Finishing a Basement in Denver? Read This About Radon First

If you're about to finish a basement in Denver, do one thing before you frame a single wall: test for radon. Colorado is one of the highest-radon states in the country, and a basement is exactly where it collects. The good news is that radon is one of the cheapest, most fixable problems a house can have — if you catch it before you close up the walls. Handle it first, and you'll never think about it again. Skip it, and you risk spending real money to open finished space back up later.

Why is radon such a big deal in Denver?

Radon is a naturally occurring radioactive gas that comes from uranium breaking down in the soil and rock beneath your home. Colorado's geology produces a lot of it, and our houses — sealed up and heated for much of the year — pull it inside through cracks, sump pits, and gaps where pipes pass through the slab.

The numbers are genuinely worth knowing. The EPA places most of the Denver metro in Zone 1, its highest radon-potential category, and roughly half of Colorado homes that get tested come back at or above the action level of 4.0 pCi/L (picocuries per liter). Radon is also the second-leading cause of lung cancer overall and the leading cause among people who have never smoked. It's invisible and odorless, which is exactly why testing is the only way to know.

Do I really need to worry about it if I'm just finishing the basement?

This is the part people miss. An unfinished basement is usually storage — somewhere you pop down to grab holiday bins and a furnace filter. A finished basement is a bedroom, a gym, a playroom, a home office. You're taking the room closest to the soil and turning it into the room where someone breathes for hours at a stretch.

That changes the math. Radon concentrates at the lowest level of the house, so the basement is where readings run highest — and finishing it means people will now spend real time in that exact air. It's the single best reason to test before the project starts, not after.

An unfinished basement is storage. A finished one is where your kid sleeps. Test the air before you decide the room is done.

How do I test for radon before finishing?

Testing is easy and inexpensive. You have two routes:

• Short-term test — a charcoal kit or a continuous monitor that runs 2 to 7 days. Fast, cheap, and great for a first read. Colorado's dry climate and big temperature swings can make a single short test bounce around, so treat one as a snapshot, not the final word.
• Long-term test — a detector left in place for 90+ days. It averages out the seasonal swings and gives you the most honest picture of what you're actually living with.

The benchmark to remember is 4.0 pCi/L. At or above that, the EPA recommends mitigation; the agency also notes there's no truly "safe" level, so plenty of Denver homeowners choose to mitigate in the 2–4 range too, especially before adding a bedroom downstairs. Run the test now, while the basement is still open — it's the cleanest moment to find out.

What does radon mitigation actually involve?

Less than you'd think. The proven fix is a system called sub-slab depressurization: a sealed PVC pipe runs from beneath your foundation slab up and out above the roofline, with a quiet inline fan that continuously pulls soil gas out from under the house before it can seep into the room. Cracks and the sump pit get sealed as part of the work so the system can do its job.

It's not a renovation — most systems go in within a day, and a well-designed one routinely brings high readings down below 2.0 pCi/L. Cost-wise it lands somewhere in the range of a few hundred to a couple thousand dollars, which is a rounding error next to the price of cutting into finished drywall, flooring, and built-ins to add one later.

One thing worth saying plainly: sealing cracks alone is not mitigation. It helps, but it doesn't reliably move the number. If a test comes back high, you want an active system, not a tube of caulk.

Should you handle radon before or after finishing the basement?

Before — every time. The right sequence is simple:

• Test the existing basement before design and demo.
• Mitigate if the levels call for it, while everything is still open.
• Finish the space — framing, electrical, drywall, the good stuff.
• Retest once it's done to confirm the system is doing its job in the finished room.

Do it in that order and the whole thing is invisible and cheap. Do it out of order and you're chasing a pipe route through walls that are already painted. This is the same logic behind the other Denver-basement essentials — egress windows, permits, and moisture control — that quietly decide whether a finished basement is actually a good place to be.

Can a radon system be hidden in a finished basement?

Yes — and this is where designing and building under one roof earns its keep. The mistake we see is a mitigation pipe surprise-routed up the corner of a brand-new family room because nobody planned for it. When the system and the finishes are designed together, that pipe disappears into a mechanical chase, a closet, or the wall behind the stairs, and the fan sits somewhere it won't be heard. You get clean air and a room that looks intentional, because the unglamorous parts were drawn in from the start instead of bolted on at the end.

Quick answers

Is radon really worse in Colorado?

Yes. Colorado is one of the highest-radon states in the country, the EPA puts most of the Denver metro in Zone 1, and about half of Colorado homes that get tested come back at or above the 4.0 pCi/L action level.

Can I still finish my basement if it has radon?

Absolutely. You install a mitigation system first, confirm the levels dropped with a retest, then finish the space — so the room is safe before anyone frames a wall.

Does sealing the foundation cracks fix radon?

Not on its own. Sealing helps, but the reliable fix is active sub-slab depressurization — a sealed pipe and a quiet fan that vent radon above the roofline before it reaches the room.

We're The Curated Room, a Denver design and design-build studio that handles the whole project — design, build, and styling — under one roof. That means the boring-but-critical things like radon, moisture, and egress get planned into your basement finish from day one, not discovered halfway through. If you're thinking about turning your lowest level into the best room in the house, come say hello.