Is radon high in Highlands Ranch, Colorado?

Low. Averaging the model's ZIP-code predictions across Highlands Ranch (weighted by how much of the city each ZIP covers) gives a long-term basement mean of 1.6 pCi/L - close to the US average of 1.8 and about 41% below the Colorado average of 2.6. That is below the EPA's 2 pCi/L "consider fixing" threshold, though individual homes still vary. Highlands Ranch ranks 21 of 21 Colorado cities on this site.

Which Highlands Ranch ZIP codes have the highest radon?

Predictions for the 5 modeled ZIP codes in Highlands Ranch range from 1.4 to 2.0 pCi/L in the basement. 0% of them are predicted at or above 4 pCi/L and 40% 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 Highlands Ranch?

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

What does EPA Radon Zone 1 mean for Highlands Ranch?

Highlands Ranch sits mainly in Douglas County, which the EPA classifies as Zone 1 - highest potential (predicted average > 4 pCi/L). The zone map dates from 1993 and covers whole counties. The newer model's city average of 1.6 pCi/L does not line up with Zone 1, which is common - the EPA itself says high-radon homes exist in every zone. Neither replaces a test of your own home.

Radon levels in Highlands Ranch, Colorado

LowEPA Zone 1

Predicted long-term basement average of 1.6 pCi/L (model estimate) across the 5 modeled ZIP codes in Highlands Ranch - close to the US average of 1.8, about 41% below the Colorado average of 2.6. Ranked #21 of 21 Colorado cities on this site. Most of the census-designated place lies in Douglas County.

Test Highlands Ranch, CO once anyway - radon varies house to house

The predicted basement average here is 1.6 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.

1.6 ± 0.08

pCi/L predicted basement mean (model SD)

1.6 ± 0.07

pCi/L predicted upstairs (above-ground) mean

1.4-2.0

range of ZIP-level basement predictions in the city

of Highlands Ranch ZIPs predicted ≥ 4 pCi/L (40% ≥ 2)

What this means for Highlands Ranch

The typical Highlands Ranch home is predicted below 2 pCi/L, the lowest band. That describes the average house; the ZIP-level predictions inside the city still span 1.4 to 2.0 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 census-designated place's land in each ZIP (Census 2020 ZCTA-to-place relationship file). Note that the EPA classifies Douglas County as Zone 1 while the newer model predicts 1.6 pCi/L for Highlands Ranch; where they disagree, we grade on the model but show both.

Comparable Colorado cities: Castle Rock (1.6), Commerce City (1.7), Parker (1.9), Thornton (2.1).

ZIP codes in Highlands Ranch

ZIPs that overlap the census-designated place, 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
80126	45%	1.6 ± 0.08	1.6	Low
80129	28%	1.4 ± 0.08	1.4	Low
80130	20%	1.5 ± 0.09	1.6	Low
80125	5%	2.0 ± 0.08	2.0	Moderate
80124	3%	2.0 ± 0.08	1.9	Moderate

Testing help in Colorado

Colorado's radon program page is at cdphe.colorado.gov; it lists testing and certified-mitigator guidance. 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.

Highlands Ranch radon questions

Is radon high in Highlands Ranch, Colorado?: Low. Averaging the model's ZIP-code predictions across Highlands Ranch (weighted by how much of the city each ZIP covers) gives a long-term basement mean of 1.6 pCi/L - close to the US average of 1.8 and about 41% below the Colorado average of 2.6. That is below the EPA's 2 pCi/L "consider fixing" threshold, though individual homes still vary. Highlands Ranch ranks 21 of 21 Colorado cities on this site.
Which Highlands Ranch ZIP codes have the highest radon?: Predictions for the 5 modeled ZIP codes in Highlands Ranch range from 1.4 to 2.0 pCi/L in the basement. 0% of them are predicted at or above 4 pCi/L and 40% 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 Highlands Ranch?: Yes, once. The EPA recommends testing every home regardless of area. A short-term kit costs little and settles the question for your house; Highlands Ranch's low predicted average describes the typical home, not yours.
What does EPA Radon Zone 1 mean for Highlands Ranch?: Highlands Ranch sits mainly in Douglas County, which the EPA classifies as Zone 1 - highest potential (predicted average > 4 pCi/L). The zone map dates from 1993 and covers whole counties. The newer model's city average of 1.6 pCi/L does not line up with Zone 1, which is common - the EPA itself says high-radon homes exist in every zone. Neither replaces a test of your own home.

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