Radon Testing When Buying a Home

Radon testing is one of the most overlooked steps in the home buying process. Unlike a leaky roof or a cracked foundation, radon is invisible and odorless — you can't detect it during a walkthrough. Yet it's the second leading cause of lung cancer in the United States, responsible for an estimated 21,000 deaths per year.

When to Test

The best time to test for radon is during the home inspection period, before you close on the purchase. Most home inspectors can add radon testing to their inspection for $125–$250 extra. They use continuous radon monitors (CRMs) that record hour-by-hour readings over 48 hours, providing reliable results that are tamper-resistant.

If the home has a basement or is slab-on-grade, radon testing is especially important. These construction types have the most direct contact with the soil where radon originates. Homes with crawl spaces can also have elevated levels if the crawl space isn't properly ventilated.

What the Results Mean

The EPA's action level is 4 pCi/L. If the test comes back at or above this level, the EPA recommends taking action. Here's how to interpret results:

• Below 2 pCi/L: Low risk. No action needed.
• 2–4 pCi/L: Moderate. The EPA suggests considering mitigation, especially if you plan to use the lowest level of the home.
• 4 pCi/L or higher: Above the EPA action level. Mitigation is recommended.
• 8 pCi/L or higher: Significantly elevated. Prioritize mitigation before or shortly after move-in.

Negotiating Mitigation

An elevated radon reading is not a reason to walk away from a home. Radon mitigation systems are straightforward and highly effective, typically reducing levels by 80–99%. The cost ranges from $800 to $2,500 for a standard sub-slab depressurization system.

Common negotiation approaches:

• Seller pays for mitigation before closing — the most common arrangement
• Price reduction to cover mitigation costs — gives the buyer control over the contractor
• Escrow holdback — funds are held in escrow until mitigation is completed post-closing

A mitigation system is a permanent improvement to the home. Once installed, it continuously draws radon from beneath the foundation and vents it above the roofline, typically running on a small fan that costs $50–$100 per year in electricity.

State Disclosure Requirements

Radon disclosure laws vary by state. Some states require sellers to disclose known radon test results or the presence of a mitigation system. Others have no specific radon disclosure requirements. Regardless of state law, you can always request a radon test as a condition of your offer.

New Construction

If you're buying new construction, ask whether radon-resistant features were included. The EPA recommends radon-resistant new construction (RRNC) in Zone 1 and Zone 2 areas. These features — a gas-permeable layer under the slab, a vapor barrier, sealed cracks, and a vent pipe to the roof — add only $350–$500 during construction and are far cheaper than retrofitting later.