California’s ADU market is the most active in the country. CA YIMBY's 2024 ADU Reform Retrospective shows ADUs already accounted for nearly one in five new housing units statewide by 2022, while the Federal Housing Finance Agency has linked ADUs to higher property values and stronger value growth.
Momentum is especially clear in markets like San Diego County, where the UC San Diego Center for Housing Policy and Design has reported major growth in completed ADUs. For 2026, SB 543 reduces cost barriers by eliminating state impact fees on ADUs 750 square feet or smaller, and the CalHFA ADU Grant Program offers up to $40,000 for eligible predevelopment costs.
In this guide, our team at Streamline Design & Permitting reviews California ADU companies by local code expertise, project specialization, service transparency, and permit track record with the goal of helping homeowners choose the right partner beyond the most-marketed name.
What Type of ADU Company Do You Truly Need?
Before comparing specific firms, it helps to understand that the term "ADU company" isn’t one single type of service. It’s a few different roles, and choosing the right one can make the entire process smoother from start to finish.
Pre-construction and permitting specialists handle design, permit-ready drawings, engineering coordination, Title 24, submissions, and plan check responses. These are a good fit if you already have a builder lined up, are still deciding who to hire, or need to legalize an existing unpermitted unit.
Design-build firms manage design, permits, and construction under one contract, offering one point of accountability but less contractor flexibility.
Prefab ADU manufacturers build units off-site in a factory and then deliver them partially or fully assembled. They often offer faster timelines and predictable pricing, but allow less flexibility for custom sites, unusual lots, or strict local regulations.
Construction-only contractors specialize in building from approved plans. They require the homeowner to have already completed the design and permitting phases before engagement.
Each model has appropriate use cases. The companies we’ve outlined below are organized to represent the full range.
The 10 Best ADU Companies in California in 2026
1. Streamline Design & Permitting (San Diego County)
- Service type: Pre-construction, design, and permitting
- Service area: San Diego County, Southern Orange County, Southwestern Riverside County
- Best for: San Diego County homeowners who need permit-ready ADU drawings, code compliance documentation, ADU legalization under AB 2533, or a pre-construction partner who manages the full design-through-permit process.
Streamline Design & Permitting focuses on the part of an ADU project most homeowners don’t think about until they realize it’s essential: the pre-construction phase. Here, design decisions and permit documentation determine everything that follows. Before any contractor breaks ground, someone has to produce permit-ready drawings that satisfy local building departments, comply with California Building Code and Title 24 energy standards, and give contractors accurate information to bid and build from. That is the core of Streamline’s work.
The firm works with homeowners across San Diego County on all ADU types: detached backyard homes, garage conversions, attached additions, Junior ADUs (JADUs), and ADU legalization under California's AB 2533 amnesty program. Streamline's approach to each project type reflects current California ADU law, including the 2026 legislative package (SB 543, AB 462, AB 1154, and the updated SB 9), which the team incorporates into every submittal to ensure compliance from day one.
What distinguishes Streamline from design-build firms and general contractors is the depth of its permitting expertise. The team handles plan checks responses directly, coordinates with structural engineers and Title 24 consultants, and stays closely aligned with the City of San Diego's Development Services Department review process.
For San Diego homeowners in coastal neighborhoods such as La Jolla, Ocean Beach, and Pacific Beach, where AB 462's new coastal permit timelines apply, this regulatory fluency translates directly into faster approvals.
Streamline also specializes in code compliance documentation for properties with unpermitted structures, a service that requires careful as-built drafting and an understanding of how the DSD processes retroactive permit applications. This level of detailed, forensic documentation sets the firm apart in a market where many ADU companies focus exclusively on new construction.
2. Acton ADU (Bay Area and Northern California)
- Service type: Full-service design-build
- Service area: San Francisco Bay Area and Northern California
- Best for: Bay Area homeowners who want a single experienced firm managing design, permits, and construction for a detached backyard home or garage conversion.
Acton ADU is a long-established California ADU specialist with over three decades of experience in accessory dwelling unit construction. Unlike many firms that entered the market during the ADU boom between 2019 and 2022, Acton brings deep pre-boom permitting experience. The firm uses an in-house design and construction team, managing projects from feasibility review through final inspection.
Homeowners can choose custom ADU designs or pre-approved plans that may help reduce permitting timelines. Acton is especially active in the Bay Area, where requirements vary widely across San Francisco, Oakland, San Jose, and surrounding Northern California communities.
