Before You Hire / Flagship guide
Before Hiring an ADU Builder in California
Questions to ask before paying deposits, signing design-build agreements, or relying on an early ADU estimate in California.
Method: Official-source research, plain-English synthesis, and parcel-specific verification guidance. Read our editorial standards.
Start with feasibility, not a sales appointment
Before hiring an ADU builder in California, determine whether the property and proposed unit have a credible approval path. A polished model, fast estimate, or attractive financing offer cannot resolve an unknown jurisdiction, unusable building envelope, inadequate utilities, septic limits, fire access, or an overlay. Collect the address, APN, city or county jurisdiction, lot information, existing plans, utility facts, site photographs, and desired ADU type. Then confirm the basic planning and building path. This preparation lets builders price the same project and makes it easier to distinguish a reasoned proposal from a sales estimate built on assumptions.
Define the ADU you are actually comparing
Detached ADUs, attached additions, garage conversions, internal conversions, junior ADUs, manufactured units, modular systems, and panelized or site-built projects have different scopes. Define approximate size, bedrooms, bathrooms, use, finish level, accessibility goals, and relationship to the existing home. Note whether the property is owner occupied, rented, financed, governed by an HOA, served by septic, or located in a fire, coastal, hillside, flood, or historic area. Ask each company to identify the exact project type assumed in its proposal. Two estimates cannot be compared fairly when one assumes a simple standard model and another includes site-specific design or conversion work.
Understand design-only, permit, and design-build scopes
Some companies sell feasibility or concept design. Others provide permit drawings, a prefab unit, construction, or a full design-build service. The label “turnkey” has no value unless the contract lists every included task. Ask who measures the site, prepares the site plan, develops architectural drawings, obtains structural and energy documents, coordinates utilities, submits permits, responds to corrections, pays fees, schedules inspections, performs sitework, builds or sets the unit, connects services, completes finishes, and closes the permit. Require exclusions to be as clear as inclusions. An owner should be able to point to the responsible party for each phase.
Verify the contractor and the business
Use the California Contractors State License Board’s official tools to check the business name, license number, classification, status, bond, workers’ compensation information, and disclosed personnel. Confirm that the name on the proposal and contract matches the licensed entity. Ask for current insurance certificates and understand what they cover. Review references for comparable projects in the same region and, with permission, speak with past clients about communication, change orders, corrections, schedule, and warranty response. Online reviews can provide leads but should not replace license verification, documents, and direct references. Investigate significant discrepancies before paying a deposit.
Ask about experience in the exact jurisdiction
California ADU law creates statewide requirements, but city and county submittals, utility coordination, local amendments, plan-check practices, and site conditions still vary. Ask for recent ADU projects in the same city or unincorporated county and request permit numbers or addresses when clients have authorized sharing. Ask which departments reviewed those jobs, what corrections were common, and how the builder handled them. Experience elsewhere is still useful, but it should not be presented as proof that your jurisdiction will accept the same plans or timeline. Strong candidates explain what they know, what they need to verify, and who will obtain the answer.
Require a site-specific feasibility review
The review should address the proposed location, dimensions, setbacks, lot coverage, height, access, easements, trees, grading, drainage, utilities, electrical capacity, sewer or septic, water, fire access, and overlays. For a conversion, it should also consider the existing structure, foundation, ceiling height, moisture, openings, fire separation, electrical, plumbing, HVAC, and unpermitted work. Ask which facts were verified from records, which came from visual observation, and which remain assumptions. A feasibility review is not a permit guarantee; its value is making uncertainty visible before the owner commits to a larger design or construction contract.
Compare plans and specifications, not just square-foot prices
A price per square foot can omit design, permits, foundations, utilities, site access, upgrades, appliances, landscaping, and owner responsibilities. Request a written scope with drawings or a clearly identified model, room dimensions, ceiling heights, windows, doors, exterior materials, roofing, insulation, HVAC, water heating, cabinets, counters, flooring, fixtures, appliances, lighting, electrical devices, and paint. Note allowances and the brands or performance levels assumed. For prefab systems, distinguish the factory unit price from transportation, crane or set, foundation, marriage connections, site completion, utility hookups, inspections, and repair of delivery impacts.
Find every utility assumption
Ask whether the estimate includes electrical load calculations, panel or service upgrades, trenching, a new subpanel, utility coordination, sewer lateral work, cleanouts, connection charges, water meter changes, backflow devices, gas modifications, and restoration after trenches. If the site uses septic or a well, ask who evaluates capacity, reserve area, setbacks, permits, pump systems, water quality, and required modifications. Utility providers and public agencies control parts of this work, so builders may not be able to guarantee their timing or final charges. The proposal should distinguish included construction from third-party fees, allowances, and unresolved provider requirements.
