What Are ADU Plans?

What ADU plans mean, in plain English

ADU plans are the drawings for your backyard home. They are drawn to scale, so one inch on paper equals a set distance on the ground.

They do two jobs. First, they let the city check the design against the rules before anything is built. Second, they tell the builder exactly what to build.

People often say "plans" when they mean the floor plan, the room layout. The real plan set is much bigger. It includes the lot, the outside walls, the structure and the energy math.

Why plans matter to you

Plans are where most delays start. If a sheet is missing or a number is wrong, the city sends back a list of corrections. Each round adds time.

Plans also fix the price. Builders bid on what the plans show. Vague plans lead to vague bids and later change orders.

And plans decide your speed in California. A city-approved plan can cut the legal review clock from 60 days to 30.

What is in an ADU plan set

Custom, stock or pre-approved: which plan type

How plans move from idea to permit

1. Check what fits on the lot first with the size envelope calculator.
2. Pick a plan type: custom, stock, or one from your city's pre-approved list.
3. Have the site plan drawn for your lot, plus structural and energy sheets.
4. Submit. In California the city must tell you within 15 business days whether the application is complete. If it misses that date, the application is treated as complete (Gov. Code 66317) ².
5. Answer any correction list and resubmit.
6. Receive the decision: within 30 days for a pre-approved detached plan, or 60 days under the general rule when a home already stands on the lot ^{1 2}.

California's pre-approved plan law

Government Code 65852.27 is a live section, as amended by SB 477, effective 25 March 2024. It required every local agency to set up a program to pre-approve ADU plans by 1 January 2025.

The agency must accept submissions and may not limit who submits them. It reviews them against the ADU standards in Article 2 of Chapter 13. It may charge the same permit fees as for a same-size ADU.

Pre-approved plans are posted on the agency's website with the applicant's contact details. Posting is not an endorsement of the plan's author.

The payoff is speed. For a detached ADU, the agency must approve or deny a complete application within 30 days if it uses a pre-approved plan, or a plan identical to one it approved for a detached ADU, within the current three-year California Building Standards Code cycle. The section applies to charter cities too.

Without a pre-approved plan, the general rule in Government Code 66317 applies. Review is ministerial, meaning no hearing and no discretion. The decision is due within 60 days of a complete application when a home already stands on the lot.

Do not confuse 65852.27 with 65852.2, the old ADU law that was repealed and moved to Gov. Code 66310–66342.

The three state clocks below are the ones to track. The first tells you the set is complete, and the other two start from that point.

Sources: [1] [2]

Rules in other states

Outside California, pre-approved plan programs are local choices. Some cities offer them; many do not. Review deadlines also vary. See ADU laws by state and pre-approved plan research.

Worked example: the 30-day clock in practice

A hypothetical owner submits a complete application for a detached ADU on 1 March. They use a plan on the city's pre-approved list from the current code cycle.

Both clocks run from a complete application. Missing site plan details or utility information mean the clock has not started. A pre-approved plan helps only if the rest of the set is right. Real-world timelines are on ADU approval times.

Real situations homeowners run into

• The plan fits, the lot does not. A pre-approved plan is 20 feet wide, but the back yard is 18 feet between the side setbacks. The plan has to be changed, which ends its pre-approved status.
• The garage conversion. Pre-approved plans are for detached ADUs. A garage conversion needs drawings of the existing structure, so it is almost always custom.
• The old stock plan. A plan drawn for an earlier code cycle may need new energy and structural sheets before it can be submitted.
• The slope. A hillside lot often needs an engineered foundation, which moves part of the design outside the wood-frame exemption ³.

Where you will see plans on paper

• Design contract: the list of sheets the designer will deliver, and how many correction rounds are included.
• Permit application: the plan set is attached, often as PDFs.
• Correction letter: the city lists sheets to fix, by sheet number.
• Builder's bid: the bid should name the plan set and date it is based on. Line bids up with the bid comparison tool.

What drives the cost of plans

HyreADU does not publish plan prices. No primary dataset gives dated, sourced design fees.

The drivers are scope and fit. A custom design for a sloped lot takes more hours than a stock plan on a flat one.

Structural engineering, energy calculations and survey work may be included or extra. Correction rounds add time. Design fees count as soft costs; model the total with the ADU cost calculator.

Pre-approved plans: benefits and limits

Common misreadings

Myth A pre-approved plan means no review.

Reality The city still reviews the site plan, utilities and foundation fit. Only the building design is pre-checked.

Myth A stock plan is permit-ready.

Reality It still needs a site plan for your lot and local structural and energy documents.

Myth The floor plan is the plan set.

Reality The floor plan is one sheet. The set includes site, elevations, structure and energy.

What to check before you buy or commission plans

• Does the footprint fit your lot's buildable area?
• Is the plan on your city's list? Search with the pre-approved plan finder.
• For stock plans, what local work is excluded: site plan, structural calculations, energy compliance?
• Who holds the license or stamp if the design falls outside the wood-frame exemption ³?
• Is the plan's code cycle current? The 30-day rule applies only within the current cycle ¹.
• Who owns the drawings? A California architect's contract must state the ownership and use of the drawings (Bus. & Prof. Code 5536.22) ⁴.

Your plans checklist

1. Screen the lot with the feasibility checker.
2. Pick a plan type.
3. Get a written scope listing every sheet.
4. Confirm structural and energy work are covered.
5. Submit and diary the 15-business-day completeness date.
6. Answer corrections quickly and in full.

Key takeaways

• ADU plans are the full permit set, not just the floor plan.
• California cities must run a pre-approved plan program (Gov. Code 65852.27).
• A pre-approved detached plan gets a 30-day decision; the general rule is 60 days.
• Both clocks start only from a complete application.

Plans research and tools

• Search pre-approved plans by cityThe finder tool
• ADU design hubLayouts, sizes and design decisions
• ADU permitsWhat happens after you submit
• Permit times by cityHow long review really takes

Related terms

ADU Site Plan

An ADU site plan is a scaled, top-down drawing of the whole lot that shows where the accessory dwelling unit will sit, every existing structure, and the distances from each building to the property lines.

ADU Architect

An ADU architect is a state-licensed architect who designs an accessory dwelling unit and prepares the drawings the building department reviews, often managing plan-check corrections as well.

ADU Floor Plan

The drawing of an ADU's rooms, walls, doors and windows seen from above. Floor plans are what most buyers browse; permit sets add a site plan, elevations and structural sheets.

ADU Permit

An ADU permit is the building permit a city or county issues to allow construction of an accessory dwelling unit, after checking the plans against local zoning standards and the building code.

Ministerial Approval

Ministerial approval is a permit decision in which an official checks an application against fixed, objective standards and must approve it if they are met, with no public hearing and no discretion to deny it on judgment.

Prefab ADU

A prefab ADU is an accessory dwelling unit whose walls, floors or whole room modules are built in a factory and then shipped to the lot, where a crew sets them on a foundation and connects utilities.

ADU Design

The layout, look and specification of an ADU: room plan, height, windows, finishes and how it sits on the lot.

ADU Soft Costs

ADU soft costs are the parts of an accessory dwelling unit budget that pay for paperwork, professional services and money rather than for physical construction: design, engineering, surveys, permits and government fees, utility charges, insurance and financing costs.

Also referenced from: Prefab ADU, ADU Site Plan, ADU Bedroom, ADU Accessibility, Building Code, California Residential Code, Building Department, Permit Expediting, ADU Framing, ADU Architect, ADU Engineer