3. Abodu (Statewide)
- Service type: Prefab design-build
- Service area: Statewide (California)
- Best for: Homeowners who prioritize speed, design consistency, and pricing predictability over full customization, particularly in jurisdictions where Abodu holds pre-approved plans.
Abodu is a leading California prefab ADU provider known for fast, modern backyard homes. Its factory-built units come in standardized models from 340 to 610 square feet, with pre-approved plans in several jurisdictions to help shorten permitting timelines.
Another noteworthy point is that Abodu also publishes transparent pricing, with typical all-in costs ranging from about $150,000 to $300,000 depending on unit size and site conditions. The company has also updated its guidance around the 2026 ADU law changes.
4. Snap ADU (San Diego and Orange County)
- Service type: Full-service design-build
- Service area: San Diego County and Orange County
- Best for: San Diego and Orange County homeowners who want a full-service design-build firm experienced in Southern California's specific permitting environments.
Snap ADU is a leading Southern California ADU company serving San Diego and Orange County. The firm provides in-house design, engineering coordination, permitting, and construction, offering homeowners a guided process from initial feasibility through move-in.
Snap ADU also publishes detailed California ADU regulatory guidance, including analysis of 2026 law changes such as SB 543’s 15-day completeness review and impact fee clarifications. Its contractor-side insights show a strong commitment to client education. The company has completed detached ADUs, garage conversions, attached ADUs, and Junior ADUs throughout San Diego County, ranging from compact urban infill sites to larger inland lots.
5. ADU Geeks (San Diego)
- Service type: ADU consulting and project management
- Service area: San Diego County
ADU Geeks is a leading San Diego ADU consulting and project management firm, ranked No. 1 in the Small Business category on the San Diego Business Journal’s 2024 Fastest Growing Private Companies list after 594.3% revenue growth. Rather than building directly, the firm connects homeowners with vetted design and construction partners while managing oversight, coordination, permitting, and project guidance.
It uses an independent model ideal for homeowners seeking expert advocacy without committing to one design-build firm. ADU Geeks is especially strong when it comes to complex sites, phased projects, code compliance issues, and San Diego-specific ADU regulations and permitting requirements.
6. Cali ADU (Los Angeles)
- Service type: ADU design and permitting (with construction options)
- Service area: Los Angeles County
- Best for: Los Angeles County homeowners who want a flexible design and permitting partner, whether or not they plan to use the firm's construction network.
Cali ADU combines design, permitting, and construction coordination for Los Angeles County homeowners. The firm offers pre-designed ADU plans, which may help streamline LADBS permitting, as well as custom designs for site-specific needs. Its flexible model lets homeowners use Cali ADU for design and permits, then either manage construction independently or work through the firm’s preferred builder network.
This staged approach is ideal for owners who want more control over contractor selection or already have a trusted builder. Cali ADU also provides transparent cost and design resources, including guidance on Los Angeles ADU costs, garage conversions, and recent legislation affecting project timelines.
7. CA-ADU (Statewide)
- Service type: Full-service design, permitting, and construction management
- Service area: Statewide (California)
- Best for: Homeowners outside major metro areas who need a statewide firm capable of managing all phases of an ADU project across diverse jurisdictions.
CA-ADU provides a full-service ADU model across California, covering architecture, engineering coordination, permitting, and construction management. The firm provides a single point of accountability from feasibility review through final Certificate of Occupancy inspection. Its proactive permitting approach is a key differentiator, with specialists who manage applications, plan check responses, building department communication, and inspection scheduling for clients.
Unlike firms that treat permitting as a pass-through task, CA-ADU positions it as a core strength. The company handles attached ADUs, detached backyard homes, garage conversions, and legalization projects, with experience navigating varied ordinances across California cities and counties.
8. Nestadu (Statewide — Site-Built and Prefab)
- Service type: Custom site-built and prefab ADU design-build
- Service area: Statewide (California)
- Best for: Homeowners who want the flexibility to choose between site-built custom, semi-custom, or prefab ADU options from one firm, particularly for complex sites or multigenerational living needs.
Nestadu’s ADU model is hybrid and flexible, allowing homeowners to choose from nine signature site-built designs, create a fully custom layout, or select prefab models delivered and assembled onsite. This mix of site-built and prefab options is uncommon in California, where most ADU firms specialize in only one approach.
