How to Hire a ADU Contractor in San Diego: A Step-by-Step Guide

How to Hire a ADU Contractor in San Diego: A Step-by-Step Guide

The California Contractors State License Board fielded over 19,000 complaints in a recent year. A significant share involve projects where the homeowner chose the lowest bid without checking whether that bid included permits, engineering, or inspections, items that can add 15 to 25 percent to a project’s cost when they show up later as change orders. In San Diego, where ADU permit timelines and code requirements shift by planning district, that mistake gets expensive fast. This guide gives you the exact questions to ask and the documents to demand before you sign anything, and you can find more guides & resources on our blog.

Call (858) 264-3027

Quick Answer

Hiring an ADU contractor in San Diego means confirming a current CSLB license, workers’ compensation insurance, and a recent record of closed ADU permits in the city, not just glowing reviews or the lowest estimated price. Once those are verified, insist on a written fixed-price contract that names specific allowances for materials, includes engineering and permit fees, and penalizes nothing but the contractor’s own delays. A competent ADU contractor answers every question below in under 10 minutes and shows paperwork without being asked twice.

Table of Contents

• Step 1: Verify the CSLB License, Bond, and Workers’ Comp Before the First Meeting
• Step 2: Ask ADU-Specific Experience Questions Most Homeowners Skip
• Step 3: Read the Fixed-Price Contract Line by Line Before Signing
• Step 4: Request One Detailed Scope of Work, Then Compare Every Bid Against It
• Step 5: Recognize ADU Contractor Red Flags Before They Cost You
• Step 6: Decide Between Prefab, Modular, and Conventional Build Methods
• Common Mistakes to Avoid
• When to Call a Professional
• Frequently Asked Questions
• The Bottom Line

Step 1: Verify the CSLB License, Bond, and Workers’ Comp Before the First Meeting

The single highest-value move you can make when hiring an ADU contractor in San Diego costs five minutes and zero dollars. Go to the Contractors State License Board website, enter the contractor’s name or license number, and pull their record. What you see there tells you more than any portfolio photo or neighbor referral. A currently active license in good standing means they have met California’s minimum experience bar, passed the law and trade exams, and paid the required bond. A license that is expired, suspended, or under a different business name is your cue to end the call.

The CSLB record shows four things worth knowing before any contractor sets foot on your property:

• License status and class: An ADU contractor should hold a General Building (Class B) license. A specialty class like C-5 (framing) or C-36 (plumbing) alone does not authorize a full ADU build.
• Bond amount: California requires a $25,000 contractor’s bond. This bond compensates you if a contractor violates the law or fails to correct a valid workmanship problem. It does not cover ordinary contract disputes, which is why the next two items matter.
• Workers’ compensation certificate: If an uninsured worker gets hurt on your San Diego job site, the claim can fall on your homeowners policy. Demand a current workers’ comp certificate in writing, named to the contractor you are hiring, before work begins.
• Enforcement history: The CSLB lists complaints, citations, and legal actions. One stale dispute from 2012 is different from three open complaints filed in the last 18 months. Weight recent patterns heavily.

Reed Calloway, owner of Fielding ADU San Diego, puts it plainly: “The license check is the cheapest form of insurance you will ever buy on an ADU project. Five minutes on the CSLB site, and you know more about the person asking for a deposit than their website ever told you.”

