What is the importance of an ADU feasibility study in California and San Diego?

Key Components of a Feasibility Study

A feasibility assessment for an ADU identifies potential challenges early and gives homeowners an actionable plan and budget. It reviews zoning requirements and local zoning rules, setbacks and height restrictions, utility lines and septic system options, grading or topographic survey data, easements, and the best placement of the unit on the property. By also integrating financing options and projected rental income, a feasibility study helps determine whether an ADU project is both physically possible and financially viable (Adapt Dwellings).

Site Plan Creation

A preliminary property map outlines the maximum feasible ADU footprint and placement within state and municipal requirements such as setbacks, height, and lot coverage. This plan incorporates features like easements, boundary markers, trees, slopes, and driveways to ensure compliance. Many building departments provide worksheets and online resources to guide homeowners through this design and plan check process (City of Lacey, City of Escondido).

Utility Mapping

Feasibility studies evaluate existing sewer and town sewer access, water supply, gas, and electrical work to confirm connection capacity. Utility planning includes calculating electrical loads and identifying connection points, which helps prevent costly reroutes or upgrades during construction.

Topographic Surveys

Topographic and planimetric surveys capture property elevations, contours, and site evaluation details like retaining walls, drainage, or large trees. These surveys provide property data that directly affect grading work, foundation needs, and structural details, making them an essential part of the feasibility study.

Renderings and Design Proposals

Many feasibility studies also include schematic floor plans and 3D renderings of the proposed prefab ADU or custom unit. These detailed plans align with zoning insights and the style of the main home, giving homeowners clarity before entering into a construction contract. This stage also refines the construction scope of work, allowing budgets to be adjusted based on design, finish materials, and other inputs (Adapt Dwellings).

Always review material options and finishes during the feasibility stage—this ensures your ADU budget reflects accurate costs for both structural and design choices.

Why a Feasibility Study is Essential for a Successful ADU Project

An ADU feasibility study confirms whether your property can legally and practically support an ADU before you invest in design, engineering, and permitting. It addresses zoning bylaws and site constraints, clarifies plumbing work and utility connections, and provides a detailed report with accurate budget estimates to prevent costly surprises (HCD, City of San Diego). Streamlined approvals have helped ADUs become a more common form of middle housing, giving homeowners confidence in project management and timelines (Urban Institute). A feasibility study also highlights long-term financial benefits, from rental income to property value increases, while helping homeowners communicate effectively with city officials and a general contractor to ensure a smooth process (AARP).

Interior finishes can quickly change project budgets—a thorough feasibility study accounts for cabinetry, utilities, and finishes up front.

Common Pitfalls of Skipping the Feasibility Study

Skipping an ADU feasibility study often leads to costly mistakes and frustrating project delays. Without a clear review of local zoning rules by a town zoning officer or local zoning administrator, homeowners may only discover setbacks, easements, or grading issues after investing in plans. Utility oversights—such as missed sewer tie-ins or inadequate electrical capacity—can also add unexpected expenses, from trenching to driveway installation repairs. On the interior side, changes to planned lighting fixtures, shower heads, or glass doors mid-project can trigger budget overruns and create disputes with a general contractor. These problems may also delay agency communication with city officials, stretching out approval timelines and increasing costs. A feasibility study avoids these pitfalls by providing a detailed report upfront, flagging risks early, and offering a clear roadmap before major expenses or contracts are signed.

Understanding Zoning Ordinances (California → City of San Diego)

In California, zoning ordinances for ADUs are shaped by state law and then refined by local city regulations. The California Department of Housing and Community Development (HCD) provides statewide standards, while the City of San Diego outlines specific rules in Information Bulletin 400. A feasibility study must review both levels of requirements to ensure compliance and avoid delays during design and permitting.

• Processing time: State law requires cities to approve or deny ADU permits within 60 days of a complete application (HCD Technical Advisory Memo).
• Setbacks & height limits: State minimums allow 4-foot side and rear setbacks. Detached ADUs are generally capped at 16–18 feet, with reforms permitting up to 18 feet plus 2 feet for pitched roofs near transit corridors (HCD Technical Advisory Memo, Burke, Williams & Sorensen LLP).
• Impact fees: ADUs 750 sq ft or smaller are exempt statewide. Larger ADUs pay proportional fees based on square footage (HCD Technical Advisory Memo).
• Environmental review (CEQA): Ministerial approvals are statutorily exempt from CEQA, reducing regulatory hurdles and delays (HCD – CEQA Guidance).

By capturing these requirements in a detailed report, homeowners can minimize surprises, streamline fee coordination, and maintain smoother agency communication with city officials.

Local zoning ordinances impact placement and size—feasibility studies align design with city rules before you submit for permits.

How much does a Feasibility Report cost?

The cost of an ADU feasibility report depends on the property, scope of analysis, and the level of detail included. In San Diego, most feasibility studies range between $2,000 and $7,500, with larger or more complex sites (such as sloped lots or properties requiring extensive surveys) falling at the higher end. Reports typically cover zoning checks, site plan sketches, utility mapping, and preliminary cost estimates.

