2 per metre run of external wall, 500mm2 per m2 of floor area.”

NHBC also says that “In the case of timber floors, ventilators should be spaced at no more than 2m centres and within 450mm of the end of any wall.”

You need to work on whichever calculation for your project gives the biggest opening and air flow, and then ensure you have enough openings (or airbricks) to satisfy this requirement.

These openings then need to be placed around the building to ensure air can flow through the void. Regulations generally recommend placing the airbricks directly opposite each other on opposing walls where possible.

At What Height Should Airbricks Be Installed?

NHBC also provides guidance on the placement of airbricks in relation to ground levels. Correct airbrick height is essential to ensure effective airflow and prevent potential obstructions that could restrict that flow, such as debris or vegetation.

Ideally, airbricks should be placed 75mm above ground level, or be placed beside ground which is sloped and self-draining. If airbricks are installed lower than this, they risk becoming blocked by overgrowth, such as weeds. Areas prone to flooding may need to consider an even higher airbrick placement to ensure they won’t suffer water ingress in the worst circumstances.

As many underfloor voids do not offer the right space for airbricks to be installed directly, most construction uses cavity wall vents to bring airflow down from a higher-placed airbrick.

We stock a wide range of airbricks and cavity wall vents, meaning no matter what kind of venting solution you require, you’ll find everything you need right here at Fastbuild. With a wide range available at great trade prices, why not explore our selection today?