Substrates & Preparation
Screeding Over a Radon Membrane
In radon-affected areas of the South West, the gas membrane's continuity and sealed penetrations matter more than usual before liquid screed is poured over it.
Parts of Devon and the wider South West fall within areas identified as having elevated radon potential, meaning new floors in these locations often need a radon barrier as part of the build-up. The membrane's job is to form a continuous, gas-tight layer, and the screed sits above it — but only after the membrane's laps, joints and penetrations have been properly sealed and protected from the works that follow.
This is a similar principle to a standard DPM, but radon membranes are specifically rated for gas resistance and often need more rigorous joint sealing than a basic damp-proof membrane.
Radon Membranes — the points that decide it
- Radon membranes need continuous, sealed laps rather than simply overlapping sheets loosely, since gas will find any gap over time
- Purpose-made radon-resistant tape is used at joints and penetrations rather than generic building tape
- Service penetrations (pipes, ducts) through the membrane need collar seals or similar detailing to maintain continuity
- Where a sump and radon extraction system is specified, this needs coordinating before the membrane and screed are installed, not retrofitted afterwards
- The membrane should be protected from puncture during insulation laying and the screed pour itself, the same as any DPM
- Local building control will typically confirm whether a site falls within a radon-affected area and what level of protection is required
Why joint continuity is non-negotiable
Radon is a gas, and gases will migrate through even small gaps over time in a way that liquid water often won't. This is why radon membrane installation puts more emphasis on continuous, taped joints and properly sealed penetrations than a standard DPM might in a non-radon area — a membrane that's 95% sealed still allows gas through the remaining 5%.
Coordinating with sub-floor ventilation if specified
In higher-risk radon areas, building control may require a sub-floor sump and passive or active extraction system in addition to the membrane. This needs planning into the floor build-up before insulation and screed go in, since retrofitting extraction after the floor is finished is far more disruptive than incorporating it at the groundworks stage.
Building in a radon-affected part of Devon or the South West?
We'll work with your groundworker to make sure the radon membrane is properly protected before the screed pour.
Or call our landline on 01392 237700
Radon Membranes — your questions
In short
In radon-affected areas of the South West, the gas membrane's continuity and sealed penetrations matter more than usual before liquid screed is poured over it.
Building in a radon-affected part of Devon or the South West?
We'll work with your groundworker to make sure the radon membrane is properly protected before the screed pour.