Radon Testing When Buying or Selling in Greater Boston

By Tyler Smith | Beacon & Bond Group | August 17, 2026

If you're buying or selling in Newton, Brookline, Needham, Dedham, or Milton, radon probably isn't on your radar yet.  It should be.

Massachusetts sits on some of the oldest, most uranium-rich bedrock in the country.  Granite and glacial till — the geology under most of Greater Boston's older single-family neighborhoods — decay steadily into radon gas, which seeps up through foundation cracks, sump pits, and slab penetrations.  In Needham, average tested radon levels run around 6.0 pCi/L, already above the EPA's 4.0 pCi/L action level, and that's a town average, not a worst case.

About 21.8% of radon tests statewide come back at or above 4.0 pCi/L, according to American Lung Association tracking of Massachusetts homes.  That's roughly one in five houses.  No area of the state is exempt — new construction, century-old triple-deckers, well-sealed homes, and drafty ones can all test high, and two houses next door to each other can post very different numbers.

Here's the part that catches people off guard: none of this is mandatory.  Unlike lead paint, which Massachusetts law requires sellers to disclose on pre-1978 properties, radon has no testing requirement and no disclosure form.  It's on you — buyer or seller — to bring it up.  Radon joins a short list of inspection items that are common across Greater Boston's older housing stock but aren't legally required until a specific transaction forces the question — Title V septic systems work the same way for homes off municipal sewer.

Why This Matters More in a Caveat Emptor State

Massachusetts is a caveat emptor, or "buyer beware," state.  Sellers aren't required to volunteer information about most property conditions, radon included.  But caveat emptor has limits: a seller can't lie if you ask directly, and can't actively conceal a radon problem they already know about — say, an old test result that came back high and was never remediated.

Practically, that means the burden sits with the buyer.  If you don't test, you likely won't find out.  And if you're selling a home where a prior test flagged elevated levels, you're on safer legal ground disclosing it than hoping the question never comes up.

How Radon Testing Works During a Massachusetts Purchase

The standard Massachusetts Association of Realtors Offer to Purchase includes radon as one of several optional inspection-related contingencies, alongside the general home inspection, lead paint, and pest inspections.  You have the right to add it — most buyers just don't think to ask.

The mechanics are simple:

• Timing: Test during the inspection contingency period — typically five to ten days between your accepted Offer to Purchase and the Purchase and Sale Agreement signing.
• Method: A short-term test (48 to 96 hours) placed in the lowest livable area of the home is standard for a real estate transaction.   Long-term kits (91 days to a year) are more accurate but too slow for a transaction timeline.
• Cost: A professional radon test typically runs under $200 and is often bundled with your general home inspection for a modest add-on fee.
• Who to hire: Use a certified radon measurement specialist, not a DIY drugstore kit, if the result needs to hold up in a negotiation.

If your test comes back at or above 4.0 pCi/L, you're not stuck.  You have real options, and none of them require you to lose the house over it.

What Happens If Your Test Comes Back High

A radon result above the action level is a negotiating point, not a deal-breaker.  I walk clients through this constantly, and it almost never ends with someone walking away from a house they otherwise wanted.

Your options, roughly in order of how often I see them used:

1. Ask the seller to install a mitigation system before closing. A sub-slab depressurization system — a vent pipe and fan that pulls radon from beneath the foundation and vents it above the roofline — typically costs $1,000 to $2,500 installed and takes about a day.  Sellers often agree to this rather than risk losing the buyer.
2. Negotiate a closing cost credit covering the estimated mitigation cost, and handle the installation yourself after closing.
3. Ask for a price reduction in that same dollar range.
4. Walk away, using your inspection contingency, if the seller won't budge and you're not comfortable inheriting the cost.

Before you negotiate anything, get two or three quotes from licensed mitigation contractors.  Radon numbers can sound alarming, but the fix is usually fast, inexpensive relative to the price of the home, and something that can close in the same week as the sale.

One more thing worth knowing: mitigation works.  Homes with even significantly elevated readings typically drop well below the action level once a system is installed.  This isn't a structural problem or a reason to reconsider the whole purchase — it's a mechanical fix, like fixing a leaky roof or replacing an aging furnace.

Radon in Boston Condos Is a Different Conversation

If you're buying a condo in Boston, Brookline, or Newton rather than a single-family home, radon testing gets more complicated — and more important to ask about upfront.  If you're financing the purchase, add it to the list of diligence items sitting alongside the stricter reserve and insurance requirements now attached to conventional condo loans.

Garden-level and ground-floor units, which are common in Beacon Hill, Back Bay, and South End brownstone conversions, sit closest to the ground and face the same radon entry risk as a single-family basement.  These units should always be tested during your inspection window.

Upper-floor units in larger buildings are a harder case.  A proper radon test requires closed-building conditions for the full testing period, and in a multi-unit building, you can't control whether your neighbors keep their windows shut. Radon can also travel through elevator shafts, stairwells, and even concrete itself, meaning upper floors aren't automatically safe just because they're far from the ground.  In practice, testing an individual unit inside a larger building often isn't reliable — worth discussing directly with your inspector before you assume a test result means much.

If you're buying a triple-decker or small multi-family as an owner-occupant or investment property, radon deserves the same diligence you'd give other pre-1990 housing stock risks like underground oil tanks — you're responsible for tenant health and safety, and an elevated reading you don't catch before closing becomes your problem, and your cost, after you own the building.

Frequently Asked Questions

Is radon testing required when buying a house in Massachusetts?

No. Massachusetts has no law requiring radon testing or disclosure at sale.  It's an optional contingency in the standard Offer to Purchase, and buyers have to specifically request it — it isn't automatic.

Do sellers have to disclose radon test results in Massachusetts?

Not voluntarily.  Massachusetts is a caveat emptor state, so sellers don't have to test or disclose radon on their own.  They can't lie if a buyer asks directly, though, and can't conceal a known hazard, like an old high test result that was never fixed.

How much does radon mitigation cost in the Boston area?

Most Greater Boston homes run $1,000 to $2,500 for a standard sub-slab depressurization system, installed in about a day.  More complex foundations — multiple crawlspaces, several suction points — can push costs toward $3,000 to $3,500.

Are high radon levels common in Newton, Brookline, Needham, Dedham, and Milton?

Yes.  These towns sit on granite and glacial till bedrock that produces radon as it decays.  Needham's average tested level runs around 6.0 pCi/L, above the EPA's 4.0 pCi/L action level, and neighboring towns see similar patterns.

Can you get an accurate radon test in a Boston condo?

It depends on the unit.  Ground-floor and garden-level condos test the same way a single-family basement does.  Units in larger multi-unit buildings are harder to test accurately, since results depend on closed conditions across the whole building — talk to your inspector about whether a test is even reliable for your specific unit before you rely on the number.

Radon is a quiet issue precisely because nothing forces it into the conversation.  Nobody has to test for it, nobody has to disclose it, and it doesn't show up on a listing sheet.  But it shows up in the ground under nearly every home in Greater Boston, and the fix, when you need one, is straightforward and affordable relative to what you're spending on the house itself.

If you're getting ready to make an offer — or you're a seller wondering whether an old radon issue needs to come up — I'm happy to walk you through exactly how to handle it.  Reach out anytime.