Homeowners should also budget for permit and city fees, which in San Diego can add another $6,500 to $21,000 depending on unit size and scope. Importantly, California law waives impact fees for ADUs under 750 sq. ft., which can help keep costs down (San Diego – IB 400, Better Place Design & Build).

Investing in a feasibility study may feel like an extra upfront expense, but it helps homeowners avoid costly redesigns, permitting delays, and unexpected construction overruns—saving both time and money in the long run.

Factor feasibility report costs into your budget—catching issues upfront saves thousands in redesigns, permitting delays, and change orders later.

ADU Feasibility & Permit Cost Breakdown (San Diego Example)

Financial Considerations

ADU projects carry both upfront costs and long-term financial impacts, and a feasibility study helps homeowners understand these before committing. By surfacing hidden expenses early, homeowners can avoid unexpected redesigns or schedule changes that might disrupt construction dates. A clear analysis also produces more accurate budgets before moving into full construction drawings. At the policy level, resolving financing barriers—like appraisals that undervalue ADUs or lenders that fail to count projected rental income—could expand ADU production across California (Urban Institute).

Budgeting for an ADU Project

A realistic budget should cover design and surveys, site work such as grading and utility connections, construction, and permits or city fees. A feasibility study refines these numbers through site-specific data and early design decisions (Adapt Dwellings). Factoring in potential rental income at this stage also helps homeowners assess whether their ADU will be used for family housing or as a long-term multi-dwelling unit investment. Homeowners can also track spending more effectively by organizing payment receipts and requesting clear documentation during consultations or a home visit with a general contractor.

Cost-Benefit Analysis

ADUs often provide stronger returns than buying a separate rental property since they leverage existing land and utilities. A feasibility study can model projected rental cash flow, vacancy sensitivity, and ROI to guide decisions. According to California ADU Experts, ADUs not only increase property value but also create rental income that can offset mortgage payments. This makes them a practical choice for California homeowners seeking a balance between immediate costs and long-term financial stability.

Aligning feasibility data with rental income projections helps homeowners decide if their ADU works best as family housing or an investment.

Types of ADUs (with study tie-ins)

Accessory Dwelling Units (ADUs) come in several forms, and the right choice depends on zoning rules, lot size, and homeowner goals. Common types include detached units, attached additions, and internal conversions such as garage or attic remodels. A feasibility study is crucial for determining which type best fits a specific property while staying compliant with state and local regulations (HCD).

Detached Units

Detached ADUs are independent structures separate from the primary home, often built in backyards. A feasibility study helps confirm placement, assess grading and foundation needs, and plan utility routing. These units must align with state standards on height and setbacks, with allowances for increased height in certain transit-accessible zones (HCD 2025 Handbook).

Attached Units

Attached ADUs are built as extensions connected to the main residence, such as a new wing or over a garage. They provide additional space while maintaining proximity and privacy. Feasibility reviews evaluate critical factors like egress requirements, ceiling heights, and how the new unit ties into the existing structure (KM Acca).

Garage Conversions

Garage conversions are one of the most cost-effective ADU options, transforming existing underused space into a livable unit. Feasibility studies confirm structural safety, fire compliance, and utility requirements. They also include cost breakdowns and strategies for connecting the new ADU to existing water, sewer, and electrical lines, helping homeowners avoid costly surprises later in the project.

Garage conversions can be cost-effective, but feasibility studies must confirm structural capacity and utility tie-ins to avoid mid-project delays.

Benefits of Conducting a Feasibility Study

An ADU feasibility study gives homeowners clarity and confidence before committing to construction. By surfacing potential risks early, it ensures accurate scoping, reliable schedules, and realistic budgets. Beyond cost and compliance, feasibility studies highlight how ADUs can generate rental income, increase property value, and support multigenerational living or aging in place.

Risk Mitigation

Feasibility studies reduce the chance of mid-project setbacks by addressing zoning setbacks, easements, slope or grading issues, electrical panel capacity, and septic or sewer connection requirements before detailed design work begins. This proactive approach minimizes the risk of project delays or added costs.

Time and Cost Savings

Early steps like site surveys and utility mapping help avoid redesigns later in the process. By clarifying project requirements upfront, feasibility studies streamline permitting and keep construction on schedule. Even for prefabricated ADUs, which may have shorter build timelines, these studies ensure smoother execution by resolving potential conflicts before permits are issued.

Confidence in Project Viability

A positive feasibility study provides a preliminary budget and site plan that confirms the project can move forward. If the study identifies significant constraints or costs that make the project infeasible, homeowners save money and time by redirecting their plans early. This safeguard helps ensure investments are only made into projects with a strong likelihood of success.

A well-done feasibility study surfaces grading, utility, and zoning challenges before they cause delays—protecting your budget and timeline.

