Missouri ADU permit requirements
Last reviewed: June 20, 2026
Quick answer
Permitting an accessory dwelling unit (ADU) in Missouri means pulling a building permit from the local authority that issues it. ArchPermit tracks 11 source-cited requirements for this jurisdiction. These requirements were last reviewed June 20, 2026; confirm the exact forms and fees with the local permitting authority.
In Missouri, ADUs are regulated locally. This is a general new-dwelling starting checklist based on the building code. Confirm the exact requirements, forms, fees, and code edition with your local permitting agency.
Missouri has no statewide building code, no statewide residential energy code, and no statewide ADU law; all are set locally (e.g., Kansas City, St. Louis). Confirm allowance, code edition, and permitting with your city or county.
- Adopted building code compliancerequired
The ADU must comply with the residential building code adopted by the local jurisdiction; confirm the edition with the AHJ.
source · reviewed 2026-06-20 - Building cross-sectionsrequired
Cross-sections through the structure showing ceiling heights, wall/roof assemblies, insulation, and fire/sound-rated assemblies where required.
source · reviewed 2026-06-20 - Egress & life-safetyrequired
Emergency escape and rescue openings (egress windows), smoke and carbon-monoxide alarms, and required exits per the adopted residential code.
source · reviewed 2026-06-20 - Energy code compliancerequired
Energy-code compliance documentation for the conditioned space (typically IECC / state energy code, e.g. CF1R-style forms), printed on or submitted with the plans.
source · reviewed 2026-06-20 - Exterior elevationsrequired
Elevations of each affected building face showing height, exterior materials, and openings; existing vs. proposed where exterior changes occur.
source · reviewed 2026-06-20 - Floor plansrequired
Dimensioned floor plans of the ADU (and affected areas of the primary dwelling) showing rooms, uses, door/window locations, egress, and fixture/equipment locations.
source · reviewed 2026-06-20 - Foundation planrequired
Foundation plan with footing/stem-wall sizes and details (or a cited site-specific design), per the adopted residential code.
source · reviewed 2026-06-20 - Framing / structural plansrequired
Floor, wall, and roof framing showing member sizes, spans, spacing, connections, and lateral bracing; structural calculations where the framing is non-conventional.
source · reviewed 2026-06-20 - Local zoning / setback compliancerequiredverify locally
Compliance with the local jurisdiction's zoning: permitted use, setbacks, height, lot coverage, and any ADU-specific standards. These are set locally. Confirm with the permitting agency.
source · reviewed 2026-06-20 - Mechanical / plumbing / electricalrequired
HVAC, plumbing fixtures and lines, and electrical (panels, circuits, outlets, lighting, smoke/CO alarms) for the new unit.
source · reviewed 2026-06-20 - Site / plot plan (to scale)required
Scaled site plan showing property lines, setbacks, existing structures, the proposed ADU footprint with dimensions to property lines, driveways/parking, and utility locations.
source · reviewed 2026-06-20
Missouri ADU permit questions
- Do I need a permit to build an ADU in Missouri?
- Yes. An accessory dwelling unit (ADU) in Missouri requires a building permit. ArchPermit tracks 11 cited requirements for this jurisdiction. Always confirm the exact forms, fees, and code edition with the local permitting authority that issues the permit.
- What does an ADU permit package require in Missouri?
- Core required items include: Adopted building code compliance; Building cross-sections; Egress & life-safety; Energy code compliance; Exterior elevations; Floor plans, plus 5 more. Each requirement links to its authoritative source, and nothing is permit-ready until an independent licensed professional reviews and seals it.