Assessing and guarding against the dangerous effects of radon gas is an incredibly important and mandatory consideration.

Colourless, odourless, and created by the breakdown of tiny amounts of uranium in the earth, radon is the second highest cause of lung cancer in the UK behind smoking, causing 1,100 deaths each year.

Radon is, under normal conditions, gaseous and easily inhaled.. It is often the single largest contributor to an individual's background radiation  dose, Due to local differences in geology the level of the radon-gas hazard differs from location to location Radon gas from natural sources, such as Granite, can accumulate in buildings, especially, due to its high density, in low areas such as basements 

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Before designing a basement it is necessary to check for the likely potential levels of Radon

radon map

The only way to accurately determine radon levels is to have a full radon test performed.

When considering Public Health England’s maps, even new structures with the lowest level of risk still require basic protection. For buildings without basements, this simply consists of a radon membrane. However, in areas of higher risk, full protection requires the addition of a passive sump or ventilated void. A full radon test should then be performed once the building is occupied, and if radon is present above the action level then the sump should be activated.

By comparison, basement structures are considered as being at a significantly greater risk of radon ingress due to the fact that they are built into the earth.

Furthermore, a passive sump may not work in such scenarios if it is submerged beneath the water table.

What are your options when it comes to radon proofing?

The best solution in these cases is generally to implement a specialist sealed membrane system that combines both waterproofing and ground gas mitigation.

By combining the waterproofing recommendations of BS 8102:2009 with the gas considerations of BS 8485:2015 it is therefore possible to take a synergistic approach that mitigates against both gas and water ingress. Whilst the membranes act as both a water and gas barrier, the system employs positive pressure to manage gas into an active sump before venting it safely out of the building .

Such measures can be used to effectively protect against radon ingress. However, if carbon dioxide and methane are also dangers on a new build site then BS 8485:2015 must be employed, and the considerations become significantly more complex.

MacLennan Radon gas design detail

Why should I work with MacLennan?


We Design, supply and install. There's no split responsibility with MacLennan.


MacLennan live and breathe waterproofing, have a look at one of our free CPD seminars and find out!


MacLennan has the most comprehensive guarantees and insurances in the industry.

What MacLennan Waterproofing recommends

Site with retaining wall(s) only, built into a slope/hill side (not a full basement)

We can offer the Gas and watertight membranes installed by MacLennan and tested and verified by an independent company.

The system will provide the required Basic Radon protection. We will always recommend to  the client to install Radon sumps (these will be necessary if Full Radon Protection is deemed necessary).

Each Radon Sump will cover approx. 15m radius, clear area no obstructions (Ground beams etc). We are happy to supply or advise. If there is a block and beam floor, with a void under. Then a radon sump isn’t required as the void provides the ventilation. The client will also need to install vent pipes from the Radon Sumps.

Site with full basement

We can offer the full sealed gas and water membranes externally and PAC System.

The PAC ‘Positive Air Curtain’ 500 System is a combined basement waterproofing and ground gas mitigation system which successfully controls both water and gas levels within below ground/retaining structures.

This system combines the Cavity Drain waterproofing system, with a positive pressure air delivery system.

MacLennan design, supply and guarantee the system. It is independently verified by an integrity testing & gas resistance company and this can

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