Radon Disclosures in Colorado: Longmont Seller Guide

Worried a buyer’s radon test could derail your Longmont sale at the last minute? You are not alone. Many Colorado sellers face radon questions during inspection, and the uncertainty can lead to stress, delays, or price cuts. In this guide, you will learn what to disclose, how to test and document results, and how to handle mitigation so you can protect your timeline and your bottom line. Let’s dive in.

Why radon matters in Longmont

Longmont and greater Boulder County sit in a high radon potential area. The Environmental Protection Agency recommends taking action when indoor levels reach 4 pCi/L or higher. You can review the fundamentals in the EPA’s overview of radon, testing, and mitigation, including the 4 pCi/L action level, in the EPA’s guidance on radon and the 4 pCi/L action level.

Colorado maintains an active radon program with consumer guidance on testing and mitigation. You can find statewide resources from the Colorado Department of Public Health and Environment. Locally, Boulder County Public Health and the City of Longmont also share radon education and helpful contacts.

What Colorado sellers must disclose

In Colorado, sellers generally complete a written disclosure about known material conditions for residential sales. If you know about prior radon test results, have an installed mitigation system, or are aware of radon issues, you should disclose those facts to buyers. For precise legal obligations and the required form language, consult the Colorado Division of Real Estate or speak with your real estate broker or attorney.

Even though radon testing is not uniformly mandatory before a sale, failing to disclose known results or an existing mitigation system can create post closing disputes. Proactive testing and clear documentation reduce renegotiation risk and build buyer confidence.

A smart pre listing plan

A pre listing plan helps you avoid surprises during inspection and supports a smoother negotiation.

Choose the right test

• Short term tests: Run for 2 to 7 days. These are common in transactions because they are fast and affordable, but results can be influenced by weather and ventilation.
• Long term tests: Run for 90 or more days. These better capture seasonal and daily variation and give a stronger picture of year round average levels.
• Continuous radon monitors: These devices record hourly data and are often preferred in transactions because they provide detailed logs and defensible results. Learn more about test types and best practices from the Colorado Department of Public Health and Environment.

Decide who will perform the test

You can use a homeowner kit that is analyzed by an accredited lab or you can hire a qualified measurement professional. For transaction reliability, many buyers and agents prefer tests performed by certified testers who use continuous monitors. You can find credentialed professionals through the National Radon Proficiency Program and the National Radon Safety Board.

Gather documentation from the start

Keep a clean paper trail so you can hand buyers a complete packet.

• Full test report, including device type, device ID if applicable, lab or tester name, start and end dates and times, exact test locations, measured concentration, and lab analysis or certification.
• Chain of custody or lab receipt for homeowner kits.
• Tester credentials if a professional performed the test, including NRPP or NRSB certification and the method used.
• All results if multiple test devices or locations were used, plus a note clarifying which result was used to decide on mitigation.

If results are 4 pCi/L or higher

If your pre listing test shows 4 pCi/L or higher, you have options. The cleanest path is to mitigate before listing or early in your contract timeline, then retest and share the results with buyers.

Mitigation basics

The most common and effective approach is active soil depressurization. A fan and vent piping pull radon from beneath the home and exhaust it outdoors. The goal is to reduce indoor levels below the EPA action level. Review the EPA’s mitigation guidance for an overview of system types and performance expectations.

Permits and inspections in Longmont

Before installation, check City of Longmont Building Services for any permit requirements related to vent penetrations, electrical connections, or exterior terminations. Having clear permits and, when applicable, final inspections in your packet reassures buyers and reduces scrutiny during inspection.

Retesting after mitigation

Once the mitigator confirms the system is running, do a follow up test to verify results.

• Timing: Allow the system to operate for at least 24 to 48 hours before starting a short term retest. Many professionals prefer 48 to 72 hours and a continuous radon monitor with hourly data for a minimum of 48 hours.
• Method: Use a continuous radon monitor or a certified tester for post mitigation verification in a transaction.
• Best practice: If time allows outside a transaction, a 90 day long term test can confirm year round performance.

What to give the buyer after mitigation

• Mitigator’s certificate with system type, installation date, a simple diagram, and initial performance notes.
• Photos of the fan location, pipe routing, and exterior exhaust termination.
• Warranty or guarantee paperwork and any maintenance instructions.
• Post mitigation test report with device type, dates, and measured results.
• Permit documents and final inspection sign offs if required by the city.

