Radon in Southwest VirginiaThe zone map is a rough county estimate. Only a test answers for a house.
A zone map gives a whole county a rough label. A test gives one house a number. This guide covers the difference, how Virginia's health department says to test, who may do radon work here, and where new houses have to be built to resist it.
High results in every county, low-risk ones included
Before any map comes into it, one sentence from the Virginia Department of Health (VDH) settles the first question about a house here.
High radon test results have been found in every Virginia County - including all of those designated as "low risk".
Virginia Department of Health, EPA radon risk map for Virginia
The department's test-result page goes a step further: both low and high radon test results have been found in every Virginia city and county. That takes in every locality in this footprint, the Carroll, Grayson, Wythe, Pulaski, Montgomery and Floyd counties and the City of Galax laid out on the six-county map of the offices and rules here. The name of the county on the tax bill does not tell anyone which result a particular house will get.
VDH describes indoor radon as a colorless, odorless radioactive gas, thought to be the second leading cause of lung cancer and the leading cause of lung cancer among people who have never smoked. Nobody can see it or smell it, so the department's answer to whether a house has a problem does not change from place to place: testing is the only way to know. EPA and VDH recommend that all homes be tested, especially homes being purchased, whatever zone their locality carries.
That is the frame for radon in Southwest Virginia. It is a question about one house at a time, and the rest of this guide explains why the maps people find first cannot answer it.
A zone map drawn for jurisdictions, never for one house
EPA sorts radon risk areas into Zones 1, 2 and 3. By VDH's count, Virginia has 46 counties and 15 cities classified as Zone 1, the high-risk category, and 24 counties and 8 cities classified as Zone 2, the moderate category.
EPA developed its Map of Radon Zones in 1993 to identify areas of the country with the potential for elevated indoor radon levels. EPA's own page states the limit plainly:
The Map of Radon Zones should not be used to determine if individual homes need to be tested.
U.S. Environmental Protection Agency, EPA Map of Radon Zones
VDH's page on the map, last updated May 15, 2024, gives the reasons. The map was based on a very limited number of radon test results. It was never intended for predictive purposes, only as a rough estimate of the chances of encountering high indoor radon in a particular jurisdiction. And EPA, the page says, currently has no plans to revise it. EPA's Virginia map carries the same message in one line: all homes should be tested, regardless of zone designation.
The zone still shows up in a house sale. Virginia's residential property disclosure statement, the seller disclosure that the Virginia Residential Property Disclosure Act sets for transfers of residential property of one to four dwelling units, has a radon subdivision, Va. Code 55.1-703 B 14, in which the owner makes no representations about the locality's zone. What else that subdivision points purchasers to belongs to how radon comes up in a sale, an answer of its own.
What a statewide geology ranking cannot say about a building site
The other document owners run across is the U.S. Geological Survey's 1993 assessment of geologic radon potential. Its Virginia chapter ranks the Valley and Ridge high in geologic radon potential, with local areas of low to moderate potential.
The scale of this assessment is such that it is inappropriate for use in identifying the radon potential of small areas such as neighborhoods, individual building sites, or housing tracts.
U.S. Geological Survey, Open-File Report 93-292-C, Virginia chapter
That sentence is why this guide ties no county here to a physiographic province or a ranking. The assessment works at a scale far larger than a tract, and no source this site relies on maps which province a given parcel sits in. Even if one did, USGS itself says the ranking is the wrong tool for a single building site.
VDH's own test-result data has a gap of its own. The department notes that professional radon testers are not required to report their results to the department, so its dataset and map do not represent every radon test performed in Virginia. Any figure drawn from that data describes the tests that were reported. It says nothing about a house that was never tested, or about the house on the next parcel.
Soil and rock matter for other reasons when land is bought to build on, from drainage to septic suitability. Those questions are covered in Blue Ridge soils and what they mean, and they are separate from radon.
The lowest livable level, between late October and early May
VDH's testing guidance turns on two things about how radon behaves indoors: the season and the floor.
On the season, VDH's testing page says indoor radon usually reaches its maximum concentration during the coldest winter months. The department's Radon Facts for Virginians recommends a short-term test, three to seven days, run between late October and early May, and says to avoid testing in the summer, during periods of heavy precipitation, or during high sustained winds.
The lowest livable level of the structure should always be tested because that is where the highest radon levels in the structure are typically found.
Virginia Department of Health, radon testing and mitigation
Reading the number
Results are reported in picocuries per liter, written pCi/L. The EPA action level is 4 pCi/L: EPA's guidance is to fix the home when the level is 4 pCi/L or higher, and to consider mitigation when a result falls between 2 and 4 pCi/L. A short-term result is a reading from one stretch of days, which is one more reason the timing guidance matters.