Step 2: Ask ADU-Specific Experience Questions Most Homeowners Skip

A contractor who has built fine kitchens in Carlsbad may still fail his first ADU in San Diego. The two project types share a trades license but not much else. ADU work inside city limits means dealing with San Diego’s specific planning review process, fire safety standards for units under 16 feet from a primary home, and soils reports that vary by lot history and hillside designation. Ask these four questions and expect specific answers, not generalities:

1. How many San Diego ADU permits have you pulled in the last three years? A real number, given without hesitation, tells you the contractor has staff who know this city’s counters and inspectors. A shrug or a pivot to “we’ve done a lot of additions” is a wrong answer.
2. Which San Diego inspectors or planning reviewers do you typically work with? No contractor controls an inspector, but one who has pulled ADU permits in this city can name the kinds of objections they have fought through: fire sprinkler interpretations, setback variance questions, parking replacement rules. That fluency transfers directly to your project’s timeline.
3. Can you show a closed permit card on a completed ADU project? A closed permit card is the document that proves a project passed final inspection. Open permits are worthless to you. Ask to see one, and check that the address and scope match what the contractor claims.
4. Will you put the permit timeline in writing? Most contractors will commit to a construction schedule, few will commit to a permit schedule. Get both. San Diego’s Development Services Department publishes current review times, and an experienced ADU builder knows how to quote against them.

We have had homeowners bring us bids from contractors who could not answer any of these questions. One had “200 projects completed” listed on his site. His CSLB record showed a license that only resolved a suspension six months earlier. Those are the hires that turn into 14-month projects.

Step 3: Read the Fixed-Price Contract Line by Line Before Signing

A legitimate fixed-price ADU contract in San Diego must list a total price, a defined scope of work, and a written procedure for changes. When a contractor instead proposes a cost-plus agreement, be ready for the math: you pay every dollar of materials and labor plus a markup, typically 15 to 20 percent, and the final bill is whatever the project actually cost, not what it was quoted. Cost-plus is a tool for large commercial projects with known unknowns. For a San Diego backyard ADU, it is frequently a way to shift all the risk to the homeowner while keeping the sale price attractive.

Here is what a fixed-price ADU contract must contain before you sign:

• Line-item allowances for windows, doors, flooring, and fixtures. Vague phrases like “quality vinyl windows” are change orders waiting to happen. Your contract should name a brand, a series, or a dollar allowance per item.
• Engineering and soils report fees. If these are excluded from the fixed price, expect them to arrive as a separate invoice after prelim work begins. On a typical San Diego ADU, engineering runs $3,000 to $7,000 and a soils report $1,500 to $3,500 depending on lot conditions.
• Permit and school fee line items. The city charges specific fees, and school fees are calculated from square footage. A contract that says “permit fees extra” without a stated allowance is a blank check.
• Change order procedure in writing. It should state that changes require a signed written order with a price before the work is done. Verbal direction, no matter how pleasant the conversation, is how a $180,000 ADU becomes $230,000.
• Payment schedule tied to completed milestones, not calendar dates. Foundation poured, framing inspected, drywall complete. Never pay ahead of the work.

And before any work starts, the price should be in writing. Fielding ADU San Diego hands every client a written price before a single nail is driven, every time, with no exceptions. That price is the number on the final invoice, which is the only way a fixed-price contract means anything at all. When you compare proposals, the absence of that clarity is itself a signal. The Garrison Code, the operating standard behind Fielding ADU San Diego, reduces it to five short rules: show up in the window, price in writing, build by the book, leave it clean, and stand behind it for a year.

Step 4: Request One Detailed Scope of Work, Then Compare Every Bid Against It

The conventional advice to “get three bids” is half-right. Three bids are useful only when each one prices exactly the same scope. When one San Diego contractor prices a Tuff Shed-style shell with unfinished interior, another prices a fully finished unit with James Hardie siding, and a third prices a turnkey 500-square-foot one-bedroom, you are comparing apples, oranges, and a slab of concrete.

