ADU Design & Permit Plans in Monterey County

One housekeeping point first, because it affects everything else you will read on this subject. California ADU law used to sit at Government Code §65852.2. It was renumbered into §§66310–66342 effective March 25, 2024. The substance carried over; the citations did not.

The provisions that shape most Peninsula projects:

• The by-right category. On a lot with an existing or proposed single-family dwelling, one detached new-construction ADU of up to 800 square feet with four-foot side and rear setbacks is allowed by right (§66323(a)(2)).
• Height still applies. A local agency may set a limit — generally 16 feet detached, or 18 feet within half a mile of a major transit stop.
• Approval is ministerial — no hearing, no discretionary review, no design board weighing in on whether the neighbors will like it (§§66317(a), 66335(a)).
• Conversions have their own rule. Converting existing space or an accessory structure is not subject to the four-foot setback, only to fire and safety setbacks (§66323(a)(1)).
• Parking is mostly gone. The maximum is one space per unit or per bedroom, whichever is less, and several exemptions remove it entirely.

Requirements and timelines described here were researched in September 2026 and are typical rather than guaranteed. Verify current requirements with the building department for your jurisdiction.

Ministerial review comes with statutory deadlines rather than a queue position:

• 15 business days for the agency to determine whether your application is complete. Miss it and the application is deemed complete.
• 60 days to approve or deny once it is complete — running from completeness, never from filing. Miss it and the application is deemed approved (§66317).

Keep a dated submittal receipt and put any follow-up in writing. How a deemed approval is administered still varies by jurisdiction.

Parking rarely applies. The maximum is one space per unit or per bedroom, whichever is less, and none may be required where the ADU is:

• within half a mile walking distance of transit;
• in an architecturally and historically significant historic district;
• part of the existing primary residence or an accessory structure; or
• where on-street parking permits are required but not offered to the ADU’s occupant.

By-right units are exempt entirely.

This is the most misunderstood point in ADU work on this coastline, and the one that costs people months.

State ADU law applies in the coastal zone. It does not alter or lessen the Coastal Act (§66329). Ministerial approval is not a coastal exemption: a coastal development permit can still be required, and where it is, the coastal process runs alongside your ADU approval rather than instead of it. Recent amendments help — no public hearing is required for an ADU coastal development permit, the two processes run concurrently, and the agency must act within 60 days — but the permit itself does not disappear.

So for Carmel, Pacific Grove, Pebble Beach and the coastal edges of Monterey, the first question on any ADU is whether the parcel sits in the coastal zone and whether the local coastal program requires a CDP. That answer is parcel-specific. The full explanation of how ADU approval works.

Requirements and timelines described here were researched in September 2026 and are typical rather than guaranteed. Verify current requirements with the building department for your jurisdiction.

A complete ADU submittal set carries:

• A site plan — existing dwelling, proposed unit, setbacks, lot coverage, separation, utilities and drainage.
• Measured as-built drawings for conversions and attached units.
• Dimensioned floor plans showing the independent living facilities the definition requires.
• Elevations and sections, with heights measured the way your jurisdiction measures them.
• Framing and structural plans, coordinated with your engineer.
• Electrical, plumbing and mechanical layouts, including how the unit is served and metered.
• Title 24 documentation for the new conditioned area.

Cost moves with new construction versus conversion, whether the existing house is documented, the site, whether a coastal permit applies, and utility routing. Sewer or septic capacity and electrical panel capacity decide more ADU layouts than aesthetics do. Monterey County generally expects a geotechnical investigation, though the building official may waive a full report for detached accessory structures of 500 square feet or less, as published — what triggers a soils report.

In the City of Monterey, every ADU adds or relocates plumbing fixtures, so the Monterey Peninsula Water Management District enters the approval path and the property needs sufficient water credits. Confirm that in week one.

Requirements and timelines described here were researched in September 2026 and are typical rather than guaranteed. Verify current requirements with the building department for your jurisdiction.