Client reviews often highlight Nestadu’s responsiveness on more complex properties, including sloped lots, narrow access, and unusual configurations that can rule out prefab solutions. The CEO and COO are also noted for hands-on consultations. For multigenerational living, Nestadu’s custom design capability supports accommodation-specific layouts that standard prefab plans may not provide.
9. Fortune ADU (Sacramento, Los Angeles, San Diego)
- Service type: Full-service design-build
- Service area: Sacramento, Los Angeles, San Diego markets
- Best for: Homeowners in Sacramento, Los Angeles, or San Diego who prioritize fixed-price contract certainty and an integrated design-through-construction service.
Fortune ADU bundles feasibility review, architectural design, permitting, and construction under one contract with transparent, all-in pricing from planning to move-in. They provide a fixed-price contract before construction begins, giving clients cost clarity and reducing the open-ended expenses often seen with general contractors less experienced in ADU work.
The firm serves three major California ADU markets: Sacramento, Los Angeles, and San Diego. This is noteworthy because, while California sets statewide ADU rules, local jurisdictions add varying requirements. Fortune ADU’s multi-market experience gives it broader permitting knowledge than firms focused solely on one city.
10. Go ADU Construction (Los Angeles County)
- Service type: Full-service design-build
- Service area: Los Angeles County
- Best for: Los Angeles County homeowners wanting a fully integrated design-build firm with guaranteed pricing, milestone-based payments, and a documented track record of completed permitted ADU projects.
Go ADU Construction is a family-owned Los Angeles ADU company founded in 2017, with 120+ permitted projects completed countywide. Its promise, “We Don’t Flake,” addresses homeowner worries about delays, disappearing contractors, and surprise costs. The firm manages architecture, permitting, and construction under one contract, with written guaranteed pricing provided upfront and payments structured around project milestones.
Services include detached ADUs, garage conversions, attached ADUs, and JADUs. Design and permitting typically take 8–12 weeks, while construction adds 4–6 months, totaling about 6–9 months. With deep experience in Los Angeles County, Go ADU helps homeowners navigate LADBS reviews, corrections, and permitting smoothly.
What to Look For When Hiring an ADU Company in California
The quality and scope of ADU companies in California are significant. Here’s a practical framework for evaluating any firm before you commit.
Verify CSLB Licensing
California's Contractors State License Board maintains a public database at the Contractors State License Board (CSLB) where you can confirm a contractor's license status, bond, workers' compensation coverage, and complaint history. A legitimate ADU builder or design-build firm should be willing to provide its license number so you can verify it independently.
Confirm ADU-Specific Experience
General remodeling experience isn’t the same as ADU experience. ADU projects involve utility coordination, setback compliance, separate meter applications, and Title 24 energy documentation that differ from standard renovation work. Ask how many permitted ADUs the firm has completed in your specific jurisdiction, and request references from past clients who went through a similar process.
Ask About Permit History
What percentage of their submittals require corrections on the first plan check? Experienced ADU firms in San Diego or Los Angeles know what local reviewers look for and prepare submissions accordingly. Frequent correction cycles can be a sign that a firm isn’t fully familiar with local permitting requirements.
Understand the Contract Scope
Full-service design-build contracts should specify exactly what’s included: design phases, number of revision rounds, structural engineering coordination, Title 24 compliance, permit application, plan check response, and construction phases. Contracts that are vague about phase boundaries expose homeowners to scope disputes and unexpected costs.
Ask About Legislative Compliance
California's ADU laws changed significantly on January 1, 2026. Any ADU company advising clients on setbacks, impact fees, JADU owner-occupancy rules, or coastal permitting should be current on SB 543, AB 1154, AB 462, and AB 2533. Outdated guidance on these provisions can lead to incorrect project scope, missed exemptions, or avoidable permit delays.
Evaluate Communication Practices
ADU projects take months and involve coordination across multiple agencies, consultants, and contractors. Ask prospective firms how they communicate project status, who your point of contact will be at each phase, and how they handle plan check corrections when they occur.
Finding the Best ADU Company for Your Property
Choosing the right ADU company in California starts with understanding your project’s needs, location, budget, and permitting complexity. Whether you choose a prefab unit, a design-build firm, or a pre-construction partner for permit-ready plans, the best option is the company with proven local experience, clear communication, and current knowledge of California ADU laws.
Taking time to evaluate everything carefully upfront can help you avoid delays, unexpected costs, and compliance issues later on. For San Diego County ADU planning, contact Streamline Design & Permitting today for a free consultation.
