Pre-Approved ADU Plans in California: Where to Find Them and What They Cost

Why Pre-Approved ADU Plans Suddenly Matter in 2025

If you've been dreaming of a backyard cottage — or rebuilding after the Eaton Fire — the design and permitting phase is usually where projects stall. Custom ADU plans take months to draw up and thousands of dollars before you even reach the counter at Building and Safety.

For Altadena homeowners, that friction is especially painful right now. Many are navigating rebuild timelines while weighing whether an ADU adds living space for family, rental income, or both. The traditional path — hire a designer, wait for plan check, revise, resubmit — compounds an already exhausting process.

That's why a January 1, 2025 statewide mandate matters so much. As of that date, every California local government is required to accept ADU plans for pre-approval and publish an online list of locally pre-approved plans, according to ADU Marin and ADU Santa Clara County. Pre-approved plans are designs a jurisdiction has already reviewed for code compliance, so homeowners can skip a large part of plan check.

The change is already visible in the numbers of plans on offer:

• LA County — where Altadena falls as unincorporated territory — offers three free standard plans ranging from 800 to 1,200 square feet, per LA County Building and Safety.
• The City of Los Angeles provides its 455 sq ft YOU-ADU plan free to applicants.
• Orange County offers six downloadable floorplans, from a 393 sq ft studio to a 1,200 sq ft three-bedroom.

The stated goals of these programs are consistent: reduce pre-construction costs and speed up permit approval. Sausalito, for example, notes that pre-approved plans expedite plan review and reduce permitting costs, with Master Plan ADU permits processed within 60 days of a complete application.

Here in Altadena, the practical effect is a new starting point. Instead of beginning from a blank page, homeowners can now begin from a reviewed, code-compliant design — and LA County Planning's Standard ADU Plans Program includes both free county-owned plans and a private designer catalog for more options.

One honest caveat: pre-approval does not mean turnkey. Every jurisdiction still requires site-specific work — plot plans, Title 24 energy calculations, foundation design — and not every plan fits every lot. That's why Altadena ADU Builder recommends confirming feasibility on your property before committing to any plan set. The right plan, on the wrong lot, saves you nothing.

The Free Plan Directory: LA County, City of LA, and Orange County Programs

If you own property in unincorporated Altadena, you already have access to the most directly relevant pre-approved ADU program in California — and the plans cost nothing to download. Because Altadena sits in unincorporated Los Angeles County, the County's standard plans are the ones your permit application would actually use, while the City of LA and Orange County programs serve as useful benchmarks for what's becoming a statewide norm.

LA County Building and Safety publishes three standard ADU plans that homeowners "may be used by homeowners free of charge": Plan A (1,200 sq ft, 3 bed/1 bath), Plan B (1,200 sq ft, 2 bed/1 bath), and Plan C (800 sq ft, 1 bed/1 bath). The County frames the program as a way to "expedite the County review and approval process for homeowners seeking to create a new secondary dwelling unit."

Two rules matter before you get excited. The plans "cannot be revised and must be permitted as designed" — though you may orient them in any direction or mirror the floor plan. And pre-approval does not eliminate site work: you still need a site-specific plot plan approved by Regional Planning, plus Title 24 energy calculations and agency referrals.

Two nearby programs round out the picture:

• City of LA YOU-ADU — a free, 455 sq ft, one-story, one-bedroom plan "provided free to applicants" with no stated expiration date, per the LADBS standard plans page. Applicants still submit site-specific zoning and foundation information.
• Orange County — six free downloadable floorplans ranging from a 393 sq ft studio to a 1,200 sq ft three-bedroom, designed to "reduce pre-construction costs and improve permit approval efficiency" per OC Development Services.
• LA County Planning also runs a Standard ADU Plans Program with a free County Catalog and a Private Designer Catalog where you purchase plans directly from architects.

The catch, as regional ADU resources consistently warn: pre-approved does not mean turnkey. Not every design works on every lot — slope, setbacks, and utilities can disqualify a standard plan entirely — and most homeowners still need a professional to handle the site plan and energy calculations. That's why Altadena ADU Builder recommends a quick feasibility check before committing to a stock plan; a free consultation with a concept render and cost estimate can tell you whether a County plan fits your lot or whether a custom design makes more sense.

What Pre-Approved Plans Actually Cost — and What They Don't Cover

Downloading a free ADU plan feels like a windfall — until you discover what the plan doesn't cover. The honest answer on cost is that pre-approved plans save you design fees and review time, but no California program publishes an actual dollar figure for what you'll save.

What you get for free is real. LA County's three standard plans — ranging from an 800 sq ft, one-bedroom layout to 1,200 sq ft designs — may be used by homeowners at no charge. Orange County goes further with six downloadable floorplans from a 393 sq ft studio to a 1,200 sq ft three-bedroom. Sausalito frames the savings qualitatively: faster plan review "reduces permitting costs" and cuts design uncertainty, per the city's program page.

But pre-approval is not a turnkey permit. Every program requires site-specific work before a permit is issued:

• A site-specific plot plan, which LA County requires Regional Planning to approve, along with Title 24 energy calculations and agency referrals
• Zoning Code compliance and foundation requirements tailored to your lot, as the City of LA's YOU-ADU program specifies
• Hiring a professional in most cases, since regional ADU resources note that not all designs work on all properties
• Standard permit fees, inspections, and agency approvals — none of which pre-approval waives

Two more rules shape the real cost picture. First, plans are locked: LA County's standard plans "cannot be revised and must be permitted as designed," though you can orient them in any direction or mirror the floor plan. Second, plans expire with the building code cycle — Sausalito's pre-approved plans meet the 2025 California Residential Code and are valid only through 2028, after which new applications are required.

