Skip to content
RADON411
$5

County radon report

Get it
Learn4 min read

Can radon come through concrete?

By Radon411 Editorial TeamUpdated How we research

Short answer

Yes. Radon gets through a concrete floor or wall by its openings: cracks, the joint where floor meets wall, gaps around pipes, sumps and drains, and the pores and cavities of hollow block walls. The house is at slightly lower pressure than the soil, so it draws radon in through all of them.

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

Some concrete products give off radon, but building materials rarely cause radon problems by themselves; the soil under the slab is the main source.

Sealing the concrete helps other fixes work but is not recommended on its own, because it has not been shown to lower radon significantly or consistently. Sub-slab suction, which pulls radon from beneath the slab, is the most common and usually the most reliable fix.

What to do next: test the lowest lived-in level, and if the result is high, ask a qualified contractor about sub-slab suction.

How radon gets past a concrete floor

A concrete slab looks solid, but it is full of ways in. Radon moves up through the ground and into a home through cracks and other holes in the foundation, and a slab has plenty: cracks, the joint where floor meets wall, gaps around pipes and cables, a sump pit or floor drain. Hollow concrete block walls add small pores and open cavities.

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
Where radon gets through a concrete foundation: floor cracks, construction joints, wall cracks, gaps around pipes and wall cavities.
Openings in concrete that let radon in
OpeningWhere you find it
Cracks in the floorAnywhere in a basement floor or slab
Floor-wall jointsAround the edge of the slab, where it meets the foundation wall
Gaps around pipes and cablesWherever a service line passes through the floor or wall
Sumps and drainsOpen sump pits and floor drains
Pores and cavities in block wallsHollow concrete block walls, whose cavities let radon move

Why the house pulls radon through the slab

The openings are only half the story. Air pressure inside a home is usually lower than in the soil around the foundation, so the house acts like a vacuum and draws radon in through those cracks and openings. The house then traps the radon inside, where it can build up.

That is why basements and slabs, the parts of a home in contact with the ground, usually carry the highest levels. More on the routes is in how does radon get into a house.

Does sealing the concrete stop radon?

Sealing cracks with caulk or other materials made for the purpose limits the flow of radon, cuts the loss of heated and cooled air, and makes other radon fixes work better. It is a basic part of most radon systems. On its own, though, it is not recommended: sealing alone has not been shown to lower radon significantly or consistently.

Why sealing alone falls short
ProblemWhat happens
Hidden entry pointsThe places where radon enters are hard to identify
PermanenceOpenings are hard to seal permanently
SettlingNormal settling of a home opens new entry routes and reopens old ones

Step-by-step advice is in how to seal cracks in a basement floor for radon.

Stopping radon at the slab: suction from below

The reliable fix works under the concrete rather than on it. In sub-slab suction, one or more pipes go through the floor slab into the crushed rock or soil underneath, or below the slab from outside the home, and a fan draws the radon out and vents it outdoors while keeping a vacuum beneath the slab. It is the most common and usually the most reliable radon reduction method.

Cross-section of a house with a sub-slab depressurization system: soil gas drawn from beneath the slab into a suction point, up a vent pipe, through a fan outside the living space and out above the roofline.
Read this figure as text
Sub-slab depressurization system in a house cross-sectionGround levelLiving spaceBasement12345
  1. Soil gas drawn from beneath the slab
  2. Suction point through the slab
  3. Vent pipe
  4. Fan, outside the living space
  5. Discharge above the roofline
Sub-slab suction: a pipe through the concrete, a fan outside the living space and an exhaust above the roof.
Suction methods for concrete foundations
MethodWhere it is usedTypical reduction
Sub-slab suctionBasement and slab-on-grade floors50 to 99 percent
Block-wall suctionBasements with hollow block foundation walls; often combined with sub-slab suctionRemoves radon and depressurizes the block wall

Building a slab that keeps radon out

In new homes, radon-resistant construction deals with the concrete before it is poured. Plastic sheeting goes on top of a gas-permeable layer and under the slab to help keep soil gas out, and all below-grade openings in the foundation and walls are sealed. A vent pipe from below the slab can later take a fan if a test is high.

Radon-resistant features at the slab
FeatureWhat it does
Gas-permeable layer under the slabLets soil gas move freely to the vent pipe
Plastic sheeting under the slabHelps prevent soil gas from entering the home
Sealing and caulkingAll openings in the concrete floor are sealed
Vent pipeRuns from the gas-permeable layer through the house to the roof, venting soil gas outside

Questions about radon and concrete

Can radon pass through solid concrete?

In practice it comes through the openings: cracks, floor-wall joints, gaps around pipes, sumps and the pores and cavities of block walls.

Does concrete give off radon?

Some concrete products can, but building materials rarely cause radon problems by themselves. The soil under the home is the main source.

Will sealing my basement floor stop radon?

Not on its own. Sealing alone has not been shown to lower radon significantly or consistently, but it makes a suction system work better.

Can a slab-on-grade house have radon?

Yes. A slab has many openings that let radon in, much like a basement. See can a house have radon without a basement.

Do concrete block walls let radon in?

Yes. Hollow block walls have cavities that let radon move, and block-wall suction can be used to depressurize them.

What is the best way to stop radon coming through concrete?

Sub-slab suction, which draws radon from beneath the slab before it gets in. It is the most common and usually the most reliable method.

Learn

Related guides

What radon is, where it comes from, how it gets indoors and what it does to health.

Everything in LearnOther guide topics
  • 17 min read

    Radon gas

    What it is, where it comes from and how it gets indoors.

    Read the guide
  • 17 min read

    Radon in homes

    How it gets in, where it builds up and what to do about it.

    Read the guide