California Made Every City Publish Pre-Approved ADU Plans. Any Modification Voids the Advantage.

California's AB 1332 requires every city to publish a library of pre-approved ADU plan sets. Pull one from the shelf and your building permit review drops from 60 days to 30 days. That sounds like the fastest path to a permitted ADU. This article explains when it is — and when it is not. For a full overview of 2026 ADU law changes, see our California ADU laws hub. For permit timeline enforcement and the SB 543 completeness rules, see our permit enforcement guide.

Bottom Line

AB 1332 (2023) cut plan review time for detached ADUs using a qualifying pre-approved plan from 60 days to 30 days. [1] That is a real 30-day savings on the plan check phase alone.

The problem is plan check is not the slowest part of your project.

A soil and geotechnical report — required on many California lots regardless of whether you use a pre-approved plan or a custom design — takes 3 to 6 weeks and costs $1,500 to $7,000. [2][3] Site-specific Title 24 energy calculations are required on top of that. And any modification to the pre-approved plan — a different window size, a relocated wall, a foundation adjustment to match your soil conditions — immediately drops the application back to the 60-day standard review under AB 1332's "identical copy" rule. [4]

Three things to know before selecting a pre-approved plan:

AB 1332 applies only to detached ADUs. Attached ADUs, garage conversions, and JADUs are not eligible for the 30-day track regardless of plan source. [1]
In most cities, any modification to the pre-approved plans voids the 30-day timeline and sends the application to standard 60-day review. [4] A small number of cities may permit mirrored floor plans or minor exterior finish changes — confirm in writing with your building department before submitting.
If your lot's soil conditions require a different foundation type than the one shown in the pre-approved set, the plans cannot be modified to accommodate it. You lose the fast-track and must commission a custom design. [2]

What AB 1332 Actually Requires

AB 1332, signed October 11, 2023 and effective January 1, 2025, added Government Code Section 65852.27. [1] The law requires every California local agency to:

Establish a program to pre-approve ADU plan sets
Accept plan submissions from any applicant — architects, designers, prefab manufacturers, or homeowners
Post approved plans on the agency's website with the plan owner's contact information
Issue a building permit within 30 days of a complete application when the submitted plans are identical to a currently pre-approved plan set

The 30-day track applies to one specific scenario: a detached ADU application using plans that are either (a) currently pre-approved by that city under the active triennial California Building Standards Code cycle, or (b) identical to plans from a previously approved detached ADU application in the same code cycle. [4]

Everything else — attached ADUs, conversions, JADUs — stays on the standard 60-day track.

AB 1332 also contains no minimum requirement for how many plans a city must offer. The original draft called for at least six plan sets. That minimum was removed during the legislative process. A city can publish one plan and be legally compliant. [13]

The 30-Day Promise and What It Actually Measures

The 30-day timeline applies to the building permit plan check — one phase in a longer sequence. Both paths move through the same stages:

Phase	Pre-approved plan	Custom design
Preliminary geotechnical assessment	1–2 weeks	1–2 weeks
Site-specific documents (site plan, Title 24, soil report)	3–6 weeks	3–6 weeks
Completeness review	15 business days (SB 543) [6]	15 business days
Building permit plan check	30 days	60 days
Agency sign-offs (fire, utility, electric)	4–8 weeks	4–8 weeks
Realistic median from start to permit	3–4 months [15]	6–8 months

The 30-day savings is real. It narrows because several other phases are identical for both paths. Agency sign-offs — utility service reviews, fire department review, and connection permits — run on their own schedules and are not subject to the AB 1332 deadline.

The plan check timer also stops during correction cycles. If the building department issues a correction notice and you take three weeks to respond, those three weeks extend your calendar without counting against the statutory clock.

Site-Specific Work That Survives Every Pre-Approved Plan

A pre-approved plan set means the structural system, framing, architectural layout, and building code compliance have been reviewed and accepted by the city. It does not mean any site-specific documentation is done. Every application still requires:

Site plan. A fully dimensioned drawing of your specific parcel: property lines, setbacks, existing structures, utility lines, and the proposed ADU location. Pre-approved plans do not contain a site plan. This must be prepared for your lot. [5]

Title 24 energy calculations. The 2025 California Building Standards Code, effective January 1, 2026, requires ADUs to meet current energy standards. Pre-approved plan sets may include sample Title 24 calculations, but those calculations are based on assumed conditions — orientation, window sizes, insulation type. A site-specific energy compliance report is required for every permit submission. [8][9]

Cost: $245 to $325 for a standard ADU from an energy consultant. Timeline: 1 to 5 business days with complete information. [10] This step is fast and inexpensive relative to other phases. But it cannot be completed until architectural plans are finalized — and with a pre-approved plan, you cannot change window sizes or orientation without voiding the fast-track.

