Radon rarely comes up in casual conversation about buying or selling a house, but it’s one of the details that can quietly derail a closing timeline if it isn’t handled early. Radon is a colorless, odorless gas that forms naturally as uranium breaks down in soil and rock, and it seeps into homes through foundation cracks, sump pits, and construction joints. Maryland has a meaningful radon presence statewide, with several counties falling into the EPA’s highest risk zone, which is exactly why radon testing for home sale maryland has become a standard part of most real estate transactions in the state, even where it isn’t legally required.
Whether you’re preparing to list a home or under contract to buy one, understanding how radon testing fits into a Maryland real estate transaction, what the results mean, and what happens if levels come back elevated, can save you from last-minute surprises during the inspection contingency window.
Is Radon Testing Required to Sell a Home in Maryland?
Statewide, Maryland does not legally require radon testing before a home can be sold. However, the Maryland Radon Awareness Act, in effect since January 2018, requires sellers to disclose any existing radon test results to potential buyers. This means if a home has already been tested and the results show elevated levels, that information must be shared, even though the law doesn’t force a seller to test in the first place if no test has ever been performed.
Montgomery County is the notable exception. Since October 2016, county law has required that a single-family home or townhome be tested for radon before completing a sale, with the test result no older than one year at settlement. If the buyer doesn’t arrange the test, responsibility falls to the seller to provide one before closing. A handful of exemptions apply, including certain foreclosure sales, transfers between family trusts, and properties in a few specific municipalities, but for most typical residential sales in the county, the requirement stands.
Outside Montgomery County, radon testing is technically optional, but in practice, the overwhelming majority of purchase contracts in Maryland include a radon testing contingency, largely because both real estate agents and lenders treat it as standard due diligence.
How the Radon Contingency Works
Most Maryland purchase contracts include a radon inspection contingency, giving the buyer a defined window, often just a day or two after contract ratification, to arrange testing at their own expense. The standard approach uses a certified radon testing company to place a continuous radon monitor in the home for 48 hours under closed-house conditions, meaning windows and exterior doors stay shut to get an accurate reading. Results are typically available within 24 to 72 hours after the monitor is retrieved.
If the average reading comes back at or above the EPA’s action level of 4.0 pCi/L, the buyer generally has options within the inspection contingency period: request that the seller install a mitigation system before closing, negotiate a credit toward the buyer’s own mitigation costs after closing, or, in some cases, walk away from the contract if a resolution can’t be reached. Once the contingency deadline passes without a negotiated addendum, the property is typically accepted in its current condition, which is why timing the test early in the process matters.
Why DIY Test Kits Aren’t the Right Choice for a Real Estate Transaction
A store-bought radon kit might seem like a faster, cheaper option, but most real estate contracts specifically call for testing performed by a certified professional using EPA-approved protocols and continuous monitoring equipment. DIY kits aren’t held to the same placement and duration standards, and results from them are often not accepted as valid for contingency purposes. If a DIY test is used and later disputed, it can mean redoing the test entirely, costing more time during an already tight contingency window.
Professional testing also produces documented, dated results that both parties can rely on, which matters if the numbers end up factoring into repair credits or price negotiations later in the transaction. You can see how a professional test is conducted on our radon testing services page.
What Sellers Should Consider Before Listing
Sellers in Maryland have a choice: wait for the buyer to test during the inspection period, or test proactively before listing the home. Testing ahead of time has real advantages. It gives sellers time to address an elevated result on their own schedule, rather than under contract deadline pressure, and it can prevent a radon result from becoming a last-minute point of negotiation close to closing.
A recent, clean radon test can also work in a seller’s favor during showings, since it signals transparency to buyers and can reduce the chance of the sale stalling over a radon dispute. In Montgomery County specifically, where testing is legally required before closing, proactive testing before listing is often the more efficient path, since it removes radon entirely from the list of contingencies a buyer needs to negotiate.
