Handbook of Radon.
62. Experience with ventilation provision.
This Section deals primarily with altering natural ventilation - the special case of positive pressurisation is covered in Section 61.
Reduction of indoor radon levels by altering building ventilation has been misreported and misunderstood in the UK. Amongst the key facts are:
Draughty houses can have high radon levels.
Well sealed houses can have low radon levels, even in high radon areas.
Application of draught-proofing and double glazing may increase or decrease indoor radon levels, depending upon the building design and the measurement location.
Opening windows or removing draught-proofing on different sides of a building may have different effects.
The most important effect of increased ventilation may be pressure equalisation, rather than increased ventilation rate. Reduction in indoor radon levels may reflect decreased radon entry rate.
Reduction of indoor radon levels by altering house ventilation is a viable mitigation method but is most applicable where initial levels are moderate and the building needs improved ventilation for condensation or odour control, having previously been too well sealed or where unused chimneys that were causing depressurisation can be blocked off. Factors of between 1 (no change) and 2 can be expected in many cases, but need to be confirmed.
Improved ventilation can obviously be used as a temporary method of reducing high radon levels until permanent action is taken, but again it needs to be confirmed that a useful reduction has occurred: simply leaving a window slightly open for a few hours every day may not significantly affect the 24 hour average level.
Nevertheless, dramatic short term reductions in indoor radon levels can sometimes be effected by opening a window a few mm (half an inch), but this cannot be recommended as a universal cure, if only because no change may occur in some buildings.
The most marked improvements effected by ventilation alone have involved cellar spaces and (more commonly) provision of more air-bricks under timber floors. Much depends on individual house details, especially the problems of timber floors (see Section 57). Large reductions (up to a factor of 10) have also been seen where heating systems have been changed (see Section 56) and where the principal effect has been in the mode of room ventilation.
However, the most pervasive influence of altering house ventilation rates is sometimes not so much on the whole house average radon level (averaged over all rooms) but on the room to room variation. Since radon levels are often assessed only by pairs of detectors (one upstairs, one downstairs), the result can be determined by window opening habits.
Bedroom radon levels may be more uniform than those in ground floor rooms. Large differences can often be ascribed to opening of one bedroom window for many hours per day (or night) as is common practice.
Key facts:
Improved ventilation may be acceptable as a permanent mitigation technique in some circumstances.
The most encouraging results may be expected where previously sealed underfloor spaces can be ventilated and where windows on the windward side of the house are selected for ventilation provision.
In many houses, changes in ventilation habits may shift the long term average radon level in a room either side of the action level.