ADUs in Del Mar: Foundation and Review Questions

An accessory dwelling in Del Mar often begins as a modest idea: a place for visiting family, a caretaker’s quarters for a house that sits empty part of the year, or a long-term rental. The town’s rules for these units are set out in Chapter 30.91 of the Municipal Code. The version the City posts, dated June 2025, rewards a slow read. It changes the usual sequence of reviews in ways that put foundation questions near the front.

This entry walks through that chapter from the ground up. It is not legal advice, and the City’s planning staff interpret their own code. It is a way to arrive at the first meeting with the right questions.

Which reviews fall away

Section 30.91.030 says an ADU designed to the chapter’s standards, or a junior ADU designed to its standards, is exempt from several discretionary permits, except where an Administrative Coastal Development Permit is required. Among them:

• Design Review. Exempt from a Design Review Permit in all of the City’s zones, including the zones its code labels Carmel Valley Precise Plan and Specific Plan.
• Land Conservation Permit. Exempt for grading within the ADU’s development footprint. An excavation or grading permit still applies, and grading outside the footprint may need a Land Conservation Permit through a separate process.
• Floodplain Development Permit. Exempt in the Floodplain Overlay Zone in defined cases, described below.
• Conditional Use Permit. Exempt on bluff, slope and canyon lots and coastal bluff lots when setback conditions are met, also described below.

For owners used to Del Mar’s design review, this is a meaningful change. The chapter also says the City is to approve or disapprove a complete building permit application ministerially, within time periods set by state law. The state’s ADU Handbook, published by the Department of Housing and Community Development, explains the statewide framework behind that.

Which ones stay

Two things do not go away. Every ADU and junior ADU needs a building permit and must meet state and local building codes. And approval requires an Administrative Coastal Development Permit under Chapter 30.75, unless the project fits an exemption. The chapter notes that state ADU law does not lessen the effect of the Coastal Act, although the City is not required to hold public hearings on these coastal permits.

The foundation can decide the coastal permit

Here is where structure enters early. The chapter exempts an ADU from the Administrative Coastal Development Permit in two cases:

1. It is created by converting entirely existing, legally established habitable space inside the primary structure, without removal or replacement of major structural components. The chapter names roofs, exterior walls and foundations as examples.
2. It is directly attached to the existing house and otherwise qualifies as exempt development under the Coastal Commission’s regulation for improvements to existing single-family residences, 14 CCR 13250.

So a conversion that needs new footings, or replacement of an existing foundation, may move out of the first exemption. A careful look at the existing foundation before design is settled can tell an owner which path the project is on.

North Beach and the floodplain

Del Mar participates in FEMA’s flood insurance program, and the City posts its flood-map information on its FEMA page. For lots in the Floodplain Overlay Zone, Chapter 30.91 exempts an ADU from a Floodplain Development Permit if it sits entirely within an existing habitable structure, or within existing non-habitable space at or above base flood elevation that is converted. A new structure qualifies if:

• the lowest floor, including any basement, is at or above base flood elevation plus one foot
• the structure is anchored to prevent flotation, collapse or lateral movement from hydrodynamic and hydrostatic loads, including buoyancy
• materials are resistant to flood damage
• plumbing, electrical and mechanical equipment is designed to keep water out

Each of those is, in part, a foundation question: how high the floor sits, how it is anchored, and what it is made of. Our page on North Beach floodplain foundations covers the setting, and our post on flood vents and enclosures covers the space below the floor.

Bluff, slope and canyon lots

For lots in the Bluff, Slope and Canyon Overlay Zone, the chapter exempts an ADU from a Conditional Use Permit if it is set back at least 20 feet from the top of a steep slope and at least 10 feet from the bottom. In the Coastal Bluff Overlay Zone, the exemption applies if the ADU is built primarily above grade and set back at least 40 feet from the top edge of the coastal bluff.

In the Coastal Bluff Overlay Zone, the chapter also requires a proposed ADU to follow the recommendations of a geotechnical report when it is in a new structure, or in non-habitable space converted to habitable space. The state residential code separately lets the building official require a soil test where expansive, compressible or shifting soils are likely (CRC R401.4). Our page on bluff and hillside homes explains how slope position affects foundations here.

Flatter lots, and a word on jurisdiction

First, a boundary note. Chapter 30.91 governs lots inside the City of Del Mar. Homes in Del Mar Heights and Carmel Valley carry Del Mar mailing addresses but sit in the City of San Diego, which has its own ADU rules. Our post on Del Mar versus Carmel Valley rules explains that split.

On flatter lots inside city limits, away from the overlays, the bluff and flood conditions may not apply, but the ground still does. A new ADU often sits on a part of the lot that has never carried a building: a former yard, a filled corner, a pad near a slope. The questions are the familiar ones. Was the area cut or filled, does a soils report exist, and how will the new footings meet any existing structure?

Notes for a first conversation

Owners who arrive prepared tend to have answers to these:

1. Which overlay zones apply to the parcel, if any.
2. Whether the plan is a conversion, an attached unit or a detached unit.
3. Whether any foundation, exterior wall or roof will be removed or replaced.
4. The base flood elevation, if the lot is in the floodplain overlay.
5. Distances to the top and bottom of any steep slope or coastal bluff.
6. Any existing geotechnical or soils reports for the lot.

Variables in the foundation work

When an ADU calls for new or modified foundations, scope tends to follow a short list: overlay requirements, flood elevation and anchorage, soils report findings, the connection to existing structure, access on narrow or sloped lots, and whether the work affects the coastal permit path. We coordinate with licensed engineers as needed for soils and foundation design. We do not predict outcomes from Planning or the Coastal Commission, and we do not set timelines on their behalf.

Our design review and permits page explains how review layers fit together in Del Mar, and our foundation inspection page describes an existing-conditions visit. We serve the whole city of Del Mar. If an ADU is on your horizon, request a Free Quote for a look at the ground before the design is fixed. Owners of beachfront lots may also find our note on seawall and revetment maintenance useful.