The Vacant-Home Myth: Radon Doesn't "Build Up" Forever
Start with the fear most second-home owners have: the house has been shut for nine months — has radon been piling up the whole time? No. Radon has a half-life of 3.8 days, so indoor levels reach a steady state roughly 12 hours after a home is closed up and then hold there. A house closed for nine months has the same radon level it had after the first half-day. Your vacant home is not a pressure cooker.
Here's the flip side, though: that steady-state level is the level your house actually lives at — and in a sealed, unoccupied home there's no door traffic or ventilation habit diluting it. Whatever the soil under your foundation delivers, that's the air on the lower level when your family walks in for the holidays. Which is why the number is worth knowing, and why how you measure it matters so much.
The Caretaker Mistake That Invalidates Almost Every Second-Home Test
The most common vacant-home testing error in this valley goes like this: the owner asks for a radon test, the caretaker or housekeeper opens the place up first — airs it out, runs the ventilation, gets it guest-ready — and then sets out the test. The result comes back beautifully low, and it's meaningless. The test measured fresh mountain air, not the house.
The correct approach is the EPA's closed-house protocol: windows and exterior doors stay closed for 12 hours before the test starts and for its entire duration. For a vacant home this is actually the easiest test there is — the house is already closed. The instruction to give your property manager is one sentence: don't air it out first; test it as it sits. If the home was recently opened for cleaning, close it back up, wait 12 hours, then start.
Remote Monitoring for Owners Who Are 1,000 Miles Away
A one-time test is a snapshot; radon moves with the seasons, and winter — when the valley's homes are sealed tightest and the ground is snow-covered — is reliably the worst case. For seasonal owners, a continuous radon monitor (roughly $150–$230 retail) is the practical answer: set one on the lower level and read your levels from your phone in Chicago or Houston. You'll see the winter peak, the summer dip, and — if you ever install mitigation — instant confirmation the system is doing its job. We can recommend, place, and baseline a monitor as part of any visit.
Somebody Breathes That Air, Even When You Don't
The "we're only there five weeks a year" calculation misses everyone else in the building: renters on a season lease, short-term guests, the housekeeper who works the lower level weekly, the caretaker who overnights during freeze checks. Radon risk scales with exposure hours, and in a rented or serviced home the hours belong mostly to other people. If the house tests high, that's not just a family-health question — it's a duty-of-care question for everyone your property hosts and employs.
If You Rent It Out: What SB23-206 Requires
Since August 7, 2023, Colorado's SB23-206 puts disclosure duties on landlords: you must disclose known radon information — test results, measured levels, mitigation records — provide the CDPHE radon brochure, and obtain a signed acknowledgment from the tenant. Short-term-rental operators and the property managers who run leases for owners should treat this as part of onboarding paperwork, not an afterthought. Note what the law doesn't require: testing or mitigation. But the practical logic runs ahead of the legal minimum — a documented low test or a mitigation system with a verified number is a far better line in a rental file than "no known information."
For Property Managers: One Call, Whole Portfolio
If you manage ten or forty doors between Aspen and Carbondale, radon is easier to handle as a program than as a scramble: closed-house testing across the portfolio on one schedule, a simple record per property for SB23-206 files, mitigation quotes only where numbers warrant them, and one phone number when an owner or tenant asks a radon question. You look proactive to owners; we handle the technical side; nobody is improvising the week a tenant emails about radon.
The Aspen-Specific Rhythm
Plenty of homes here sit empty nine months a year, and the natural windows for radon work are the shoulder-season close-ups: test as the home is buttoned up in the fall (closed-house conditions arrive free of charge), or during the spring shutdown before summer occupancy. Mitigation installs also fit neatly into vacant weeks — no schedule to work around, and the 48-hour verification test runs in an empty house. If your caretaker handles the close-up checklist, radon takes one line on it.