Pre-approved ADU plans are ready-made designs a city has already reviewed for code compliance, letting you skip much of the plan-check process and get to permit faster and cheaper. Many California cities, including Los Angeles, offer them, though site-specific items still need review. Here’s how pre-approved ADU plans work in California.
Building an ADU in California can feel like two projects at once. One is the construction. The other is getting through design and permitting without surprises. That’s where pre-approved adu plans come in.
In plain English, they’re ADU plan sets that a city or county has already reviewed for code compliance. You still apply for permits, but you may spend less time in plan check and less money upfront on custom drafting.
This guide breaks down how pre-approved plans work, what California law actually says, where to find plan libraries (including Los Angeles, the Bay Area, and San Diego), and when a custom plan is still the smarter move.
Here at GreatBuildz, a free service that connects homeowners in California with reliable general contractors, we speak to homeowners every day about the details of their ADU or garage conversion project.
Key takeaways
- Pre-approved plans can expedite the plan check process, but they do not eliminate site-specific requirements.
- Some detached ADU permits using qualifying plans can fall under a faster review timeline.
- Some plans are free. Many are licensed from private designers even if they’re “pre-approved.”
What “pre-approved” means and what it does not mean
Pre-approved means the jurisdiction has already reviewed the core building plans for code compliance. Think structural framing, life-safety basics, and the usual building standards. In many programs, this reduces the time required for plan check.
It does not mean your property is automatically approved. Your city or county still needs to confirm that the ADU can be placed on your specific lot and connected safely.
A helpful way to picture it is this. The plan set is “pre-checked.” Your property is not.
What is an ADU?
California defines an ADU as a residential dwelling unit that provides complete independent living and is located on the same lot as an existing or proposed primary residence.
Read: Building an ADU: Step-by-Step Guide
The California rule that made plan preapproval a bigger deal
California has been pushing cities to make ADUs easier to permit for years. The newer piece that matters most for this topic is AB 1332.
AB 1332 requires local agencies to establish a ministerial program to preapprove ADU plans and to post approved plans online with the applicant’s contact information.
It also adds a faster review requirement in a specific scenario. If you apply for a detached ADU using a qualifying preapproved plan, some jurisdictions must approve or deny the application within 30 days.
Two important caveats for homeowners:
First, that timeline does not magically fix an incomplete application. You still need to submit the site-specific pieces your jurisdiction requires.
Second, programs can have exceptions. For example, Santa Clara County notes that expedited permitting is not available in certain hazard zones, such as Wildland Urban Interface areas, flood hazard areas, or geologic hazard zones.
How the pre-approved plan process usually works
Even though every city has its own portal and checklist, the homeowner path tends to follow the same pattern. The plan set is standardized. The site package is custom.
Here’s the typical flow.
- Choose a plan that fits your goal
Start with the basics. Do you want a simple studio for family visits, a one-bedroom for long-term rental, or a two- or three-bedroom for multi-generational living? Plan libraries often publish multiple sizes and styles. - Confirm your site constraints early
This is where many delays happen. Setbacks, easements, slope, existing structures, and utility locations can quietly rule out a plan you love. If you’re in Los Angeles, the permitting review still checks zoning compliance and foundation requirements even when the plan is standard. If you’re in San Diego, preapproved-plan applications still must comply with the San Diego Municipal Code development regulations. - Build your site-specific submittal package
Most jurisdictions still require some combination of a site plan, energy documents, and structural items tied to your property. Santa Clara County spells this out clearly. When an applicant uses the county’s pre-approved plan, they still submit a project-specific site plan, Title 24 energy calculations, and a roof truss design. County staff then reviews site-specific factors like zoning compliance and energy code requirements. The County of San Diego’s “dwelling unit building plans” are another good example. The county notes these plans are about 85 percent complete and require you to fill in project-specific information. - Submit for permits
At this point, your plan set may reduce plan check time, but the city still reviews your site items. Los Angeles describes the purpose of its standard plan program as a simplified permitting process, with reduced time required for plan check and a review focused on site-specific factors. - Build like a normal ADU project
Inspections, scheduling, and construction quality still matter. A pre-approved plan doesn’t protect you from a bad contractor or a sloppy build.
If you’re trying to compare bids or find a contractor who actually builds ADUs in your area, call GreatBuildz at 818.317.3567. We can match you with vetted contractors and help you avoid the classic budget and scope traps.
Why pre-approved plans can save time and money
The big advantage is simple. You are not paying someone to reinvent a code-compliant plan set from scratch.
Los Angeles explicitly says standard plans reduce the time required for plan check and are reviewed and pre-approved for compliance with building, residential, and green codes.
