St. Louis, MO Accessory Structures: ADU Impact Fees (2026)

Missouri municipalities lack general statutory authority to impose true impact fees on residential development. Missouri courts have held that fees on new construction must be tied to actual user services or to specific statutory authorization (see Home Builders Ass'n of Greater St. Louis v. City of St. Peters, 868 S.W.2d 187 (Mo. App. 1994), which struck down a parks fee adopted without state enabling authority). As a result, St. Louis ADU costs are limited to: Building Division permit fees calculated from construction valuation under SLRC Title 25; plan-review and trade-permit fees (mechanical, plumbing, electrical); Metropolitan St. Louis Sewer District (MSD) connection charges, set by MSD's published rate schedule based on actual fixture units and capacity; and water connection fees from the St. Louis Water Division if a new tap is required. There is no St. Louis Public Schools impact fee, no parks fee, and no transportation impact fee tied to an ADU. The Real Property Tax Department will reassess the parcel for property tax based on the added improvement, but that is a property-tax consequence, not an impact fee. ADUs that share existing MSD and water service with the principal dwelling typically avoid new connection fees.