ADUs in Coastal Zones

Can you build an ADU in a coastal zone? Learn all about permitting, timeline, budget, and design considerations for building an ADU on the California coast.

Last updated 
May 15, 2023
ADUs in Coastal Zones

Otto's Guide to Building ADUs in Coastal Zones

Building an accessory dwelling unit (ADU) is a popular way to increase living space, rental income, and overall home value. However, if you are a homeowner in one of California’s coastal areas, you may be unsure about coastal zone requirements and their impact on ADU development—or if ADUs are even allowed within coastal zones at all.

In this blog post, we’ll answer some of the most common questions about ADUs in coastal zones and share considerations and best practices for designing and building coastal casitas.

What is the Coastal Overlay Zone?

California has about 840 miles of coastline, and while it only makes up 22% of the state’s land mass, these coastal areas account for 68% of the population and 80% of GDP.

The California Coastal Act, passed in 1976, led to the creation of the California Coastal Commission (CCC) and the development of Coastal Overlay Zones (COZs). The goal of these Coastal Overlay Zones is to protect California’s wetlands, beaches, shoreline access, and scenic views.

The CCC works with municipalities to create additional building requirements for coastal areas, called Local Coastal Programs (LCPs), to support conservation of the California coast and its resources.

Can You Build an ADU in a Coastal Zone?

Yes, ADUs are allowed within Coastal Overlay Zones—in fact, the CCC encourages the building of new ADUs in existing residential areas as a means to increase lower-cost housing options with fewer adverse environmental impacts. However, ADU development within COZs is more complex than in non-coastal zones, and there are often additional requirements (see “Special Considerations for Coastal ADUs” section below).

As a general rule, the closer your property is to the beach, the more restrictive the design and building guidelines. Permitting will likely be more expensive and time-consuming as well.

Bear in mind that it can be difficult to secure ADU permits for properties located within the following sensitive ecological zones (many of which apply to parts of the COZ):

  • Bluff Top Site
  • Environmentally Sensitive Habitat Area
  • Hillside Overlay Zone
  • Very High Fire Hazard Area
  • Wildland Urban Interface Site

Building Department. vs Coastal Overlay Zone Requirements

All construction within COZs must adhere to the city’s building requirements as well as LCP (Local Coastal Program) review. This can sometimes be confusing, as the guidelines may contradict each other.

This is one of many reasons why it’s best to work with an experienced full-service ADU company like Otto, as it can be very challenging and time-consuming for a homeowner to navigate alone (or for a contractor with little ADU experience).

HOAs and Neighborhood Associations/Planning Departments

Homeowners Associations and neighborhood planning departments cannot veto ADU development, but they can slow down the permitting process and place limits on what you can and can’t do. For example, your HOA might say you can’t convert your garage into an ADU because no driveway or off-street parking is allowed, or place limits on the height and external appearance of the unit.

Do ADUs Require Coastal Development Permits?

In most cases, an accessory dwelling unit located within a Coastal Overlay Zone requires a Coastal Development Permit (CDP). However, some attached and conversion ADUs may be exempt from CDPs.

Conversions of existing residential structures that do not require the removal or replacement of major structural components—such as exterior walls, foundations, and roofs—may not meet the Coastal Act’s definition of “development.” As such, these projects may be exempt from coastal permit requirements.

Special Considerations for Coastal Zone ADUs

Additional Requirements

The most common restrictions on accessory units in coastal zones concern parking, building height/view corridors, and environmental impact.


While parking requirements are generally waived for ADUs within a half-mile walking distance of public transit, they still apply to certain properties within the COZ. These include properties  within limited parking areas or within 500 feet of the coast.

View Corridors

Because scenic ocean views are a fundamental part of coastal property values, new developments (including ADUs) may not block or otherwise interfere with a neighbor’s ocean view. As a result, building heights are limited within coastal zones.

Environmental Impact

Keeping with the CCC’s mission of protecting California’s coastline, ADUs (as well as all other developments) within the COZ must adhere to rigorous standards to ensure that neither the construction nor the structure itself will have any adverse effects on the delicate coastal ecosystem.


As a general rule, ADUs within coastal zones take longer to permit than non-coastal units. Depending on the particular Coastal Overlay Zone and the property’s proximity to the beach, additional permitting time can be anywhere from three months to two years.

The good news is that the coastal zone review usually happens in tandem with the building department review, so you don’t need to wait for one set of permits to be issued before starting to secure the other.


In addition to the increased timeline, coastal ADUs are often more expensive to build.

There is an additional fee for the Coastal Development Permit on top of the Building Department Permit fee, which is usually a few thousand collars. Specialized design requirements can also add to a beachside ADU’s cost.

In more restrictive areas (i.e. areas closer to the beach), one can expect to spend up to $16k on additional costs.


Separate from Building Department and Local Coastal Program design requirements, you’ll want to factor in some design considerations of your own.

As with any ADU, consider your intended usage. Will your in-law unit be a short-term home for visiting family, a home office or studio, or a full-time rental unit? The primary intended usage will impact your design choices. This approach also applies if you’re envisioning a flexible space, such as a home office that can double as a guest house.

Consider the demographics of the surrounding area, particularly if you’re planning on renting out your backyard home. If your neighborhood is urban and densely populated, you might want to add additional bedrooms and parking spaces to make your unit more desirable to prospective tenants. Read our article on how to vet and keep great tenants for more ideas on making your ADU renter-friendly.

Finally, if you have a view of the coast, design your granny flat to maximize it! Consider floor-to-ceiling windows in the living room or a bedroom terrace with French doors overlooking the ocean. Your guests or tenants will thank you.


ADUs can be an excellent addition to your coastal property. The process is a little more involved than building an ADU outside of the coastal zone, but well worth the extra time and money.

Because seaside ADUs and more nuanced and complex, it’s best to work with a firm experienced with building ADUs in coastal zones. Otto has extensive experience designing and building accessory dwelling units all over Southern California, including within Coastal Overlay Zones.

Contact Otto today for a free consultation to start planning your beautiful beachfront ADU.

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