ADU coastal development permit: building an ADU in the coastal zone

When an ADU needs a coastal development permit

California's Coastal Act requires a coastal development permit (CDP) for most new development in the coastal zone, a strip that runs the length of the state and reaches inland by different distances in different places. A city with a certified Local Coastal Program (LCP) issues these permits itself, under rules the Coastal Commission has approved. Where there's no certified LCP, the Commission issues them.

The ADU laws didn't switch this off. Government Code section 66329 says the ADU article doesn't supersede or lessen the Coastal Act, with one practical carve-out: a city doesn't have to hold a public hearing on an ADU's coastal permit. So an ADU coastal development permit is an added review, not a new discretionary fight over whether you can build at all. The state's ADU handbook makes the same point: a coastal permit for an ADU must be decided within 60 days.

Whether your particular project needs a CDP depends on what you build. In the City of San Diego, the dividing line is whether the unit adds anything new. Under the city's coastal exemption rules, an ADU or JADU that isn't completely contained in the existing main house, adds habitable area or converts non-habitable space is treated as a new residential unit and can't use the exemption for improvements to existing homes.

Source: Ordinance O-21477, amending SDMC § 126.0704. Other exemptions in the city's code have their own exceptions, such as work on a beach or near a coastal bluff, so a city planner has the last word on your lot. For the basics of each ADU type, see what an ADU is and our comparison of attached vs. detached ADUs.

What state law says about coastal zone ADUs

Section 66329 sets the ground rules for every coastal city in California. In plain terms, the statute says:

• The Coastal Act still applies. A coastal city can apply its certified LCP to ADUs.
• No hearing is required. The city doesn't have to hold a public hearing on the ADU's coastal permit.
• 60 days. The city must act on the coastal permit within 60 days of a complete application, and the coastal review runs at the same time as the regular ADU review rather than after it.
• Where there's no certified LCP, the Coastal Commission itself must approve or deny the ADU's coastal permit within 60 days.
• A possible wait. If the ADU is filed together with a new main house on the same lot, the Commission can hold the ADU decision until it acts on the house.

The 60-day clock matches the deadline for ordinary ADU permits that we cover in California ADU laws. What the coastal layer adds is a second set of standards: the LCP's policies on things like public access, sensitive habitat and shoreline hazards.

The Coastal Commission has said it expects cities to follow both laws. In its guidance to local governments, the Commission rejected the idea that a city can avoid the ADU statutes by simply never amending its LCP. It also said ADUs can't conflict with the Coastal Act's Chapter 3 policies, such as those protecting wetlands, habitat, public access and coastal agriculture, but that most ADU applications raise none of those issues.

The Legislature pushed further with SB 1077 in 2024. The resulting law required the Commission, working with HCD, to publish guidance by July 1, 2026, on how cities can simplify ADU permitting in the coastal zone through LCP amendments. The Commission issued that guidance dated July 1, 2026. It's written for cities, covering minor and de minimis LCP amendments and categorical exclusions, so it doesn't change your permit by itself. It matters because it gives coastal cities a template for cutting coastal review for ADUs, which could make some future projects simpler.

Building an ADU near the beach in San Diego

In the City of San Diego, the coastal zone is mapped as the Coastal Overlay Zone. If your lot is in it, the city's ADU code applies with a few coastal differences. These are the ones that shape a design near the beach:

• Height. The voter-approved 30-foot coastal height limit applies to ADUs like any other building. We cover how it's measured, and where its boundary runs, in our two-story ADU guide. See also the ADU height limit in California.
• Parking. San Diego requires ADU parking only in the Beach Impact Area outside transit priority areas. That rule exists because the Coastal Commission asked for it: the city accepted Commission modifications on ADU parking in the Beach Impact Area in 2022. Details are in our guide to ADU parking requirements.
• Setbacks. The 4-foot side and rear setback applies to a taller ADU in the coastal zone until the city's 2024 update is certified there. See ADU setbacks in California.
• Shoreline and sea level rise. The same ordinance added limits on shoreline protection for ADUs in areas mapped for future sea level rise. If your lot is close to the water, expect questions about hazards.

