Maryland has significant radon risk, particularly in its western and central counties overlying the Reading Prong and Piedmont geological formations. The Maryland Department of the Environment estimates that approximately 40% of Maryland homes have radon levels above the EPA action level of 4.0 pCi/L. Maryland has enacted contractor licensing requirements and, for certain counties, RRNC requirements for new construction.
EPA Radon Zone Designation
Maryland counties are Zone 1 in the western and central portions of the state — Montgomery, Frederick, Carroll, Baltimore, Harford, Cecil, Howard, and Washington counties show the state’s highest average radon levels. These counties overlie Piedmont crystalline rock and Reading Prong granite. Eastern Shore and southern Maryland counties are generally Zone 2 to Zone 3.
Radon Contractor Licensing in Maryland
Maryland requires radon contractors to hold a Maryland state radon license for both measurement and mitigation work. The Maryland Department of the Environment administers the state radon licensing program. Licensure requires passing state examinations or demonstrating NRPP/NRSB certification, carrying liability insurance, and completing continuing education. The MDE maintains a searchable database of licensed radon professionals. Performing radon work without a Maryland license is a violation of state law.
Radon Disclosure Requirements in Maryland
Maryland requires sellers to disclose known material defects under the Maryland Residential Property Disclosure and Disclaimer Statement. This form includes radon-related questions — specifically whether the property has been tested for radon and what the results were, and whether a mitigation system is installed. Maryland sellers with knowledge of elevated radon test results must disclose them. Radon testing is standard practice in western and central Maryland real estate transactions.
Radon-Resistant New Construction in Maryland
Maryland has enacted RRNC requirements for new residential construction in Zone 1 counties through adoption of IRC Appendix F in certain jurisdictions. Montgomery, Frederick, Carroll, and other high-radon counties have incorporated RRNC requirements into local building codes. Buyers of new construction in Maryland’s Zone 1 counties should confirm RRNC compliance with the builder and local building department.
Frequently Asked Questions
Does Maryland require radon contractor licensing?
Yes. Maryland has comprehensive state radon licensing for both measurement and mitigation contractors, administered by the Maryland Department of the Environment. Verify license status through MDE before hiring any contractor.
What parts of Maryland have the highest radon?
Western and central Maryland counties — Montgomery, Frederick, Carroll, Baltimore, Harford, Cecil, Howard, and Washington counties — have the state’s highest radon potential, overlying Piedmont and Reading Prong geology.
Does Maryland require RRNC for new homes?
Some Zone 1 Maryland counties have adopted RRNC requirements locally. Verify with your local building department — requirements vary by jurisdiction.
Maryland Radon Data and County-Level Information
The Maryland Department of the Environment publishes county-level radon data from the Maryland Radon Survey and ongoing testing results. MDE’s county data shows that Montgomery County has among the state’s highest average indoor radon concentrations, driven by the Reading Prong granite geology beneath much of the county. Frederick County, Carroll County, and Harford County consistently show elevated averages. The MDE radon program website provides county-level maps and average concentration data for homeowners researching their specific area.
Baltimore Area Radon Risk
Baltimore City and Baltimore County are Zone 1 to Zone 2, with meaningful radon risk throughout the Baltimore metropolitan area. Howard County — which spans the suburban corridor between Baltimore and Washington — is Zone 1. Anne Arundel County (Annapolis area) is Zone 2. The Baltimore metropolitan area’s mix of older housing stock (pre-1980 homes with basement blocks, stone foundations, and minimal sealing) and Zone 1 geology makes testing an urgent priority for Baltimore-area homeowners who have not yet checked.
Maryland Testing Resources
The Maryland Department of the Environment Radon Program provides resources including a certified contractor database, educational materials, and guidance on interpreting test results. Maryland participates in EPA’s State Indoor Radon Grant (SIRG) program, which funds testing assistance and public education. Contact MDE directly for the most current list of licensed Maryland radon contractors and any available test kit assistance programs.
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