Everything You Need to Know About Wall Air Brick Vents

This page aims to answer common questions about air bricks, what they are, the different types available, where you’ll usually find them and what you can expect to happen if they’re placed in the wrong location or become blocked.

Not every home will have ventilation air bricks, but those that do will need them for a good reason, so think twice before you block or remove them.

What Are Air Bricks?

Air bricks are made of either cement, plastic or metal and are similar in size and shape to a regular house brick; they also have holes in them for ventilation.

They are primarily used to create an airflow underneath a suspended ground-level timber floor that has a void underneath it.

Without adequate ventilation, suspended timber floors will experience a buildup of condensation in the colder months; this can lead to damp problems, rot, insect infestation and the structural collapse of the floor.

Here is a photo of a typical air brick; plastic and metal variants are also popular:

Plastic air brick

Standard Air Brick

Why Do Some Homeowners Block The Vents?

The air bricks create an airflow underneath the floor; this can lead to drafts that pass through the floorboards into the home.

Due to rising energy prices and a desire by many to reduce heating bills, some people choose to block the vents.

This approach isn’t recommended and can lead to all sorts of problems down the line.

We suggest you leave the vents in place and seal any gaps in the floor joists, so the draft remains under the floor.

Are There Any Situations When It’s Okay to Block Wall Air Brick Vents?


If the suspended timber floor has been removed and replaced with a solid concrete floor, the void will also be filled in with concrete, so there’s nothing to ventilate.

In this situation, the air bricks can either be blocked or replaced with regular bricks, but first check with a builder or surveyor before you do this.

How Many Air Bricks Are Needed?

How many vents you’ll need will depend on the size of the void underneath the floor.

As a general rule of thumb, you should place one air brick every one and a half metres to two metres along the wall.

For large buildings, install the air bricks placed at one and a half metres and consider using larger air bricks.

See this photo of a more significant air brick:

Wall airbrick to reduce humidity

Large airbrick

How Far Above the Ground Should They be Placed?

The NHBC (National House Building Council) states that air bricks should ideally be placed at least 75mm above ground level.

If the ground is solid, perhaps tarmac or concrete, they can be placed lower, provided the ground slopes away from the wall.

If the ground is flat or consists of soil, grass or any other soft material, the vents should be placed at least 75mm from ground level. This is to prevent a build-up of dirt, leaves, grasses etc. that may block the vents.

See the two diagrams below:

Air brick diagram 1

Air brick diagram 2

Options For High Ground Levels

There are occasions when the outside ground level is too high; you have three options:

  1. Lower the external ground level or;
  2. Cut out a continuous channel 600mm wide along the length of the wall and to the required depth, also make a provision for drainage or;
  3. Install periscope air bricks.

The photo below shows a periscope vent (aka telescopic air brick) and the second picture explains how it works:

Periscope vent

Periscope vent installed to wall

What Happens if the Wall Vents Become Blocked?

There are several reasons why these wall vents may become blocked:

  • The homeowner didn’t know how important they are and filled them with a sealant or cement.
  • A previous owner or tradesperson rendered the wall and the vents blocked.
  • Soil, leaves, grass and plants etc. have been left to overgrow.
  • The outside ground level has been raised, perhaps by placing concrete, tarmac or a patio on top of the existing hard standing (it’s cheaper to overlay than to dig up and replace a patio/driveway so this often happens).
Blocked wall vent

Blocked wall vent Image source

If the vents become blocked or even partially blocked, moisture and gasses from the ground will not be able to escape. During the winter some condensation will form, usually near the external wall, this could even be confused with rising damp, which is another story altogether.

Condensation in the underfloor void may lead to:

  • A damp musty odour in the home.
  • Mould and damp patches on the floor and the lower part of the external wall.
  • Ruined carpets and floor coverings.
  • Insects love wet, damp timber so the floor may become infested.
  • Damaged plasterboard, plaster and walls.
  • Rot, leading to the failure of the suspended floor.

Below you’ll find a great video from Square Conduct Services Ltd, here you’ll see what happens when vents are blocked and breached:

Can Air Bricks Be Used Through Cavity Walls?


You can insert wall vent bricks into either a solid wall or through two walls with a cavity between them.

Some brick vents require a tray, while others are clipped together until you reach the required length.

The photo below shows a typical installation through a cavity wall:

Ventilation though a cavity wall

Remember: Not Every Home Will Have or Require These Wall Vents

You’ll typically see these vents on homes with floating (suspended) timber floors. Solid concrete or lime-based floors do not require wall vents, these shouldn’t be confused with floating concrete floors, which do require ventilation as they have a void underneath them.

If your home has buried or blocked vents, first check that the original floating timber or concrete floor is still in place and hasn’t been replaced with a solid floor that doesn’t require ventilation.

Can Wall Air Bricks be Used to Reduce Condensation in Other Areas of the Home?

Air brick wall vents are designed to create an airflow underneath a suspended floor. Air is pulled in through one side of the home and exits the opposite side.

If you place them further up the wall, you may find the draft inside the home to be excessive, and there are better options to consider.

Instead of using air bricks for in-home condensation, consider installing window trickle vents, extractor fans (for bathrooms and kitchens) or a positive input vent system.

Window trickle vents

Window trickle vents

Air vent system to reduce condensation

Positive Input vent (PIV) system. Read reviews on Amazon

If you are experiencing condensation on windows, walls, ceilings or other areas away from the floor, explore our in-depth guide to curing condensation here.

Further Reading

Brick vents shouldn’t be confused with weep vents which are small strip vents that allow moisture trapped in a cavity to escape (see these images if you’re unsure).

This page is part of our series of guides to home ventilation.

Check out these related pages:

How to get rid of and prevent mould on windows.

What is the ideal humidity level for the home?

How much does home insulation cost and what options do you have?

A guide to getting rid of condensation in the home.

Loft condensation causes and cures.

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This was written by and was last updated in April 2022.

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Author - Danny Woodley
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