Briefing summary
- All of Solana Beach is in the Coastal Zone. The City’s Building Services page says development applications need Coastal Commission approval, and the applicant supplies the approval letter to the City.
- ADU and JADU rules are in SBMC 17.20.040(D), as amended by Ordinance 525. The City’s June 2025 submittal handout lists the plan items it expects.
- The handout says a drainage study by a registered civil engineer may be required for new ADUs outside the existing building footprint, and that a soils report prepared by a civil engineer may also be required after review.
- Foundation choices depend on whether the unit is a conversion, an attachment or a detached structure, and on the soil and slope at that spot.
- Outcomes and schedules belong to the reviewing agencies. Nothing here predicts either.
1. Know which kind of unit you are planning
The ordinance describes three ways to create an ADU: inside the existing walls of the house or an accessory structure, as an addition attached to the house, or as a new detached structure on the same lot. A junior unit is limited to 500 square feet and sits within a single-family home.
Each type puts different demands on the ground:
- Interior conversion. The foundation is already there. The question is whether it can carry the new use, and whether a garage slab, for instance, is fit to become a living-space floor.
- Attached addition. New footings meet old ones. The connection is a design problem in its own right.
- Detached unit. A new foundation on soil that may never have carried a building.
The ordinance’s height limits differ by type: 16 feet for a typical detached unit, with higher limits in specific cases, and up to 25 feet or the local limit, whichever is lower, for an attached unit. Setbacks of four feet apply to most new side and rear placements. Taller and closer to a line both affect how the foundation is designed.
2. A second permit track near the shore
The City’s Building Services page is direct about the order of things. Coastal development permits, waivers and exemptions are reviewed and approved by the Coastal Commission, not by the City. On a coastal bluff property, the City’s initial planning review will not be approved until the Coastal Commission letter is in hand. Off the bluff, owners are told to confirm with Planning whether Commission approval is needed.
The ADU handout repeats the point: the building permit application goes in with the plans and a copy of the Commission’s approval letter.
For an owner, the practical meaning is that foundation decisions made late can mean revisiting documents already reviewed by two agencies. Our page on Coastal Commission permits and foundation work and the earlier post on why the Commission signs off here explain the background.
3. What the submittal handout asks of engineers
Section 8 of the City’s handout, Engineering Requirements, is where foundation questions start to surface. It calls for:
- a topographic and grading plan prepared by a registered civil engineer or land surveyor, in two-foot contours, showing existing and proposed grades and drainage
- a drainage study by a registered civil engineer, which may be required for new ADUs outside the existing building footprint
- calculations of existing and proposed pervious and impervious areas, with a detention basin, hydrology report or soils report possibly required
- a soils report prepared by a civil engineer, which may be required after review of those items
None of those is a structural design by itself. Together they describe the ground and the water, which is what the foundation design depends on.
4. Treat the soil at the new footprint as unknown
A house pad was prepared for a house. The side yard, the back corner, or the slope behind the garage may not have been. The County’s 2023 hazard annex for Solana Beach ranks expansive soils as a low hazard citywide and landslide as medium. That is a citywide view. Conditions under one corner of one lot are a site question.
The Residential Code lets the building official require a soil test where expansive, compressible or shifting soils are likely, and adds setback rules for footings near slopes. On bluff-top lots, the geotechnical questions are broader still.
5. Look at the existing house before you attach to it
For a conversion or attachment, the condition of what you already have matters:
- Is the existing slab or raised floor level, or already showing settlement or cracking?
- Is there a crawl space, and is it dry?
- Are there signs of salt-air corrosion at exposed steel or connectors?
- Does water already collect on the side where the new unit goes?
A foundation inspection can document that before design. Our post on raised foundations under Solana Beach homes describes what the space under an older house often holds.
6. If you live in an HOA
Condominium and planned-development owners should read the CC&Rs and architectural rules before anything else. Common-area ground, shared drainage, and party walls can all bring the association into the decision. Boards weighing structural questions with their members may find our briefing on communicating findings to owners useful.
7. What changes the size of the foundation job
- Unit type: conversion, attachment or detached
- Soil conditions and any soils report findings at the new footprint
- Slope, bluff proximity and setback requirements
- Drainage changes from the new roof and paving
- Condition of the existing foundation where it is reused or connected
- Access for equipment on a tight coastal lot
- Coordination among the reports the City and the Commission ask for
Numbered takeaways
- Decide the unit type early, because it decides the foundation question.
- Read the City’s handout, especially the engineering items.
- Plan for Coastal Commission review as part of the sequence, without assuming an outcome.
- Get soil and drainage information for the new footprint.
- Check the existing foundation before you rely on it.
A contractor experienced with coastal foundations can review existing conditions with you and coordinate with licensed engineers as needed for the design. If you are planning an ADU anywhere in Solana Beach, request a Free Quote. The City’s planning page also describes a Pre-Approved ADU program worth reviewing, keeping in mind that pre-approved plans still sit on your particular soil.