Permit Required? Required
Typical Fee Range $1,000–$3,500 Includes building, zoning, and utility capacity fees.
Fee Method Valuation-based
Apply Online Apply at Building Division →

What's Required in St. Louis

  • Building permit required for all secondary dwelling units.
  • Must have full kitchen and bathroom facilities for habitation.
  • Requires professional architectural plans including foundation.
  • Must meet lot coverage and setback rules for the zoning district.
  • Owner-occupancy of the primary home is often required.
  • Maximum size capped by specific neighborhood zoning.

How to Get a ADU Permit in St. Louis

1

Step 1: Zoning Verification

Confirm an ADU is allowed on your lot via the Building Division.

2

Step 2: Design Documents

Prepare detailed site plans and architectural drawings.

3

Step 3: Submit Application

Apply for a New Accessory Structure permit online.

4

Step 4: Multi-Agency Review

Checked by Building, Zoning, and Fire departments.

5

Step 5: Inspections

Full series from footings to final occupancy sign-off.

Frequently Asked Questions

Yes, provided it meets all building codes for habitation.
Often yes, though sub-metering from the main house may be allowed.
Expect 6-8 weeks for a new detached ADU.