Does Radon Exist in NYC?
Yes. Radon is a naturally occurring radioactive gas produced by the decay of uranium in soil and rock. It exists everywhere in the ground — including under New York City. While NYC's high-rise density and sealed building construction reduce radon risk relative to rural single-family homes, radon is a real concern for:
High-rise apartments above the third floor have effectively zero radon risk — radon concentrations decrease dramatically with height above ground level.
EPA Action Level and NYS Mandatory Reporting Threshold
EPA 4 pCi/L action level: The U.S. Environmental Protection Agency recommends mitigation when a home tests at or above 4 pCi/L (picocuries per liter). At 4 pCi/L, lifetime lung cancer risk is estimated to be equivalent to approximately half a pack of cigarettes per day. The national average indoor radon level is 1.3 pCi/L; average outdoor is 0.4 pCi/L.
NYS 20 pCi/L mandatory reporting threshold: Under 10 NYCRR §16.140, New York State requires reporting to the NYS Department of Health when a measurement of 20 pCi/L or higher is detected. This is a mandatory reporting requirement — both the property owner and NYS DOH must be notified. At 20 pCi/L, mitigation is strongly recommended and may be mandatory depending on circumstances.
Our radon measurement reports explicitly flag results relative to BOTH thresholds.
Which NYC Neighborhoods Have Higher Radon Risk?
Radon risk in NYC varies by geology and building type. Higher-risk areas include:
Staten Island: Highest radon risk of the five boroughs. The metamorphic rock and glacial till underlying the island contains uranium-bearing minerals that produce elevated soil radon. Detached homes in New Dorp, Tottenville, Eltingville, and Annadale with full basements should be tested.
Northern Bronx and Westchester border: Areas near the Fordham Gneiss and Inwood Marble geological formations (which extend under the northern Bronx and into Westchester) have elevated radon geology.
Northern Manhattan: Inwood and Washington Heights rest on the Inwood Marble formation, one of the uranium-bearing geological units associated with elevated radon. Ground-floor units in low-rise buildings in these neighborhoods have higher radon risk than midtown Manhattan.
Queens and Brooklyn: Generally lower radon risk than Staten Island or northern Manhattan, but ground-floor and basement units in detached homes (particularly in eastern Queens and southern Brooklyn) warrant testing.
The Testing Protocol
A valid short-term radon test requires closed-building conditions:
This protocol is specified in the EPA's "Protocols for Radon and Radon Decay Product Measurements in Homes" and ANSI/AARST standards. Closed-building conditions are essential — an open-window test will produce artificially low results that don't reflect normal winter occupancy.
Radon in Real Estate Transactions
The EPA recommends radon testing for all homes at the time of purchase. For NYC apartments, this is most relevant for:
Real estate contracts in New York State allow purchasers to conduct a radon test as part of home inspection contingency. Results at or above 4 pCi/L are typically grounds for requesting mitigation or price adjustment.
Mitigation Options
If testing reveals elevated radon, common mitigation approaches include:
Sub-slab depressurization (SSD): The most effective mitigation for slab-on-grade or full basement buildings. A pipe penetrates the slab and a continuously running fan draws radon out from under the slab and vents it above the roofline. Effective, relatively inexpensive, and widely used.
Foundation sealing: Sealing cracks, joints, and penetrations in foundation walls and slabs reduces radon entry. Most effective as a supplement to active depressurization, not as standalone mitigation.
Pressure equalization: Creating slight positive pressure in the building relative to the soil beneath. Less common in residential applications.
Post-mitigation testing is required to verify that mitigation brought levels below the EPA action level.