Mountain City made a specific appendix choice.
The town’s list includes ten appendices and excludes Appendix F. Radon-resistant features may still be installed voluntarily, but they are not required by that adoption.1
The county picture
A thin safety net in a mountain housing market.
Mountain City adopted the 2018 IRC but left Appendix F—the radon appendix—out. Outside town, Johnson County is absent from the state’s residential-permit list, pointing to no state residential enforcement program. Buyers cannot assume even a new home has passive radon controls.12
Official risk profile
EPA Zone
2
Zone 2 is the moderate-potential category, associated with predicted average indoor levels of 2–4 pCi/L. It is a county-scale planning estimate, not a reading for an address.56
The dashboard gave one useful—but fragile—signal.
TN Radon Testing dashboard · one live load
4.5 pCi/LObserved average for a tooltip that explicitly identified Johnson County. The same tooltip showed a 6.4 maximum; its median label had no rendered value.7
The sample size was not shown, and four attempts after reload did not reproduce the tooltip.
6.4Observed maximum, pCi/L
—Median did not render
?Sample size unknown
!Treat 4.5 as weak evidence, not a county verdict
The value came from one successful county-labeled render and failed to reproduce on a second load. The dashboard’s 2022–2023 charts show Northeast Region aggregates, not Johnson County counts or percentages.7
A home-level test remains the only way to know a property’s radon level.
Building codes
No code-enforced radon backstop
Adopting the IRC does not automatically adopt its optional appendices. The appendix list decides whether radon-resistant construction is mandatory.
Jurisdiction
Radon status
What the record supports
Town of Mountain CityOptional
Municipal Code §12-101 adopts the 2018 IRC through Ordinance #1714, December 2021, with appendices A, B, C, E, G, J, K, N, P and Q. Appendix F—Radon Control Methods—is absent. The MTAS-hosted code should be checked against the town recorder’s current copy.1
Unincorporated Johnson CountyOutside state list
Johnson County does not appear among the seven counties where the SFMO currently requires residential permits in unincorporated areas. That points to no state-enforced IRC program here, but the county opt-out resolution number and date were not found online.23
Public rules & transactions
No special local radon regime was found
The reviewed municipal code and web sources showed no Johnson County- or Mountain City-specific radon rule for public buildings, schools, rentals or home sales. Direct local confirmation would close that question.
Schools
Tennessee law encourages local education agencies to run indoor-air-quality programs that may include radon testing. It does not make testing mandatory.10
Home sales
No Tennessee radon-test mandate was found. Sellers disclose known material defects, while buyers can make radon testing an inspection contingency.11
Free test kits
TDEC’s Radon Program offers free kits to homeowners. Time-sensitive transactions may call for a certified professional.12
How do I find a certified radon professional in Johnson County?
Tennessee doesn't license radon testers or mitigators, so national certification is the best way to check qualifications. The Tennessee Radon Program points residents to two directories: search them by ZIP code and widen the radius if nothing is listed nearby.
We don't recommend or rank companies. Before you hire, check the certification number in the directory yourself and ask for a follow-up test after any system is installed. Questions to ask a radon professional.
Homebuyer guidance
Testing is buyer-driven here.
The market is small, rural and lightly permit-tracked. None of that lowers the importance of a property-specific result.
01
Put the test in writing
Tennessee does not require a radon test at sale. Add it to the inspection contingency and leave enough time for a proper measurement.11
02
Do not equate new with radon-ready
Mountain City’s appendix list omits radon controls, and the unincorporated county is outside the state permit list. Ask what was installed, then test.12
03
Recheck credentials
The only local NRPP listing was near expiry at the time of research. Verify current certification in the directory before scheduling.8
County context: Census QuickFacts reports 18,718 residents in 2025, up 4.3% from 2020; 8,847 housing units; 77.5% owner occupancy; a $178,600 median owner-occupied value; and only 6 building permits in 2025.13
Questions answered
Johnson County radon FAQ
Short answers grounded in the code record, EPA zone map, Tennessee dashboard and certification directories.
Yes. It is EPA Zone 2. A Tennessee dashboard tooltip showed a 4.5 pCi/L average and 6.4 maximum on one load, but the sample size was unknown and the values did not reproduce after reload.
No. Mountain City adopted the 2018 IRC with appendices A, B, C, E, G, J, K, N, P and Q. Appendix F is not included.
Johnson County is absent from the current State Fire Marshal list of counties requiring state residential permits. That points to no state IRC program, but the county opt-out resolution is not yet confirmed.
One NRPP measurement professional was listed in Mountain City on October 16, 2026. His certification was due to expire October 31, so verify current status before hiring. No Tennessee NRSB measurement pro appeared within 50 miles.
No radon-specific testing mandate was found. Sellers disclose known defects; buyers can add a radon inspection contingency, and TDEC offers free homeowner test kits.
Source ledger
Read the record
Official records establish the code framework. Dashboard and professional-directory findings are dated observations from October 16, 2026.
- Mountain City Municipal Code, Title 12 — code, appendices and Ordinance #1714.
- Tennessee SFMO permit jurisdiction list.
- Tennessee SFMO Residential Permits.
- MTAS opt-out explainer.
- EPA Map of Radon Zones.
- EPA Map of Radon Zones: Tennessee.
- Tennessee Radon Testing dashboard.
- NRPP listing: Matt Leukroth.
- NRPP professional directory.
- NRSB Find a Professional.
- T.C.A. §49-2-121.
- Tennessee residential disclosure form.
- Tennessee Department of Environment and Conservation.
- Census QuickFacts: Johnson County.
- Mountain City aerial image source.