Foundation and utility plans. Pre-approved sets show the structural system based on assumed soil bearing capacity. Site-specific foundation and utility plans, prepared by a licensed engineer for your actual soil conditions, are still required before permit issuance. [5]

The Soil Report Problem

California Building Code Section 1803 requires a geotechnical investigation when a site has any of the following conditions: slopes steeper than 1:3 (horizontal:vertical), potential for soil liquefaction or landslide, expansive clays, high groundwater, or loose fill material. [2] These conditions are common across California residential lots, particularly in the Bay Area, coastal zones, and hillside neighborhoods in Los Angeles.

The soil report process has three steps: site visit and sample collection (1 to 2 days), laboratory testing (1 to 2 weeks), and report writing and delivery (1 to 2 weeks). Total timeline: 3 to 6 weeks from contract to delivery. Cost: $1,500 to $4,000 for a standard flat lot; $6,000 to $7,000 for sites with slopes, fill material, or complex geology. [2][3]

Flat lots with standard soil conditions may qualify for a building department exemption — typically allowed when using a conservative foundation design (deeper continuous footings or a thickened slab) and the site shows no indicators of problematic soil. Whether your lot qualifies is determined at plan check, after you submit. You cannot confirm exemption eligibility in advance.

This creates the central conflict with pre-approved plans. A pre-approved set includes a specific foundation design — typically a standard continuous footing or concrete slab based on assumed soil parameters. If your soil report recommends a different foundation type, you face a direct conflict: the plans you cannot modify specify a foundation that your geotechnical engineer says is inappropriate for your site.

The typical resolution is to switch to a custom design that incorporates the engineer's recommendations, placing you on the 60-day track. In some jurisdictions, submitting a revised plan through a new pre-approval cycle may be possible, but this is uncommon and jurisdiction-specific. Most homeowners in this situation will have invested several weeks in a path that did not work for their lot.

Spending $300 to $500 on a preliminary geotechnical opinion before selecting a pre-approved plan is the most effective way to avoid this outcome. Many firms offer a site visit and written assessment in 1 to 2 weeks. If the preliminary opinion indicates non-standard soil conditions, switch to a custom design before committing to a pre-approved plan.

The Identical Copy Rule

AB 1332's 30-day fast-track applies only when the submitted plans are "identical" to the pre-approved set. [4] The ABAG ADU State Laws Summary (July 2025) makes this explicit: if submitted plans differ from the approved set in any way, the application automatically reverts to the 60-day review timeline. [4]

The City of Lincoln states the rule plainly: "Pre-approved master ADU plans may not be altered in any manner. Any deviation from the approved plans will result in full independent plan review." [11]

San Jose's pre-approved program documentation specifies that floor plans cannot be modified. [12]

Change type	Effect on 30-day track
Mirrored floor plan	Varies by city — confirm in writing before submitting
Exterior color or material substitution	Varies by city
Window size or location change	Voids fast-track
Room layout modification	Voids fast-track
Foundation type adjustment (per soil report)	Voids fast-track
Any structural change	Voids fast-track

The rule forces a binary choice: accept the plan exactly as pre-approved or build a custom design. For homeowners with standard lots who are satisfied with available plan configurations, this is not a problem. For homeowners with site-specific constraints — irregular lot geometry, slope, mature tree roots, soil conditions, or specific space requirements — the pre-approved route frequently leads to discovering the mismatch at plan check, not before it.

The 2025 Building Code Cycle Reset

AB 1332 ties the 30-day fast-track to the current triennial California Building Standards Code cycle — meaning a plan pre-approved under one code cycle does not automatically carry that status into the next, per ABAG's interpretation of the statute. [4]

The 2025 California Building Standards Code took effect January 1, 2026. [8] Pre-approved plans developed under the 2022 CBC cycle — which ended December 31, 2025 — may not qualify for the 30-day track unless the city has re-reviewed and re-approved them under the 2025 code.

The 2025 code introduced substantive changes to residential energy requirements, including expanded heat pump provisions and updated solar system sizing. [8][9] An ADU plan set designed under 2022 CBC energy standards may not meet 2025 compliance, which would require revisions to the plan set and a new pre-approval by the city under the current cycle.

Many city pre-approved libraries were assembled in 2023 and 2024 in response to AB 1332's January 2025 effective date. Whether those libraries have been updated for the 2025 code is inconsistent across jurisdictions, and there is no centralized public tracker. [13]

Before selecting any plan from a city's library, confirm with the building department that the plan set carries a pre-approval issued under the 2025 California Building Standards Code. For 2025 CBC requirements as they apply to ADU energy compliance, see our 2026 California building standards guide.

What City Libraries Actually Offer

Los Angeles operates the largest pre-approved ADU plan program in California, with 96 approved plan sets as of early 2026 — 95 from private firms and one city-designed option (YOU-ADU). [7] Sizes run from 200 to 1,200 square feet, covering studio through three-bedroom configurations. LA's program is well-maintained and broad enough to serve most standard lot configurations in the city.