Expose sitework before signing
Sitework is one of the easiest places for an attractive early price to expand. Ask about demolition, clearing, tree protection or removal, grading, export or import of soil, drainage, erosion control, retaining walls, foundations, difficult access, temporary fencing, staging, crane setup, street use, driveway work, and restoration of patios, landscaping, or paving. Ask whether soil, topographic, boundary, arborist, civil, or geotechnical work is included. Walk the proposed route for workers, equipment, modules, and trenches. A builder who excludes sitework should still identify the likely sitework interfaces so the owner can obtain coordinated pricing.
Clarify permit responsibility and plan-check corrections
The contract should state who prepares each submittal, who signs as applicant, who communicates with departments, who tracks the application, and who responds to corrections. Ask how many correction cycles or design revisions are included and what causes additional fees. Determine whether planning, building, fire, public works, utilities, environmental health, coastal, historic, or HOA review is anticipated. Permit fees and agency charges should be listed as included, excluded, or allowances. Ask who keeps the approved plans onsite, schedules inspections, corrects failed inspections, obtains final approvals, and provides the owner with the complete permit record.
Treat schedule claims as a set of dependencies
Ask for a schedule that separates feasibility, design, owner selections, engineering, agency review, utility work, procurement, factory production if applicable, site construction, inspections, and closeout. Identify which dates are estimates and which obligations are contractual. Weather, owner changes, hidden conditions, utility design, discretionary approvals, correction cycles, product lead times, and inspection availability can affect completion. A credible builder explains dependencies and notification procedures rather than giving one unexplained finish date. Ask how delays are documented, whether time extensions require written change orders, and what happens when a delay is caused by the builder, owner, agency, supplier, or unforeseen condition.
Review deposits, progress payments, and change orders
California home-improvement contracts are regulated, and owners should review current Contractors State License Board guidance before signing. The payment schedule should connect payments to defined work or delivered materials rather than vague percentages. Understand deposit limits and other applicable contract requirements from official sources or qualified counsel. Require written change orders that describe the changed work, price, and schedule effect before work proceeds, except where an urgent safety condition requires a documented response. Ask how credits are handled when work is removed. Keep invoices, conditional and unconditional lien releases, payment records, approvals, and correspondence in one project file.
Understand allowances and selections
Allowances are placeholders for products or work not fully selected. Ask what quantity, quality level, tax, delivery, labor, overhead, and waste assumptions each allowance includes. A low cabinet, fixture, appliance, flooring, tile, lighting, or utility allowance can make a proposal appear less expensive while shifting predictable costs to later change orders. Establish selection deadlines and a process for documenting upgrades or credits. Confirm whether owner-supplied products are allowed, who verifies compatibility, who receives and stores them, and who bears responsibility for delay, damage, missing parts, warranty, or installation problems.
Ask how hidden conditions are handled
Conversions and older properties can conceal foundation damage, rot, termites, asbestos-containing materials, lead hazards, inadequate wiring, undocumented plumbing, moisture, or unpermitted alterations. New detached ADUs can encounter unknown utilities, poor soil, buried debris, groundwater, rock, or boundary discrepancies. The contract should explain investigation, notice, pricing, and authorization when concealed conditions appear. Ask what preconstruction inspections or testing would reduce uncertainty and whether demolition assumptions are stated. A hidden-condition clause should not become permission for undefined charges; the builder should document the condition, explain options, and obtain written authorization.
Review insurance, responsibility, and site protection
Ask who carries general liability, workers’ compensation, builder’s risk or installation coverage, vehicle coverage, and any design professional insurance relevant to the scope. Consult the owner’s insurer and lender before work begins because a major project can affect coverage and loan requirements. Clarify responsibility for security, weather protection, dust, noise, sanitation, temporary power, fencing, neighboring property, pets, children, stored materials, and damage to existing improvements. For occupied properties, agree on work hours, access, shutoffs, parking, and communication. Insurance does not replace careful contract allocation, but missing or mismatched coverage is a warning sign.
