Radon in Montana: The Hidden Risk New Homes Need to Prepare For
Radon is something most homeowners do not think about until an inspector brings it up or a neighbor mentions it, but in Montana it is common enough that it should be part of your building plan from day one. After building homes all over the Helena Valley, I can tell you firsthand that radon is simple to prepare for during construction and far more complicated to fix once the home is finished.
If your new home will sit on a crawl space foundation, understanding how radon works and how to prevent it is a crucial part of building a safe, healthy, long lasting home in Montana.
Why Radon Is So Common in Montana
Radon is a naturally occurring radioactive gas produced by uranium in the soil. You cannot see it or smell it, but it can move into your home through the ground if you do not plan ahead.
Montana consistently ranks among the highest radon states in the country because of our geology. Around the Helena Valley, radon levels tend to be elevated due to:
Rocky and fractured soil
Tight modern construction that traps air
Cold air settling into valleys
Limited natural ventilation in winter
All of this makes radon planning an important part of new home construction here.
How Radon Enters a Home
Radon moves upward through the soil and enters homes through:
Exposed crawl space soil
Small cracks in foundation walls
Gaps around plumbing
Pipe penetrations
Any unsealed openings under the home
Once radon collects in the crawl space, it can rise into the living space through the floor system.
Why Crawl Spaces Need Special Radon Planning
Crawl spaces have a large amount of exposed soil unless they are sealed correctly. A vented or unfinished crawl allows radon to accumulate under the home, especially in winter when airflow decreases and warm air rising through the home naturally pulls air from the crawl space upward.
This is why modern building practice in Montana has shifted toward sealed, conditioned crawl spaces and radon ready venting installed during construction.
How We Prepare New Homes for Radon
Here is how we build crawl space homes so they are ready for radon mitigation long before the first radon test ever happens.
Full Vapor Barrier Over the Crawl Space Floor
We install a durable vapor barrier across the entire crawl space floor and seal it at all edges and around every pipe penetration. This controls moisture, isolates the living space from the soil below, and is the foundation of good radon prevention.
Every Home Is Built Radon Ready
On every project, we make the home radon ready, no matter what future testing shows. That means we install a vertical radon vent pipe during construction that runs from the crawl space up through the mechanical area and exits through the roof.
The home does not have a full mitigation system at this point, but all the expensive, invasive work is already done upfront.
Passive System by Default
Because the vent line is installed during construction, every new home starts out with a passive radon setup. Natural upward airflow helps vent soil gases outdoors.
How the System Becomes Fully Active If Ever Needed
If future radon testing shows elevated levels, upgrading the radon ready system to a fully active mitigation system is simple.
To activate it, we would:
Install a small inline radon fan on the existing vent pipe
Add a perforated pipe system in the crawl space beneath the vapor barrier to help collect radon gas more efficiently
Because the home already has the vent line in place, adding the perforated pipe and a fan does not require tearing into walls or reworking the structure.
Sealing the Crawl Space
We seal gaps around plumbing, wiring, and penetrations. This improves radon control and boosts overall efficiency and moisture protection.
Post Construction Radon Testing
Even with a radon ready vent installed, testing the home after construction is important. Radon test kits are inexpensive and give you peace of mind. Most sealed crawl homes with passive venting already fall well within safe levels.
Why This Matters for Montana Homeowners
Radon is extremely common in Montana, but it is also one of the easiest issues to manage if you handle it during construction. By installing a radon ready vent line and designing a proper sealed crawl, you protect your family and avoid expensive retrofits.
Final Thoughts
Building a home in Montana means planning for our real local conditions, not just design choices. Radon is part of our landscape here, and the best time to prepare for it is before the home is finished.
If you want help planning a radon ready crawl space or want to go over your site conditions before building, contact us for a free pre build consultation. We will walk you through crawl space design, radon ready venting, and everything needed to keep your Montana home safe and built the right way.
