Radon & Gas Barriers

Radon and gas barriers are low permeability membranes installed within the floor construction to stop harmful ground gases, including radon, methane and carbon dioxide, from entering a building. They are laid as a continuous, sealed layer that closes off the pathway between radon affected or contaminated ground and the spaces above. The range covers polythene radon barrier membranes, multi-layer gas barriers for sites with wider ground gas risks, liquid applied and self adhesive options, and the jointing accessories needed to complete a sealed installation. Because the same low permeability material also resists ground moisture, many of these membranes act as a damp proof membrane as well, giving dual protection against ground gas and damp in a single layer across concrete slab, block and beam and suspended timber floor construction.

What is a radon barrier?

A radon barrier, also referred to as a radon gas barrier, is a low permeability sheet membrane laid beneath the floor to prevent radon from passing out of the ground and into the building above. Radon is a naturally occurring radioactive gas formed by the decay of uranium in rocks and soil. It is colourless, odourless and tasteless, and it can accumulate inside a building where there is a gas pathway from the ground and ventilation is limited. A correctly specified and installed radon barrier forms a sealed envelope across the floor that blocks that pathway. As the polythene used also resists moisture, a radon barrier will usually function as a damp proof membrane too, which is why these products are often described as a radon barrier dpm.

When radon protection is required

Radon is present to some degree in nearly all buildings, and it is recognised as the largest source of natural background radiation in the UK and the second largest cause of lung cancer after smoking. The level of risk depends largely on local geology, so the requirement for protection varies considerably from one site to the next.

Radon affected areas and the UK radon map

Areas with higher concentrations of uranium and radium bearing rock, such as parts of the South West of England, Wales, Derbyshire, Northamptonshire and parts of Yorkshire, carry a higher radon risk. Before specifying protection, developers and contractors should check the UK radon map published by the UK Health Security Agency to confirm whether a site falls within a radon affected area and what level of protection applies.

Radon protection and building regulations

Where a property is being built or significantly extended in a radon affected area, building regulations require radon protective measures to be incorporated. The level of protection, either basic or full, is determined by the local radon risk and set out in BR 211, Radon: Guidance on Protective Measures for New Buildings. Basic protection generally calls for a radon barrier across the floor, while full protection adds a passive sub floor depressurisation provision, such as a radon sump, that can be activated later if testing shows it is needed.

Radon barrier membranes

Radon barrier membranes are the standard solution for new build and extension projects in radon affected areas. They are manufactured from low permeability polythene and laid either above or below the floor slab to form a continuous barrier. A common question is whether an ordinary damp proof membrane can be used as a radon barrier. While most radon barriers also perform as a dpm, the reverse does not hold: a standard polythene dpm is not tested or certified for radon resistance, so it should not be used in place of a dedicated radon barrier where protection is required. Radon barrier membranes are available in a range of thicknesses and performance grades, including heavier gauge and reinforced options for sites needing a higher level of protection.

Radon barriers for different floor types

A radon barrier can be used across all the main floor construction types. Under a concrete floor slab the barrier is laid on the substrate or blinding and lapped into the wall damp proof course at the perimeter. On block and beam floors it is laid over the beam profile, and on a suspended timber floor it is dressed across the structure. In each case all joints are sealed and the perimeter is turned up to maintain a continuous barrier. Choosing a radon barrier for under slab, block and beam or suspended timber floor construction comes down to the installation detail rather than a different class of product.

Gas barriers for methane and contaminated ground

A gas barrier is a higher performance membrane used where a site investigation has identified ground gases beyond radon alone, typically methane and carbon dioxide from landfill or former industrial land, and in some cases volatile organic compounds and hydrocarbons from contaminated ground. These gas barrier membranes use a multi-layer construction to deliver very low permeability across a range of gas types and concentrations. The grade of gas barrier required is determined by the ground gas regime established on site, and the system should be designed in line with BS 8485, with the installed barrier verified in line with CIRIA C735, and meet the relevant NHBC requirements. For mixed or elevated gas risk, a low permeability multi-layer gas barrier is specified in place of a basic polythene radon barrier.

Liquid applied gas barriers

Where sheet installation is impractical, or a fully bonded solution is needed, a liquid applied gas barrier provides an alternative. It is brush or roller applied directly onto a prepared concrete substrate to form a seamless gas resistant layer, and it suits retrofit work and complex detailing around penetrations where a sheet membrane would be difficult to seal. Once cured, a liquid radon barrier offers the same continuous protection as a sheet system.

Installing radon and gas barriers

The performance of any radon barrier or gas barrier depends as much on the installation as on the membrane itself. A barrier with unsealed laps, missing detailing at pipe penetrations or a poorly closed perimeter will allow gas to bypass it, whatever the grade of membrane specified. This is why correct radon barrier installation detail matters as much as product selection, and why the membrane must form a fully sealed envelope across the floor.

Sealing, jointing and detailing

When installing a radon barrier, sheets should be lapped and sealed in line with the manufacturer's instructions, typically by a minimum of 300mm, using the appropriate radon barrier tape or gas membrane jointing tape. Preformed top hats are fitted at all service penetrations, and the membrane is dressed up and lapped with the wall damp proof course at the perimeter to keep the barrier continuous. DIY kits that bring the membrane, jointing tape and top hats together in one pack are a convenient option for smaller projects.

Passive radon sumps

On sites requiring full protection, a passive radon sump and pipework is installed within or below the slab. It sits dormant once the barrier is in place but allows the system to be upgraded to an active one by fitting an extract fan if post construction testing shows radon levels remain elevated. It is this combination of a sealed barrier and a contingency sump that makes a full radon protection system both effective and able to be upgraded later.

Choosing the right radon or gas barrier

The right product follows from the ground conditions established for the site. For most new build and extension projects in radon affected areas, a polythene radon barrier provides the protection required under BR 211. For sites with elevated methane, carbon dioxide or mixed ground gas risk from contaminated land, a multi-layer gas barrier specified to BS 8485 is needed. Where sheet installation is impractical, a liquid applied membrane is the alternative.

It is worth being clear on what these products do and do not do. Radon and gas barriers are designed to resist ground gas and ground moisture, and many also serve as a damp proof membrane, but they are not a waterproofing system for resisting liquid water under hydrostatic pressure. Where a structure is below the water table or otherwise subject to water pressure, a dedicated tanking system is required, which you can find in our Tanking range.

Why choose Construction Supplies UK for radon and gas barriers

Complete ground gas protection in one place: From polythene radon barriers and multi-layer gas barriers to liquid applied membranes, jointing accessories and passive sump components, we stock what is needed to specify and complete a sealed installation for basic or full protection.

Trusted industry brands: Shop leading manufacturers including Novia, Visqueen, ITP and Principal Building Products.

Competitive trade prices: Radon and gas barriers at competitive trade prices with no minimum order value.

Fast UK-wide delivery: Reliable nationwide delivery with free shipping on orders over £300.

Expert support when you need it: Our team can help you confirm the right specification for your project. Contact us at sales@constructionsuppliesuk.co.uk or call 03300 55 32 02.