The city's ADU bulletin notes that the Coastal Commission certified the city's 2024 ADU rules for the coastal zone, but some later amendments were still awaiting certification, so a coastal lot can be under an older version of the code than an inland one. Ask which version applies before you finalize plans. The full city process, from application to final inspection, is in our guide to the ADU permit process in San Diego.

Appealable and non-appealable areas

Not all of the coastal zone is treated the same. Near the shoreline, a local coastal permit can be appealed to the Coastal Commission. The Coastal Act defines that appeal area to include land between the sea and the first public road parallel to it, land within 300 feet of the inland edge of a beach, land within 100 feet of a wetland, estuary or stream, and land within 300 feet of the top of a coastal bluff.

• Non-appealable area. In the City of San Diego, a coastal permit there is a Process Two staff decision by Development Services, which can be appealed to the Planning Commission. That report involved two homes with 310 sq ft ADUs in the coastal zone.
• Appealable area. The city's final decision can also go to the Coastal Commission. For a lot between the sea and the first public road, the same section limits the grounds for appeal to a claim that the project doesn't meet the certified LCP or the Coastal Act's public access policies.

An appeal by a neighbor or the Commission can add months, so lots in the appeal area benefit most from a design that plainly meets every LCP standard. Ask the city early whether your parcel is in the appeal area.

Other coastal cities in San Diego County

Each coastal city in the county, from Oceanside to Imperial Beach, runs coastal permits its own way, under its own LCP or through the Commission where an area has no certified LCP. The state rules above apply in all of them, but the details differ.

Encinitas is a good example of how this tends to work. The city requires a coastal permit for ADUs and JADUs that aren't completely inside the existing main house, add habitable area, convert non-habitable space or are detached. You apply for the building permit online, and the reviewer opens the coastal permit record from that application, so you don't file two separate packages. Encinitas also publishes pre-approved ADU plans, which the City of San Diego accepts too.

Before you buy plans or sign with a builder, call the planning counter in your city and ask three things: is the lot in the coastal zone, is it in the appeal area, and does the coastal permit run with the building permit or separately.

How to find out if your lot is in the coastal zone

The official coastal zone boundary is set by maps the Coastal Commission adopted. Online maps are copies. SANDAG's coastal zone layer for San Diego County, for example, notes that its digital boundaries haven't been adopted by the Commission and don't replace the official version. Use them to get a first answer, then confirm:

• City of San Diego: ask Development Services whether the parcel is in the Coastal Overlay Zone, whether it's in the appealable or non-appealable area, and whether it's in the Beach Impact Area. Each changes what you can build.
• Other cities: ask the planning department, or look for the coastal zone on the city's zoning map.
• A title report or past permits for your home may also note a coastal permit, which tells you the lot has been reviewed before.

A lot near the edge of the zone is worth confirming in writing. Being a block outside it can mean no coastal permit, no 30-foot cap and no Beach Impact Area parking.

Planning a coastal ADU

The coastal permit adds review, not a different building. A few habits keep it from adding much time:

• Design to the LCP from day one. Height, setbacks and parking in the coastal zone are where redesigns come from.
• Keep the project inside existing space if it fits your goals. A unit carved out of existing living space may skip the coastal permit in San Diego. A junior ADU is often the simplest version of that.
• Watch the bluff and the beach. Lots near a bluff edge or the sand face hazard questions and appeal rights that an inland lot never sees.
• File complete. The 60-day clock starts with a completed application, so missing items only delay it.
• Budget for it. A coastal permit adds design and review work. We don't have a verified figure for the added fee, so ask the city for a current estimate, and see what an ADU costs in San Diego for the rest of the budget.

Choose a builder who has taken ADUs through coastal review in your city, and ask to see one of their coastal permits. Start with verified ADU builders in San Diego, check a contractor's license before you sign, and read how to hire an ADU contractor. If the lot is also on a slope or in brush, read our guide to building an ADU in a fire hazard zone.

Common questions