Plymouth, MN Accessory Structures: ADU Rules (2026)

04 lets an ADU be incorporated into an existing single-family home, attached to it, built above an attached or detached garage, or stand alone as a detached accessory structure, but only on a residential lot in the FRD, RSF-1, RSF-2, RSF-3, or single-family residential PUD district that contains a single-family detached home. ADUs are barred from any property containing an apartment building, townhome, manor home, twin home, duplex, or any structure with more than one existing dwelling unit. Only one ADU is allowed per single-family detached lot, and it requires an administrative permit applied for before or alongside the building permit.

Every ADU, attached or detached, must meet the same minimum building setbacks as the principal home, and detached ADUs above a detached garage or standing alone follow the accessory building rules of Section 21120. Size is capped by type: an ADU attached to or incorporated into the home cannot exceed 30 percent of the home's gross floor area or 1,000 square feet, whichever is less, while a detached ADU is capped at 30 percent of the rear yard area or 700 square feet, whichever is less; every ADU must be at least 200 square feet.

Height is likewise tiered: an ADU attached to the home or above an attached garage cannot rise higher than the living portion of the principal building, a detached stand-alone ADU is capped at 15 feet or the principal building's height, whichever is less, and an ADU above a detached garage is capped at 21 feet or the principal building's height, whichever is less. The unit must match the home's architectural style, roof pitch, colors, and materials, connect to the same municipal sewer and water with no separate utilities, carry the same street address as the principal dwelling, and have a permanent foundation.