Radon Testing During Real Estate Transactions

Testing during a Colorado real estate transaction follows different rules than testing your own home. The result has to be defensible to a buyer's lender, the seller, and potentially an attorney. The method matters more, the tester's credentials matter more, and Colorado has a specific disclosure law that controls what the seller has to share.

This page walks through SB23-206 (Colorado's mandatory radon disclosure law), the test methodology that's standard for real estate, who can place a test, how the inspection objection process works, and what happens when the result comes back high.

Effective August 7, 2023, Colorado law (SB23-206, codified at CRS § 38-35.7-112) requires sellers of residential property to provide buyers with:^[1]

• Any known prior radon test results for the property.
• Documentation of any radon mitigation work that has been performed.
• The CDPHE radon brochure.

The law applies to both sales and residential leases. It does not require sellers to test or mitigate — only to disclose what they already know. The disclosure is delivered through the Seller's Property Disclosure form (revised by the Colorado Real Estate Commission post-SB23-206).^[2]

What this means in practice:

• If the seller had a prior test, you should see the result in the SPD form before you go under contract.
• If the seller had mitigation done, you should have the system documentation and post-mitigation test result.
• If you discover elevated radon during inspection that wasn't disclosed, and the seller knew about a prior test, that's a fact pattern worth showing your real estate attorney.
• If you mitigate after closing, the system becomes your required disclosure when you eventually sell.

Real-estate testing almost always uses a professional continuous radon monitor (CRM) placed by a DORA-licensed, NRPP or NRSB certified tester.^[3] The reasons:

• Defensibility. The result must hold up if the seller, buyer, or lender disputes it. CRMs record hourly readings, time-stamp the data, and produce a written report on lab letterhead.
• Anti-tampering. CRMs detect closed-house violations and movement. If a window is opened during the test or the monitor is moved, the hourly data shows it.
• Speed. CRMs typically run for 48 hours and produce results in 48–72 hours total. That fits a standard Colorado inspection objection window.
• Standard professional practice. The Colorado Association of Realtors and Pikes Peak Association of Realtors treat CRM results as the standard.

Cost: $150–$300 in Colorado Springs. Usually paid by the buyer as part of inspection costs, though it can be negotiated.

Colorado is one of the few states with state-level radon professional licensing. To place a real-estate-grade radon test in Colorado, the tester must:

• Hold a current DORA radon measurement license (Office of Radon Professionals, 4 CCR 754-1).^[3]
• Hold a current NRPP or NRSB measurement certification.^[4]
• Use an EPA-listed or AARST-certified continuous radon monitor.
• Follow AARST measurement standards (MAH or MS-MAH for residential).

Many Colorado home inspectors are also licensed radon testers — the credentials stack. If your inspector isn't a licensed tester, they should refer to one. Don't accept a real estate radon test from anyone who can't provide both DORA and NRPP/NRSB credentials.

A typical Colorado real estate timeline for radon:

The buyer's options under the inspection objection are covered on the real-estate-deadlines cost page.

If the seller's disclosure shows a prior mitigation system, the buyer should verify a few things before relying on it:

• Post-mitigation test result. What was the system's verified outcome? It should be below 4.0 pCi/L.
• System age. Fans typically last 5+ years. A 10-year-old fan may be nearing replacement.
• Manometer condition. Look at the system. The manometer columns should be at different levels (system pulling vacuum). If they're equal, the fan isn't running.
• System documentation. The seller should have the contractor's invoice, system certification, DORA license info, and post-mit test result.
• Re-test the home. Run a current short-term test during the inspection period to confirm the existing system is still bringing levels below 4.0 pCi/L.

Most Colorado sellers honestly haven't tested. In that case the disclosure says "no known test result." The buyer's typical move:

1. Include a radon test in the inspection (most Colorado home inspectors offer this as an add-on).
2. If the result is above 4.0 pCi/L, file an inspection objection and proceed through the buyer-options process.
3. If the result is below 4.0 pCi/L but above 2.0, decide whether to ask for a credit anyway (some buyers do; this is a negotiation issue, not a legal one).
4. If the result is below 2.0 pCi/L, the home is fine for now. Plan to retest every 2 years after closing.

CRMs include tamper detection because real estate testing has a long history of attempts (usually by sellers) to bias the result. Common signs the tester will flag:

• Hourly data shows a sudden drop coinciding with window operation.
• Sustained spikes that look like the test was moved closer to a soil-gas source.
• Temperature or humidity changes inconsistent with normal home conditions.
• Motion-detected disturbance of the monitor.

A flagged test should be re-run. The cost of the second test is typically the seller's if tampering is documented; it's the buyer's otherwise.