Radon Gas in Southwest Washington: High-Risk Zones and Testing Protocols
Radon is an invisible, odorless radioactive gas that enters homes through foundation cracks and crawl spaces. It is the #1 cause of lung cancer among non-smokers. Here is what buyers in Southwest Washington must know.
Zachary Bradley
Licensed Home Inspector · WA Lic #26014533
Key Inspector Takeaways
- ✓EPA Action Level is 4.0 picocuries per liter (pCi/L); mitigation is recommended between 2.0 and 4.0 pCi/L.
- ✓Clark County and glacial gravel deposits in Thurston County exhibit higher average radon levels than coastal Pacific County.
- ✓Professional testing requires 48-hour continuous digital monitoring under closed-building conditions.
- ✓Sub-slab depressurization mitigation systems typically cost between $1,500 and $2,800 to install.
Where Does Radon Come From?
Radon is a radioactive gas formed by the natural radioactive decay of uranium found in soil and rock. As it rises through the ground, it enters homes through foundation slab cracks, sump pump openings, and porous crawl space dirt.
Testing Protocol During a Real Estate Inspection
We place calibrated continuous radon monitors (CRM) in the lowest livable level of the home for a minimum of 48 hours. The house must maintain closed-building conditions (doors and windows shut except for normal entry/exit) for accurate readings.
Frequently Asked Questions
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