When a house is under contract, the test also has to fit a calendar, and no radon rule sets that calendar: the purchase contract's own terms, such as a due diligence period, do. How radon comes up between a seller and a buyer is its own answer: does radon come up when a house sells here.
Who may do radon work in Virginia, and the system VDH describes
Virginia regulates who does radon work. Under Va. Code 32.1-229.01, no person may conduct or offer to conduct radon screening, testing or mitigation in the Commonwealth unless that person is listed as a professional by the National Radon Proficiency Program or the National Radon Safety Board, or meets other proficiency measures acceptable to EPA or the Board of Health.
The statute's word is "listed." Both programs are also named in the disclosure statement's radon subdivision, which points purchasers to their websites.
When a result calls for a fix, VDH describes the most common type of system as sub-slab depressurization, and says it does not require major changes to the home. How a system is laid out for a particular foundation is the mitigator's decision, made after looking at the house.
Radon-resistant construction, where a locality has adopted it
For a house not yet built, VDH describes a local option. Virginia allows counties and cities that EPA has designated high risk to adopt Appendix F of the International Residential Code into their local building code.
Doing so would require the use of RRNC techniques in most new residential single-family dwellings. Homes built over ventilated crawl spaces and multi-family buildings are currently exempt.
Virginia Department of Health, radon-resistant new construction
RRNC stands for radon-resistant new construction. VDH's list of Virginia jurisdictions known to require it, on a page last updated November 3, 2023, includes Montgomery and Wythe counties, along with Blacksburg, Christiansburg and Radford, among others. The list says which jurisdictions require the technique. It does not say what zone any of those localities carries, this guide infers none from it, and a list dated 2023 can change.
Whether a new house on a particular lot has to be built this way is settled by the building official who issues its building permit and the other permits a Virginia house needs. In Wythe County that office is Wythe County Building Inspection, 290 South Sixth Street in Wytheville, (276) 223-4505. Elsewhere it is the local building official.
Shorter questions about radon, disclosure and selling a house sit in the answers library.
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Good questions, straight answers.
Can a radon test from the house next door stand in for a test on this one?
No. VDH says the only way to know whether a particular home has a radon problem is to test it, and both low and high results have been found in every Virginia city and county. USGS says its geologic assessment is inappropriate for individual building sites, and EPA says its zone map should not be used to decide whether individual homes need testing. A neighboring result describes that house, on the days it was tested.
When in the year does VDH recommend testing a house for radon?
VDH recommends a short-term test of three to seven days between late October and early May, and says to avoid testing in the summer, during periods of heavy precipitation or high sustained winds. Its testing page adds that indoor radon usually reaches its maximum concentration during the coldest winter months, and that the lowest livable level should always be tested, because that is where the highest levels in a structure are typically found.
What does a radon result between 2 and 4 pCi/L mean?
It is below EPA's action level of 4 pCi/L, the point at which EPA's guidance is to fix the home, but inside the range where EPA suggests mitigation be considered. The decision in that range belongs to the owner. A radon professional listed by the National Radon Proficiency Program or the National Radon Safety Board can explain what mitigation would involve for that house.
Does a new house in Wythe County have to be built radon resistant?
VDH lists Wythe County among the Virginia jurisdictions known to require radon-resistant new construction, on a page last updated November 3, 2023. Where a locality has adopted Appendix F of the International Residential Code, the technique applies to most new single-family dwellings, and VDH says homes built over ventilated crawl spaces are currently exempt. Wythe County Building Inspection in Wytheville confirms what applies to a given permit.
Where this page's facts come from
Every rule, office and figure above traces to one of these. Rules change; check the office before you act on one.
- Indoor Radon Program Virginia Department of Health
- EPA radon risk map for Virginia (last updated May 15, 2024) Virginia Department of Health
- Radon testing and mitigation Virginia Department of Health
- Radon testing results Virginia Department of Health
- Radon Facts for Virginians Virginia Department of Health
- Radon-resistant new construction (RRNC), last updated November 3, 2023 Virginia Department of Health
- EPA Map of Radon Zones U.S. Environmental Protection Agency
- Virginia map of radon zones U.S. Environmental Protection Agency
- Open-File Report 93-292-C, geologic radon potential (Virginia chapter) U.S. Geological Survey
- Va. Code 32.1-229.01: radon screening, testing and mitigation Code of Virginia
- Va. Code 55.1-703: required disclosures for buyer to beware (B 14, radon) Code of Virginia