Gas Resistant Membranes

A gas membrane is a low-permeability barrier installed within a building's structure to prevent harmful ground gases from migrating into occupied spaces. In construction, the term covers a range of products installed beneath or around below-ground structures: sheet membranes laid under concrete floor slabs, self-adhesive membranes bonded to vertical concrete walls and pile caps, pre-applied membranes positioned ahead of the concrete pour, and liquid applied coatings used to seal complex details, corners and service penetrations. All share the same core function: creating a continuous, gas-tight layer between the ground and the building interior.

Gas resistant membranes go a step further than standard radon barriers. Where a standard radon barrier is engineered primarily for ground floor slab installation on greenfield or low-risk sites, a gas resistant membrane is a structural product capable of simultaneously resisting hydrostatic water pressure and providing a certified barrier against ground gas ingress. This makes them the correct specification where a building is below ground level and exposed to both water and gas risk.

When is a gas resistant membrane required?

Ground gas is a concern wherever the soil beneath a site contains materials capable of producing, or has been exposed to, hazardous gas concentrations. Methane and carbon dioxide are generated by the decomposition of organic material and are a particular risk on brownfield land, former landfill sites and areas of made ground. Radon is a naturally occurring radioactive gas present at varying levels across the UK, arising from the decay of uranium in rocks and soils. Volatile organic compounds and hydrocarbons are associated with former industrial sites and petrol stations. Any combination of these gases may be present on a single site, which is why the gas protection system must be designed to the specific conditions identified in the ground investigation.

Contaminated land and brownfield sites

The redevelopment of brownfield land is a significant and growing part of the UK's construction programme. Former industrial, landfill and made-ground sites frequently carry elevated concentrations of methane, carbon dioxide and VOCs, and the level of gas protection required is directly proportional to the risk characterisation for that site. Where ground investigation data indicates a gas hazard, a gas protection system designed in accordance with current guidance is required before any below-ground structure or occupied ground floor slab can be constructed.

Building regulations and design standards

Ground gas protection for new buildings is governed by BS 8485:2015+A1:2019, the code of practice for the design of protective measures against methane and carbon dioxide ground gases. This standard provides the framework for site characterisation, risk assessment and the selection of appropriate gas protection measures, and requires installation to be verified by a competent person. Where a below-ground structure also requires waterproofing, BS 8102:2022 applies, governing the design and construction of waterproofing systems for basements and earth-retained structures. Gas resistant membranes that carry dual compliance with both standards are the appropriate solution wherever these requirements overlap.

Gas resistant membrane types

The range of gas resistant membranes reflects the variety of structural situations and gas risk profiles encountered on site. Selecting the right format requires an understanding of the floor construction type, the level of gas hazard, the presence of hydrostatic pressure, and the detailing requirements for the specific installation.

Sheet and self-adhesive gas membranes

Sheet membranes are the most widely used format for horizontal applications below concrete ground floor slabs. They are manufactured from polymer film, often incorporating an aluminium foil layer which significantly reduces gas permeability, and are available at a range of thicknesses to suit the gas hazard classification of the site. Products within this range also function as a damp proof membrane, removing the need for a separate DPM layer in the floor build-up.

Self-adhesive gas membranes are used where the membrane needs to bond to a substrate rather than simply being laid flat. This makes them the standard choice for vertical applications on concrete retaining walls, basement walls, pile caps, lift pits and stepped foundations, and in locations where the sheet cannot be loose-laid. The self-adhesive construction creates a direct bond to the concrete face, reducing the risk of gas tracking beneath the membrane at joints and edges. Pre-applied membranes, applied to blinding or formwork before the concrete is poured, form a fully bonded system once the slab is cast, which is particularly effective in ensuring continuity at wall-to-floor junctions.

For VOC-contaminated sites and those where a wider range of chemical contaminants is present, specialist multi-layer gas membranes with enhanced chemical resistance are available, providing protection against hydrocarbons and other compounds beyond the scope of standard gas barriers.

Liquid applied gas membranes

Liquid applied gas membranes are brush, roller or spray-applied coatings that cure to form a seamless, flexible gas and waterproof barrier. Their primary strength is in complex detailing: service penetrations, pipe entries, awkward corners, junctions between different construction types and retrofit situations where a sheet membrane cannot be accommodated. They bond to porous and non-porous substrates and can be used in both horizontal and vertical applications. In a complete system they are frequently used alongside sheet or self-adhesive membranes, applied as a first-stage treatment to details and transitions before the main sheet membrane is laid, ensuring continuity across the most vulnerable points in the installation.

