Low Risk

ZIP Code 98581

Cowlitz County, Washington — Ryderwood

Zone 3EPA Classification
<2Predicted pCi/L
47.4%Above action level
0246810
<2pCi/L
Below action level

What This Means

Cowlitz County, Washington is in EPA Radon Zone 3, the lowest risk category. Predicted average indoor radon levels are below 2.0 pCi/L. However, the EPA recommends testing all homes — even in low-risk areas, individual homes can have elevated radon due to local geology and construction factors.

What You Should Do

1
Testing is still recommended. Even in low-risk zones, individual homes can have elevated radon due to localized geology, foundation type, and construction factors.
2
If your result is below 2.0 pCi/L, no action is needed. Re-test every 2–5 years, or after major renovations that alter your foundation or ventilation.
3
If your result is 4.0 pCi/L or above, install a mitigation system — even in low-risk zones, some homes require active radon reduction.

EPA Zone Details

ZIP Code98581
CountyCowlitz
CityRyderwood
StateWashington (WA)
EPA Radon ZoneZone 3 — Low
Predicted Indoor Radon<2 pCi/L

Source: EPA Map of Radon Zones

CDC Testing Data

Homes Tested19
Above 4.0 pCi/L9
% Exceeding Action Level47.4%

⚠ Limited testing data for this county (<20 tests). Results may not be representative.

Source: CDC Environmental Health Tracking Network

Radon & Your Basement in Cowlitz County

Cowlitz County is in EPA Zone 3, the lowest risk category. However, basements in any zone can have elevated radon due to local soil conditions, foundation cracks, and construction factors.

Radon concentrations are typically highest in the lowest level of a home. However, radon does not stay confined to the basement — it migrates to upper floors through stairways, HVAC ducts, and gaps in flooring. Even if your basement is unfinished or rarely used, elevated radon there can affect the air quality on your main living floors. Always test on the lowest livable level.

Cowlitz County Radon Map

Counties colored by EPA radon zone. Red = Zone 1 (high), Orange = Zone 2 (moderate), Green = Zone 3 (low).

Check Another ZIP Code

Nearby ZIP Codes

98579 Rochester, WA Low 98580 Roy, WA Low 98582 Salkum, WA Low 98583 Grays Harbor, WA Low 98584 Shelton, WA Low

Frequently Asked Questions

What is the radon risk level for ZIP code 98581?

ZIP code 98581 is in Cowlitz County, Washington, which is classified as EPA Radon Zone 3 (low risk). The predicted average indoor radon level is <2 pCi/L.

Should I test for radon in 98581?

Yes. The EPA recommends testing all homes for radon regardless of zone. Even in lower-risk areas like 98581, individual homes can have elevated radon.

What county is ZIP code 98581 in?

ZIP code 98581 is in Cowlitz County, Washington (WA).

Is it safe to live in ZIP code 98581?

ZIP code 98581 is in a lower-risk EPA Zone 3 area. Most homes in this zone have radon levels below the action level. However, the EPA still recommends testing, as individual homes can have elevated levels due to local geology.

Does radon in the basement affect upper floors in Cowlitz County?

Yes. Radon enters through the foundation and can migrate to upper floors through stairways, HVAC systems, and structural gaps. While concentrations are typically highest at the lowest level, upper floors in Cowlitz County homes can still have measurable radon. Always test on the lowest livable floor.

How much does radon mitigation cost in Washington?

In Washington, radon mitigation systems typically cost between $800 and $2,500 depending on home size, foundation type, and local labor rates. The most common system (sub-slab depressurization) averages $1,000-$1,500. The fan lasts 10-15 years and costs $150-$300 to replace. Some states offer financial assistance programs for radon mitigation.