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What is radon?

Radon is a naturally occurring radioactive gas, that means it continuously decays and releases radiation. It is produced from minerals in soil, such as uranium and radium. It is colorless, odorless and tasteless.

Why is radon important?

Although radon is a naturally occurring gas in our environment, it’s also the second leading cause of lung cancer deaths in the U.S. The Surgeon General and the U.S. Environmental Protection Agency recommend testing for radon because one out of every 15 homes has unsafe levels indoors. Millions of Americans have had their homes tested, and you should, too.

Why is radon a common problem in Minnesota Homes?

Much of the soil in the Upper Midwest contains widespread uranium and radium. These minerals continuously break down to release radon gas. Therefore, Minnesota's geology provides an ongoing supply of radon.
In addition, a large percentage of Minnesota homes have elevated levels of radon in the indoor air because of how they are built and how they operate in our climate. One important factor is that many Minnesota homes have basements that are uses as living spaces.

MDH estimates that about one in three (1/3) Minnesota homes have enough radon to pose a significant risk to the occupants' health over many years of exposure.



Zone 1 counties have a predicted average indoor radon screening level greater than 4 pCi/L (pico curies per liter) (red zones)

Highest Potential

Zone 2 counties have a predicted average indoor radon screening level between 2 and 4 pCi/L (orange zones)

Moderate Potential



How does radon enter a home?

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.

Major Radon Entry Routes

Major Radon Entry Routes

  1. Cracks in concrete slabs.
  2. Spaces behind brick veneer walls that rest on uncapped hollow-block foundations.
  3. Pores and cracks in concrete blocks.
  4. Floor-wall joints.
  5. Exposed soil, as in a sump or crawl space.
  6. Weeping (drain) tile, if drained to an open sump.
  7. Mortar joints.
  8. Loose fitting pipe penetrations.
  9. Open tops of block walls.
  10. Building materials, such as brick, concrete, rock.
  11. Well water (not commonly a major source in Minnesota homes).


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