Crawl space radon mitigation works a little differently from a basement job, because there's often a dirt floor instead of a slab. Radon can come up through that soil and into the rooms above. EPA describes the main fix and a few backups, and this page walks through them along with what the work tends to cost.
Submembrane suction
EPA says an effective method for crawl space homes is to cover the earth floor with a high-density plastic sheet [1]. A vent pipe and fan then pull radon from under the sheet and vent it outside [1]. EPA calls this submembrane suction and says that, when done right, it's the most effective way to lower radon in a crawl space home [1].
Other options
- Active crawl space depressurization. A fan draws air straight out of the crawl space. EPA says it generally doesn't work as well as submembrane suction. It also needs special attention to backdrafting of combustion appliances and to sealing the crawl space off from the rest of the house [1].
- Ventilation. Opening vents or adding a fan can lower levels in some homes [1]. In cold climates, EPA notes that water pipes, sewer lines and appliances in the crawl space may need insulation [1].
Mixed foundations
EPA points out that it's common to have a basement under part of a house and a slab or crawl space under the rest [1]. A system for that kind of home may need a suction point in each area. Ask the contractor to show every suction point on the plan.
What it costs
HomeGuide's February 2026 guide lists crawl space encapsulation at $3,000 to $15,000, or $3 to $10 a square foot [2]. Angi's September 2026 guide lists added encapsulation, when needed, at $1,500 to $15,000 and gives a crawl space without a slab as the example [3]. Both are national ranges, and full encapsulation can go beyond a basic radon membrane. Ask for the radon work and any moisture work to be priced on separate lines. See radon mitigation cost.
Testing after the work
Iowa's mitigation rule calls for a test before and after the work unless the owner waives it on a state form. The post-test has to start between one and 30 days after installation [4]. If anyone will sleep or spend time above the crawl space, test there. EPA says to test in the lowest lived-in level [5].
FAQ
Can I just open the vents?
EPA lists ventilation as an option that may lower levels in some cases, but submembrane suction is the method it calls most effective [1].
Does the plastic need to be sealed?
Ask. EPA describes the sheet as covering the earth floor, with suction drawn from underneath [1].
Get a quote
Ask for a crawl space quote and tell us how high the space is.
We're a referral service, not a contractor. We send mitigation requests only to contractors on Iowa HHS's current credentialed list and testing requests only to state-certified radon measurement specialists, but we don't otherwise vet them, a referral is not an endorsement, and independent contractors may pay us for referrals.
Sources
- U.S. EPA, Consumer's Guide to Radon Reduction, EPA 402/K-10/005 (2025 edition, PDF). https://www.epa.gov/sites/default/files/2016-12/documents/2016_consumers_guide_to_radon_reduction.pdf
- HomeGuide, "How Much Does a Radon Mitigation System Cost? (2026)," Kristen Cramer, Feb 5, 2026. https://homeguide.com/costs/radon-mitigation-cost
- Angi, "How Much Does a Radon Mitigation System Cost? [2026 Data]," Mitchell Grant, updated Sep 28, 2026. https://www.angi.com/articles/how-much-does-it-cost-remove-radon-gas.htm
- Iowa Administrative Code 641, Chapter 44, Radon Mitigation (ARC 0290D, IAB 5/13/26, effective 7/1/26). https://www.legis.iowa.gov/docs/iac/chapter/641.44.pdf
- U.S. EPA, A Citizen's Guide to Radon, EPA 402/K-12/002 (2025 edition, PDF). https://www.epa.gov/sites/default/files/2016-12/documents/2016_a_citizens_guide_to_radon.pdf