What Buyers Should Know Before Making an Offer
Buyers should confirm whether a radon contingency is included in the contract, and if it isn’t automatically added by the agent or template being used, ask for it. Because Maryland’s radon zones vary block by block in some areas, a clean result on a neighboring home doesn’t guarantee anything about the property being purchased. It’s worth budgeting for the test itself, typically $150 to $300 for a standard 48-hour test, and understanding that if levels come back elevated, mitigation costs generally fall in the $1,000 to $2,000 range depending on the home’s foundation and layout.
Buyers should also pay close attention to contingency deadlines. Radon testing typically needs to happen quickly after the contract is ratified, since results have to come back and be reviewed before the contingency window closes. Pairing a radon test with a general home inspection as soon as the contract is signed, rather than waiting, gives more breathing room if a retest or negotiation ends up being necessary.
What Happens After an Elevated Result
An elevated radon reading isn’t a reason to walk away from an otherwise good home, but it does need to be addressed. The standard fix is a sub-slab depressurization system, which uses a vent pipe and fan to draw radon gas from beneath the foundation and release it safely above the roofline. Most systems can be installed in a single day and typically cost $1,000 to $2,000 for a standard installation, with more complex foundations, such as split-levels or homes with multiple foundation sections, sometimes requiring additional suction points.
Whoever ends up responsible for installing the system, buyer or seller, a post-installation retest should always follow, usually performed within a day or two of the system going live, to confirm the radon level has actually dropped below the action threshold. Without that follow-up test, there’s no real proof the investment worked.
Getting Reliable Results for Your Transaction
Because radon results can directly affect a purchase price, a repair credit, or a closing timeline, using a certified tester who follows EPA protocols isn’t optional in any meaningful sense, it’s what protects both sides of the transaction. DeepSeek Home Inspections offers radon testing as part of full home inspections across Maryland, giving buyers and sellers documented, reliable results on a timeline that fits real estate contingency deadlines. You can schedule an inspection directly online, or contact our team with questions about your specific timeline.
Frequently Asked Questions
Do I have to test for radon before selling my home in Maryland?
Statewide, no, unless you’re in Montgomery County, where testing is legally required before a single-family home or townhome sale can close. Everywhere else in Maryland, testing is optional under state law, but the Maryland Radon Awareness Act does require you to disclose any existing test results to a buyer, and most purchase contracts include a radon contingency regardless of county.
How long does a radon test take during a home sale?
A standard real estate radon test runs for 48 hours under closed-house conditions, with results typically available within 24 to 72 hours after the monitor is retrieved. Given how tight contingency deadlines can be, scheduling the test as soon as the contract is ratified is the safest approach for buyers.
Can a seller refuse to fix a radon problem found during the sale?
In most of Maryland, a seller isn’t legally obligated to install a mitigation system even if radon levels come back elevated. What happens next depends on the language in the radon contingency: buyers can typically request repairs, negotiate a credit, or in some cases exit the contract if the two sides can’t reach an agreement within the contingency window. In Montgomery County, the testing requirement itself doesn’t force remediation either, though buyers can add a separate radon inspection contingency to negotiate for it.
Does a high radon reading lower a home’s value?
Not permanently. Radon is a fixable problem, and a mitigation system typically resolves it within a day of installation. Where it can affect a transaction is in the short term, either through a price credit negotiated to cover mitigation costs, or through added time on the closing timeline while the issue gets resolved. A home with a documented, successful mitigation system in place is generally viewed no differently than one that never had elevated levels to begin with.
Who pays for radon testing, the buyer or the seller?
In most transactions outside Montgomery County, the buyer arranges and pays for the test as part of their inspection contingency. In Montgomery County, if the buyer doesn’t order a test, responsibility shifts to the seller to provide one before closing, since the county requires a valid test on file regardless of who requests it.
Final Thoughts
Radon testing is a small part of a Maryland real estate transaction on paper, but it can have an outsized effect on the closing timeline if it’s left until the last minute. Sellers benefit from testing early and addressing problems on their own schedule, while buyers benefit from scheduling the test as soon as the contract is signed and understanding their options if results come back elevated. Either way, working with a certified radon professional keeps the process moving and gives both sides a result they can actually rely on.
