Short Answer: What Does Hiring an ADU Builder Involve?
Hiring an ADU builder involves 7 steps: define your project scope and goals, find qualified candidates, screen those candidates for ADU experience and license, vet your short list through references and insurance verification, get at least 3 itemized bids, review the contract before signing, and confirm key details before construction begins.
Step 1: Define Your Project Before You Search
Before you contact any builder, have a clear enough picture of your project to have a useful conversation. Builders assess each project differently depending on what you want to build and why.
Know, at minimum:
ADU type: Detached new construction, garage conversion, attached addition, prefab, or JADU (junior accessory dwelling unit, which is a unit created within the existing footprint of a primary residence).
Project goal: Rental income, housing for a family member, guest house, home office, or property value. Your goal affects how a builder evaluates feasibility and what they recommend.
Rough budget range: You do not need a final number, but knowing whether you are planning a $150,000 garage conversion or a $350,000 custom detached ADU shapes every conversation.
Financing approach: Whether you have financing in place, are using a HELOC, or are still exploring options matters to both the timeline and the builder's project assessment.
If you are still working through project type decisions, the San Diego ADU cost guide and the San Diego ADU permit guide can help you understand the tradeoffs before you start calling builders.
Step 2: Find Qualified Builder Candidates
Once you know what you want to build, identify builders who have done it before. A general contractor with 20 years of commercial experience may not be the right fit for a residential ADU project that requires specific permit process knowledge in your city.
For a full walkthrough of where to search and what signals to look for, see how to find a qualified ADU contractor. In brief: search ADU-specific directories, look for builders who mention ADUs or accessory dwelling units specifically on their websites, ask neighbors who have completed ADU projects for referrals, and check Google reviews for builders who list ADU work in their service descriptions.
Aim to contact 5 to 7 candidates initially. That number gives you enough information to identify the qualified ones without creating an unmanageable amount of coordination.
Step 3: Screen Candidates to a Short List of Three
After initial contact, narrow 5 to 7 candidates to 3 for full vetting. The screening stage focuses on a few key signals that take minimal time to check.
Check the CSLB license first
In California, contractors performing ADU construction must hold a valid license from the California Contractors State License Board (CSLB). For ADU projects, the relevant license is typically a Class B-General Building Contractor license. Specialty subcontractors (plumbing, electrical, HVAC) must also hold their own active licenses.
Verify any candidate's license at the CSLB's public license check tool at cslb.ca.gov. Confirm the license is active, the name and entity match what the contractor provided, and that there are no disciplinary actions or suspensions on the record.
Ask about ADU-specific experience
A contractor can hold a valid Class B license and have zero experience navigating an ADU permit process. Ask directly:
- •How many ADU projects have you completed in the past two years?
- •Which cities have you pulled ADU permits in?
- •Do you handle permit coordination in-house or through a separate design firm?
- •Can you provide references from recent ADU projects specifically?
Drop candidates who cannot provide a valid CSLB license number, who cannot name recent ADU projects, or who are vague about how permit coordination works. Move your 3 strongest candidates to full vetting.
Step 4: Vet Your Short List
Full vetting goes deeper than initial screening. For a complete checklist, see how to vet an ADU builder. The key steps are:
Review the ADU portfolio: Look at photos and project descriptions from recent ADU work specifically, not general construction. Ask about the project type, city, and construction timeline for each example.
Call 2 to 3 references: Ask to speak with homeowners from recent ADU projects. Ask about communication habits, how unexpected problems were handled, and whether the project came in near the original budget and timeline.
Verify insurance certificates: Request current certificates of general liability insurance and workers' compensation insurance. Confirm the certificates are current and that coverage is adequate for a residential construction project of this scale.
Assess the company itself: How long have they been operating? Who manages day-to-day communication on active projects? Are they using in-house crews or primarily subcontractors? These factors affect both quality and accountability during construction.
Step 5: Get Itemized Bids and Compare Them
Request written bids from all 3 vetted candidates. A useful ADU bid is itemized, not a lump-sum number. You need enough detail to compare what each contractor is actually including.
Good ADU bids break down the project by category: design and engineering, permit fees, site work, foundation, framing, roofing, electrical, plumbing, HVAC, insulation and drywall, exterior and interior finishes, and contingency. When comparing bids, pay close attention to:
Inclusions and exclusions: A bid that is $30,000 lower than the others may be leaving out permit fees, utility connection costs, or landscaping restoration. Confirm what each bid explicitly excludes.
Allowances vs. fixed prices: Allowances are placeholders for items not yet specified, such as kitchen fixtures, tile, or appliances. Low allowances often become overages once you select real products.
Permit coordination responsibility: Some builders handle design-build in-house. Others require you to hire a separate architect or designer before they can bid at all. Clarify who prepares permit-ready drawings and who pays for them.
Payment schedule structure: The bid should show when payments are due and what triggers each payment. Milestone-tied payments protect you better than calendar-based ones.
Note: Cost figures for ADU projects vary considerably based on project type, site conditions, local permit fees, material costs, and market conditions. Treat any range you see online as a rough reference. Get detailed written bids from at least 3 licensed contractors who have evaluated your specific property before committing to a budget.
Step 6: Review the Contract Before You Sign
A signed contract is your primary protection in an ADU project. Do not sign a vague document that covers the basics and leaves the rest to verbal agreements.
