Gaithersburg, MD Fence Regulations: Retaining Walls (2026)

The city's local amendments to the International Residential Code (2021), adopted at section 5-4 and modified at section 5-5, rewrite the code's work-exempt-from-permit list. ' Anything taller than 3 feet falls outside that exemption and requires a building permit before construction. 3(B)(1), treats retaining walls as the one exception to its corner-lot sight-triangle rule, which otherwise caps structures to 3 feet for 25 feet from a street intersection: retaining walls are permitted there specifically where changes in street grade, width, or alignment have made them necessary.

Larger commercial or site-development retaining walls tied to grading, stormwater, or floodplain work are also treated as regulated 'development' under section 4550 of the floodplain chapter, which requires an engineering analysis before a retaining wall or similar erosion-control structure is approved in a mapped floodplain, on the theory that it could divert floodwaters onto neighboring elevated structures. Because Gaithersburg's own text mixes a flat height trigger for a residential permit with a narrower sight-triangle exception, and reserves engineered review for floodplain locations, homeowners planning anything over 3 feet, or any wall near a mapped floodplain, should confirm with Permits and Inspection Services before building.