"A single-family home located in the County must be tested for radon before completing a sale of the home."
That sentence sits inside Montgomery County Code Section 40-13C, and it governs every detached house and townhouse sale in Bethesda, whether the property is a 1940s Cape Cod off Wilson Lane or a new build in Edgemoor. What the sentence does not say is just as important. It does not say what happens after the test comes back. It does not give either side a right to walk away because of a number. And it does not require anyone to fix anything.
Buyers and sellers who read the law for the first time tend to assume the mandate and the remedy travel together. They do not. The county built a rule that forces information into the open. It left the negotiation over what to do with that information entirely to the two parties and their contract.
What the ordinance actually covers
The law took effect October 1, 2016, making Montgomery County one of the only jurisdictions in the country that ties radon testing directly to a home sale rather than leaving it optional. It applies to single-family detached homes and townhouses. Condominiums and cooperative units are excluded entirely, so a Bethesda rowhouse triggers the law while a unit at a high-rise a few blocks away does not.
A handful of transactions are carved out by statute: sales exempt from the state transfer tax, transfers by a lender through foreclosure or deed in lieu, sheriff's sales and tax sales, transfers by a fiduciary settling an estate or trust, and sales of a home the buyer intends to demolish or convert to nonresidential use. Three towns and one city sit outside the county's radon jurisdiction as well: Rockville, Kensington, Poolesville, and Barnesville. Everywhere else in the county, including Bethesda, Chevy Chase, and Potomac, the test is not optional paperwork. It is a condition of settlement.
The mechanics are specific. The test has to be performed within one year of the settlement date. Either the seller or the buyer can be the one to run it, but if the buyer declines the opportunity, the obligation falls back on the seller. Both parties are entitled to a copy of the results regardless of who paid for the test or which way it came back.
Here is the part that catches people mid-contract: the statute stops at disclosure. It does not require the seller to remediate an elevated reading, and it does not give the buyer a right to cancel based on the number. Montgomery County solved an information problem, not a repair problem.
Two forms, two different jobs
This is where the contract mechanics matter more than the law itself. Every Montgomery County transaction runs through the GCAAR Regulations, Easements and Assessments Disclosure and Addendum, which is required on all listings and sales contracts in the county. That form is how the radon requirement gets satisfied on paper. It states that a test will be performed in accordance with Section 40-13C, and it is the document that keeps the transaction compliant with county law.
Compliance with the county, though, is not the same as leverage in the deal. If a buyer wants the right to ask for remediation, a credit, or an out if the reading comes back elevated, that right does not come from the disclosure form. It comes from a separate document: the Radon Inspection Contingency, found in Paragraph 4 of GCAAR's Addendum of Clauses. That contingency has to be affirmatively added to the offer. It is not automatic, and it is not implied by the disclosure requirement.
Real estate attorneys who reviewed the county's rollout flagged exactly this gap between the two documents. The disclosure form tells the seller and buyer that a test is happening and satisfies the county's requirement. It does not, by itself, obligate the seller to do anything if the number is bad. A buyer who assumes the mandatory test comes bundled with mandatory protection is working from the wrong document.
Practically, that means a Bethesda buyer who wants real recourse needs to make sure the Radon Inspection Contingency is written into the offer at the time the contract is signed, not treated as something to sort out after the test results arrive. Once a contract is ratified without that contingency, asking a seller to remediate becomes a request rather than a right.
Why the basement changes the math
Montgomery County sits in the EPA's Radon Zone 1, meaning the predicted average indoor radon screening level for the area is at or above the EPA's action threshold of 4.0 picocuries per liter. The national average indoor level is roughly 1.3 pCi/L, so a county-wide Zone 1 designation is a meaningfully different starting point than most of the country works from.
What that designation means for a specific Bethesda address depends heavily on how the house is built and used. Radon enters through cracks and openings in a foundation and settles in the lowest livable level of a home, which is why finished basements and lower-level bedrooms carry more practical weight than the reading alone suggests. A great deal of Bethesda's housing stock was built well before 1995, when the county began requiring radon-resistant construction techniques, and many of those older homes have since had their basements finished into media rooms, guest suites, or home offices. A reading that would be a minor footnote in a house with an unfinished crawlspace carries more practical weight in a Colonial where the lower level functions as a bedroom.
The EPA's own guidance treats readings between 2.0 and 4.0 pCi/L as worth considering for mitigation, even though they fall under the hard action level. That range matters more in a home where the basement is finished living space than in one where it is storage. The test result is the same number either way. The exposure is not.
What the paperwork costs, in time and dollars
A standard short-term radon test in the Montgomery County market typically runs somewhere between $100 and $250. If the result comes in at or above the 4.0 pCi/L action level and the parties agree to address it, a typical mitigation system installation runs roughly $800 to $2,500 depending on the home's foundation and layout. Both figures are modest against a Bethesda transaction, which is exactly why the friction here is rarely about money. It is about timing and leverage.
The one-year testing window sounds generous until a listing sits on the market and a seller's original test ages out before a buyer is under contract. Sellers who test early, before listing, have results ready to hand a buyer on day one. Sellers who wait are betting that a buyer will be comfortable ordering a fresh test on a tight inspection timeline, which adds a step to an already compressed contingency period.
A short checklist before the radon paragraph gets signed
- Confirm the property is a detached home or townhouse in Montgomery County outside Rockville, Kensington, Poolesville, and Barnesville. Those jurisdictions fall outside Section 40-13C.
- Check whether an existing radon test is less than a year old at the time of the sale. If not, someone still needs to order one before settlement, regardless of what the disclosure form says.
- If leverage over an elevated result matters, make sure the Radon Inspection Contingency is written into the offer at signing, not added after the fact.
- Ask for the chain of custody on any test result, including the device type and who administered it, since the law requires an approved testing device.
- Remember that a passing test satisfies the county. It does not, by itself, tell you how the lower level of the home is used or whether that use changes your actual exposure.
The county's radon law is a real requirement, not a formality to skim past in a stack of closing documents. It guarantees that both sides of a Bethesda sale will know the number before they sign at settlement. It does not guarantee that number will be acted on, and the difference between those two things is decided in the contract, not the statute.
If you are preparing to list a Bethesda property this fall or you are already under contract and want someone who reads every paragraph of the county forms as closely as the property itself, Donna Leanos works through exactly this kind of contract detail with clients across Bethesda, Chevy Chase, and the wider DMV. Get Access to My Private Listings to start the conversation before the paperwork does the deciding for you.
