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Radon, because it is a gas, is able to move though spaces in the soil or fill material around a home's foundation. Minnesota homes tend to operate under a negative pressure - this is especially true in the lowest portions of the home and during the heating season. This negative pressure acts as a vacuum (suction) that pulls soil gases, including radon, into the lower level of the structure. Some causes of home vacuum are:
- Heated air rising inside the home (stack effect).
- Wind blowing past a home (downwind draft effect).
- Air used by fireplaces, wood stoves, and furnaces (vacuum effect).
- Air vented to the outside by clothes dryers and exhaust fans in bathrooms, kitchens, or attics (vacuum effect).
Radon can enter a home through the floor and walls -- anywhere there is an opening between the home and the soil. Examples of such openings include dirt floor crawl spaces, unsealed sumps, cracks in slab-on-grade floors, utility penetrations, and the tiny pore spaces in concrete block walls. A basement, of course, provides a large surface area that contacts soil material.
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