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ADU Construction · St. Mary's County, Maryland
Permit required
In Maryland, a ADU Construction requires a building permit.
An accessory dwelling unit (ADU) always requires a building permit because it adds a habitable dwelling, including electrical, plumbing, mechanical permits and egress/zoning review. Plans are reviewed under the Statewide + local code (IRC 2021); apply through Montgomery County Department of Permitting Services before work begins.
Source: Statewide + local, IRC 2021 · Verified 2026 by StateDataIndex
Building an Accessory Dwelling Unit requires complex zoning, structural, and utility permits.
With a growing population of around 115,126 residents, St. Mary's County maintains a relatively streamlined permitting process compared to major urban hubs. Processing typically takes 1 to 3 weeks.
Code Compliance & Inspections
Work on your ADU Construction in St. Mary's County will be inspected to ensure full compliance with the current Maryland Building Performance Standards.
Concurrent Permits & HOAs
For St. Mary's County residents, we highly recommend reviewing your neighborhood HOA covenants before paying any municipal fees. Often, homeowners associations maintain stricter rules regarding materials and dimensions for your ADU Construction than the county itself.
Zoning & Cost Factors
Maryland integrates local zoning with state-level "Smart Growth" initiatives, heavily restricting sprawl and protecting the Chesapeake Bay watershed. Fortunately, Maryland maintains relatively builder-friendly regulations, keeping base permit fees competitive.
Estimated municipal base fee: $383–$585
This is a planning estimate only — actual fees in St. Mary's County depend on your project valuation. A typical breakdown looks roughly like:
- Application Fee: ~$135
- Plan Review Fee: ~$90
- Inspection Fee: ~$225
Always confirm exact fees with your local building department before applying.
Cost Comparison: St. Mary's County vs State Average
State Average Base Fee
St. Mary's County Estimated Base Fee
*Chart represents median application base fees and does not include project valuation percentages.
St. Mary's County Building Department
Office: Montgomery County Department of Permitting Services
Address: 2425 Reedie Dr 7th floor, Wheaton, MD 20902, USA
Phone: (240) 777-0311
Source: official St. Mary's County government records. Hours and procedures can change — call ahead to confirm.
How to Apply in St. Mary's County
In St. Mary's County, you or your contractor typically submit blueprints and a property survey to the local building department. Call ahead to confirm hours and accepted payment methods.
ADU Construction Requirements in St. Mary's County
Typical Submittal Package
When applying for a ADU Construction permit, you or your contractor will generally need to submit the following documentation for the city's review:
- Comprehensive architectural and structural plans
- Foundation engineering reports
- Sewer, water, and utility connection plans
- Site plan showing property lines and setbacks
Standard Ordinances & Processing Time
Key code points for a ADU Construction in St. Mary's County: ADUs typically have maximum square footage limits (often 800-1200 sq ft), height restrictions, and usually require dedicated off-street parking depending on local zoning.
Estimated processing time in St. Mary's County: 10 to 14 business days.
Frequently Asked Questions
What happens if I build a ADU Construction without a permit in St. Mary's County?
Building without authorization is considered a code violation. The local government can issue a Stop Work Order, forcing you to halt construction immediately. You may be subject to retroactive permit fees (often double the original cost), daily fines, or even a mandate to tear down the unpermitted work at your own expense.
Can a homeowner pull their own ADU Construction permit in Maryland?
Yes. Maryland generally allows property owners to act as their own general contractor under an Owner-Builder exemption. If you take this route, you assume full legal and financial liability and must ensure all work complies with the Maryland Building Performance Standards.
How much does a ADU Construction permit cost in St. Mary's County?
As a planning estimate, base municipal fees for a ADU Construction permit in St. Mary's County typically fall between $383 and $585. The final amount depends on your project valuation, so confirm the exact figure with the local building department.
How long does it take to get a ADU Construction permit in St. Mary's County?
Based on the size of St. Mary's County, the typical processing time is 10 to 14 business days. Times vary with the season and the building department application volume.
Where do I apply for a ADU Construction permit in St. Mary's County?
You can apply through the Montgomery County Department of Permitting Services or online via the county permit portal. For questions, call (240) 777-0311.
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Read GuideBuilding It Yourself? Here's What You'll Need
Planning an ADU? Tools homeowners use in the design and layout phase:
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Backyard ADU Design Guide (Book)
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Laser Level
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Franklin ProSensor Stud Finder
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25ft Tape Measure
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Other Permit Types in St. Mary's County
Planning another home improvement project? Check the requirements and fees for:
Nearby Jurisdictions in Maryland
Building near the county line? Check requirements for neighboring areas: