Radon in Cheyenne Basements

Radon is a naturally occurring radioactive gas produced by uranium decay in soil and rock. It enters buildings through the lowest level and accumulates there. Long-term exposure is a recognised lung cancer risk, which is why it matters more once a basement becomes a bedroom rather than a storage space.

Laramie County carries an EPA Radon Zone 1 designation, the highest of three, which predicts an average indoor screening level above the EPA action level of 4 pCi/L.

Prediction versus measurement

Here is the nuance most pages on this topic skip. The Zone 1 designation is predictive: it is a geological classification, not a survey of local homes. Aggregated results from actual radon tests in Laramie County come in somewhat lower, around 3.3 pCi/L on average.

Both numbers are accurate and they are measuring different things. Neither number should push you toward panic or complacency. What matters is that neighbouring houses can differ by a factor of ten, because radon depends on the specific soil beneath one specific slab and on how that particular building draws air. A county figure — high or low — tells you nothing reliable about your address.

What it does tell you is that testing is clearly worthwhile here.

Testing

A short-term test kit sits in the lowest lived-in level of the house for a few days, under closed-house conditions, then goes to a lab. It costs very little. Longer-term tests run for months and give a better picture of annual average exposure.

Winter is the honest season for testing in Cheyenne. Houses here are sealed tight for months, and heating drives the stack effect that pulls soil gas up through the slab, so readings are typically highest exactly when the house is most closed up. A winter test reflects the realistic worst case, which is what you want to design around.

Cheyenne–Laramie County Public Health publishes radon information for residents and is a sensible independent starting point.

What the numbers mean

• 4 pCi/L and above, the EPA action level. Mitigation is recommended.
• Roughly 2 to 4 pCi/L, the EPA suggests considering mitigation. If the basement is about to become a bedroom, the case is stronger than for a storage space.
• Below 2 pCi/L — generally considered low, though re-testing every few years is sensible because levels change as a house and its ground change.

Why this matters before you finish

Two reasons, and the second is the practical one.

Use changes exposure. An unfinished basement is a place you visit. A finished one is a place someone sleeps for eight hours a night. The same concentration represents a very different exposure once the space is occupied.

Installation is far cheaper during construction. A mitigation system runs a pipe from beneath the slab up through the building and out above the roofline. During a finish, that pipe hides inside a framed chase that was going in anyway. Afterwards, it either runs exposed through your new living space or means opening finished walls. A system costs roughly $700 to $1,300 in Wyoming either way, but the disruption is completely different.

See radon mitigation for how a system works, or full basement finishing for where it fits in the sequence.