Montana Radon Guide for Billings Homeowners (2026)

Updated October 19, 2026. This guide is general information, not legal or engineering advice. Rules change, so confirm with the agency listed before you start work.

Quick reference

Topic	What to know	Source
EPA zone map	County-level only; EPA says test every home regardless of zone	EPA map of radon zones (Montana)
Local test data	2,352 Yellowstone County tests; mean 5.4 pCi/L; 42.4% at or above 4 pCi/L	MSU radon report for Montana DEQ (2006)
Statewide	Roughly half of Montana homes tested are at or above 4 pCi/L	Montana DEQ (2026)
Action level	4 pCi/L; consider fixing from 2 to 4 pCi/L	Montana DEQ; MSU Extension
Mitigator licensing	None in Montana; DEQ suggests NRPP or NRSB certification	Montana DEQ
Contractor registration	Required for construction contractors with employees; verify at (406) 444-7734	Montana Dept. of Labor & Industry
Home sales	Seller must give a radon warning and any known test results (MCA 75-3-606)	Montana Code Annotated
Test kits & help	DEQ Radon Control Program hotline 1-800-546-0483; discounted mail-in kits while supplies last	Montana DEQ
Retesting	Every 2 to 5 years; at least every 2 years with a system	Montana DEQ

How common is high radon around Billings?

Common. A Montana State University report prepared for the state compiled 2,352 radon tests from Yellowstone County homes in its 2005 data. The combined mean was 5.4 pCi/L, 42.4 percent of results were at or above 4 pCi/L, and results ranged up to 182.1 pCi/L. The same report's 1997 data had 787 county tests averaging 4.1 pCi/L, with 35.5 percent at or above 4. These are tests people chose to run, not a random survey, but they show high results are far from rare here.

Statewide, Montana DEQ says roughly half the homes tested are at or above the action level and that the state's geology makes it prone to elevated radon. MSU Extension reports that Montana ranks third in the nation for homes above 20 pCi/L and fifth for homes above 4 pCi/L.

What does the EPA zone map mean for my house?

Very little on its own. The EPA's 1993 radon zone map assigns each county a zone from geology and other county-level data. Montana DEQ notes that elevated levels have been found in all three zones and that the map isn't meant to decide whether a particular home should be tested. Test your own house.

How and when should I test?

Test the lowest occupied floor with the house closed up. MSU Extension describes short-term charcoal kits that run 2 to 7 days and long-term alpha track detectors that run three months to a year; for real estate, the EPA recommends two short-term tests averaged together. Montana DEQ recommends testing again after structural changes or when you start using a lower floor, and retesting every two to five years even after a low result. DEQ's Radon Control Program has offered discounted kits by mail during January's National Radon Action Month, with postage and lab analysis included, while supplies last.

When should I fix it, and how?

The EPA action level is 4 pCi/L, and MSU Extension notes the EPA also suggests considering action between 2 and 4 pCi/L. The usual fix in basement and slab homes is sub-slab depressurization, a pipe and fan that pull soil gas from under the floor and vent it outside. Crawl spaces get sub-membrane depressurization, with a sealed plastic or rubber sheet over the soil and suction underneath.

Who can install a radon system in Montana?

Anyone, legally speaking. Montana's Radon Control Program states that certification is not required under Montana statute, and DEQ says it does not certify or require proof of certification for the contractors on its provider list. DEQ encourages hiring a trained contractor certified by the National Radon Proficiency Program (NRPP) or the National Radon Safety Board (NRSB), collecting at least three written bids, checking insurance and references, and using an independent tester for the post-mitigation test.

Separately, Montana's Department of Labor and Industry requires construction contractors with employees to hold a Construction Contractor Registration. You can confirm a registration is in good standing on the department's website or by calling (406) 444-7734.

What does Montana require when a house is sold?

Montana Code 75-3-606 requires the seller or seller's agent to give the buyer a standard radon warning in a document signed before or with the offer. If the seller knows the building was tested, they must provide the results and any evidence of mitigation. The law doesn't require a test, and it doesn't create a contingency or a right to cancel unless the contract says so.

Common questions

Does Montana license radon mitigation contractors?

No. Montana law doesn't require radon certification, and DEQ doesn't certify contractors. DEQ recommends hiring someone with NRPP or NRSB certification.

Is Billings a high-radon area?

It can be. A 2005 MSU compilation found 42.4 percent of county tests at or above 4 pCi/L. Test every home.

Where can I get a radon test kit in Billings?

Hardware stores sell kits, and Montana DEQ's Radon Control Program has offered discounted mail-in kits. Call 1-800-546-0483 to ask what's available.

Montana radon guide for Billings and Yellowstone County homeowners (2026)