There are two ways to get a set of ADU plans in San Diego, and they lead to genuinely different projects.
You can start from a pre-approved plan — a standardized design a public agency has already reviewed, which the City of San Diego commits to reviewing in 30 days. Or you can have a custom plan drawn for your specific lot, which takes longer through design and plan check but is built around your property instead of around an average one.
Neither is the automatic right answer. The honest version of the decision looks like this:
| Pre-approved plan | Custom design | |
|---|---|---|
| City of San Diego review | Stated 30-day review | Standard track, correction rounds are normal |
| Design time before submittal | Short — the building is already drawn | Longer — concept, layout and engineering |
| Fits an unusual lot | Only if the lot is straightforward | Yes, that is the point |
| Size and layout choice | Fixed menu | Whatever the code and the lot allow |
| Still needs site-specific drawings | Yes | Yes |
| Best for | Flat, clear, conventional backyards | Slope, tight access, easements, specific use |
The rest of this page covers what “pre-approved” actually means here, exactly which plans San Diego accepts, what those plans do not include, and how to tell which path your property is really a candidate for.
What “pre-approved” means in San Diego — and what it doesn’t
Since January 1, 2025, California law has required every city and county in the state to run an ADU plan pre-approval program. Government Code section 65852.27, added by AB 1332, requires each local agency to accept ADU plan submissions for pre-approval, approve or deny them, and post the approved plans and the plan author’s contact information on its own website.
That is why pre-approved plan libraries suddenly appeared across San Diego County. It is a statewide mandate, not a local promotion.
Here is the part most articles get wrong. The City of San Diego does not publish its own catalogue of house designs. What the City does is accept pre-approved plan sets produced by three other jurisdictions:
- ✓County of San Diego Standard ADU Plans
- ✓City of Chula Vista Standard ADU Plans
- ✓City of Encinitas Permit-Ready ADU Plans
If you live in the City of San Diego and you want the fast track, you are choosing from those three libraries. The City’s own Development Services ADU page states that “applications that utilize preapproved plans will be subject to a 30-day review” and that the plans must be designed to the codes and standards currently adopted at the time you submit.
One more thing the City says plainly, and it matters: you contact the plan provider directly about licensing costs. A pre-approved plan being publicly listed does not automatically mean it is free to use in your project.
The County of San Diego plan set, by size
The County’s library is the one most City of San Diego homeowners end up looking at first, and it is the most concrete thing in this entire topic — so here it is in full.
The County’s Dwelling Unit Building Plans page publishes eight standard plans. Six of them may be used as an ADU:
| Plan | Size | Layout |
|---|---|---|
| Plan A | 1,200 sq ft | 3 bedroom, 1 bath |
| Plan B | 1,200 sq ft | 2 bedroom, 1 bath |
| Plan C | 1,200 sq ft | 2 bedroom, 2 bath |
| Plan D | 1,000 sq ft | 1 bedroom, 1.5 bath |
| Plan E | 800 sq ft | 1 bedroom, 1 bath |
| Plan F | 600 sq ft | 1 bedroom, 1 bath |
Plans G and H are single-family dwelling plans only and are not ADU options.
Each plan is published as a downloadable drawing set — full-size and half-size PDFs, plus a CAD file. Two details are worth reading carefully:
- ✓The County describes the plans as “approximately 85% complete”, requiring you to fill in project-specific information. There is a published checklist identifying exactly what has to be provided and where.
- ✓The County’s own plans are intended for use in the unincorporated areas of the County. Their acceptance inside the City of San Diego comes from the City’s pre-approved plan policy, not from the County’s.
That 85% figure is the single most useful number on this page, and it is the one homeowners most often miss.
The 15% nobody mentions
A pre-approved plan covers the building. It does not cover your property. The remaining work is where pre-approved ADU projects actually get delayed, and it typically includes:
- ✓A site plan showing where the unit sits, its setbacks, and its relationship to the main house and property lines
- ✓Foundation design for your soil — the same building on expansive clay and on decomposed granite is not the same foundation
- ✓Utility routing — where sewer, water, gas and electrical actually come from, and whether the existing panel has capacity
- ✓Grading and drainage, which is where sloped San Diego lots get expensive
- ✓Title 24 energy compliance for your orientation and glazing
- ✓Fire access and defensible space, depending on where the property sits
None of this is a flaw in the pre-approved program. It is simply what a standardized building plan cannot know about your backyard. The mistake is budgeting and scheduling as though downloading the plan set is most of the way to a permit. It is the part of the work that is already done, not the part that decides your project.