Evaluate communication and project management
Ask who will be the salesperson, designer, permit contact, project manager, superintendent, and emergency contact. Determine how often updates are provided and where decisions, photos, schedules, requests for information, selections, and change orders are recorded. Meet the person expected to manage the work, not only the salesperson. Ask how many concurrent projects that person handles and how subcontractors are coordinated. During references, ask whether the company communicated bad news promptly and documented solutions. A clear communication system cannot prevent every problem, but it reduces disputes about what was decided, when it changed, and who was responsible.
Ask about inspections, completion, and closeout
Define substantial completion, final completion, and the process for creating and resolving a punch list. Ask who schedules agency inspections and whether reinspection work caused by the contractor is included. Final payment should be tied to the contract and applicable law, with attention to approved work, required documents, releases, and unresolved items. Request copies of approved plans, permits, inspection records, warranties, manuals, model and serial information, subcontractor contacts where appropriate, finish schedules, paint colors, utility documents, and final agency authorization. An ADU should not be marketed, rented, or occupied based only on physical completion when required final approvals remain outstanding.
Compare warranty and post-completion service
Read the written warranty rather than accepting “standard warranty” as an answer. Identify coverage periods, exclusions, manufacturer warranties, response procedures, emergency contacts, and responsibility for diagnostic or travel costs. Ask prior clients how the company handled callbacks after final payment. Confirm who services factory-built components, appliances, HVAC, roofing, windows, plumbing fixtures, and other systems. Preserve maintenance requirements because failure to maintain equipment can affect coverage. The contract should not promise more than the responsible party can deliver, and verbal warranty statements should be added to the written agreement if they are part of the bargain.
Warning signs in an ADU proposal
Warning signs include pressure to sign before property research, refusal to provide a license number, a contract name that differs from the licensed business, large unexplained upfront payments, cash-only demands, no written scope, missing exclusions, permit guarantees, a fixed completion claim that ignores agency review, and unwillingness to provide comparable references. Also be cautious when the proposal treats utilities and sitework as someone else’s problem without explaining interfaces, or when a prefab unit is described as turnkey while foundation, delivery, crane, connections, permits, and finish work are omitted. One concern may be correctable; several together justify stopping.
A fair bid-comparison method
Give competing builders the same project brief and ask them to price the same scope. Create a comparison table with design, engineering, permit handling, agency fees, sitework, foundation, unit construction, transportation, utilities, finishes, allowances, owner work, exclusions, schedule assumptions, payment milestones, warranty, and contingency. Normalize the bids by adding reasonable placeholders for known exclusions rather than comparing only totals. Then score documentation quality, local experience, references, communication, and unresolved risk. The lowest bid may still be the right choice, but only after the owner understands whether it is genuinely lower or simply contains less work.
What to complete before paying a major design or construction amount
Confirm the licensed contracting entity, written scope, property assumptions, project type, design deliverables, jurisdiction, permit responsibility, sitework, utilities, allowances, exclusions, schedule dependencies, payment milestones, change-order process, insurance, warranty, dispute terms, and cancellation rights. Collect the preliminary feasibility evidence and identify remaining investigations. Review the complete contract and attachments; do not rely on renderings or proposal slides that are not incorporated. Seek legal, insurance, tax, lending, or technical advice where the commitment warrants it. The objective is not to eliminate all uncertainty, which construction cannot do, but to assign known work and create a fair process for unknowns.
Bottom line
The best ADU builder is not simply the company with the most appealing model or lowest first number. It is the team whose license and references check out, whose scope matches the property, whose assumptions are visible, and whose contract explains design, permits, utilities, sitework, payments, changes, inspections, and closeout. Begin with parcel feasibility, compare equivalent scopes, and preserve a written record. A careful hiring process also improves the builder’s chance of success because decisions, responsibilities, and unresolved site questions are addressed before construction pressure begins.
Official sources and research starting points
Use the current official pages below, then confirm the parcel-specific interpretation with the responsible local department.
Frequently Asked Questions
Is there one statewide answer for this issue?
No. California rules create starting points, but parcel-specific local confirmation is required.
Which department should I contact first?
Start with the planning department for the parcel's city or unincorporated county area, then confirm building, utility, environmental health, and fire authority requirements as needed.
Can I rely on this guide instead of contacting local officials?
No. Use this guide to organize questions and documents, then confirm the answer directly with the appropriate local departments before spending money or submitting plans.
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TinyHomeNavigator provides educational information only. Rules vary by parcel, zoning district, city, county, overlay, utility provider, fire authority, and environmental health department. Always confirm directly with the local planning department, building department, environmental health department, fire authority, and utility providers before buying land, designing, permitting, placing, or building any structure.