Radon Gas Mitigation & Structural Waterproofing
Radon is a naturally occurring radioactive gas produced by the decay of uranium found in soil and rocks. It is invisible, tasteless, and odourless, making it impossible to detect without proper testing.
Outdoors, radon disperses harmlessly into the atmosphere, but indoors it can accumulate to dangerous levels, especially in basements and below-ground structures.
Prolonged exposure to high radon concentrations is a significant health risk, linked to lung cancer.
This is why radon protection is now a critical part of building design and waterproofing strategies.
A Gas-proof PAC system combines the benefit of waterproofing and gas mitigation - the best of both worlds, in one package.
The only way to accurately determine radon levels is to have a full radon test performed.
When considering Public Health England’s maps, even new structures with the lowest level of risk still require basic protection. For buildings without basements, this simply consists of a radon membrane. However, in areas of higher risk, full protection requires the addition of a passive sump or ventilated void. A full radon test should then be performed once the building is occupied, and if radon is present above the action level then the sump should be activated.
By comparison, basement structures are considered as being at a significantly greater risk of radon ingress due to the fact that they are built into the earth.
Furthermore, a passive sump may not work in such scenarios if it is submerged beneath the water table.
You can't rely solely on Radon Maps
Do not assume that if your project site does not appear on a radon map, you are safe.
Radon maps provide general guidance, but:
- Local variations in geology can cause unexpected radon concentrations
- Many local authorities now require radon testing after construction and occupation, even in areas marked as low risk
- Maps are updated regularly, and risk classifications can change
The only way to confirm radon levels is through site-specific testing.
What are the main types of ground gas in the UK?
Carbon Dioxide (CO2)
Carbon Dioxide; commonly referred to it’s periodic compound, CO2; is a toxic, asphyxiating gas. Its maximum permissible levels 0.5% by volume for long term exposure and 1.5% by volume for short term exposure.
Methane
Methane is a colourless, odourless, yet highly flammable gas. It forms an explosive mixture in the air at levels of 5-16% by volume.
Methane is a gas that naturally occurs from piles of peat in the agricultural industry but can also be a product landfilling. Typically, it’s the main component that is used to generate electricity and heat homes around the world.
VOC's
VOCs (volatile organic compounds) are compounds that naturally occur and easily become vapors or gases.
How does radon get into a building?
Radon moves from the soil into buildings because of pressure differences:
- Indoor air pressure is usually lower than the pressure in the soil beneath the structure
- This draws soil gases, including radon, through cracks in floors, gaps around service penetrations, and joints in walls
- Once inside, radon can accumulate to harmful levels if ventilation is inadequate
This is particularly relevant for basements and below-ground waterproofing systems, where airtight membranes can inadvertently trap radon gas.
When installing a polyethylene cavity drain membrane system (CDM):
- CDM systems act as vapour barriers, which is excellent for moisture control but can also restrict natural ventilation
- If not designed correctly, these systems can trap radon behind the membrane, creating concentrated pockets of gas
- To mitigate this, CDM systems must be integrated with radon sumps and ventilation systems, and sometimes positive pressure systems to safely vent radon outdoors
Testing and Compliance
Testing
Always carry out radon testing after construction and occupation.
Radon Detected
If elevated levels are detected, additional measures such as radon sumps and ventilation systems, or gas-rated membranes may be necessary
Why should I work with MacLennan?
WE’RE INDEPENDANT
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WE’RE PASSIONATE
MacLennan live and breathe waterproofing, have a look at one of our free CPD seminars and find out!
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MacLennan has the most comprehensive guarantees and insurances in the industry.
Gas Mitigation in Basements
What are the options?
The best solution in these cases is generally to implement a specialist sealed membrane system that combines both waterproofing and ground gas mitigation.
By combining the waterproofing recommendations of BS8102 with the gas considerations of BS8485 it is therefore possible to take a synergistic approach that mitigates against both gas and water ingress. Whilst the membranes act as both a water and gas barrier, the system employs positive pressure to manage gas into an active sump before venting it safely out of the building.
Such measures can be used to effectively protect against radon ingress. However, if carbon dioxide and methane are also dangers on a new build site then BS8485 must be employed, and the considerations become significantly more complex.
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