Is radon high in Seattle, Washington?

Low. Averaging the model's ZIP-code predictions across Seattle (weighted by how much of the city each ZIP covers) gives a long-term basement mean of 1.3 pCi/L - about 28% below the US average of 1.8 and about 18% below the Washington average of 1.6. That is below the EPA's 2 pCi/L "consider fixing" threshold, though individual homes still vary. Seattle ranks 27 of 29 Washington cities on this site.

Which Seattle ZIP codes have the highest radon?

Predictions for the 27 modeled ZIP codes in Seattle range from 1.1 to 1.5 pCi/L in the basement. 0% of them are predicted at or above 4 pCi/L and 0% at or above 2. The city is fairly uniform, so the city-wide number is a reasonable guide for any neighborhood.

Should I test for radon in Seattle?

Yes, once. The EPA recommends testing every home regardless of area. A short-term kit costs little and settles the question for your house; Seattle's low predicted average describes the typical home, not yours.

What does EPA Radon Zone 3 mean for Seattle?

Seattle sits mainly in King County, which the EPA classifies as Zone 3 - low potential (< 2 pCi/L). The zone map dates from 1993 and covers whole counties. The 2001-2021 model agrees with the zone for the city. Neither replaces a test of your own home.

Radon levels in Seattle, Washington

LowEPA Zone 3

Predicted long-term basement average of 1.3 pCi/L (model estimate) across the 27 modeled ZIP codes in Seattle - about 28% below the US average of 1.8, about 18% below the Washington average of 1.6. Ranked #27 of 29 Washington cities on this site. Most of the city lies in King County.

Test Seattle, WA once anyway - radon varies house to house

The predicted basement average here is 1.3 pCi/L, below the EPA's 2 pCi/L "consider fixing" threshold. That's good news for the area - but the EPA still recommends every home be tested, because foundation cracks, soil pockets and ventilation make one house very different from its neighbor. One inexpensive kit settles it.

Get a short-term test kit →Or track it with a continuous monitor

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Predicted (model estimate). The pCi/L figures on this page are long-term area averages from a peer-reviewed national model built on millions of real radon tests (2001-2021). They describe the typical home in this area - not your home, which can be several times higher or lower. The EPA radon zone is a separate, 1993 county-level classification. How the numbers work.

1.3 ± 0.07

pCi/L predicted basement mean (model SD)

0.6 ± 0.09

pCi/L predicted upstairs (above-ground) mean

1.1-1.5

range of ZIP-level basement predictions in the city

of Seattle ZIPs predicted ≥ 4 pCi/L (0% ≥ 2)

What this means for Seattle

The typical Seattle home is predicted below 2 pCi/L, the lowest band. That describes the average house; the ZIP-level predictions inside the city still span 1.1 to 1.5 pCi/L.

The city figure is not a separate estimate: it is the mean of the model's ZIP-code predictions, weighted by the share of the city's land in each ZIP (Census 2020 ZCTA-to-place relationship file). The 1993 EPA zone (3) for King and the 2001-2021 model agree here.

Comparable Washington cities: Sammamish (1.3), Shoreline (1.3), Kirkland (1.3), Everett (1.3).

ZIP codes in Seattle

ZIPs that overlap the city, largest share of its land first. Predicted basement and upstairs means are model estimates; ZIPs the model does not cover show a dash.

ZIP	Share of city	Basement	Upstairs	Grade
98115	8%	1.3 ± 0.06	0.6	Low
98118	7%	1.4 ± 0.06	0.7	Low
98108	7%	1.5 ± 0.06	0.7	Low
98125	7%	1.3 ± 0.06	0.7	Low
98106	6%	1.4 ± 0.06	0.7	Low
98103	6%	1.1 ± 0.12	0.5	Low
98199	5%	1.4 ± 0.07	0.6	Low
98105	5%	1.2 ± 0.07	0.6	Low
98117	5%	1.3 ± 0.08	0.6	Low
98134	4%	1.3 ± 0.06	0.7	Low
98144	4%	1.3 ± 0.06	0.6	Low
98112	4%	1.2 ± 0.08	0.6	Low
98116	4%	1.3 ± 0.07	0.6	Low
98126	4%	1.4 ± 0.07	0.6	Low
98133	4%	1.3 ± 0.08	0.6	Low
98119	3%	1.2 ± 0.08	0.5	Low
98122	3%	1.1 ± 0.09	0.5	Low
98136	3%	1.3 ± 0.06	0.7	Low
98107	3%	1.2 ± 0.09	0.6	Low
98177	3%	1.3 ± 0.07	0.6	Low
98109	2%	1.2 ± 0.07	0.5	Low
98102	2%	1.1 ± 0.08	0.5	Low
98178	1%	1.5 ± 0.06	0.6	Low
98104	1%	1.2 ± 0.08	0.6	Low
98146	1%	1.4 ± 0.06	0.7	Low
98101	1%	1.2 ± 0.08	0.5	Low
98121	1%	1.2 ± 0.06	0.6	Low
98195	1%	—	—	no model
98154	<1%	—	—	no model
98164	<1%	—	—	no model
98174	<1%	—	—	no model

Testing help in Washington

Washington's radon program page is at doh.wa.gov and, when we checked it, offered a limited supply of free radon test kits. EPA state radon contacts page. If a test comes back at 4 pCi/L or higher, mitigation typically costs $800-$2,500 installed; use EPA find-a-professional and read the mitigation guide.

Seattle radon questions

Is radon high in Seattle, Washington?: Low. Averaging the model's ZIP-code predictions across Seattle (weighted by how much of the city each ZIP covers) gives a long-term basement mean of 1.3 pCi/L - about 28% below the US average of 1.8 and about 18% below the Washington average of 1.6. That is below the EPA's 2 pCi/L "consider fixing" threshold, though individual homes still vary. Seattle ranks 27 of 29 Washington cities on this site.
Which Seattle ZIP codes have the highest radon?: Predictions for the 27 modeled ZIP codes in Seattle range from 1.1 to 1.5 pCi/L in the basement. 0% of them are predicted at or above 4 pCi/L and 0% at or above 2. The city is fairly uniform, so the city-wide number is a reasonable guide for any neighborhood.
Should I test for radon in Seattle?: Yes, once. The EPA recommends testing every home regardless of area. A short-term kit costs little and settles the question for your house; Seattle's low predicted average describes the typical home, not yours.
What does EPA Radon Zone 3 mean for Seattle?: Seattle sits mainly in King County, which the EPA classifies as Zone 3 - low potential (< 2 pCi/L). The zone map dates from 1993 and covers whole counties. The 2001-2021 model agrees with the zone for the city. Neither replaces a test of your own home.

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