When a pre-approved plan is genuinely the better choice
Pre-approved plans do real work for the right property. They are usually the stronger option when:
- ✓The backyard is flat, open and conventional — no significant slope, no tight side-yard access, no easements running through the buildable area
- ✓One of the six County layouts already matches the use you have in mind
- ✓Speed matters more than specificity — a 30-day review track is a meaningful advantage
- ✓The ADU is primarily a rental or income unit, where a proven, efficient layout is worth more than a bespoke one
If you are building an ADU to rent, an unremarkable, well-organized floor plan is often exactly right. Read our guidance on planning an ADU for rental income before you pick a size — the number of bedrooms has more effect on your return than the finishes do.
When custom design earns its extra time
A custom plan is the better path when the property or the purpose has a requirement the menu cannot meet:
- ✓Slope, retaining or difficult access. A standard plan assumes a buildable flat pad. When the lot does not offer one, the plan has to be designed around the grading rather than dropped on top of it.
- ✓A specific person is moving in. Designing an ADU for a parent means step-free entry, door and hallway widths, a bathroom that works with a walker, and a location close to the main house. Those are layout decisions, not upgrades — we cover them in designing an ADU for aging parents.
- ✓The ADU has to look like it belongs. On a custom or architecturally distinct primary residence, a standardized unit can read as an outbuilding rather than part of the home.
- ✓You are converting, not building. A garage conversion starts from an existing structure, so a pre-approved detached plan does not apply at all. See ADU types in San Diego for how conversions, modular and prefab compare.
- ✓You are near the maximum footprint the lot allows. When every foot counts, a fixed plan wastes some of them. Our page on ADU size, setback and parking rules covers what actually constrains the envelope.
Choose the purpose before you choose the plan
The most common sequencing error in ADU design is picking a floor plan first and deciding what the unit is for afterwards.
A plan optimized for a tenant and a plan optimized for a parent are not the same plan. The rental version wants durability, privacy from the main house, and a layout that reads well to a stranger on a listing. The family version wants proximity, step-free circulation, and sightlines to the main home. A unit meant to become a home office or a guest suite wants something different again.
Decide what the unit does. Then the size, the bedroom count and the entry location stop being preferences and start being requirements — which is also what makes a pre-approved plan easy to accept or easy to rule out.
What a floor plan has to resolve before it’s final
Whichever path you take, a plan is not finished until it answers these:
- ✓Entry location and privacy — where the ADU’s door faces, and what each building sees of the other
- ✓Plumbing and venting placement — kitchen, bathroom and laundry positioned against where the sewer and vents can realistically go
- ✓Genuine storage, not closet outlines on a drawing
- ✓How the unit reads from the street and from the main home’s windows
- ✓The site’s real slope and access, not a flat-lot assumption
- ✓Where the mechanical equipment lives, before it ends up outside a bedroom window
Getting from a plan to a buildable design
A floor plan that looks right on paper still has to clear plan check and work on the actual lot. That is why we test design options against the property’s real constraints — setbacks, easements, utilities, access and grade — during feasibility, rather than finalizing a plan and discovering the conflicts after submittal.
In practice, that means the pre-approved-versus-custom question usually answers itself once the property has been looked at properly. On a clear, flat lot where one of the County layouts fits the use, the 30-day track is a real advantage and we will tell you so. On a sloped or constrained lot, a standardized plan tends to generate site work and revisions that quietly erase the time it was supposed to save.
San Diego ADU plan FAQs
Deciding which path fits your property
The cheapest hour in an ADU project is the one spent deciding this correctly, before drawings exist.
Schedule a consultation and we’ll look at your lot, your grade and access, and what you want the unit to do — then tell you honestly whether one of the accepted pre-approved plans is a real option for you, or whether a custom design will get you a better building for the same money. If a standard plan fits your property, we will say so.
