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What Causes Radon in Basements?

Basements are considered to be one of the highest risks from radon in a home. Even if your house is not in a radon affected area then you are still at risk from radon gas.

This article will look at what the causes of high levels of radon gas in basements are and what can be done to reduce those levels.

Causes of Radon in Basements

The main reason for high levels of radon in basements is because the basement is below ground level and invariably some areas will come into contact with soil which allows the gas to permeate into the basement.

Another contributing factor for radon in a basement is that the pressure below ground level is usually low, meaning that the air will be pulled in from the rock and soils into the property. The concrete foundation of the basement will also allow radon to enter the building.

How To Lower Radon Levels In Your Basement?

Radon gas can affect any property no matter where your home is located in the UK. It is very unlikely that you can drop your radon levels to 0 Becquerels, however, there are ways you can reduce radon levels in your basement with a few simple changes:

  • Opening windows and doors whenever you can will allow the radon gas to exit the property and allow for the fresh air to enter the house
  • Reducing the rapid increases in high and low temperature inside your house lowers the pressure increase that allows the process of radon to be “sucked” into the property.
  • Sealing the sump well cover can lower levels of radon in your home as there will be less exposed soil in direct access with your basement

These tips will only reduce the radon levels slightly so if you have substantially higher radon levels then having a radon mitigation system installed is the best way forward to reduce the levels of radon.

Radon Remediation For Your Basement

There are two methods of radon remediation that should be carried out by a radon specialist.

One of the methods is to have a radon sump installed underneath the building. This is a small void beneath the building that collects the radon beneath the ground and a radon fan vents it away safely at a higher level. There are often cases where using a radon sump is not applicable for example if the basement area is waterlogged.


The other method that could be used is to have a positive pressure system installed. This involves having a special fan to disperse air through the building. The ‘extra’ air raises the internal pressure thus reducing the gas being drawn from the soil.

Need To Waterproof Your Basement? How Can Radon Affect This Process

Specialist waterproofing contractors are often employed to design and install the essential waterproofing elements of a basement conversion, however, methods of water management may conflict with gas management.

It is vital that radon should be taken into account in the design and installation of a waterproofing system and the following extracts from BR 211 provide an example of how this may be achieved.

6.12 Basements or occupied spaces below ground

It is important to ensure that basements and other occupied spaces below ground level are suitably protected against radon. These areas are more at risk because walls are in contact with the ground as well as the floor.

For a house with a basement under the entire house, the area in contact with the ground could be several times that of a similar house without a basement. This, coupled with reduced natural ventilation below ground level, increases the risk of elevated radon levels. All basements are at increased risk of elevated levels of radon, regardless of geographic location.

Where a new basement is to be created, or an existing cellar converted, waterproofing will be required. A well-constructed waterproofing should be designed to protect against radon also.

Guidance and recommendations on basement waterproofing are contained in BS 8102:2009, which also advises that radon must be taken into account when designing and implementing waterproofing schemes.

Below-Ground Waterproofing and Radon Management

Below-ground waterproofing and radon management are specialist activities that can conflict with one another. It is therefore recommended that dual protection systems are designed and installed by specialists who are suitably qualified in both waterproofing and radon management.

Internally located cavity drain membrane systems are often used to provide belowground waterproofing. Some cavity drain membrane systems are certificated as providing an effective barrier to radon gas.

However, using these to line the internal surfaces of a basement could cause the gas to be simply displaced up the cavity into the ground floor accommodation.

It is therefore important to ensure that the basement wall membrane fully closes the cavity at its head where it meets the radon barrier within the ground floor or external cavity wall above ground. The cavity behind the membrane could be used later as part of a subfloor depressurisation system.

If the ground around a basement is likely to be waterlogged, there is little benefit in installing a radon sump as subfloor depressurisation is unlikely to work continuously.

As with all radon-protective measures installed during construction, the first aim should be to provide a passive solution. This should also be the aim with basement protection.

6.14.3 Non-domestic buildings

It is not a requirement of national building regulations to test new non-domestic buildings. Employers must ensure the health and safety of employees and others who have access to their work environment.

An assessment of health and safety risks under national regulations should include radon where the workplace is in a radon affected area, or in any location where there is a basement that is regularly occupied.

BRE recommends testing on completion or occupation of all new buildings, extensions and conversions with protection fitted. Buildings that have had significant alterations made to them should also be tested.

Need Further Advice On Reducing Radon Levels In Basements?

We hope this article has helped provide you with an explanation of how radon occurs in a basement and ways of reducing those levels. It is always best to contact an expert in radon and here at PropertECO we have several experts how are on hand to help with any of your radon gas issues.

To get in touch with our team simply click the link down below for more information:

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