Some programs also reduce plan review fees when you use the plan without changes. Santa Clara County notes that minimum plan review fees apply for applications using their pre-approved plans without modification, and that modifying the plans can remove eligibility for the expedited review path. Pre-approved plans usually save the most time in plan check. They do not remove site costs like surveys, soil work when required, utility planning, and energy forms.
They also don’t eliminate design decisions. You still pick finishes, windows, exterior materials, and the “how it lives” details.
Where to find pre-approved ADU plans in California
Most homeowners find pre-approved plans in one of two places. The city building department site or the county planning and development site. Below are real examples across California. Use them as a model for what to search for in your own city.
Los Angeles
Los Angeles has an ADU Standard Plan Program through LADBS. LADBS explains that using standard plans reduces plan check time and that LADBS reviews site-specific factors for your property even when you use an approved standard plan. The listings include at least one city-owned plan that can be used free of charge, plus many designer-owned plans that you purchase directly from the plan owner.
San Diego
The City of San Diego states that applicants may apply for a permit using preapproved plans and that applications using preapproved plans are subject to a 30-day review. The city also notes you may need to contact the ADU plan provider to learn the cost to license the plan.
The County of San Diego publishes “dwelling unit building plans” that may be used as an ADU in unincorporated areas, and notes that the plans require project-specific information.
Bay Area examples
Santa Clara County publishes free pre-approved plan options for unincorporated areas and explains the added site-specific items required for permit submittal. It also flags that expedited permitting is not available in certain hazard overlay areas.
Many cities also host their own plan libraries. The key is to search your city name plus “pre-approved ADU” or “standard ADU plan.”
How to choose the right plan for your lot and your life
Picking pre-approved ADU plans is about more than square footage. The real question is whether that plan fits your property and your city’s rules. Even with a standard plan, the jurisdiction still reviews site-specific factors like zoning compliance and often foundation requirements.
California is not one climate. Coastal Los Angeles can mean marine layers and salty air. The Bay Area can mean fog and cool evenings. Inland areas can mean serious heat. Choose a plan that will be comfortable where you live, not just pretty on paper.
Will it fit your lot?
Look for a layout that works with your available building area, driveway, and utility runs. If your property is in a hazard overlay, confirm you can still use the plan and whether any expedited path applies.
Will it work for the way you’ll use it?
Decide upfront if you need a true bedroom, extra storage, or a separate entrance.
Can you use it as designed?
Many programs limit changes. If you want a custom layout, you may be better off with a custom plan.
When a custom plan is usually the better choice
Pre-approved plans are a strong fit when your lot is straightforward and you’re happy with a proven, standard layout. A custom plan is usually the better option when your property has quirks, you’re bumping up against constraints, or you need the ADU to be built in a very specific way.
You may want a custom design if you have:
- A steep or oddly shaped lot
- Tight setback or easement constraints
- A complicated existing home layout, driveway situation, or utility routing
- A property in a hazard overlay area where expedited review may be limited or not available
- A strong architectural match goal, especially if the ADU needs to mirror a historic style
Custom also makes sense if you want a highly specific layout, like a separated bedroom wing for privacy or a sound-isolated office studio.
Common homeowner mistakes with pre-approved ADU plans
Pre-approved plans can shorten the road, but you can still take a wrong turn. These are the mistakes we see most.
Assuming the plan means automatic approval: Your lot still needs to meet zoning and site rules.
Forgetting about licensing: Many plans are owned by designers, and you may have to pay to use them.
Modifying the plan and expecting the fast track: Many programs treat modifications as a normal plan-check path, and you may lose expedited review.
Not budgeting for site-specific documents: Plan libraries do not usually include everything your lot needs, like a project site plan, energy forms, or truss designs.
FAQ
Can I modify a pre-approved ADU plan?
Often, small changes take you out of the “pre-approved” lane. Some cities require you to use the plan as-is, and others allow changes but then treat it like a normal plan check with full review.
Are pre-approved ADU plans free in California?
Sometimes. Los Angeles lists at least one city-owned standard plan that can be used free of charge, but it also lists many private plan owners whose plans are purchased directly from them.
Do I still need an architect or engineer?
You might not need a custom architect for the base plan, but you often still need professionals for site-specific items. For example, some programs still require energy documents and truss designs tied to your build.
Do pre-approved plans guarantee a 30-day permit?
Not always. The 30-day rule applies in specific circumstances for detached ADUs using qualifying plans, and the application still needs to meet your local development rules and be complete.
Where do I start if my city does not have a plan library?
Start with your county and nearby major cities. Some jurisdictions accept certain preapproved plans from other agencies, and many areas publish plan lists or vendor libraries online.
If you’re considering a pre-approved plan and want help picking the right approach, getting clean bids, and hiring someone reliable, call GreatBuildz at 818.317.3567. We’ll match you with vetted contractors and help you move forward with clear scope and expectations.
