What Does an ADU Architect Do?

Key takeaways

• An ADU architect is a licensed pro who designs your unit and draws the plans the city checks.
• In California, you do not always need one. Anyone may draw a simple wood-frame home of up to two stories ¹.
• Parts that go beyond normal wood framing must be drawn or signed by a licensed architect or engineer ¹.
• A California architect must give you a written contract before work starts, with set items in it ⁴.
• Fees come as a fixed fee, an hourly rate or a share of build cost. Compare the scope, not just the price.
• A city pre-approved plan can replace much of the custom design work.

What an ADU architect is, in plain English

An ADU is an accessory dwelling unit. That is a small second home on the same lot as a house. Some people call it a granny flat or backyard cottage.

An ADU architect is the person who designs that small home. They also draw the plans the building department reviews. Those plans are called the permit set. They show the layout, the structure, and how the unit meets the codes.

The word "architect" is a license, not a job title anyone can use. In California, the license comes from the California Architects Board. A designer or drafter can do much of the same drawing, but does not hold that license.

Why it matters to you

The plans decide almost everything that follows. They set what the city approves, what builders bid on, and what gets built.

Weak plans can mean more rounds of plan check. Plan check is the city review where staff send back a list of corrections. Each round adds time. Missing details also lead to change orders during the build. A change order is a paid change to the contract.

Choosing between an architect and a designer is a real decision. It affects your fee, your risk, and who answers for the design.

Architect, designer, engineer or design-build

California's rule: Business and Professions Code 5537

Section 5537(a) says the architects' licensing chapter does not prohibit any person from preparing plans for single-family dwellings of woodframe construction not more than two stories and basement in height, multiple dwellings of up to four units under the same limits, and garages or other structures appurtenant to those buildings.

A detached or attached wood-frame ADU generally fits inside that exemption. The catch is in Section 5537(b): if any portion deviates from substantial compliance with conventional framing requirements in Title 24 or the local building code's tables, the building official must require that portion to be prepared by, or under the responsible control of, a licensed architect or registered engineer, with their stamp and signature.

Steel moment frames, large openings, steep hillside foundations and non-wood systems commonly trigger it.

Other states draw the line differently, and some require a licensed professional for more work. See ADU laws by state.

Sources: [1]

ADU architect cost: how fees are structured

Architects and designers usually price ADU work in one of three ways: a fixed fee for a defined scope, hourly billing, or a percentage of construction cost. Scope changes the number more than the method does: site visits, a survey, structural engineering, Title 24 energy calculations and plan-check rounds may be included or billed separately.

Design fees sit in your soft costs, alongside permit and impact fees.

HyreADU does not publish a typical architect fee because no primary dataset with dated, sourced fee quotes is available to us; compare written proposals line by line instead, using the bid comparison tool, and model the total in the cost calculator.

When an architect is worth it

The decision guide sorts common California ADU projects by who may draw them. The list after it covers when hiring an architect pays off anyway.

• Hillside, small or irregular lots where the footprint is hard to fit; the site plan must show every distance to the lot lines ³.
• Two-story units, large glazing or structural work that falls outside conventional framing ¹.
• Historic districts or design review areas.
• Owners who want one professional to manage plan check and observe construction.

What to check in a design proposal

• Whose license covers the work, and whether structural engineering is in the price.
• How many plan-check correction rounds are included.
• Whether the site plan, energy compliance and utility layout are included.
• Who owns the drawings, and whether they can be reused or handed to any contractor.
• Whether a city pre-approved plan would do the job for less ².

Misconceptions

Myth Every ADU in California needs an architect.

Reality Not for conventional wood-frame units up to two stories and basement; Section 5537 lets anyone prepare those plans ¹.

Myth A designer's plans skip structural review.

Reality The building department still checks them, and can require a licensed architect or engineer for any non-conventional portion ¹.

Related guides

• ADU design hubLayouts, sizes and design choices
• Find a professionalHow to shortlist designers and builders
• How we vetWhat HyreADU checks before listing a professional

How working with an ADU architect usually goes

Firms name these phases differently. The order is close to this on most ADU jobs.