Deposit limits
Under California Business and Professions Code Section 7159 (BPC 7159), a contractor cannot require a deposit exceeding 10% of the contract price or $1,000, whichever is less, on residential home improvement projects. If a contractor requests a large upfront payment before any work begins, that is a violation of California law.
Scope of work in writing
The contract should describe exactly what is being built, including the materials, finishes, and systems to be installed. Anything not in the written scope can become a change order later, often at additional cost.
Payment schedule tied to milestones
Payments should be tied to construction milestones, not calendar dates. Common milestones include permit issuance, foundation completion, rough framing, rough inspections passed, and final inspection. Milestone-based payments give you leverage if work stalls.
Change order process
Any change to the scope, materials, or price should require a written change order signed by both parties before work proceeds. A contract that does not address this leaves you exposed to disputed charges.
Permit responsibility
The contract should specify who is pulling the permits, who pays for permit fees, and what happens if the permit process requires design revisions. If the builder is responsible for permit coordination, that should be explicit.
Timeline with milestones
A realistic start date and a project schedule tied to construction milestones give both parties something to measure progress against. No schedule in the contract means no accountability for delays.
Note: Contract terms and legal requirements can vary. The points above cover general considerations, not legal advice. For a project of this size, consider having an attorney review the contract before you sign, particularly if there are unusual terms, large payment amounts, or unclear scope language.
Step 7: Confirm Final Details Before Work Starts
Before construction begins, a few confirmation steps protect you from common early-stage problems.
Confirm the building permit is in hand: Do not allow any construction to begin before the permit has been issued. The permit card should be posted on-site before ground is broken. Starting work before permit issuance is one of the most costly mistakes in residential construction.
Hold a pre-construction site meeting: Walk the property with the project manager before work starts. Confirm where materials will be staged, where temporary facilities will be placed, and how the job site will be secured at the end of each day.
Establish your communication plan: Agree on how frequently you will receive progress updates, who your day-to-day contact is for questions, and how change orders will be communicated and approved. Document this in writing.
Homeowner Hiring Checklist
- ☐Defined ADU type (detached, garage conversion, attached addition, prefab, JADU)
- ☐Confirmed project goal (rental income, family housing, guest house, home office)
- ☐Set a rough budget range and confirmed financing approach
- ☐Contacted 5 to 7 builder candidates
- ☐Verified CSLB license for each candidate at cslb.ca.gov
- ☐Asked each candidate about ADU-specific experience and which cities they have permitted in
- ☐Narrowed to 3 candidates for full vetting
- ☐Reviewed portfolio from recent ADU projects specifically
- ☐Called at least 2 references per candidate from recent ADU work
- ☐Requested and reviewed current general liability and workers' compensation insurance certificates
- ☐Received 3 written, itemized bids
- ☐Compared bids line by line: inclusions, exclusions, allowances, permit responsibility, payment schedule
- ☐Reviewed contract scope, deposit limits, change order process, and permit responsibility
- ☐Confirmed building permit is issued before authorizing any site work to begin
Final Thoughts
Finding the right ADU builder is not fast work. Between researching candidates, checking licenses, calling references, reviewing bids, and reading contracts, a careful hiring process can take 4 to 6 weeks. That time is worth spending.
The contractors who perform well on ADU projects tend to have clear communication habits, experience with local building departments, and bids that hold up once construction starts. Warning signs tend to appear early: vague scope descriptions, pressure to sign quickly, large upfront deposit requests, reluctance to provide references from recent ADU work.
Take your time at the hiring stage. Once construction starts, you will be in a relationship with this company for the next several months.
Ready to start comparing options? Compare local San Diego ADU builders on the directory, or get matched with ADU builders for your specific project and property.
Frequently Asked Questions
How long does it take to hire an ADU builder?+
How many bids should I get for an ADU project?+
Does the contractor pull the permit, or do I?+
What is the deposit limit for a California home improvement contract?+
Should I hire a design-build firm or separate the design and construction contracts?+
What is a Class B license and why does it matter for ADU projects?+
Disclaimer: This article is for informational purposes only and does not constitute legal, zoning, permitting, financial, or construction advice. Requirements vary by property, city, and project type. California contractor licensing requirements and deposit limit laws can change. Consult a licensed professional before making decisions about your ADU project or signing any construction contract.
Sources and Official Resources
- •California Contractors State License Board — License Check and Classifications — California CSLB. cslb.ca.gov — verify any contractor's license status before hiring. Last accessed June 2026. Confirm current versions before relying on them.
- •California Business and Professions Code Section 7159 — Home Improvement Contracts — California Legislature. leginfo.legislature.ca.gov — includes deposit limits and required contract terms for residential projects. Last accessed June 2026. Confirm current versions before relying on them.
- •California Department of Housing and Community Development — ADU Handbook — California HCD. hcd.ca.gov/policy-research/accessory-dwelling-units. Last accessed June 2026. Confirm current versions before relying on them.
- •California Building Code (Title 24) — Residential Standards — California Building Standards Commission. dgs.ca.gov/BSC. Last accessed June 2026. Confirm current versions before relying on them.
This guide draws on California state law and CSLB requirements current as of June 2026. ADU regulations and contractor licensing rules change. Always verify current requirements with the CSLB and applicable building department before starting a project.