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