Most homebuyers approach radon as a single event — the inspection test — rather than as a multi-stage evaluation that starts before the offer and continues through closing. A buyer who only thinks about radon when the 48-hour charcoal canister comes back at 6.0 pCi/L is already in reactive mode. A buyer who works through the following 12-point checklist from the start controls the process and avoids the most common radon-related transaction failures.
Before Making an Offer
1. Check the EPA Radon Zone for the County
Before making any offer on a home with a ground-contact foundation, know the EPA radon zone designation for the county. Zone 1 means the county has the highest predicted radon potential (predicted average above 4.0 pCi/L); Zone 2 is moderate; Zone 3 is lowest. Zone designation does not predict your specific home’s level — every home must be tested — but it calibrates expectations and informs how aggressively to negotiate contingency terms. The EPA radon zone map is searchable at epa.gov/radon by state and county.
2. Ask the Seller for Prior Radon Test Results
In states with radon disclosure requirements, sellers are obligated to provide known test results. In all states, you can request them. Useful questions to ask before or at offer time: Has the property ever been tested for radon? When was the most recent test, and what were the results? Is a radon mitigation system installed? Have results ever exceeded 4.0 pCi/L?
A seller who cannot or will not answer these questions is not necessarily hiding something — many sellers genuinely do not know. But a seller who provides documentation of a recent clean test (below 2.0 pCi/L within the last two years) has removed a significant uncertainty from your due diligence.
3. Include a Radon Contingency in Your Offer
A radon contingency must be in the initial offer — you typically cannot add it after the fact once the contract is signed. The contingency should specify the action level threshold (typically 4.0 pCi/L), the testing protocol (certified professional, 48-hour short-term test, closed-house conditions), the available remedies if elevated (seller installs, seller credits, buyer terminates), and post-mitigation testing requirements. See our full radon contingency guide for complete language.
During the Inspection Period
4. Schedule Radon Testing with a Certified Professional
Order a radon test immediately when the inspection period begins — do not wait until other inspection results are in. Radon testing takes 48 hours minimum and results take 3–7 business days to return from the lab (or 48–96 hours for on-site professional continuous monitors). In a 7–10 day inspection period, there is no time to spare. Use an NRPP- or NRSB-certified measurement professional, or a state-licensed professional in states with licensing requirements. In some states, real estate radon tests must be conducted by certified professionals.
5. Confirm Closed-House Conditions
Closed-house conditions must be maintained for 12 hours before and throughout the radon test — all windows and exterior doors closed, no whole-house fans. Coordinate with the seller’s agent to ensure the home will be in closed-house conditions when the test device is placed. A test conducted without closed-house conditions may produce artificially low results. Note whether the seller cooperated with closed-house requirements — a seller who opens windows during the test period has compromised the result.
6. Inspect Any Existing Mitigation System
If a mitigation system is already present, inspect it during the home inspection. Items to check:
- U-tube manometer: The liquid column should be displaced (one side higher), indicating the fan is creating negative pressure. A level liquid column means the fan is off or failed.
- Fan location: Fan should be in unconditioned space — attic, exterior, or garage. A fan located in finished living space may violate AARST standards.
- Pipe integrity: Visible PVC pipe should be uncracked, all joints cemented (not dry-fitted). Pipe should be clearly labeled as a radon reduction system.
- Required labeling: The pipe should have a label identifying it as a radon reduction system with the installer’s credentials and installation date.
- Discharge location: Confirm the discharge terminates above the roofline and not near windows or doors.
7. Request Mitigation Documentation
For homes with existing mitigation systems, request the complete documentation package: installer’s name, license number, and certification; installation date; system specifications (fan model, suction point location); pre-mitigation radon level; post-mitigation test result; and any warranty documents. This documentation is your evidence that the system was properly installed and that the radon problem was confirmed and addressed — not just that a pipe was installed without a documented result.