Reduce renegotiation risk

A clear process and complete documentation help you keep leverage during inspection and appraisal.

Smart contract timelines

If a test finds elevated levels and you will mitigate, use specific timelines to set expectations.

• Obtain bids within 7 to 10 business days of receiving the test result.
• Complete mitigation within 14 to 21 days of contract acceptance, or agree on an extension if needed.
• Provide post mitigation verification within 3 to 7 days of completion, depending on the test method used.

If the buyer plans to test during the inspection window, define acceptable devices or methods and clarify who will pay for retesting or mitigation if the threshold is exceeded.

Credits vs doing the work

You can offer a credit or price concession instead of installing a system yourself. If you choose this route, base the amount on written bids from certified mitigators and include that information in your disclosures. Many sellers prefer to mitigate before listing or early in escrow since completed work, verified results, and warranties reduce buyer uncertainty and limit last minute negotiations.

Your documentation checklist

Use this list to prepare a buyer ready packet for your disclosures and MLS.

• Original test report or reports with complete details and lab or tester credentials.
• Chain of custody and lab receipt, if you used a homeowner kit.
• If you mitigated: contractor invoice and contact info, system description, photos, warranty paperwork, post mitigation test report, and any permits or inspection sign offs.
• Written seller disclosure that clearly states known radon test results, any mitigation history, and relevant dates.
• Device calibration or lab certificates if available.

Common pitfalls to avoid

• Incomplete test reports that omit device type, dates, or lab signatures.
• Homeowner kits with no lab receipt or chain of custody details.
• No post mitigation verification after a system is installed.
• Undisclosed prior test results or undocumented mitigation work.

Local resources for Longmont sellers

• EPA radon basics and mitigation guidance. Start with the EPA’s radon information hub.
• Colorado Department of Public Health and Environment radon program. Find statewide guidance and links to certified professionals.
• Boulder County Public Health radon information. Access local education, potential test kit programs, and community contacts.
• City of Longmont Building Services. Confirm permit requirements related to radon system installation.
• Professional lists and standards. Search credentialed pros through the National Radon Proficiency Program and the National Radon Safety Board, and review standards and guidance from AARST.

Action plan before you list

1. Gather any prior radon reports or mitigation documents you already have. Save originals.
2. Order a pre listing radon test. If time allows, run a long term test. If you need results quickly, schedule a continuous monitor test with a certified professional.
3. If results are 4 pCi/L or higher, get two or three bids from certified mitigators and decide whether you will mitigate before listing, offer a credit, or negotiate terms in a contract.
4. After mitigation, verify performance with a follow up test and collect the mitigator’s documentation and warranty.
5. Check permit needs with the City of Longmont for any roof or wall penetrations and electrical work.
6. Work with your listing agent to include the test and mitigation documents in your disclosures and MLS so buyers see complete, credible information up front.

Final thoughts

You do not have to guess your way through radon when selling in Longmont. A simple plan that includes pre listing testing, clear disclosures, and complete documentation can reduce inspection friction and help you protect your price and timeline. If you want a tailored strategy for your home, reach out for guidance on planning, disclosures, and buyer expectations.

Ready to price your home and map your next steps? Get Your Home Valuation with Megan Beck to start a confident, well planned sale.

FAQs

Do Colorado home sellers have to test for radon before listing?

• Colorado does not uniformly require testing before a sale. You must disclose known radon facts and prior results. Pre listing testing is strongly recommended to avoid last minute renegotiation.

What radon level triggers action in a Longmont sale?

• The EPA recommends taking action at 4 pCi/L or higher. Many buyers and professionals use 4 pCi/L as the transactional threshold, although contracts can specify terms.

Who pays for radon mitigation in a Colorado transaction?

• It depends on the deal. Common approaches include the seller mitigating before listing, the buyer requesting mitigation after inspection, or a negotiated credit. Spell out responsibilities in the contract.

How should you retest after a mitigation system is installed?

• Allow the system to run for at least 24 to 48 hours, then use a continuous radon monitor or a certified tester for a follow up short term test. In non urgent situations, a 90 day long term test provides strong confirmation.

What documentation should I give the buyer about radon?

• Provide complete test reports, the mitigator’s certificate and warranty if installed, post mitigation test results, photos, and any permits or final inspections. Include a clear radon section in your seller disclosure.

Where can I find certified radon pros near Longmont?

• Search for credentialed testers and mitigators through NRPP and NRSB. You can also consult CDPHE and Boulder County Public Health for guidance and local contacts.