Montgomery County is one of the only jurisdictions in Maryland that legally requires radon testing before the sale of any single-family home or townhome — a law on the books since October 2016. The test must be completed within one year of settlement and costs $100–$200. If levels reach 4.0 pCi/L or higher — the EPA’s action threshold — you have real negotiation options during your inspection contingency window, even though the seller is not legally required to remediate.
Does Montgomery County require radon testing when buying a home?
Yes. Montgomery County, Maryland law (effective October 2016) requires that every single-family home and townhome be tested for radon before the sale is completed. The test results must be no older than one year at settlement. Either the seller or the buyer can order the test — but one of them must, and both parties receive a copy of the results. The law does not require remediation, but if levels come in at or above 4.0 pCi/L (the EPA action level), buyers have real negotiation options within the inspection contingency period.
By Pey Behin | May 18, 2026
When you’re under contract on a home in Bethesda, Potomac, or Chevy Chase, radon testing isn’t optional — it’s the law.
Montgomery County passed a radon testing ordinance that went into effect October 1, 2016. It’s one of the only jurisdictions in Maryland — and one of the very few counties in the country — to make radon testing a legal requirement for every residential home sale. If you’re buying a single-family home or townhome in Montgomery County, this applies to your transaction regardless of what the seller wants or what’s in the contract.
Here’s what you need to know before you get to the inspection period.
Why Montgomery County Has a Radon Law
Radon is a colorless, odorless, radioactive gas that forms naturally from the decay of uranium in soil and rock. It seeps into homes through cracks in foundations, gaps around pipes, and directly through the soil. Long-term exposure is the second leading cause of lung cancer in the United States, according to the EPA — second only to smoking.
Maryland sits in EPA Zone 2 radon territory, meaning homes carry a moderate potential for elevated radon levels. Montgomery County decided that “moderate potential” was still reason enough to require a test before any home sale. The EPA sets its recommended action level at 4.0 picocuries per liter (pCi/L). Between 2.0 and 4.0 pCi/L, the EPA suggests considering mitigation. The national average indoor radon level is about 1.3 pCi/L.
For context: radon accumulates in the lowest levels of a home. Finished basements, lower-level bedrooms, and slab-on-grade construction are highest-risk spaces. Many homes in Bethesda, Potomac, and North Bethesda have walk-out basements or fully finished lower levels — exactly the spaces where radon concentrates most.
Which Properties Are Covered
The law applies to detached single-family homes and townhomes throughout Montgomery County. A few municipal carve-outs apply — the ordinance does not cover properties in the Town of Barnesville, the City of Rockville, the Town of Kensington, or the Town of Poolesville.
Condominiums and co-ops are exempt. If you’re buying a condo in Bethesda or Chevy Chase, the Montgomery County radon ordinance doesn’t require a test — though you can always request one voluntarily.
If you’re buying in North Bethesda, Potomac, Chevy Chase, or unincorporated Bethesda, you’re in scope. The requirement applies, and no one can waive it by contract or mutual agreement.
Who Orders the Test — and Who Pays
This is where buyers often get tripped up. The law sets up a responsibility waterfall:
- The seller must either perform the radon test themselves or give the buyer the opportunity to do it.
- If the buyer is offered the option and declines, the seller must order the test. There’s no skipping it.
- Either the seller, buyer, or a third party — such as a home inspector or certified radon tester — can perform the test using an approved device.
- The results must be no more than one year old at settlement.
- Both the seller and the buyer must receive a copy of the test results.
In practice, most radon tests in Montgomery County are conducted as part of the home inspection. Your inspector will often place a 48-hour passive radon test device simultaneously with the general inspection. The device is collected two days later and results typically come back within 24–48 hours. A standalone radon test costs $100–$200 in the DC metro area — a modest expense relative to everything else on your buyer cost sheet.
If the seller already has a recent test on file — performed within the past year — that result satisfies the legal requirement. No new test needed. Your agent should ask for it upfront before you duplicate the cost. This is one of those line items that fits into the broader picture of what buyers pay in closing costs and transaction expenses in Bethesda.
Who pays? Whoever orders it. If the seller tests before listing, they absorb the cost. If the buyer orders it during the inspection period, it comes out of the buyer’s due diligence expenses.
What Happens After You Get the Results
This is the part that surprises buyers most: the Montgomery County law requires testing, but it does not require remediation. No matter what the radon level shows, the seller has no legal obligation under the ordinance to install a mitigation system.
So what are your actual options?
If levels come in below 2.0 pCi/L: You’re in excellent shape. That’s well below the EPA’s consideration threshold. No action needed.
If levels come in between 2.0 and 4.0 pCi/L: The EPA suggests considering mitigation in this range. Whether you negotiate repairs, ask for a credit, or accept the home as-is is a decision between you and the seller — there’s no legal trigger here.
If levels come in at or above 4.0 pCi/L: The EPA recommends action. This is where your inspection contingency does its job.
If you’re within your inspection contingency period — which in most Maryland contracts runs 7–14 days from contract acceptance — you can request that the seller install a radon mitigation system before closing, ask for a purchase price reduction or closing credit to cover installation yourself, or, depending on your contract terms, exit the deal if the seller won’t address it.