After Receiving Test Results
8. Interpret Results Correctly
Understand what your result means before responding to the seller. A result below 2.0 pCi/L: no action needed, retest in 2 years. Between 2.0 and 3.9 pCi/L: consider mitigation — especially with young children or smokers. At or above 4.0 pCi/L: EPA recommends mitigation; exercise your contingency. At or above 8.0 pCi/L: mitigate without waiting for confirmatory testing. A single short-term test in the 4.0–8.0 pCi/L range can be confirmed with a second test if timeline allows, but it is not required before proceeding.
9. Get a Mitigation Quote Before Submitting Your Response
Before notifying the seller that results are elevated, contact a certified local mitigator and obtain a written quote. This takes 24–48 hours in most markets and grounds your remedy request in real numbers. A buyer who requests a $3,500 credit for a job that costs $1,200 is not negotiating in good faith and may damage the transaction. A buyer who provides the seller with the actual mitigation quote and requests that amount as a credit — or asks for seller-installed mitigation at that cost — is negotiating transparently and efficiently.
10. Negotiate the Right Remedy for Your Situation
Choose between seller-installed mitigation and a closing cost credit based on your priorities:
- Seller-installed: Best when closing timeline allows (10+ days for installation and post-mitigation testing) and you want confirmed post-mitigation results before you own the home. Requires specifying that closing is contingent on post-mitigation results below threshold.
- Closing cost credit: Best when closing timeline is tight or you prefer to control contractor selection. You receive the credit and arrange mitigation after closing. Risk: you own the home during the mitigation process and results are not confirmed before closing.
Before Closing
11. Verify Post-Mitigation Test Results Before Closing
If the seller installed a mitigation system, confirm that post-mitigation test results are in hand and below the contract threshold before closing. Do not close on a promise that results will be below threshold — results must be confirmed. The post-mitigation test should be conducted by a certified professional independent of the installing contractor, and results should be provided to you at least 2–3 business days before closing to allow for review.
12. Obtain Complete Mitigation Documentation Before Closing
Before signing closing documents, confirm receipt of: the contractor’s license number and certification credentials; the installation date and system specifications; the pre-mitigation radon level; the post-mitigation test result and the certified professional’s report; and any manufacturer warranty documentation for the fan. This documentation packet serves two purposes: it confirms the problem was properly addressed, and it provides the disclosure documentation you will need when you eventually sell the home. A buyer who closes without this documentation may face difficulty proving the radon issue was resolved when they become the seller.
Frequently Asked Questions
Do I need a radon inspection for every home I buy?
For any home with a ground-contact foundation — basement, crawl space, or slab-on-grade — yes. This covers virtually all single-family homes and ground-floor condominiums. Upper-floor condominium units above the second floor have lower radon risk and testing is optional, though not unreasonable. There is no home type where radon testing carries a downside — the cost is minimal and the information is material.
What if I forget to include a radon contingency in my offer?
You may be able to add one through an amendment if the seller agrees, but sellers are under no obligation to accept an amendment adding a contingency after the contract is signed. If you discover elevated radon during inspection and have no contingency, your options are limited: negotiate informally with the seller (who has no contractual obligation to remediate), or walk away and forfeit your earnest money. Prevention — including the contingency in the initial offer — is far preferable.
What should I look for when checking an existing radon mitigation system?
Check six things: (1) U-tube manometer shows displaced liquid (fan is running); (2) fan is in unconditioned space (attic, exterior, or garage); (3) pipe is labeled as a radon reduction system; (4) visible pipe and joints are intact and cemented; (5) discharge terminates above the roofline; (6) complete documentation — installer credentials, installation date, pre- and post-mitigation test results — is available. A system that passes all six checks is operating correctly and has a documented history.
Should I still test if the home already has a mitigation system?
Yes, always. A system installed 5–10 years ago may have a declining fan, new entry pathways from foundation settling, or incomplete coverage from design changes made to the home (finished basement, addition). Request post-mitigation documentation from the seller and conduct an independent current test during the inspection period. The test confirms the system is currently performing — not just that it was installed at some point in the past.
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