Most of us breathe in natural radioactive gas throughout our lives. Radon disperses harmlessly into the air but some passes from the ground and collects in spaces under or within buildings. Breathing in too much radon increases the risk of developing lung cancer, so an effective radon barrier is essential when building in areas where radon gas is more prevalent.

Does your development need a radon barrier? What does a barrier look like and how can you avoid the most common defect? This article explains.

Do you need a radon barrier?

The Building Regulations are clear under Part C (2) “Site Preparation and resistance to contamination and moisture” that in areas affected by higher levels of radon, relevant precautions need to be taken. Some areas of the UK are more prone to radon than others. To check if your site needs protection against radon, visit Public Health England’s interactive radon map. A more specific assessment of your site will normally be contained in either the Phase 1- Desk Top Study or Phase 2- Site Investigation report.

The basic elements of an effective radon barrier

An effective radon barrier must cover the entire footprint of the property. This includes garages or storerooms where habitable accommodation is above or where there is direct access to the property. Installation can be made more complicated if your building has changes in internal floor levels, for basements or lift pits for instance. In these cases, it’s a good idea that such areas form part of your risk-based inspections.

More complications arise in the case of timber frame constructions, which we discuss in a separate article here.

As a minimum, a barrier of 300 micrometre (1200 gauge) polyethylene (Polythene) is sufficient. Other proprietary barriers are available but do check with the manufacturer for their suitability.

Connecting radon barriers and damp proof course – the most common defect

A common approach is to build a wide section of barrier into the external and internal walls, linking to the floor barrier overlaying the floor. The thinking here is that this section of barrier can act as both the radon barrier and damp proof course. However, as surveyors, the most common defect we come across with radon barriers is where corners or overlaps are not sealed, so the barrier is not gas-tight. The following images illustrate the case:

Common radon barrier, first example Common radon barrier defect, second example

Defective radon barrier, third example

In all these cases, the radon membrane is not sealed. Ask yourself the question: "Is this gas-tight?"

Ensuring your radon barrier is gas-tight

The best approach is to make sure your radon barrier is sealed before the bricklayer starts work above the barrier. All laps or joints must be fully sealed where sitting within a wall, not just sealed either side of a wall. Surveyors will focus their attention on these areas at an early stage.

Seal the barrier with adhesive tapes or for a more effective seal, use double-sided, self-adhesive synthetic rubber strip sealants. Many manufacturers recommend double-sided butyl tape and additional jointing tape used for securing laps and joints. A minimum 150mm lap is recommended or anything over this as advised by the manufacturer.

Surveyors will also look at seals around any service or periscope vent penetrations. Make sure barriers are properly sealed around periscope vents. For subfloor ventilators, the joints between upper and lower halves of the ventilators should be taped to reduce the risk of radon entering the cavity. If you can’t avoid service penetrations, prefabricated “top hat” sections are a good means of sealing the barrier around pipe entries.

Dispersing radon

Another effective means of dealing with radon is to help it disperse through ventilation. If your building includes suspended (beam and block) ground floors, airbricks help disperse radon from the void beneath. Airbricks should be installed where possible on all sides of the building, at intervals large enough to give an actual opening equivalent to 1500 mm2 for each metre run of wall on two opposite sides. In most cases this means that vents should be positioned at 2m maximum centres along the external walls and not more than 450 mm from corners.

More information

The BRE produces a useful guide on effective radon barriers. BRE 211 Radon: Guidance on protective measure for new buildings can be obtained from their bookshop.

Chapter four of the LABC Warranty Technical Manual covers site investigation reports, geology and contamination.

Every care was taken to ensure the information in this article was correct at the time of publication. For the most up to date LABC Warranty technical guidance please refer to your Risk Management Surveyor and the latest version of the LABC Warranty technical manual.

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