1. First visit and brief. You share your goals, budget and lot. The architect looks at zoning and the site.
2. Feasibility. They check what fits: type, size, setbacks and utilities. See ADU feasibility.
3. Schematic design. Rough floor plans and a first look at the outside. You pick a direction.
4. Design development. The plan firms up. Windows, kitchen layout, structure and finishes get set.
5. Permit set. Full drawings, the site plan, energy forms and engineering go to the city.
6. Plan check. The city sends corrections. The architect revises and sends the plans back.
7. Construction support. If your contract includes it, they answer builder questions and visit the site.

Types of design help for an ADU

Worked example: lining up two design proposals

A hypothetical case. Two firms quote the same detached ADU. The point is the scope, so we show what each fee covers, not prices.

Proposal B has the lower base fee. But it leaves out three items that A covers, and a third plan-check round costs more. Add every extra to B before you compare totals. The cheaper-looking quote is not always cheaper.

Where you will see the architect’s role

• Design contract. The scope, fee and who owns the drawings.
• Permit set. The name, and the stamp and signature where a licensee is needed.
• City letters. Plan-check comments come back to whoever submitted the plans.
• Builder bids. Contractors price from the drawings. Gaps in the drawings show up as exclusions.
• Loan papers. Some construction lenders ask for the plans and budget. See ADU financing.

California’s written-contract rule for architects

Business and Professions Code 5536.22 says a California architect must use a written contract with you. Both of you sign it before work starts. The only exception is if you knowingly agree in writing that work may start first ⁴.

The contract must describe the project and the services. It must state how the fee is set and how you pay. It must list the architect’s name, address and license number, plus your name and the project address ⁴.

It must also explain how changes are handled and how either side can end the contract. And it must say who owns and may use the drawings. The law calls drawings "instruments of service" ⁴. That last item matters if you later switch builders.

A designer without a license is not covered by this section. Ask for the same items in writing anyway.

Sources: [4]

What drives the design fee

We do not publish a typical fee. No dated, sourced fee data meets our standard. What we can tell you is what moves the number.

Size and shape matter less than you think. Complexity matters more. A two-story unit, a slope, or a tight lot means more drawings and more engineering.

Scope is the big driver. Ask whether the fee covers survey, structural work, energy forms, plan-check rounds and site visits. A low base fee with many extras can cost more than a high all-in fee.

Then add the design fee to your soft costs and test the total against your budget. See also ADU cost statistics.

Benefits and limits of hiring an architect

What to ask an ADU architect before you sign

• How many ADUs have you designed in this city? Can I see the permit numbers?
• What is your license number? (Then look it up yourself.)
• Is structural engineering in the fee, or extra?
• How many plan-check rounds are included?
• Who owns the drawings if I stop after the permit?
• Will you visit the site during the build? How often?
• Would a pre-approved plan work here instead?
• What do you need from me: a survey, a soils report, utility letters?

Checklist: hiring design help for your ADU

1. Run a quick check on your lot with the feasibility checker.
2. Decide if your design is simple wood frame or not. That tells you if a licensee is needed ¹.
3. Get two or three written proposals for the same scope.
4. Line up the scopes in a table, like the example above.
5. Check each license with the state board.
6. Read the contract for the items California requires ⁴.
7. Agree on the drawing-ownership terms before you sign.
8. Keep every plan-check letter and revision in one folder.

Related terms

ADU Plans

ADU plans are the set of scaled drawings and documents that describe an accessory dwelling unit well enough for a building department to check it against zoning and building codes and for a contractor to build it.

ADU Contractor

An ADU contractor is a licensed construction business that contracts to build an accessory dwelling unit, either doing the work itself or running the subcontractors who do the trades.

ADU Design-Build

ADU design-build is a way of delivering an accessory dwelling unit in which one firm is responsible for both designing the unit and building it, usually under one contract or a design agreement that rolls into a construction contract.

ADU Engineer

An ADU engineer is a licensed engineer who designs the parts of an accessory dwelling unit that carry loads or deal with the ground, such as the foundation, beams and earthquake bracing, and signs the calculations the city reviews.

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.

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 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.

Also referenced from: ADU Plans, ADU Site Plan, Permit Expediting, ADU Contractor, ADU Engineer