San Jose maintains a library of more than 20 pre-approved designs from vendors including Abodu (330 to 747 square feet) and Alto Housing (up to 966 square feet). Complete applications using a San Jose pre-approved plan can receive same-day building permit issuance when site-specific documentation is accurate and complete. [12]

Beyond the major cities, the picture is mixed. Because AB 1332 requires no minimum number of plans, a small city under resource pressure can publish a single plan and satisfy the legal requirement. Whether that plan suits the typical lot in the jurisdiction is a separate question. Cities without staff capacity to run ongoing programs may also lag in updating their libraries for the new code cycle.

AB 1332's enforcement mechanism adds another layer of complexity. Based on a review of AB 434's listed provisions and the AB 1332 statute, Government Code §65852.27 — the pre-approved plan requirement — does not appear to be explicitly included among the ADU code sections subject to direct HCD enforcement authority. [1][14] HCD retains broader ADU oversight tools under AB 434 and SB 543, but those apply to other provisions. No publicly documented enforcement actions specifically tied to §65852.27 non-compliance have been reported as of early 2026, though HCD's general housing oversight authority may still apply.

When Pre-Approved Plans Make Sense

Use a pre-approved plan when:

Your lot is flat with standard soil conditions and no indicators of expansive clay, fill, or liquefaction risk
You can confirm the plan has been re-approved under the 2025 CBC cycle
The available designs match your size and configuration needs without modification
You are building a detached ADU — attached units, conversions, and JADUs are not eligible for the 30-day track
Shorter plan review time is the priority and design customization is not required

Use a custom design when:

Your lot has soil complexity: slope, hillside location, bay area clay, fill material, or high groundwater
You need specific layouts, window placements, or architectural features
The city's pre-approved library has limited options that do not match your program
You are building an attached ADU, garage conversion, or interior conversion
Your lot has geometry that affects foundation placement or setback compliance

Factor	Pre-approved plan	Custom design
Building permit plan check	30 days [1]	60 days
Full permit-to-approval (median)	3–4 months [15]	6–8 months
Design flexibility	None — identical copy required [4]	Full
Soil report still required?	Yes, on many lots [2]	Yes, same conditions
Title 24 calcs still required?	Yes, site-specific [9][10]	Yes, site-specific
Architecture fee savings	$5,000–$10,000 (industry estimate)	Baseline
Eligible unit types	Detached ADU only [1]	Any ADU type
Risk of losing fast-track mid-process	Present (soil, code cycle mismatch)	Not applicable

Five Checks Before You Commit to a Pre-Approved Plan

Confirm the plan is approved under the 2025 CBC. Ask the building department directly: "Was this plan set re-reviewed and re-approved under the 2025 California Building Standards Code?" A yes means it qualifies for the 30-day track. Anything else means it does not.
Get a preliminary geotechnical opinion first. A $300 to $500 site visit and written assessment from a geotechnical engineer takes 1 to 2 weeks and tells you whether a full soil report will be required and what foundation conditions to expect. If the preliminary suggests non-standard conditions, move to a custom design before investing further in the pre-approved route.
Confirm your ADU type qualifies. The 30-day track applies to detached ADUs only. Garage conversions, attached additions, and JADUs are outside the scope of AB 1332 regardless of which plan set you use.
Read the city's modification rules in writing. Ask the building department what changes, if any, are permitted without voiding the fast-track. Some programs allow mirroring the floor plan. None allow structural changes. Verbal assurances are not reliable — get the answer in writing before hiring anyone to adapt the plans.
Verify which site-specific documents must be complete before the 30-day clock starts. An application is only "complete" when all required documents are submitted. If your city requires a soil report, site plan, and Title 24 calculations before the application is considered complete, the 30-day period does not begin until all of those are in hand. Confirm the completeness checklist with the building department before starting work.

References

[1] AB 1332 (2023). Adds Government Code Section 65852.27. Signed October 11, 2023, effective January 1, 2025. Bill text.

[2] GatherADU. "Soil Reports for ADU Construction: What California Homeowners Need to Know." Link.

[3] SnapADU. "ADU Grading Plan and Soils Report: Do You Need One?" Link.

[4] Association of Bay Area Governments (ABAG). "ADU State Laws Summary and Checklist," July 2, 2025. PDF.

[5] Solano County Building and Safety. AB 1332 Pre-Approved ADU Program — required site-specific submittals. Link.

[6] SB 543 (2025). Codifies ADU permit timelines, size definitions, and fee exemptions. Effective January 1, 2026. Bill text.

[7] LADBS ADU Standard Plan Program. Los Angeles Department of Building and Safety. Link.

[8] California Building Standards Commission. 2025 California Building Standards Code, effective January 1, 2026. Link.

[9] California Energy Commission. 2025 Building Energy Efficiency Standards — ADU FAQs. Link.

[10] GetTitle24. "Cost of a Title 24 Report." Link.

[11] City of Lincoln. AB 1332 Pre-Approved ADU Plans. Link.

[12] City of San Jose. Preapproved ADU Program. Link.

[13] CALBO (California Building Officials). Pre-Approved ADU Plans overview. Link.

[14] AB 434 (2023). Expands HCD enforcement authority for ADU law compliance. Government Code §65585(j). Bill text.

[15] GatherADU. "How Long Does ADU Plan Check Take in California?" Link.