Colorado sits in EPA Zone 1 — the highest radon potential in the country. If your home has a dirt crawlspace, that's the largest opening between the soil and the air you breathe.
Radon is a colorless, odorless radioactive gas produced when uranium in soil and rock breaks down. You cannot see it, smell it, or taste it. It is the second leading cause of lung cancer in the United States and the leading cause among people who have never smoked.
The same geology that built the Front Range produces uranium-bearing rock and soil. Boulder, Gilpin, Clear Creek and Jefferson counties are all designated EPA Zone 1, meaning predicted indoor radon averages above the 4.0 pCi/L action level. This isn't a rare problem here — it's the baseline condition.
Radon moves upward through soil. Any opening where your home touches the ground is a pathway — foundation cracks, utility penetrations, sump pits, and above all, exposed dirt in a crawlspace. A bare-earth crawlspace isn't a small crack; it's an open floor of soil directly beneath your house.
It gets worse from there. Warm air rises and escapes through the upper levels of a house, creating slight negative pressure at the bottom. That vacuum actively draws soil gas up out of the crawlspace and into your living space. The building itself pulls radon inside. This is the stack effect, and it runs strongest in winter — exactly when your windows are closed.
A properly installed, fully sealed vapor barrier puts a continuous membrane between the soil and your home. Seams taped, penetrations sealed, sump lid gasketed, barrier carried up the foundation walls. That meaningfully reduces the pathway soil gas uses to get in, and it's a substantial improvement over open dirt.
But sealing alone is not a mitigation system. A tested active system uses a fan to depressurize the space beneath the barrier and vent that gas above the roofline. Encapsulation reduces entry. Mitigation actively removes the gas. They work together, and the barrier is what any active system depends on to hold suction.
Not every vapor barrier is equal here. Some products publish a radon diffusion coefficient — meaning they've been specifically tested against radon, not just water vapor. We use barrier material appropriate to the situation and will tell you which product is going in your home and what it's rated for.
This is the most cost-effective thing a homeowner can do while a crawlspace is already open.
Before the barrier goes down, we set a suction point in washed gravel beneath where the membrane will sit, run a sealed rigid riser up through the barrier, seal that penetration airtight, and cap it. Then we label it. The port sits there inert.
If a radon test later comes back elevated, a licensed mitigation professional connects a fan and vent stack to that existing port. No cutting into your finished encapsulation. No re-excavating gravel. No tearing up a sealed barrier you just paid for. Roughing it in during the work costs a small fraction of retrofitting it afterward.
Radon mitigation is a licensed profession in Colorado. Installing an active system — fans and vent stacks — requires state licensure through DORA. Caribou Construction is currently in the process of obtaining that license. Until it's in hand, we install radon-ready rough-ins and radon-rated barriers as part of construction work, and we refer active mitigation to licensed professionals. We'd rather be straight with you about that than take on work we aren't yet licensed to perform.
Yes. Colorado has some of the highest radon potential in the country. A large share of the state — including Boulder, Gilpin, Clear Creek and Jefferson counties — sits in EPA Zone 1, the highest-risk designation. The geology that gives us the mountains also produces uranium in the soil, and radon is what it decays into. The EPA action level is 4.0 pCi/L, and a significant percentage of Colorado homes test above it.
Radon is a soil gas. It moves up through the ground and enters a home through any opening in contact with the earth — and a crawlspace with exposed dirt is the largest possible opening. Warm air rising in the house creates a slight vacuum at the bottom, which actively pulls soil gas up out of the crawlspace and into the living space. That's called the stack effect.
A continuous, properly sealed vapor barrier significantly reduces soil gas entry by putting a physical membrane between the earth and your home. It's not a substitute for a tested mitigation system, but it's a meaningful improvement over exposed soil — and it's the foundation any future active system would be built on.
While your crawlspace is open, we install a suction point in gravel beneath the vapor barrier, run a sealed riser up through the barrier, and cap it. That port sits there doing nothing until it's needed. If a later radon test comes back elevated, a licensed radon mitigation professional can connect a fan and vent stack to it without cutting into your finished encapsulation. Doing it during construction costs a fraction of retrofitting it later.
Not currently. Radon mitigation is a licensed profession in Colorado, and installing an active system — fans, vent stacks, and the rest — requires a state license through DORA. We are in the process of obtaining that licensure. In the meantime we install radon-ready rough-ins and radon-rated barriers as part of construction, and we refer active mitigation work to licensed professionals. We'd rather tell you that plainly than take work we aren't yet licensed for.
Short-term test kits are inexpensive and widely available, and reusable digital monitors run around $150. Test in the lowest lived-in level of the home, with windows and doors closed, for the duration the kit specifies. If a short-term test comes back at or above 4.0 pCi/L, follow up with a longer test or a licensed professional measurement.
Sealed encapsulation and radon-ready rough-ins for homes in Nederland, Boulder, Black Hawk, Central City, Idaho Springs, Evergreen, Conifer, Golden, Arvada, Westminster and the surrounding foothills.
See also: Crawlspace Encapsulation · Project Gallery · Nederland, CO · Boulder, CO
It costs very little while the space is open and saves thousands if you ever need a system.
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