Lafayette, LA Accessory Structures: ADU Rules (2026)

Section 89-74 governs accessory apartments across the City of Lafayette and the unincorporated areas of Lafayette Parish. Only one accessory apartment is allowed per lot, and its maximum living area is set at whichever figure is larger: 25 percent of the principal dwelling unit's gross floor area, or 800 square feet flat. The apartment generally has to meet the same minimum setback requirements that apply to the principal structure on the lot, but the code carves out an exception for the "RS" (Single-Family Residential) and "RM" (Mixed Residential) zoning districts, where an accessory apartment's rear setback drops to a flat five feet regardless of what the principal structure's setback would otherwise require.

The rule sits inside Article 5 (Use Standards) of the Lafayette Development Code, alongside the separate provisions on detached accessory buildings (Sec. 89-73) and garages/carports (Sec. 89-81), and it was most recently amended by Ordinance No. JO-067-2024 on November 18, 2024. Because the size cap and setback rule apply regardless of whether the apartment sits inside the main house, above a detached garage, or in its own small structure, a homeowner planning a "granny flat" or garage apartment in Lafayette needs to run the math against both the 25-percent and 800-square-foot thresholds before finalizing floor plans, since exceeding either cap takes the unit out of compliance with this section.