Radon and Gas Membranes

This technical post looks at the importance of radon gas exposure and the key considerations for the design and detailing of radon and gas membranes. Scroll to the end to view our range of radon gas membrane construction details!

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Chimneys and Fireplaces: Design Considerations

Radon is a naturally occurring odourless radioactive gas that can be found in our environment.

DL246B Custom built chimney example
Radon is a naturally occurring odourless radioactive gas that can be found in our environment.

It is produced by the radioactive decay of natural uranium in the earth’s crust. It eventually becomes the gas radon that rises and can seep and accumulate in buildings.

Certain areas and ground conditions are more susceptible to radon exposure. Exposure to high levels for long periods increases the risk of developing lung cancer.

Just about half of the average annual radiation dose to people in the UK comes from our exposure to radon. When this gas gets drawn into a building and gets trapped, it can build to high levels, risking health with prolonged exposure.
In areas of exposure, installing a high performance gas membrane or radon membrane to new foundations can help prevent the gas infiltrating into the building.

All gas membranes should meet BS 8485:2015 + A1:2019. Suppliers of damp proof membranes (DPM) and damp proof courses (DPC) can advise on detailing with this type of membrane.

When designing a new foundation, it is important to make sure that there are no holes or gaps where gas can leak through between the DPC and membrane.

One option to achieve this seamless gas DPM is to extend the DPC to the ground floor where the gas membrane can overlap the DPC, connected with suitable double sided tape, and the visible junction sealed with gas resistant tape. Insulation and the remaining floor build up can then be installed above this.

Masonry system chimney example

Different foundation and exposure types will call for more robust junctions or membranes. High exposure areas will need a higher grade membrane and more robust seals. Basements may require a self adhesive membrane on vertical elements exposed to the ground. A liquid applied membrane is a flexible membrane solution without joints and can be ideal for complex detailing and difficult to reach areas.

Other gases such as methane and carbon dioxide can also be in the ground and filter through a foundation into a building. Presence of these gases may be flagged through a desktop study of site history showing past agricultural, landfill or industrial use. In-situ gas monitoring undertaken by a specialist through boreholes, trial pits or a portable meter can help to assess the amount of carbon dioxide and methane levels present in the ground. A suitable foundation design and robust membrane installation can mitigate the risks of these gases entering a new building.

Radon within existing buildings


There are a number of ways of measuring radon levels within existing buildings. UK Radon provides one of these services which involves a pair of readers being placed in a number of rooms over a period of around 3 months. These are then tested to see how high the levels of radon are within the spaces.

If dangerous levels of radon are found in an existing building, there are a number of remedial options that can be undertaken based on the ground floor construction types and exposure level.

Built in appliance
Freestanding appliance in a recess
Radon sump

Radon sumps work best under existing solid floors and under existing suspended floors where the ground is covered with concrete or a membrane. In these cases, a sump is the most effective way to reduce indoor radon levels. This method involves drilling a large hole under the floor slab and installing a pipe with a fan, drawing radon away from the building. Passive sumps without a fan may also reduce radon levels.

Positive Ventilation

This can also be a suitable solution for existing buildings with solid floor types. It involves a small quiet fan that blows fresh air, usually from the roof space, into the building.

Passive under-floor ventilation

If the building has a suspended ground floor with a space underneath, making sure this is well ventilated can be enough to reduce radon concentration level filtering into the spaces above.

Active under-floor ventilation

Mechanical ventilations is used to either continuously blow air into or extract air out from the space below a suspended floor. This method can be used when passive under-floor ventilation is not sufficient in reducing the radon level.

Radon levels in cellars and basements

Radon accumulation in cellars and basements can be more tricky as accessing external air sources or underneath this space can be tricky. However, many of the techniques above can also be used, depending on the use of the space and construction types. For more details follow this link.

Radon Barrier Details


Radon can be a dangerous gas if allowed to build up within buildings. For new foundations and floors, simple DPC and membrane detailing can prevent leaks into rooms. For existing buildings, there are a number of retrofit options to suit every construction type, including difficult basements.

We have put together a selection of useful details to help when detailing radon barriers or gas membranes. Check out the following details:

Download the Guide

19 Radon and Gas Membranes


Written by Aida Rodriguez-Vega, architect and researcher. At the Detail Library, Aida keeps busy by carrying out technical research and drawing new details for the ever-growing library.

Links and Image Credits

Source URL: https://www.ukhsa-protectionservices.org.uk/radiationandyou/

Image URL: https://www.ukhsa-protectionservices.org.uk/cms/assets/gfx/content/misc_image_3615csd8c9d05ec6.jpg


Source URL: https://www.ukradon.org/radonmaps/

Image URL: Screenshot from above


Source URL: https://www.ukradon.org/radonmaps/

Image URL: Screenshot from above