For Altadena homeowners, this means a free county plan can genuinely trim pre-construction costs, but the site-specific work — plot plans, Title 24, foundation design — is where your remaining design budget goes. That's why we at Altadena ADU Builder suggest a feasibility check before committing to a stock plan: a free consultation with a cost-quiz concept render tells you whether a pre-approved design fits your lot, or whether a custom approach serves you better.

Free County Plans vs. Paid Designer Plans: Choosing What Fits Your Lot

Free plans sound like an easy win — until you read the fine print. LA County's pre-approved ADU plans cost nothing upfront, but they come with rules that can make or break their usefulness on your particular lot.

The Free County Catalog: Rigid but Fast

LA County Building and Safety offers three standard plans that homeowners "may be used free of charge": Plan A (1,200 sq ft, 3 bed/1 bath), Plan B (1,200 sq ft, 2 bed/1 bath), and Plan C (800 sq ft, 1 bed/1 bath), according to the County's pre-approved ADU program. The catch is significant: these plans "cannot be revised and must be permitted as designed." You can orient the building in any direction or mirror the floor plan, but the design itself is locked.

That rigidity is the trade-off for speed. The County frames the program as a way to "expedite the review and approval process," and the plans have already cleared code review. If one of the three layouts fits your property, you save design costs and shorten plan check.

The Private Designer Catalog: Paid, More Choice

LA County Planning also operates a Private Designer Catalog, where homeowners purchase plans directly from the architect or designer. Pricing isn't published by the County, but you get far more design variety than the three county-owned options. Some jurisdictions, like San José and Cupertino, take a vendor-based approach where you contract with a pre-approved builder and still submit a property-specific site plan, per regional ADU resources.

Why a Stock Plan May Not Fit Your Lot

Here's the honest caveat every program buries in the fine print: pre-approval does not eliminate site-specific work. Even with a free county plan, you still need a site-specific plot plan approved by Regional Planning, Title 24 energy calculations, and agency referrals. Regional guidance is blunt — not all designs work on all properties, and homeowners likely need to hire a professional anyway.

For Altadena specifically, common lot conditions can disqualify a stock plan quickly:

• Sloped lots requiring custom foundation design the standard plans don't anticipate
• Fire-zone requirements that trigger additional standards beyond the base plan
• Setback and placement constraints that a fixed 800–1,200 sq ft footprint simply can't accommodate

A Simple Decision Framework

Choose the free County Catalog if your lot is relatively flat, outside high fire-hazard areas, and one of the three layouts genuinely works for you. Choose a paid designer plan — or a fully custom design — if your site has slope, fire-zone, or setback complications. "Pre-approved" is never "turnkey"; it means the design review is done, not your homework.

If you're unsure which category your property falls into, Altadena ADU Builder offers a free ADU feasibility consultation with a cost-quiz concept render — a practical way to find out whether a stock plan fits your lot before you spend anything on it.

Your Next Steps: Verifying a Plan Works on Your Altadena Property

A pre-approved plan only pays off if it actually fits your lot — and because Altadena sits in unincorporated LA County, the county's programs are the ones that apply to you. Before falling in love with a floor plan, take a few concrete steps to confirm it works on your property.

Start with the official lists. LA County Building and Safety's Pre-Approved ADU Standard Plans Program offers three free plans — Plan A (1,200 sq ft, 3 bed/1 bath), Plan B (1,200 sq ft, 2 bed/1 bath), and Plan C (800 sq ft, 1 bed/1 bath) — while LA County Planning maintains a Standard ADU Plans Program with both a free County Catalog and a Private Designer Catalog you purchase directly from the designer.

Next, check the fine print that trips up most homeowners:

• LA County standard plans cannot be revised and must be permitted as designed, though you may orient them in any direction or mirror the floor plan.
• Every plan still requires a site-specific plot plan approved by Regional Planning, plus Title 24 energy calculations and agency referrals.
• Code-cycle expiration matters: pre-approved plans are tied to a building code cycle, and new applications are required when codes are adopted.
• Not all designs work on all properties — slope, setbacks, access, and utilities in Altadena's hillside-adjacent lots can disqualify a plan that looked perfect on paper.

Once you've identified a candidate plan, submit through EPIC-LA or a Building and Safety District Office, as the county directs. Keep in mind that even with a pre-approved plan, inspections must be requested within 12 months of permit issuance, with follow-up inspections every 180 days — so your project schedule needs to be realistic before you commit.

This is where a site-specific review earns its keep. Regional ADU resources consistently caution that even pre-approved plans require property-specific planning and that homeowners likely need to hire a professional. A local contractor who knows Altadena's lots can tell you quickly whether Plan C's 800 square feet fits your rear setback, or whether a custom design serves you better than a locked plan you can't modify.

If you want that answer before spending money on plans, Altadena ADU Builder offers a free ADU feasibility consultation paired with a cost-quiz concept render — a practical way to test a pre-approved plan against your actual lot. If you'd rather have one team handle site adaptation and construction, featured builder JMB Builders LLC (CSLB #1103479), an Altadena-based licensed general contractor whose work is documented at jmb-builders.com, is a local option for adapting plans to your property and building the ADU itself.

socialProofText: Altadena homeowners use our free feasibility consultation and cost-quiz concept render to test pre-approved plans against their actual lots before spending a dollar.

ctaText: Get your free Altadena ADU feasibility consultation with a cost-quiz concept render — see what fits your lot before you commit to any plan.