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Can a house have radon without a basement?

By Radon411 Editorial TeamUpdated How we research

Short answer

Yes. Radon gets into any building through the parts that touch the ground, so slab-on-grade homes, crawlspace homes and manufactured homes can all have high levels. Any home may have a radon problem, with or without a basement, and a test on the lowest lived-in floor is the only way to know.

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

A slab poured at ground level has many of the same openings as a basement floor, and a crawlspace is directly connected to the soil. Indoor air pressure is usually a little lower than the soil's, so the house draws radon in through whatever openings it has.

Foundation type changes how radon is fixed, not whether a home can have it. Slab homes are usually treated with soil suction under the slab, and crawlspace homes with a sealed plastic sheet and a fan drawing from under it.

What to do next: test a regularly used room on the ground floor with a short-term kit, and follow up if the result is high.

How radon gets into a house with no basement

Radon from the soil is the main cause of radon problems, and it does not need a basement to get in. It moves up through the ground and into a home through cracks and other holes in whatever part of the building meets the ground, and the house traps it inside, where it can build up. A slab poured at ground level and a crawlspace both touch the soil.

Foundation types and how radon reaches the living space
FoundationHow radon gets in
Slab-on-grade (concrete poured at ground level)Many openings that let radon in, much like a basement, such as cracks in the slab and floor-wall joints
Crawlspace (a shallow unfinished space under the first floor)Directly connected to the soil, creating a pathway into the home
Manufactured home with solid skirtingActs like a crawlspace, with a direct connection to the soil
BasementA large surface area in contact with the soil, with several entry pathways
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
Entry points where a building meets the ground; a slab or crawlspace has many of the same ones.

The driving force is the same for every foundation. Indoor air pressure is usually lower than in the soil, so the house acts like a vacuum, and that pressure difference pulls radon in through whatever pathways exist.

Why foundation type is no guide to your level

It is a common belief that radon is a basement problem. The guidance says otherwise: any home may have a radon problem, including new and old homes, well-sealed and drafty homes, and homes with or without basements. Radon can build up in any building, whether it has a basement, is sealed or drafty, or is new or old.

What actually shapes a home's radon level
FactorWhy it matters
Local geologyThe soil and rock under the home are the source
Construction materialsAmong the factors that can affect the level
How the home was builtAlso among those factors, whatever the foundation
The house next doorNot a guide: levels vary considerably even between adjacent buildings

Testing a home without a basement

A test goes in the lowest lived-in level of the home: the basement if it is used often, otherwise the first floor. In a slab or crawlspace home, that is the ground floor. Pick a room that could be used regularly, such as a bedroom, family room or den, and keep the device out of the crawlspace itself, closets, hallways, stairways, kitchens and bathrooms.

Table comparing a short-term radon test, a long-term radon test and a continuous radon monitor: how long each runs and what each is for.
Read this figure as text
TestHow long it runsWhat it is for
Short-term testStays in the home from 2 to 90 days, depending on the device, and for a minimum of 48 hours.A faster screening result. Because radon levels vary from day to day and season to season, it is less likely than a long-term test to tell you the year-round average.
Long-term testStays in the home for more than 90 days.It is more likely than a short-term test to tell you the home's year-round average radon level.
Continuous monitorLogs readings for the whole test, run as a short-term or a long-term test under the same durations in EPA guidance.Logs a graph over time, so you can see trends and spot anomalies rather than a single number.
A short-term test is the usual first step in any home; a long-term test gives the year-round picture.

EPA recommends fixing a home when the radon level is 4 or higher. EPA recommends considering a fix when the level is between 2 and 4 pCi/L. Those levels apply to every home, basement or not. More on the decision is in do I need a radon test if I don't have a basement, and on placement in where should a radon test be placed.

Fixing radon on a slab or over a crawlspace

Foundation type changes the fix, not the need for one. In slab-on-grade homes, as in basements, radon is usually reduced with soil suction: one or more pipes reach the soil under the slab, through the floor or from outside the home, and a fan draws the radon away. In crawlspace homes, the most effective method is submembrane suction: the earth floor is covered with a high-density plastic sheet and a vent pipe and fan draw the radon from under it.

  • Slab-on-grade

    Concrete poured at ground level.

    • Active subslab suctionThe most common and usually the most reliable radon reduction methodSuction pipes may also be inserted below the concrete slab from outside the home.
    • Drain-tile suctionSuction on drain tiles or perforated pipe is often effective in reducing radon levels.
    • Passive subslab suctionUsually associated with radon-resistant features installed in newly constructed homes.

  • Crawlspace

    A shallow unfinished space under the first floor.

    • Submembrane suctionWhen properly applied, the most effective way to reduce radon levels in crawlspace homesA high-density plastic sheet covers the earth floor, and a vent pipe and fan draw the radon from under the sheet and vent it to the outdoors.
    • Active crawlspace depressurizationA less-favorable option that draws air directly from the crawlspace using a fan; it generally does not work as well as submembrane suction.
    • Crawlspace ventilationIn some cases, radon levels can be lowered by ventilating the crawlspace passively, or actively, with the use of a fan.

Any type of home

  • Sealing cracks and openingsA basic part of most approaches, but EPA does not recommend the use of sealing alone to reduce radon.
  • House or room pressurizationShould only be considered after the other, more-common techniques have not sufficiently reduced radon.
  • Heat recovery ventilator (HRV)More effective in reducing radon levels when used to ventilate only the basement.
  • Natural ventilationShould normally be regarded as only a temporary radon reduction approach.

Some homes have more than one foundation design feature. In these situations, a combination of radon reduction techniques may be needed to reduce radon levels to below 4 pCi/L.

The reduction methods for slab-on-grade and crawlspace homes, and the ones that work in any home.

Other options for a crawlspace include drawing air out of the crawlspace with a fan, which generally works less well, and ventilating it, passively or with a fan. Many homes mix foundations, such as a basement under part of the house and a slab under the rest, and then need a combination of methods. The right system depends on the design of your home; see how to reduce radon.

Upper floors and apartments

Height above the ground lowers the odds but does not remove them: considerable radon can be found above the ground floor too. Testing is recommended for all homes below the third floor.

Where to test in homes without a basement
HomeWhere the test goes
Single-story slab or crawlspace houseA regularly used room on the ground floor
Manufactured homeA regularly used room on the main floor
Apartment or condo below the third floorThe lowest level within your unit
Home with a partial basementThe basement if it is used often, otherwise the first floor

Questions about radon without a basement

Can a slab-on-grade house have radon?

Yes. A slab has many openings that let radon in, much like a basement, and any home can have a radon problem whatever its foundation.

Do crawlspace homes get radon?

Yes. A crawlspace is directly connected to the soil and gives radon a pathway into the home. Covering the earth floor with a sealed plastic sheet, with a fan drawing from under it, is the most effective fix.

Can a mobile or manufactured home have radon?

Yes. A manufactured home with solid skirting acts like a crawlspace home, with a direct connection to the soil.

Is radon lower in homes without basements?

Radon is usually highest in spaces in contact with the ground, but every home has some, and levels vary greatly from home to home. Only a test shows yours.

Where do I put a radon test if I have no basement?

In the lowest level used regularly, usually a ground-floor room such as a bedroom or den, not in the crawlspace, a kitchen or a bathroom.

Should second-floor apartments be tested?

Testing is recommended for all homes below the third floor, so yes: place the test in the lowest level within your unit.

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