Radon Testing and Mitigation in Johnstown, CO
Johnstown has changed shape faster than almost anywhere in Northern Colorado, adding residents at roughly 29 percent over five years to reach an estimated 22,294 in 2025, up from 17,303 at the 2020 census. That growth shows up in the master-planned communities spreading across town: 2534 near I-25 and US-34, Thompson River Ranch, Johnstown Farms and The Overlook at Johnstown Farms, Revere at Johnstown, Ledge Rock, and Johnstown Village. Weld County led all Colorado counties in new residents in 2023 to 2024, and a large share of that arrival landed here. A brand-new home, though, is not a radon-free home.
Why radon matters in a fast-growing new-build town
Johnstown is a home-rule municipality that sits primarily in Weld County and extends into Larimer County. Both counties are classified as EPA Radon Zone 1, the highest-potential tier, meaning the predicted average indoor screening level is greater than 4.0 pCi/L. You can see the classification on the EPA map of radon zones. Zone 1 describes the geology of the area, not the reading inside any single house, so a test is the only way to know where your home stands.
The new-construction character of Johnstown deserves a specific note. Many recently built subdivisions include a passive radon rough-in, a stack of pipe run through the slab during construction. That is a good starting point, but a passive rough-in is not a finished, verified system. It does not pull air until a fan is added and the result is confirmed by a test. If you bought in 2534, Revere, or Ledge Rock and assumed the builder handled radon, the responsible next step is still a measurement. Our radon testing page walks through how short-term and long-term tests differ.
The 4.0 pCi/L action level
The EPA action level is 4.0 pCi/L, and the EPA advises fixing a home at 4.0 pCi/L or higher (see what the EPA action level means). Statewide, CDPHE reports that about half of Colorado homes have elevated radon levels, a Colorado figure rather than a Johnstown-specific one. Because radon varies house to house even on the same street, two homes in Johnstown Farms built the same year can read very differently. A high test result is the trigger that moves a household from testing to mitigation.
How the matching works
NoCo Radon Pros is a free matching service, not a contractor. We do not test, we do not install systems, and we never hold a Colorado radon license. Colorado licenses radon measurement and mitigation professionals through the state, and that license belongs to the professional you are matched with, never to this brand. Verify any contractor’s license yourself on the Colorado DORA license lookup.
When you reach out, we connect you with an independent, Colorado-licensed radon professional serving Johnstown. That professional tests first, and if the result is 4.0 pCi/L or higher, discusses a mitigation plan and gives a firm quote. For a new-build home with an existing passive stack, that often means activating the rough-in with a fan, a smaller job than a full retrofit. For an older or crawl-space foundation, the approach differs, and you can read more on our crawl space and basement radon page. Our radon mitigation page covers the common system types.
Cost depends heavily on the foundation. For most Colorado homes a standard sub-slab system runs about $1,000 to $2,500, with roughly $1,500 common. Activating a builder’s passive rough-in, the situation many Johnstown households find themselves in, is usually lighter at about $500 to $800. A crawl-space job can run higher. Because the number turns on what the professional finds under the slab, the honest answer is that you get a real quote after a real look, not before. Our mitigation cost guide lays out the ranges in detail.
Buying, selling, or renting in Johnstown
With so much turnover in Johnstown’s housing market, radon comes up often at closing. Colorado’s disclosure law (C.R.S. 38-35.7-112) requires a bold-faced radon warning in residential real estate contracts and requires sellers to disclose known radon information. If you are on either side of a sale, our guide to selling a house with high radon explains what the statute asks for. Landlords have separate written-disclosure duties under C.R.S. 38-12-803. You can read the full picture in the Colorado radon law guide.
Get matched with a Johnstown radon professional
Whether you are in a 2020s subdivision off US-34 or an older home closer to Old Town, the process is the same: test, review the number against 4.0 pCi/L, and mitigate if needed. Start on our contact page, or first see how we operate on the how we make money page. To compare Johnstown with nearby towns, visit locations.