Derwood Accessory Structures: Garage Conversions Rules (2026)

Garage conversions in Montgomery County require a residential building permit from the Department of Permitting Services (DPS). The converted space must comply with all IRC requirements for habitable rooms, including minimum ceiling height of 7 feet, natural light (window area at least 8 percent of floor area), natural ventilation or mechanical HVAC, insulation meeting Maryland energy code (IECC), and at least one egress window meeting IRC R310 (minimum 5.7 sq ft, sill no more than 44 inches above floor). Electrical, plumbing, and HVAC modifications each require separate permits. If the garage space being converted satisfies the minimum parking requirement under the zoning ordinance (typically 1-2 spaces per dwelling), the owner must demonstrate that replacement parking can be provided on-site (driveway, carport, or other covered area). Fire separation between the converted space and any remaining garage area must meet IRC requirements (1/2-inch drywall minimum, self-closing fire-rated door). The garage door opening must be properly infilled with a wall meeting structural and energy code requirements. If the conversion creates an ADU, the ZTA 19-01 ADU standards also apply.