Accessory dwelling units in Spring Valley, CA, are permitted by San Diego County, not a Spring Valley city hall. That distinction changes where you submit plans. On septic parcels, it also changes what must happen first.
Unincorporated means the County permits it, not a city
Spring Valley appears on San Diego County’s official list of unincorporated communities. That makes County Planning & Development Services, commonly called PDS, the building permit authority for an ADU project there.
This matters because nearby cities maintain their own forms and local procedures. A City of San Diego ADU checklist isn’t the correct starting point for a Spring Valley parcel. Neither are forms published by La Mesa or El Cajon. Begin with the County’s ADU information and confirm that your property falls within unincorporated San Diego County.
The proposed use also matters. An ADU needs complete, independent living facilities. A garage converted only into an office, gym, or bedroom follows a different use and permit path. Tell PDS what the finished space will contain, rather than calling every conversion an ADU.
A detached garage can’t become a junior accessory dwelling unit. California law requires a JADU to sit within a single-family residence. An attached garage may qualify under the JADU rules, but a freestanding garage follows the full ADU path. Confirm the current classification with PDS before design begins.
Our Spring Valley garage conversion page explains how we match homeowners with licensed, independent local professionals. Garage Convert SD doesn’t design, permit, or build the unit. The contractor and other professionals you hire handle that work directly.
Where the application actually goes
San Diego County requires a building permit for an ADU in an unincorporated community. The application goes to PDS, where the plans are reviewed for zoning, building, health, and safety requirements.
For an existing garage conversion, County guidance says the conversion isn’t subject to an ADU size limit. The structure may expand by up to 150 square feet only when that space accommodates ingress and egress. It isn’t a general allowance for a larger kitchen, bedroom, or living area.
Existing walls don’t make a garage residential space. The conversion remains subject to building and fire requirements for a dwelling. County guidance tells applicants to contact the Building Division and the responsible fire district about required upgrades. Plans for residential projects also need coordination with the fire authority serving the property.
Our overview of ADU permits and plans can help you organize the design and contractor side. Ask PDS for its current submittal checklist before assuming a drawing package is complete.
California’s statewide ADU framework is explained through the California HCD ADU program. State law requires an agency to approve or deny a completed ADU application within 60 days. That clock begins with a completed application, not the first upload. It can also pause when the applicant requests a delay.
That rule is a decision window, not a construction schedule or approval promise. The County’s own handbook tells applicants to expect its process to take several weeks. Check the application’s current status with PDS rather than relying on a general timeline.
Septic parcels: DEHQ approval comes before the building permit
A public sewer connection and an onsite wastewater treatment system create different starting points. If the Spring Valley property uses septic, San Diego County advises getting Department of Environmental Health and Quality approval before submitting the building permit application.
The required step is approval of an OWTS Layout Application. OWTS means onsite wastewater treatment system. The County tells applicants to contact an OWTS professional, who selects a design and prepares the application for DEHQ.
The sequence protects the project from advancing around a wastewater plan that won’t work. The County warns that DEHQ approval might not be possible for a proposed layout. It also says the required system may be more involved than the applicant expected.
An existing, working septic system doesn’t automatically have capacity for another dwelling. County guidance treats an ADU as a second dwelling, whether attached or detached. Its DEHQ FAQ says an ADU addition would exceed the existing septic tank and disposal area’s maximum capacity in almost every case.
The outcome depends on the site. A proposed ADU may need another septic tank when a new kitchen and bathroom add load. If the existing disposal field can’t handle that load, a separate septic system may be needed. Those decisions belong to DEHQ and the OWTS professional.
Don’t lock the garage floor plan before this review. Kitchen, bathroom, access, and wastewater decisions affect one another. Early coordination gives the designer and contractor confirmed site constraints to work from.
What an OWTS layout application has to show
The OWTS Layout Application must address both the primary home and proposed ADU. County guidance says the site plan and supporting information must show a system meeting current standards for location, size, and design.