The better move is to pay for one detailed, line-itemed scope of work from a competent contractor or a design professional. Then issue that exact scope to every bidder and require them to price it as written. The differences you see after that are labor rates, overhead, and honesty, not scope ambiguity. Here is how to run the process in five steps:

1. Hire a designer, architect, or detailed draftsperson to prepare plans and a written scope. This costs $5,000 to $15,000 in San Diego but is the highest-leverage money you will spend on the project. It gives you bid comparability and a document to hold contractors to.
2. Include specific allowances in the scope. Not “mid-range tile” but “$4 per square foot tile allowance.” Not “energy-efficient windows” but “Milgard Tuscany series or equivalent aluminum window, U-factor no greater than 0.30.”
3. Send the scope to three licensed San Diego ADU contractors. Require each to return a line-item proposal that maps to your scope exactly, with no exclusions buried in footnotes.
4. Redline the proposals against each other. Any line that one bidder excludes and another includes is a question, not a savings. Ask the excluding bidder why, and put the answer in writing.
5. Do not weight price heavily until scopes match. Once they do, a spread of $30,000 to $60,000 on a $200,000 project is normal and mostly reflects overhead, supervision hours, and warranty capacity.

Cost ranges help here. In San Diego as of 2025, a conventional 500-square-foot attached ADU typically runs $180,000 to $260,000 before permit fees, while a garage conversion typically lands between $110,000 and $170,000. Prefab ADUs from brands like Cover and Dvele often price between $220,000 and $320,000 installed, depending on site work and utility extensions. These figures move, but they give you a basis for spotting a bid that is either unrealistically low or padding an easy job.

Step 5: Recognize ADU Contractor Red Flags Before They Cost You

Most bad contractor relationships start with an ignored signal in the first two conversations. The specific red flags below are the ones we see repeatedly in San Diego, where permit timelines and soils requirements make vague contracting unusually dangerous. When you see one, ask for it in writing. When the contractor refuses, end the process.

• Vague window and finish allowances. “Standard windows” and “builder-grade finishes” are not numbers. The moment the contractor orders them and hands you the change order, you will learn what the “standard” actually prices at.
• No mention of a soils report. San Diego has expansive clay, hillside lots, and fill areas that all affect foundation design. A contractor who does not bring up soils reports in the first conversation has either never permitted an ADU in this city or is planning to skip the step and deal with the consequences later.
• Verbal promises on permit timelines. “Permit will take six weeks” means nothing unless it is written and tied to a specific submission date. The city controls the clock, not the contractor, but a contractor who knows San Diego’s review process can commit to a realistic range and put it on paper.
• A down payment over 10 percent or $1,000, whichever is less. California law caps the initial deposit on home improvement contracts at that amount. A San Diego contractor asking for $30,000 to “hold the slot” is breaking the law before the job starts.
• No fixed date for start or completion. A contract without dates is a promise to work on your ADU when nothing better is available. Require a start date and a stated number of working days to substantial completion, with written allowances for weather and inspection delays.
• Willingness to skip permits to “save you $8,000 on fees.” An unpermitted ADU in San Diego triggers enforcement risk, insurance gaps, and resale disclosure problems that dwarf the fee savings. This one is an automatic no.

Step 6: Decide Between Prefab, Modular, and Conventional Build Methods Before You Hire

Hiring the right ADU contractor in San Diego partly depends on which build method fits your budget, lot, and timeline; see our ADU Cost Breakdown: The San Diego Homeowner’s Reference for 2026 for detailed figures. Each method carries different cost structures and site requirements, and some contractors specialize in only one. Understanding the trade-offs before you solicit bids prevents you from hiring a conventional framer for a prefab project or vice versa.

The three main approaches in San Diego:

• Conventional stick-built on site. A General B contractor frames, insulates, and finishes the ADU on your property. This method handles odd lots and custom layouts best, but it is most exposed to weather and labor scheduling. Typical pre-permit cost: $180,000 to $260,000 for a 500-square-foot unit, with a 5 to 9 month timeline from plan approval to final inspection.
• Prefab panelized systems. Dvele and Mighty Buildings ship wall and floor panels to the site for assembly. The controlled factory environment produces tighter tolerances and faster enclosures. Site work, foundations, and utilities remain local. Expect $220,000 to $300,000 installed on typical San Diego lots, with meaningfully shorter framing phases.
• Factory-complete modular units. Cover builds complete units in its factory and delivers them on a trailer. The site needs crane access, a prepared foundation, and utility stubs ready to connect. A smaller 400-square-foot unit can arrive on-site in a single day. Common range: $230,000 to $320,000 installed, with the fastest overall timeline.

