Substrates & Preparation
Detailing Ground Gas Membranes Before Liquid Screed
Sites with methane or other ground gas risk need a gas-resistant membrane detailed to a specific gas protection scheme before insulation and screed go down.
Beyond radon, some sites — particularly former agricultural land, sites near old landfill, or ground with naturally occurring methane — need protection against other ground gases as part of the foundation and floor design. The specific gas protection measures are set out in a scheme designed by the site's geotechnical or environmental consultant, and the screed floor build-up needs to sit compatibly with whatever that scheme specifies.
This is a more site-specific and technically involved area than a standard DPM, and the detailing requirements will vary considerably depending on the gas risk classification for the site.
Ground Gas Membranes — the points that decide it
- Ground gas protection measures are set out in a scheme specific to the site, typically following guidance referenced by building control and any environmental consultant's report
- Membrane specification, venting requirements and detailing around penetrations all depend on the gas risk classification identified for the site
- Sub-floor venting (passive or mechanical) is sometimes required in addition to a membrane, and this needs coordinating with the floor build-up
- Membrane integrity testing is sometimes specified before insulation and screed are laid over it, given the consequences of an undetected breach
- Service penetrations need purpose-made gas-tight seals rather than generic tape or sealant
- The screed installer's role is to protect and work compatibly with the specified gas protection system, not to design it
Following the site-specific scheme
Unlike a standard DPM, ground gas protection isn't a one-size-fits-all detail — it follows a scheme derived from site investigation data specific to that plot, which sets out the membrane type, required venting, and how robustly joints and penetrations need to be sealed. Anyone working on the floor build-up needs sight of that scheme before installing insulation or screed, rather than assuming standard DPM practice is sufficient.
Protecting the membrane through subsequent trades
Given the consequences of an undetected breach in a gas membrane, protecting it from puncture during insulation laying, service installation and the screed pour itself is taken seriously on these sites. Some schemes call for integrity testing or inspection sign-off on the membrane before it's covered, which needs building into the programme rather than treated as an afterthought.
Building on a site with a ground gas protection scheme?
Share the scheme details with us before the pour so we can plan insulation and screed installation around the required detailing.
Or call our landline on 01392 237700
Ground Gas Membranes — your questions
In short
Sites with methane or other ground gas risk need a gas-resistant membrane detailed to a specific gas protection scheme before insulation and screed go down.
Building on a site with a ground gas protection scheme?
Share the scheme details with us before the pour so we can plan insulation and screed installation around the required detailing.