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A Guide to Radon Gas Barrier Installation

Radon is a colourless and odourless gas given off by ground that contains uranium and radium. In parts of the UK, that typically means areas of the country where there is granite under the ground. The Health Protection Agency provides detailed maps of affected areas, which include Aberdeenshire and Inverness, North Wales, Devon and Cornwall.

Despite its apparently innocuous nature, radon gas is harmful to health. Public Health England estimates the gas is responsible for around 1,100 cases of lung cancer a year in the UK. As a result, regulations require that homes and buildings constructed in areas where it is present are built in a way that minimises the possibility of the gas getting into the interior. Depending on the design of the building, it may also be necessary to design some form of extract or positive air system, to ensure that any radon gas beneath the ground floor structure is vented to the outside.

What is a radon gas barrier?

Typically, a radon gas barrier is a type of tough plastic sheeting that must be installed within a ground floor structure, such as a concrete slab. The sheeting may also double up as a moisture barrier, or damp proof membrane, at the same time. It's vital that the gas barrier is installed with great care to prevent the possibility of leaks into the premises. It's also important that the design and layout of the barrier does not create other problems, such as possible damp patches.

How is a gas barrier installed?

A gas barrier should be installed within the design of the floor structure, often on top of structural concrete and beneath a floor screed. It is laid across the floor in sheets, with adjacent sheets not simply overlapping, but actually stuck together. Depending on the type of membrane material used, it may be advisable to use both a double sided tape to stick the overlap together, and then confirm the airtight joint with a second sealing tape along the upper exposed edge of the joint. Installers should refer to instructions, or to advice from local building control officers and engineering consultants.

Image of Gas Barrier

Importance of making sure everything is 'airtight'

At any point where something goes through the barrier sheet, such as a toilet downpipe set in the floor, then careful attention is needed to prevent the danger of radon leaking into the building. Many suppliers provide "top hat" fittings that will fit tightly around a pipe, and again these need to be securely taped into place so that the fit between the top hat component and the surrounding membrane is airtight.

Image of Gas Barrier

A similarly careful approach is needed around the perimeter, to ensure that there is no possible path for the radon gas to get into the interior. Careful detailing of the joint between floor and wall is needed, and particularly at the corners of a structure. It is also vital to consider where water will move in a structure, as the use of airtight membranes can, inadvertently, lead to the creation of a water trap that could lead to dampness. Again, a qualified engineer can provide guidance, while organisations such as the National House Building Council provide recommended details for such junctions, designed to avoid potential damp and water ingress problems.

Gas barrier protection

Building sites are busy places, so any newly installed radon gas barrier needs to be protected against damage while it remains exposed. A simple act, such as someone dropping a brick on the membrane, could create a small hole and therefore compromise its airtight performance. For as long as the sheet is left uncovered, with the potential for people to walk on it, the material should be protected by temporary materials such as sheeting. Ideally, the gas barrier sheeting should be installed immediately prior to further finishing work, such as the installation of the floor screed, to minimise the potential for damage.


Depending on the design of a building floor, it may be necessary to install some type of venting that stops radon gas building up beneath a floor. Several methods of venting can be used, depending on the specific circumstances of a building and the design of the floor. While some buildings can rely on natural ventilation, others require an electric pump to draw out underfloor air. Whichever of these options is selected, it will be necessary to install what is referred to as a radon sump, in the substructure of the floor. Clearly this needs to be designed in at an early stage of construction, with the routes of venting pipes carefully planned to ensure the radon gas is safely removed.

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