The plan must also identify a reserve area equal to 100 percent of the future replacement area. That land can’t be treated as leftover yard space. Its location can affect where an ADU, driveway, patio, or other site feature fits.
Percolation testing is another required part of the County’s layout process. DEHQ says applications must include testing data from every proposed disposal and reserve area. The OWTS professional uses that site information when selecting and documenting the proposed system.
This is why a garage’s existing footprint doesn’t settle feasibility. The building may already exist, but the ADU introduces independent living facilities and additional wastewater demand. The usable space outside the garage can become as important as the interior plan.
DEHQ layout approval also expires after one year. If the building permit package or design work stretches beyond that point, ask DEHQ what must be updated. Don’t assume an expired approval will remain acceptable.
Keep the approved wastewater layout aligned with later architectural plans. Moving a bathroom or changing the ADU footprint could affect the documented proposal. The designer, OWTS professional, and licensed contractor should work from the same site information.
County guidance doesn’t establish one septic solution for every Spring Valley property. Soil conditions, the existing system, and available reserve space require parcel-specific review. DEHQ, not a contractor’s general rule of thumb, determines whether the submitted layout meets County standards.
Wells and site plans
Properties with both a well and an OWTS need careful site documentation. San Diego County says PDS will reject building permit site plans that omit the well and OWTS locations.
Show the existing well, septic tank, disposal area, and reserve area on the project site plan. The proposed ADU and related work must also match the layout reviewed by DEHQ. Missing or conflicting locations can stop the building review before construction details are considered.
DEHQ may make well water test results a condition of OWTS layout approval. The approved County materials reviewed for this page didn’t confirm a County-wide well-yield number or a standard “proof of water availability” test for every ADU. Ask DEHQ what testing applies to the specific parcel.
That distinction matters. A private checklist may suggest a test that doesn’t match the County’s current request. It may also omit a condition tied to the property’s well or wastewater layout. Get the requirement from the reviewing agency before ordering work around an assumed standard.
A clear site plan also helps the project team compare the garage footprint with wastewater constraints. Plumbing routes, exterior access, and proposed additions must fit the approved layout. The professional preparing the building plans should receive the DEHQ documents, not just a verbal summary.
If the property uses public sewer, County guidance says the ADU may connect to that system. Confirm the connection process with PDS and the serving utility. Don’t apply septic guidance to a sewer parcel, or assume a nearby property’s utility arrangement matches yours.
The fee waiver that ended, and free County plans
San Diego County’s trial ADU impact fee waiver has ended. The County states that it began January 9, 2019, and ended January 9, 2024. Don’t rely on older articles that describe it as a current County program.
A separate statewide impact-fee rule remains. California law bars impact fees on an ADU with 750 square feet of interior livable space or less. Larger ADUs may receive proportional impact fees based on the primary dwelling’s square footage.
“Impact fee” has a narrow legal meaning. The state exemption doesn’t mean every charge disappears. Plan-check, building permit, utility connection, and school fees aren’t all erased by that threshold. No current County permit amount could be confirmed from the approved source material for this page. Ask PDS for the charges tied to the current plans and parcel.
The County also offers dwelling plans that may be used for detached ADUs. It describes those plans as approximately 85 percent complete because owners must add project-specific information. The site plan, foundation conditions, utilities, fire review, and other property details still need attention.
Those plans don’t replace a garage-conversion plan set. The County describes them as detached ADU plans, while a conversion starts with an existing structure. A converted garage needs drawings based on its actual dimensions and condition. Our guide to detached garage conversions explains how that existing structure changes the planning discussion.
Free County plans also don’t confirm septic feasibility. On an OWTS parcel, DEHQ review still comes first. Treat the plans as a possible design resource, not blanket approval for the property.
When to call us
A Spring Valley conversion needs a licensed ADU professional when the garage must become legal living space and coordinate structural, plumbing, electrical, permit, or wastewater work. You can verify a contractor’s license through the California Contractors State License Board.
Call (858) 400-4935. The number plays a recording-consent notice and records both sides. If nobody picks up, use the contact form.