What This Requirement Covers
Radon is a naturally occurring radioactive gas that seeps from the ground into buildings. Long-term exposure increases the risk of lung cancer. Approved Document C and BR 211 (Radon: guidance on protective measures for new buildings) require radon protection in buildings located in radon-affected areas.
Key Requirements
Radon Risk Assessment
- The UK Health Security Agency publishes radon maps showing the probability of homes exceeding the Action Level (200 Bq/m3)
- Protection measures are required where the probability of exceeding the Action Level is 3% or more (basic protection) or 10% or more (full protection)
- Site-specific radon testing (using passive detectors over 3 months) provides the most accurate risk assessment
Protection Measures
Basic radon protection (3-10% probability):
- A radon-proof membrane across the ground floor, sealed at all joints, edges, and penetrations
- The membrane must be resistant to radon gas and be continuous (no holes or tears)
Full radon protection (10%+ probability):
- Radon-proof membrane (as above), PLUS
- A radon sump beneath the floor slab, connected to a ventilation pipe rising through the building to discharge above the roof
- The sump can be passive (relying on natural stack effect) or active (with an extractor fan)
- The passive system should be designed so that a fan can be added later if passive ventilation proves insufficient
Existing Buildings
- If radon testing reveals levels above 200 Bq/m3 in an existing building, remedial measures should be taken
- A radon sump with an electric fan is the most effective remedial measure (typically reduces levels by 90% or more)
- Improved under-floor ventilation (additional airbricks) can reduce radon levels in buildings with suspended timber floors
- Positive pressurisation (a fan in the loft blowing filtered air into the building) can reduce radon levels by creating a slight positive pressure that resists radon ingress
Practical Compliance Tips
- Check the radon risk before designing foundations; radon-affected areas require protection built into the ground floor construction
- Install a radon sump at construction stage even in basic protection areas; it is very cheap to install during construction and provides a ready-made route for active ventilation if needed later
- Ensure the radon membrane is not damaged during construction; protect it from trades working on the floor slab
- Seal the membrane at all penetrations (pipes, cables, columns) using compatible tapes and sealants
- For existing buildings, commission a 3-month radon test before deciding on remedial measures
- If a radon sump fan is installed, it should run continuously; the electricity cost is approximately GBP 30-50 per year
- Keep radon test results and protection installation details for the building file