Engaging Professional Assistance

Hiring professionals with experience in zoning, permitting, and construction-informed budgeting can streamline the entire ADU process—from feasibility studies to completed permits. Their knowledge helps homeowners avoid delays, missteps, or overlooked costs by ensuring all design and compliance requirements are addressed early. Working with experts also provides access to tailored design proposals and accurate cost estimates, helping homeowners move forward with confidence.

Detailed Onsite Inspections

A professional feasibility study often begins with an onsite inspection. Qualified personnel document the property’s topography, usable space, and physical constraints, ensuring accurate planning before design or construction begins (Adapt Dwellings). This step helps identify challenges—such as grading, easements, or limited lot coverage—before they become costly problems.

Utility Evaluations

Professionals also evaluate existing utilities to confirm whether upgrades are required. This includes checking electrical panel capacity, sewer and water access, and potential rerouting needs. By mapping and planning utility connections at the feasibility stage, homeowners can avoid expensive mid-project changes and keep the build process on schedule.

Architectural Proposals

Once feasibility is confirmed, experts can translate findings into a customized architectural proposal. This may include schematic drawings, 3D renderings, and refined cost estimates tailored to site conditions and homeowner preferences. Aligning design concepts with local regulations from the start helps ensure a smoother permitting process and prevents costly redesigns later (Adapt Dwellings).

Compliance with Local Regulations

Building an ADU in San Diego requires compliance with both California state law and local city rules. Statewide ADU laws establish minimum standards for setbacks, height, and fees, while the City of San Diego provides specific permit instructions through Information Bulletin 400. A feasibility study ensures that project plans align with both sets of regulations to avoid delays or rejections.

Legal Requirements

California law mandates that ADU permit applications be processed ministerially—without discretionary review—within 60 days of submission. Units 750 square feet or smaller are exempt from impact fees, while larger units pay proportional fees. Detached ADUs are generally limited to 16 feet in height, with allowances of 18 feet (plus 2 feet for pitched roofs) in designated transit-accessible areas. Additionally, ministerial ADU approvals are statutorily exempt from CEQA, which speeds up approvals by eliminating environmental review requirements (HCD Technical Advisory Memo).

Permitting Process

In San Diego, the permitting process follows a structured path:

1. Feasibility Study – confirm zoning, utilities, and site constraints.
2. Surveys & Mapping – prepare site plan, utility mapping, and topographic surveys.
3. Concept Design – produce schematic drawings and preliminary renderings.
4. Permit Submittal – submit documents per the city’s IB 400 checklist.
5. City Review – track progress against the state’s 60-day decision deadline.

This combination of state protections and city-specific processes ensures homeowners have a clear, enforceable pathway to approval if requirements are met.

Always cross-check state ADU laws with your city’s bulletin; compliance early on avoids costly resubmittals and stalled projects.

Location-Specific Considerations

San Diego

San Diego applies state ADU standards while layering on its own local requirements through Information Bulletin 400, which outlines the city’s permit process, fees, and submittal requirements for ADUs and Junior ADUs (JADUs).

The city has gained national recognition for its Bonus ADU Program, which incentivizes affordable housing production. Since 2019, the program has produced more than 220 deed-restricted units and contributed to over 4,500 ADU approvals (City of San Diego). In 2025, the San Diego City Council began considering caps on bonus units and exploring the possibility of allowing ADUs to be sold as separate properties under California’s AB 1033 (Axios).

To ensure compliance, homeowners should always check the latest version of IB 400 and track council updates on density and ownership rules (San Diego IB 400 – Nov. 2024 update).

Los Angeles

Los Angeles also follows California’s ADU laws but adds city-specific overlays related to design review, height limits, and parking requirements. For example, detached ADUs must meet state baselines of 4-ft side and rear setbacks and are subject to a 60-day ministerial approval timeline, but additional restrictions may apply depending on neighborhood design boards or zoning overlays (HCD Technical Advisory Memo).

While this guide focuses on San Diego, homeowners in Los Angeles should review both state rules and local planning department resources to confirm feasibility for their property.

Here’s a polished rewrite of your Transitioning from Vision to Reality section with the keywords worked in naturally. I kept the same word count and overall meaning intact while weaving the terms in a way that flows with the content.

Transitioning from Vision to Reality

An ADU feasibility study serves as the key decision point for moving forward with what can often feel like a small home project. If the study confirms both buildability and budget feasibility, homeowners can proceed with confidence; if not, they may need to adjust the ADU’s size, type, or placement. The next steps typically include finalizing design concepts, completing construction documents (CDs), and submitting permit applications through the City of San Diego’s Information Bulletin 400. Along the way, a home inspection or site phone/Zoom consultation with a designer or contractor can help clarify details before submission. Once an application is filed, state law requires cities to approve or deny ADU permits within 60 days, providing homeowners with a predictable and enforceable path toward construction while reducing risks like disputes or warranty claims later on.

From Feasibility to Build: ADU Timeline