A radon mitigation system in the DC metro area — typically a sub-slab depressurization setup — costs between $800 and $2,500 depending on the home’s size and foundation type. On a $1.2M Bethesda purchase, that’s a manageable number. The key is resolving it before closing rather than inheriting an unmitigated problem.
This is exactly why decisions around waiving the home inspection in Bethesda’s competitive market require careful thought. Radon is precisely the kind of issue a no-inspection offer leaves unchecked. Even when seller competition is intense, giving up your due diligence window entirely means you’re also giving up your ability to respond to what a radon test reveals.
How This Fits Into Your Transaction Timeline
Here’s how radon typically plays out in a Montgomery County purchase transaction:
Days 1–3 after contract acceptance: Schedule your home inspection and radon test simultaneously. Most inspectors in the DC metro area are familiar with the county law and will coordinate the 48-hour test device as part of their service.
Days 3–5: Radon device is collected. Results processed and returned, usually within 24–48 hours.
Days 7–14 (inspection contingency window): All inspection and radon results are in hand. If levels are elevated, this is your window to respond — request remediation, negotiate a credit, or make a decision about proceeding.
Understanding how contingencies work in a Maryland real estate contract is essential here. Once the inspection contingency deadline passes without a negotiated addendum, you’ve generally accepted the property’s condition as-is. Radon results that come in late — because the test was delayed or disorganized — can put you in a tough spot if you’re up against that deadline.
A Word for Sellers in Bethesda, Potomac, and Chevy Chase
If you’re listing a home in Montgomery County, you have a choice: order the radon test yourself before the home goes on market, or let the buyer do it during their inspection period.
Testing before you list has clear advantages. You know the results upfront and can address elevated levels before any buyer is under contract. If you install a mitigation system before listing, you can market the property as tested and remediated — which signals to informed buyers that you’ve done your due diligence. It also removes a potential renegotiation variable at exactly the moment when momentum matters most.
If you wait and let the buyer order the test, you’re handing them a possible negotiation chip at the worst possible time. Given everything you’re already navigating — commissions, Maryland transfer and recordation taxes, title costs — it’s worth removing this variable early. You can see how the radon decision fits into the full picture of seller closing costs in Bethesda.
The Bottom Line
Radon testing is a small step in a large transaction — but in Montgomery County, it’s a required one. The test is fast, affordable, and straightforward once you understand what you’re looking for and what your options are if the numbers come in high.
What trips buyers up isn’t the test itself. It’s not knowing what the results mean or how much leverage they actually have when levels are elevated. Now you do: if your results come in at or above 4.0 pCi/L and you’re within your contingency window, you have options. Use them.
If you’re buying in Bethesda, Potomac, Chevy Chase, or anywhere in Montgomery County and want to understand what due diligence looks like from contract to closing, I’m happy to walk you through the process. Reach out anytime.
Frequently Asked Questions
Is radon testing required when buying a home in Montgomery County, MD?
Yes. Montgomery County law (effective October 2016) requires that every single-family home and townhome be tested for radon before a sale is completed. The test must be no more than one year old at settlement. Condominiums and co-ops are exempt. A few municipalities within the county are excluded: the Town of Barnesville, the City of Rockville, the Town of Kensington, and the Town of Poolesville.
Who is responsible for ordering the radon test in Montgomery County?
The law gives the seller first responsibility: they must either perform the test or offer the buyer the opportunity to do it. If the buyer declines, the seller must order the test. In practice, most tests are coordinated as part of the buyer’s home inspection, and both parties receive a copy of the results. A certified home inspector, radon testing professional, or either party can order the test using an approved device.
What happens if the radon test comes in above 4.0 pCi/L in Montgomery County?
The Montgomery County law does not require the seller to remediate even if radon levels exceed 4.0 pCi/L — the EPA’s recommended action level. However, if you’re within your inspection contingency period, you can negotiate: ask the seller to install a mitigation system, request a credit to cover remediation costs post-closing, or, depending on your contract terms, use the results as grounds to exit the deal. A radon mitigation system in the DC metro area typically costs $800–$2,500.
Do condo buyers in Bethesda need a radon test?
No. The Montgomery County radon ordinance applies only to detached single-family homes and townhomes. Condominiums and cooperative housing units are explicitly exempt. Buyers of condos in Bethesda or Chevy Chase can still request a test voluntarily, but sellers are not legally required to provide one.
Can a seller use an existing radon test when listing a home in Montgomery County?
Yes. If a radon test was performed within the past 12 months, that result satisfies the legal requirement — no new test is needed. Sellers who proactively test before listing benefit from having this resolved before any buyer makes an offer, removing a potential negotiation variable mid-contract.
Radon testing is one of those Montgomery County-specific requirements that catches buyers — and even experienced sellers — off guard, especially those coming from jurisdictions where testing isn’t legally mandated. Once you understand the rules, it’s a manageable step that fits cleanly into your inspection period. For a full picture of what that window looks like and what else to expect from contract to closing, read my guide to the Maryland buyer closing process — or reach out directly.
About Pey Behin
Pey Behin is a residential real estate agent serving the Washington, DC metro area, with a focus on Bethesda, Montgomery County, and Northern Virginia. He works with buyers and sellers who want clear strategy, data-driven pricing, and direct guidance throughout the transaction process. His approach combines market analytics, negotiation expertise, and modern marketing to position clients effectively in competitive conditions.