Fielding ADU San Diego has built with each of these methods, including conventional James Hardie-clad projects, which means the recommendation you get is driven by your lot and budget, not the sales quota for a single factory. A contractor who only installs one system will naturally price that system, whether or not it fits your site. A contractor who works with several can tell you honestly why a 23-foot narrow lot favors panelized over modular, or why a hillside in Clairemont pushes you toward conventional framing. Hire for that fluency, and the build method question answers itself.

For a full breakdown of what ADU construction involves in this market, start with our ADU Builders in San Diego guide, which maps project phases and cost drivers. If your project is a garage conversion instead of a new structure, our Garage Conversion Contractor in San Diego page covers the different code triggers and realistic pricing. And if you are still deciding between an ADU and a bump-out addition, the Room Addition Contractor in San Diego guide compares both paths line by line.

Common Mistakes to Avoid

• Skipping the CSLB work comp check because the contractor “seems busy and reputable.” A busy schedule is not an insurance policy. One uninsured fall off a ladder on your San Diego property and your homeowners carrier is writing the check.
• Comparing bids without matching scopes. When one bid excludes site work and another includes it, the lower price is an illusion. Get one detailed scope in writing, then hold every bidder to it, no exceptions.
• Paying a security deposit over the California legal cap. The cap is $1,000 or 10 percent, whichever is less. A larger ask is a felony under state law. Walk away and report the contractor.
• Accepting a verbal quote as binding. A price spoken across a kitchen table is a rumor until it is in the contract. If the number changes later and nothing was written, you have no document to enforce.
• Not confirming whether the ADU meets fire separation requirements before design approval. San Diego fire codes for detached ADUs closer than 16 feet to the primary home involve sprinklers or rated walls. Discovering that after framing is a five-figure fix.
• Believing the permit timeline quoted by a contractor with no recent San Diego ADU permits. The city’s review times change quarterly. A contractor who pulled his last ADU permit in 2019 is quoting a process that no longer exists.
• Signing a contract without a written change order procedure. Once work starts, every “little tweak” becomes a discussion. Give yourself a written process that requires a price and your signature before anything changes.

When to Call a Professional

Call a professional the moment any of these appear in your process: a bid that is 30 percent below the nearest competitor, a contractor who resists the CSLB check, a contract without line-item allowances, or a scope that keeps shifting between conversations. Each is a signal that the distance between the quote and the final bill will be measured in tens of thousands. You should also call when you have a lot condition such as a hillside, a narrow side yard, or an existing structure under 4 feet from the property line, because setback variances and soils engineering are not beginner-level conversations. Fielding ADU San Diego offers free estimates in San Diego, call (858) 264-3027 and ask for a written scope review. We answer the phone, a live person picks up, and the price you see before work starts is the price you pay when the permit card closes.

Frequently Asked Questions

The Bottom Line

Hiring an ADU contractor in San Diego is a process of eliminating the people who cannot document their work. Verify the CSLB license, bond, and workers’ comp. Ask how many San Diego ADU permits they have pulled and demand to see a closed permit card. Insist on a fixed-price contract with line-item allowances and a written change order process. Then stop asking “what is the lowest price” and start asking “who put the price in writing and can prove they finished the last one.” A contractor who clears all of those steps will not be the cheapest bid, and that is the point. The cheapest bid is the one that becomes a change order. Fielding ADU San Diego home offers free written estimates and backs every build with the Garrison Standard, a full year of written guarantee, and a live person on the phone when you call (858) 264-3027.

Written by Reed Calloway, Owner at Fielding ADU San Diego, serving San Diego since 2006.