[GSBN] Radon

Tue Apr 9 09:35:09 UTC 2013

There are soil tests which can measure the amount of radon present, but these prove inaccurate in predicting what the radon levels in a finished house will be. So they are not recommended.

In Ireland, a nationwide survey was carried out of randomly selected houses in 10km2 grids. The results from these surveys were turned into a radon map. In high radon areas, over 20% of the houses tested had unacceptable levels of radon. So if you live in one of these areas, it is highly recommended that you get your house tested. For new-builds it is recommended that you carry out the test shortly after you move in. There is not much point in testing before the house is occupied, as ventilation levels within the house will naturally increase once the occupants move in.

It is true that levels above 400 Bq/m3 are not so common (as John said) - but they are common enough to cause concern, in this country anyway. For example, of 54,000 houses surveyed, 6,828 had radon levels between 200 Bq/m3 and 799 Bq/m3. 814 had radon levels of 800 Bq/m3 and above. Looking at the worst cases on a county by county basis, the average was in the region of 3,128 Bq/m3.

Looking at my own county (which is a high radon county) - 75% of houses surveyed were ok. 21% had levels 200 - 799 Bq/m3. 4% had level over 800 Bq/m3. The worst case was 5,600 Bq/m3.

In Ireland, lung cancer is the second biggest killer at 6%. It is estmated that about 12% of these deaths are caused by radon exposure.

Testing is carried out by placing two palm-sized detectors in the main bedroom and the living room (the rooms most occupied). The detectors contain a plastic film. When radon particles strike against the film, they etch into it. After 3 months, the detectors are returned to a laboratory. By analysing the number of etch marks, they can work out the radon levels for that house. Radon testing is not a requirement here, but it is recommended. Particularly if you live in a high radon area according to the national radon map.

When I talk about a sub-floor - I mean the compacted crushed rock zone immediately under a typical ground floor concrete slab (or limecrete or cob floor). The top of a radon sump will lie against the underside of the floor slab (or the underside of the insulation if this is where the insulation is located). With internal loadbearing walls, there will be foundations in this zone - so it is important to remember to build air-bridges in the foundations, even though they are buried within the crushed rock layer.

With the suspended ground floor over a crawl space, where the area under the floor is essentially closed in on all sides, there still can be an issue. Making sure that there are air-bricks and that they are not blocked up will help. Also making sure they are logically located to get good cross-ventilation and eliminate dead spaces will also help. There are plastic air "bricks" available which have a greater open surface than standard clay air-bricks. According to the RPII, good natural ventilation below a suspended floor is effective up to 700 Bq/m3.  Adding a fan will increase effectiveness up to 900 Bq/m3.

If you were to build a completely elevated suspended floor, using the space underneath for storage, etc (like the Australian Queenslanders), then ventilation would not be an issue at all. (But you might have a problem with disability access regulations).

Regarding breathable floors - radon and damp proof membranes are vapour tight and are not recommended for use with vapour diffuse floor materials. Particularly in conservation work, but also in new-builds where clients want as many natural, vapur permeable materials as possible, we install limecrete and even mud floors. We use compatible breathable insulations - such as LECA (lightweight expanded clay aggregate) and rely on French drains and drained foundations and sub-floors to cope with ground moisture, rather than inserting damp proof membranes. It is especially important in conservation work, as damp proof membranes often only serve to push ground moisture into the base of existing walls. I have seen a few "renovated and upgraded" houses with lovely mushroom crops at the base of their internal walls, following the installation of a dpm.

Feile

Féile Butler

MRIAI B.Arch Dip. Arch Conservation Grade III

Mud and Wood

Grange Beg, Skreen, Co. Sligo, Ireland

T:  +353 (0) 71 930 0488 

M: +353 (0) 86 806 8382

E : feile at mudandwood.com

W: www.mudandwood.com

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