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Do all homes have radon?

By Radon411 Editorial TeamUpdated How we research

Short answer

Every home has some radon, because all outdoor and indoor air has some in it; the average indoor level is about 1.3 pCi/L. What differs is the level, and nearly 1 in 15 homes in the United States is estimated to have an elevated level, in every state and in every kind of home.

Next step: a test is the only way to know your home's level. How to test your home

Radon comes from the natural decay of uranium found in nearly all soils, moves up through the ground and enters homes through cracks and other holes in the foundation. Outdoors it quickly dilutes; indoors a home traps it, where it can build up.

Any home can have a radon problem: new and old, well-sealed and drafty, with or without a basement. Local geology, construction materials and how the home was built are among the factors that affect the level, and levels vary greatly from home to home.

EPA's Map of Radon Zones shows which areas have the greatest potential, but homes with elevated levels have been found in all three zones, and the map should not be used to decide whether an individual home needs testing.

What to do next: test the lowest lived-in level of your home with a of at least 48 contiguous hours under , or a of more than 90 days, and read the result with the interpreter.

Every home has some radon

Yes, in the sense that all outdoor and indoor air has some radon in it. Radon comes from the natural decay of uranium found in nearly all soils, and it moves up through the ground and into homes through cracks and other holes in the foundation. The difference between homes is the level.

How much radon homes have
MeasureLevel
Average indoor level (U.S.)About 1.3 pCi/L
Normal outdoor level (U.S.)About 0.4 pCi/L
Homes estimated to have an elevated levelNearly 1 in 15
Range in homes, schools and offices worldwide10 to more than 10,000 Bq/m3

Any kind of home can have a problem

Radon can be a problem in homes of all types: old homes, new homes, drafty homes, insulated homes, homes with basements and homes without them. Local geology, construction materials and how the home was built are among the factors that affect the level.

Cross-section drawing of a house with a basement and a crawl space, numbered at the seven ways EPA lists for soil gas to get in: cracks in solid floors, construction joints, cracks in walls, gaps in suspended floors, gaps around service pipes, cavities inside walls, the water supply.
Read this figure as text
House in cross-section showing where soil gas entersGround levelSoil and rockBasementSolid floorCrawl spaceSuspended floor1234567
  1. Cracks in solid floors
  2. Construction joints
  3. Cracks in walls
  4. Gaps in suspended floors
  5. Gaps around service pipes
  6. Cavities inside walls
  7. The water supply
The routes soil gas takes into a house; most exist in any foundation.

Even a new home built radon-resistant should be tested after occupancy. See do I need a radon test without a basement.

Why some homes have more than others

What makes one home's radon higher than another's
FactorEffect
Local geologyAmong the main factors that affect radon levels in homes
ConstructionHow the home was built affects its radon level
MaterialsConstruction materials are among the factors
TrappingIndoors, radon is trapped and builds up; outdoors it quickly dilutes

Levels are usually higher in basements, cellars and living spaces in contact with the ground. And they vary greatly from home to home, even between neighbors.

No area is radon-free

High radon levels have been found in every state. EPA's Map of Radon Zones shows which areas have the greatest potential, but homes with elevated levels have been found in all three zones, and the map should not be used to decide whether an individual home needs testing.

Bar chart of how many U.S. counties are in EPA radon Zone 1, Zone 2 and Zone 3, and how many have no zone on file, from the EPA Map of Radon Zones.
Read this figure as text

Predicted potential

Counties per EPA radon zone
ZoneBarCountiesShare of all counties
Zone 1Highest predicted potential1,07133.1%
Zone 2Moderate predicted potential1,03432.0%
Zone 3Lower predicted potential1,03332.0%
No zoneNo EPA zone on file932.9%

3,231 counties in all.

An EPA radon zone describes predicted potential across a whole county. It is not intended to determine whether any individual home should be tested, and homes with elevated levels occur in all three zones. EPA recommends testing every home regardless of zone, and testing is the only way to know the radon level in a specific building.

How many counties fall in each EPA radon zone. A prediction of potential, not a measurement of any home.

See where radon is most common.

How radon gets into a home

Air pressure inside a home is usually lower than pressure in the soil around its foundation, so the house acts like a vacuum, drawing radon in through foundation cracks and other openings. Every foundation has some of those openings, which is why every home has some radon.

Common radon entry points
Entry pointWhere
Cracks in floors and at floor-wall junctionsBasement and slab floors
Gaps around pipes or cablesWhere services pass through the foundation
Pores in hollow-block walls and cavity wallsBlock foundations
Sumps and drainsBasements

If your home's level is high

A high level is fixable. The method primarily used is a vent pipe and fan that pulls radon from beneath the house and vents it outside; some systems cut levels by up to 99 percent, and most homes can be fixed for about the same cost as other common home repairs.

So should every home be tested?

EPA and the Surgeon General recommend testing all homes below the third floor for radon, and testing is the only way to know if you and your family are at risk. Place the test in the lowest lived-in level of the home.

Questions about radon in every home

Does every house have radon?

Every house has some, because all air has some radon in it. The level is what varies.

Do new homes have radon?

They can. Every new home should be tested after occupancy, even if it was built radon-resistant.

Do homes without basements have radon?

They can. Radon can build up in any home, with or without a basement.

What percentage of homes have high radon?

Nearly 1 out of every 15 U.S. homes is estimated to have an elevated radon level.

Is radon only a problem in some states?

No. High radon levels have been found in every state.

Can I lower the radon in my home?

Yes. Some radon reduction systems cut levels by up to 99 percent, and most homes can be fixed for about the same cost as other common home repairs.

Does a well-sealed house keep radon out?

No. Well-sealed and drafty homes can both have radon problems.

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