Radon in Blaine County: why this county is different.
Published
Blaine County is the only Idaho jurisdiction that addresses radon in its building code, and the EPA places it in Zone 1, its highest-risk designation. Radon enters from beneath a building and cannot be identified by smell. Testing establishes the level; the EPA recommends action at 4.0 pCi/L or higher.
The source is below the building
Radon forms as uranium and radium break down in soil. It can enter a house through foundation cracks, a crawl-space floor, a sump opening or a utility penetration. It is colorless and odorless. A clean house, a recent remodel and an absence of damp smells do not tell you the radon level. The issue is separate from whether the property has a visible moisture problem, even though the same foundation may need attention for both.
Idaho is a high-radon state, and testing is especially important in Blaine County. Each house needs its own measurement. What is beneath the foundation and how the building is constructed matter. Two similar houses on the same street can produce different results. Borrowing a neighbor's result cannot answer the question for the home you live in or intend to buy.
Zone 1 and the county code answer different questions
The EPA's Zone 1 designation is its highest-risk designation, making testing important here. It is not a test result for a particular property. A buyer still needs a measurement, and an owner still needs verification after mitigation. A county classification is not proof of a home's level or proof that a newer home is already protected. Keep the classification separate from the property's test and post-mitigation verification.
Blaine County also addresses radon in its building code, unlike other Idaho jurisdictions. That does not mean every existing house, addition or permit has the same requirement. Construction type and permit scope affect the specifics. Ask the county building department what applies to the project you are planning. Code requirements and measured levels are separate questions.
Why the winter reading matters
Radon levels vary with season and weather. Levels are highest in winter, when houses are closed up tight. The valley's long heating season makes that an important condition to examine rather than dismiss. A low reading in another season does not establish the year-round level. Record the timing and conditions of the test along with the result.
Follow the instructions for the test being used. Do not improvise the placement or change the building's conditions to try to produce a preferred number. If a sale is involved, ask the testing provider and the people handling the transaction what test and documentation they need. The result needs to describe the property under the required conditions. A number without its test information is harder to interpret and less useful when everyone is trying to make a decision on a deadline.
Short-term and long-term tests are not interchangeable
Short-term tests run two to seven days and are commonly used in real estate transactions. They fit a shorter decision window and establish a reading for the conditions during that test. Long-term tests run more than ninety days and give a better view of the annual average because they include more of the seasonal variation. Choose the test for the question and time available.
For an owner without a closing deadline, ask whether a longer test would be useful for understanding the home over time. For a buyer, the inspection schedule determines the time available for testing. Make the testing plan early and identify who receives the report. A first-look kit can be useful, but a transaction or post-mitigation result should be arranged with a professional provider and the parties who will rely on that documentation.
What the 4.0 pCi/L action level means
The EPA recommends taking action at 4.0 pCi/L or higher. Discuss mitigation when a result reaches or exceeds that level. The report should identify the measured value and the test period. Ask the provider to explain the next step in relation to that result, including how the proposed work will be verified afterward.
An action level is not a substitute for testing and it is not a predicted result after installation. The system needs to be designed for the foundation and checked after it operates. A quote that says a fan will be installed is describing equipment, not documenting performance. Keep the initial test, the installation scope and the post-mitigation result together. Those records make it possible to show what was found, what changed and whether the completed system did what it was intended to do.
Plan the work before the closing date becomes the problem
Sub-slab depressurization draws from beneath the building and vents above the roofline through sealed piping and a continuously running fan. A crawl space may require a sealed membrane rather than the same suction arrangement used beneath a slab. Mixed foundations and additions need to be assessed before the design is settled. Existing passive piping still needs testing to establish whether it is sufficient or requires a fan. New construction is not a reason to skip that measurement.
In a sale, arrange access for the assessment, installation and re-test rather than leaving verification as an afterthought. Ask for the system description and the post-mitigation report in writing. Agents, inspectors, buyers and sellers can then work from the same record instead of relaying fragments of a conversation. The business can explain the physical work and the testing sequence; your transaction professionals handle contract questions. A tight deadline calls for a clear sequence.