Permits by Project
Do You Need a Permit for Basement apartment or English basement unit?
Basement apartment / English basement: creating or legalizing a rental unit (egress, ceiling height, certificate of occupancy).
Of the 10 areas we checked, a permit is required in 6 and we found no official answer in 4.
Washington, DC
Washington, DC
Permit required- When it applies
- creating a separate basement rental unit
- Permits
- Building, Certificate of occupancy, Rental license
- Notes
- Alteration and Repair building permit via DOB; Certificate of Occupancy via DOB; BBL 'One Family Rental' category (DLCP) required to rent; zoning must allow the unit. Egress/ceiling height per construction codes.
Source: DOB How to Get a Permit; DLCP Business Licensing FAQs, checked 2026-10-07
Maryland
Anne Arundel County, MD
Permit required- When it applies
- finished basement / ADU as two-unit multiple dwelling (Bill 6-23, 18-10-122)
- Permits
- Building, Electrical, Plumbing, Mechanical, Zoning certificate of use, Rental license
- Who pulls it
- A licensed contractor
- Notes
- 'Residential Finish Basement' requires a permit. ADU allowed as two-unit multiple dwelling; MDL requires Zoning Certificate of Use + Health/Fire Marshal inspection + MDE lead compliance. Egress/ceiling height per code — not detailed on pages reviewed.
Source: I&P Do I need a Permit?; MDL page, checked 2026-10-07
Charles County, MD
Permit required- When it applies
- accessory apartment per Code 3.01.700
- Permits
- Zoning permit, Building, Electrical, Plumbing, Mechanical
- Notes
- One accessory apartment per SF dwelling; min 300 sq ft; ≤50% of dwelling (in-building) or ≤50% of accessory structure with ≤2 BR; County Health Dept water/sewer approval before zoning permit; no street-facing entrance added. ZTA 25-189 (ADU flexibility) introduced 4/2026, hearing 7/7/2026 — outcome not confirmed.
Source: Charles County Code 3.01.700, checked 2026-10-07
Montgomery County, MD
Permit required- When it applies
- accessory dwelling unit (ADU) on single-family detached lot
- Permits
- Building, Electrical, Plumbing, Mechanical, Rental license
- Notes
- DHCA Class 3 ADU: SF-detached only; owner must occupy principal dwelling or ADU; attached ≤1,200 sq ft (basement-only may equal basement sq ft); detached ≤ least of 50% principal footprint, 10% lot, 1,200 sq ft; parking required (waived near transit). 'All applicable building permits must be obtained through DPS and/or WSSC and finalized before DHCA can approve the license.'
Source: DHCA ADU Requirements; DHCA Licensing and Registration, checked 2026-10-07
Prince George's County, MD
Permit required- When it applies
- creating/finishing a basement dwelling unit
- Permits
- Building, Certificate of occupancy, Rental license
- Notes
- 'Put up partitions and finish rec room B Y'; 'Construct, dig or enlarge a basement under existing dwelling B Y.' Finished basements need Use & Occupancy approval; single-family rental license via DPIE (Momentum) before renting. Egress/ceiling-height details per code — not detailed on pages reviewed.
Source: DPIE Homeowner's Guide to Permits; DPIE Code Enforcement (rental licenses), checked 2026-10-07
Northern Virginia
Arlington County, VA
Permit required- When it applies
- accessory dwelling
- Permits
- Building, Electrical, Plumbing, Mechanical
- Notes
- County regulates accessory dwellings (Declaration of Covenants process); interior-alteration submission + mechanical plans required (no mechanical waiver). Zoning/occupancy/size rules apply — see county accessory-dwelling materials.
Source: Arlington Residential Building Permit page, checked 2026-10-07
City of Alexandria, VA
Not confirmed- Notes
- No official answer found. no official Alexandria ADU/basement-apartment page found in this research.
Ask the permit office: Department of Code Administration — Alexandria Permit Center
Fairfax County, VA
Not confirmed- Notes
- No official answer found. no official Fairfax County ADU page found in this research.
Ask the permit office: Land Development Services (LDS)
Loudoun County, VA
Not confirmed- Notes
- No official answer found. no official Loudoun ADU page found in this research.
Ask the permit office: Building and Development
Prince William County, VA
Not confirmed- Notes
- No official answer found. no official PWC accessory-apartment page found in this research.
Ask the permit office: Building Development Division, Department of Development Services
Summarized from each area’s official permit pages and codes, as of October 2026. Some Maryland municipalities issue their own permits, rules change, and many answers depend on the exact scope, so confirm with the permit office before work starts. This is general information, not legal advice.
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