Gas resistant membranes and waterproofing

One of the key distinctions between a gas resistant membrane and a standard radon barrier is the capacity to resist hydrostatic pressure. A standard radon barrier is not designed for use where the membrane will be subject to water pressure from the surrounding ground; in that situation it will not perform as a waterproofing layer and a structural waterproofing solution is required.

Gas resistant membranes in this range, including structural self-adhesive and pre-applied options, are designed to provide Type A waterproofing protection in accordance with BS 8102:2022, working in conjunction with or as part of a structural waterproofing system for below-ground applications. This means that on sites where both ground gas and groundwater are present, a single correctly specified gas resistant membrane can address both risks within one system, subject to the specific requirements of the site and the design.

For projects where the primary requirement is waterproofing against significant hydrostatic pressure and ground gas resistance is a secondary consideration, see our Tanking Slurry and Membranes range. Note that products in this range and in that collection serve different primary functions; any specification combining gas resistance and waterproofing should be confirmed against the relevant technical datasheets and current standards.

Installing gas resistant membranes

Gas membrane installation is a detail-critical activity. The membrane itself provides the protection, but a continuous, correctly lapped and properly sealed system is required for it to perform. Any breach, unsupported joint or unsealed service penetration represents a potential gas ingress point. For this reason, ground gas protection systems must be installed by a competent contractor and the installation should be subject to inspection and verification by an independent specialist in accordance with BS 8485:2015+A1:2019.

Sheet membranes are typically laid onto a prepared blinding layer beneath the reinforced concrete slab, with laps formed to overlap in the direction of the pour. Lap joints must be sealed using the manufacturer's specified tape or detailing strip to maintain continuity. Pre-applied membranes are installed onto the substrate before the concrete is placed, with the membrane bond activated by contact with the fresh concrete. Self-adhesive membranes are applied to a clean, primed substrate; primer is typically required for vertical or sloping surfaces to ensure full adhesion, and the substrate should be free from contamination, dust and standing water at the time of application.

Penetrations for services, drainage pipes and structural elements passing through the membrane are among the most critical details in any gas membrane installation. Liquid applied membrane products are used to seal around penetrations and at wall-to-floor junctions, providing a flexible, fully bonded detail that a sheet membrane alone cannot achieve. Gas membrane tape provides additional security at laps where required by the specification. All details should be carried out in strict accordance with the manufacturer's installation guidance and the design drawings for the project.

Choosing the right gas membrane

The correct gas membrane for a project is determined by the site risk, the construction type and the regulatory requirements that apply, not by product preference. A gas risk assessment carried out as part of the site investigation will characterise the type and level of gas hazard, and from that characterisation the appropriate level of protection can be selected. Where radon is the only gas of concern and no below-ground waterproofing is required, a standard radon barrier from our Radon Barriers and Gas Membranes range may be the more appropriate product. Where methane, CO2 or VOCs are present, or where the structure is below ground level and exposed to water pressure, a gas resistant membrane from this range is the correct starting point.

Format selection follows from construction type: sheet membranes for standard below-slab horizontal applications; self-adhesive and pre-applied for structural vertical and composite applications; liquid applied for detailing.

Why choose Construction Supplies UK for gas resistant membranes

Specialist range for structural gas protection: Our gas resistant membranes are selected for below-ground and earth-retained applications where both waterproofing and gas resistance are required, with products rated to BS 8102:2022 and BS 8485:2015+A1:2019.

Trusted brands across all formats: We stock gas resistant membrane products from Visqueen, RIW, ITP and Principal Building Products, covering sheet, self-adhesive, pre-applied and liquid applied formats for the full range of structural gas protection applications.

Free delivery on orders over £300 ex VAT: With no minimum order value, we supply trade and retail customers across mainland UK, making it straightforward to order the right quantity for your project.

Technical product information: Full technical datasheets, compliance certifications and installation guidance are available for all products. If you need help matching a product to a specification or ground gas report, the team is available to assist.

Direct supply: Order online or contact us directly at sales@constructionsuppliesuk.co.uk or 03300 55 32 02. We supply groundworkers, waterproofing contractors, groundwork engineers and main contractors direct, without the delays of a distributor in the middle.