Montana has among the highest radon levels in the western United States, with an estimated statewide average around 5.7 pCi/L and approximately 45% of Montana homes testing above the EPA action level. Montana’s geology — including granitic batholiths, uranium-bearing rock formations, and glacial deposits — creates high radon potential across much of the state. Every Montana county is designated Zone 1 or Zone 2 by EPA.
EPA Radon Zone Designation
Montana is predominantly EPA Radon Zone 1. Most Montana counties are Zone 1. The highest-radon areas are concentrated in western Montana where granitic rock formations (including the Boulder, Idaho, and Bitterroot batholiths) produce significant uranium and radon. Central Montana counties overlying shale formations also show elevated levels.
Radon Contractor Licensing in Montana
Montana requires radon contractors to hold current NRPP or NRSB national certification. Montana’s radon program is administered through the Montana Department of Environmental Quality. Montana does not have a separate state radon contractor licensing statute beyond the national certification requirement. The DEQ provides resources on radon testing and maintains information on certified professionals. Verify contractor credentials directly at nrpp.info or nrsb.org.
Radon Disclosure Requirements in Montana
Montana’s real estate disclosure requirements include the Montana Residential Property Disclosure Act, which requires sellers to disclose known material defects. Elevated radon is a known material condition that sellers should disclose under this general duty. Montana does not have a radon-specific disclosure statute, but the standard Montana real estate disclosure form includes questions about environmental conditions. Buyers should include radon contingencies in purchase offers and conduct independent testing.
Radon-Resistant New Construction (RRNC) in Montana
Montana does not have a statewide RRNC mandate for new construction. However, given Montana’s high radon prevalence and Zone 1 designation across most of the state, EPA and MDEQ strongly recommend RRNC for all new Montana residential construction. Some Montana municipalities may have adopted local RRNC requirements. Buyers of new Montana construction should request RRNC features — the incremental cost during construction is minimal compared to post-construction remediation.
Highest-Radon Counties and Areas in Montana
Western Montana counties overlying granitic batholiths have the highest radon levels in the state: Missoula, Ravalli, Mineral, Sanders, and Powell counties in the western region. Cascade County (Great Falls) and Lewis and Clark County (Helena) in central Montana also show elevated levels. The MDEQ publishes county-level radon data from testing surveys.
Testing Resources for Montana Residents
The Montana Department of Environmental Quality administers the state radon program and provides resources for homeowners including lists of certified contractors, low-cost or free test kit programs (availability varies by year and funding), and technical guidance on radon mitigation. Contact the state radon program directly for the most current contractor list, any available test kit distribution programs, and jurisdiction-specific requirements that may have changed since this page was last updated.
Frequently Asked Questions
Is Montana a high-radon state?
Yes. Montana has among the highest radon levels in the western U.S., with an estimated average of 5.7 pCi/L and approximately 45% of homes above the EPA action level. All Montana residents should test their homes.
Does Montana require radon contractor licensing?
Montana requires NRPP or NRSB national certification. There is no separate Montana-specific licensing. Verify contractor credentials at nrpp.info or nrsb.org before hiring.
What parts of Montana have the highest radon?
Western Montana counties overlying granitic batholiths — including Missoula, Ravalli, Mineral, Sanders, and Powell counties — have the highest concentrations. Central Montana counties also show elevated levels.
Leave a Reply