How the ADU permit process works in Walnut Creek and Contra Costa County
What homeowners in Walnut Creek and nearby cities should expect when permitting a backyard ADU: zoning checks, plan submittal, review timelines and inspections.
California's statewide ADU laws set a baseline that every city has to follow, and local rules fill in the rest. In practice, that means a backyard unit in Walnut Creek follows the same broad path as one in Lafayette, Concord or Danville, with different submittal portals, fees and lead times along the way.
Here is the sequence we walk our clients through before any concrete is poured.
1. Feasibility and zoning check
We start at the parcel: lot size, existing coverage, setbacks, easements, septic or sewer, panel capacity and access for equipment. This is also where we confirm whether an attached unit, a detached new build, or a garage conversion gives you the most usable square footage for the money.
2. Design and construction documents
Plans include the site plan, floor plans, elevations, sections, structural details and Title 24 energy compliance. Utility routing — water, sewer, gas and electrical — is decided here, because it drives a meaningful share of the budget.
3. Plan check submittal
The application goes to the building division with the plan set and calculations. Expect at least one round of corrections; responding quickly with a complete resubmittal is the single biggest factor in how fast approval lands.
4. Permit issuance and construction
- Site prep, foundation and underground utilities
- Framing, roofing and exterior weatherproofing
- Rough electrical, plumbing and mechanical, then inspection
- Insulation, drywall, finishes, cabinets and fixtures
- Final inspection and certificate of occupancy
Costs to plan for beyond construction
- Design, engineering and Title 24 documentation
- City plan check and permit fees
- Utility connections or a separate meter
- Site work: grading, drainage, hardscape and landscaping repair
Timelines vary by city and by how complete the first submittal is. If you want a realistic read on your own lot, we will do a walkthrough and tell you plainly what is and isn't feasible before you spend money on plans.