How do I know if my site needs radon protection?

Check the UK Radon Map at ukradon.org or request a report from the British Geological Survey. If 3-10% of homes in the area exceed the action level (200 Bq/m³), basic protection (membrane only) is required. If more than 10% exceed it, full protection (membrane + sump) is needed. Building Control will specify the requirement based on the postcode.

What is the difference between basic and full radon protection?

Basic protection uses a gas-resistant membrane across the ground floor with sealed joints and upstands — sufficient for lower risk areas. Full protection adds a radon sump (a void beneath the floor slab connected to an external vent pipe) which can be activated with an electric fan if radon levels remain high after occupation. Full protection is required in higher-risk areas.

What membrane should I use for radon?

The membrane must comply with BS 8485 and BRE Report 211. It should be a minimum 1200 gauge (300 micron) polyethylene or purpose-made radon barrier. Visqueen Radon Membrane and Proofex Engage are popular UK choices. The membrane must be continuous, with all joints lapped by at least 150mm and sealed with proprietary tape. Penetrations must be sealed with top-hat details.

How does a radon sump work?

A radon sump is a small void (typically 50L) formed beneath the ground floor slab, connected to a 110mm pipe that rises through the building and exits above the roof. In passive mode, the stack effect draws radon from beneath the slab and vents it safely above roof level. If radon levels are still high after testing, an in-line fan can be added to the pipe to actively extract radon.

When should radon be tested after construction?

Test radon levels 6-12 months after occupation, once the building is sealed and heated. Use a pair of passive detectors (one in the living area, one in a bedroom) for a minimum of 3 months — available from ukradon.org for about £50. The action level in the UK is 200 Bq/m³. If levels are above this, activate the sump fan and re-test.

TradeCalculator

Radon Protection Calculator — Membrane, Sump & Ventilation

Calculate radon protection requirements based on BRE radon risk area. Covers membrane area with laps, sump kits, and joint tape quantities.

Ground Floor Area

Total ground floor footprint

Floor Perimeter

Total perimeter length

Protection Level

From BRE radon report

Price Per Roll (optional)

Include radon sump kit

Required for full protection

How We Calculate This

This calculator determines radon protection materials based on floor area and the level of protection required. It calculates membrane area including laps and upstands, joint tape, and sump kit quantities.

The formula

Membrane area = (Floor area + Perimeter upstand) × Lap factor

Rolls = Ceiling(Membrane area ÷ Roll coverage)

Joint tape = Perimeter + Internal joints

Sump kits = 1 per 250 m² floor area (full protection)

For example, 80 m² floor with 36m perimeter: Upstand = 36 × 0.15 = 5.4 m². Membrane = (80 + 5.4) × 1.04 = 88.8 m². At 4m × 25m rolls (100 m²) = 1 roll. Tape: 36 + 20 = 56m = 2 rolls. 1 sump kit for full protection.

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.