ADU architects and designers: who can draw your plans and what it costs

Who can design an ADU in California

Architecture is a licensed profession in California, but the Architects Practice Act carves out common houses. Under Business and Professions Code section 5537, any person may prepare plans for:

• single-family dwellings of wood-frame construction, no more than two stories and a basement in height;
• multiple dwellings with no more than four units, under the same wood-frame and height limits;
• garages and other structures appurtenant to those buildings.

A house plus an ADU, or a house plus an ADU and a JADU, stays inside those limits. That's why most ADU plan sets in California are drawn by building designers and drafters, not licensed architects.

The exemption has firm edges:

• Wood frame only. The California Architects Board's guide for building officials says the exemption refers only to wood-framed structures, so a steel-framed unit isn't exempt. The same guide says grading and drainage plans need a licensed professional even for an exempt building.
• Conventional framing only. If any part of the building departs from conventional wood-frame rules, the building official must require plans or calculations for that part from a licensed architect or engineer, stamped by them.
• Four units, total. The law won't let an unlicensed person design clusters of units that add up to more than four on one lot.

Source: California Architects Board design limitations chart and Business and Professions Code section 5537. Your city has the last word on borderline cases.

Do I need an architect for an ADU?

For a standard detached or garage-conversion ADU, usually not. The City of San Diego's submittal manual says plans must be stamped and signed by a California-registered architect or engineer “unless otherwise exempt per B&P Code Section 5537.” But San Diego's municipal code also lets the Building Official require a licensed professional even where state law doesn't, and puts the burden on you to show the exemption applies when an unlicensed person drew the plans.

An architect earns the fee in a few situations:

• An attached ADU or one built into the house. The design has to work with the existing roof, structure and floor plan. See attached vs. detached ADUs.
• A second story or an ADU over a garage. Loads, stairs and lateral bracing get harder. See two-story ADUs.
• A steep, tight or unusual lot where grading, drainage or retaining walls need licensed design anyway.
• A fully custom design where the look matters as much as the cost.
• Non-wood construction such as steel framing, which falls outside the exemption.

For a simple rectangular unit on a flat lot, a building designer or a pre-approved plan does the same legal job for less.

ADU architects vs. ADU designers

Only a person licensed by the California Architects Board can call themselves an architect. The board says an unlicensed person or firm can't use “architect,” “architectural” or similar terms to describe their services. So an “ADU designer,” “building designer” or “drafting service” is usually unlicensed, and that's legal for an exempt ADU.

An architect must use a written contract signed before work begins, unless you knowingly agree in writing that work can start first. The board lists what it must contain: the services, the amount and method of payment, both parties' details, how added services are handled and how either side can end the contract.

What an ADU designer delivers

Whether you hire an architect or a building designer, the product is a permit-ready plan set. For the City of San Diego, the ADU bulletin points single-family projects to the city's submittal manual. A typical ADU set includes:

The design work itself usually runs in stages: a site visit and measurements, a concept layout you approve, the construction drawings, then the permit submittal. After you submit, the city has 60 days to approve or deny a complete ADU application. If plan check issues corrections, the designer answers them, so it matters whether that work is in the fee. For the full permit sequence, see ADU permits in San Diego and how long it takes to build an ADU.

Design is also where most of the budget gets decided. Size, roof shape, the number of bathrooms and how far the unit sits from the sewer and power lines all show up in the construction price later. A good designer tells you which choices cost the most before the drawings are final, not after the bids come back.

The rest of the design team

Whoever draws the floor plan, a permit-ready ADU plan set usually has more than one author.

Structural engineer

A wood-frame ADU built to conventional framing rules may not need an engineer. Anything outside those rules does: a large opening, a heavy roof, a second floor over an old garage, a hillside foundation. The local building official decides where the line falls. Check an engineer's license on the engineering board's license lookup; civil engineers carry a “C” and structural engineers an “S.”

Title 24 energy consultant

Every ADU needs an energy compliance report with the permit. The California Energy Commission treats a new detached ADU as a new building, which usually means new solar panels, while an attached ADU is treated as an addition with no solar requirement. Many designers subcontract this report to an energy consultant. The consultants' association says certification isn't required to prepare Title 24 documents; its Certified Energy Analyst credential is voluntary. For the details, see ADU solar and Title 24.

Civil engineer or surveyor

The Architects Board's guidance says grading and drainage plans need a licensed professional, even when the building itself is exempt. A flat lot often needs none; a sloped one usually does.

ADU architect cost

No state body publishes architect fees, and quotes vary with the scope. The figures below are what builders publish, so treat them as planning numbers, not prices.

Sources: Block Renovation's June 2026 Sacramento cost guide and Snap ADU's guide to pre-approved plans. Both are builders, not official sources. Snap ADU also estimates construction is 90–95% of the total budget, so the design fee matters less than the build. For the full budget, see what an ADU costs in San Diego or try the ADU cost calculator.

Ask any designer whether their quote includes structural engineering, the Title 24 report, a site survey, grading and drainage plans, and responses to plan-check corrections. Those are the items most often priced separately.

Four things move a design fee more than anything else. A custom layout costs more than adapting a standard plan. An attached ADU or conversion means measuring and drawing the existing house first. A sloped or crowded lot adds engineering and drainage work. And a design that goes back and forth with you, or with plan check, takes more hours. If you want to keep the fee down, settle the size and layout early and change as little as possible once the construction drawings start.

Using pre-approved plans instead

State law requires every city and county to run a program for pre-approved ADU plans, and to approve or deny an application for a detached ADU that uses a pre-approved plan within 30 days. The County of San Diego gives away plans in sizes from about 600 to 1,200 square feet, and the City of San Diego accepts them.

A pre-approved plan replaces the floor plan and most of the building design, not the whole design team. You or a designer still add a site plan for your lot, energy calculations and any engineering your site needs. It's a good fit for a detached unit on a flat lot. It's a poor fit for a garage conversion or an attached ADU, which have to be drawn around what's already there. See pre-approved ADU plans in San Diego and ADU floor plans.

Hiring an ADU architect or designer

Before you sign, the California Architects Board recommends checking the license, calling recent clients with similar projects, and keeping every invoice and message. Look up any architect on the board's license search; it licenses individuals, not firms. Its Consumer's Guide to Hiring an Architect walks through contract terms.

Questions to ask:

• “How many ADUs have you permitted in this city?” Local plan-check experience saves correction rounds.
• “Who prepares the structural, Title 24 and grading work, and is it in your fee?”
• “Are plan-check corrections included?”
• “Will you design to a construction budget, and how will you check it?” Ask a builder to price the design before it's final.
• “Who owns the plans?” You may want to take them to several builders for bids.
• “Do you work during construction?” Site visits and answering the builder's questions are often extra.

Choosing between a separate architect and a builder who designs in-house is its own decision; see design-build vs. architect for an ADU. When the plans are ready, read how to hire an ADU contractor, check a contractor's license and compare verified ADU builders in San Diego.

Common questions