ADU Construction: What to Expect from Start to Finish

Unlock New Space with Expert ADU Construction

Homeowners across San Jose, CA are finding that adding an accessory dwelling unit is one of the smartest investments they can make. ADU construction opens the door to a versatile new living space on your existing property — whether you want to generate rental income. Brother & Brother Builders has supported hundreds of local homeowners see these visions to life with craftsmanship and transparency.

The demand for ADU construction has grown rapidly in recent years, and it's no mystery. California state law has simplified the process for homeowners to build these secondary units, and local municipalities like San Jose have supported the trend as a way to address housing needs. Whether you want to build a detached backyard cottage, a garage conversion, or an attached addition, ADU construction gives you more control over how your property serves your household.

At Brother & Brother Builders, we bring years of hands-on experience to every ADU construction project. Our team is familiar with city and county requirements, the engineering requirements, and the design choices that make an ADU functional. Should you want to learn about what ADU construction could do for your property, this guide covers everything you need to know.

What Is the ADU Construction Process?

ADU construction involves the process of planning, approving, and constructing an accessory dwelling unit on a residential property. An accessory dwelling unit is a fully independent living space — including a kitchen, bathroom, sleeping area, and its own entryway — that exists on the same lot as a primary residence. ADU construction comes in multiple configurations, including detached backyard units, attached additions, garage conversions, and even basement or interior conversions.

Mechanically, the work starts with a detailed site assessment, where our builders evaluate lot dimensions, existing structures, soil conditions, and local code requirements. From there, design plans are prepared and submitted to the city for permit approval. Once approvals are in place, ADU construction enters the physical build phase — which covers everything from foundational work, framing, roofing, plumbing, electrical, insulation. The result is a move-in-ready living unit adjacent to or detached from your main home.

What sets quality ADU construction apart is the level of craftsmanship at every stage. Materials must be selected to align with the neighborhood's character. Systems like plumbing and electrical must be sized for independent daily use. Brother & Brother Builders treats each project with the same high standards we apply to large-scale custom home projects.

Key Reasons to Choose ADU Construction

• Boosted Home Equity — ADU construction contributes significant market value to your property, often returning more than the build cost when it's time to sell.
• Rental Income Potential — A completed ADU may be listed as a long-term rental or short-term vacation unit, creating ongoing passive income for the homeowner.
• Multi-Generational Living — ADU construction offers family members a self-contained residence without leaving the property.
• Customization Options — From modern studio layouts, ADU construction can be tailored to your specific needs.
• Simplified Regulatory Path — Recent state legislation has cut down the red tape associated with ADU construction, making the process that is faster and less expensive than ever before.
• Responsible Property Development — Building an ADU uses your existing lot instead of consuming open land, which contributes to sustainability goals.
• Independent Living Areas — Unlike a bedroom addition, ADU construction delivers a genuinely independent unit where occupants have full privacy.
• Lasting Financial Benefit — A well-built ADU holds its value for many years and generates both usable housing and equity growth.

The ADU Construction Process Step by Step

1. Initial Property Assessment and Feasibility Review — Our experts review your property to evaluate setbacks, lot coverage limits, and utility connections. This step tells you exactly what's possible before any resources go toward planning.
2. Architectural Drafting and Space Planning — Our design team create comprehensive blueprints tailored to your needs. Every square foot is planned to create practical, comfortable living.
3. Permitting and City Approval — ADU construction in San Jose requires submitting plans to the city's building department for sign-off and verification. Our team handles all submissions on your behalf, resolving any revision requests promptly.
4. Ground Prep and Structural Base — Once permits are approved, physical construction begins. This involves leveling and prepping the ground, completing foundation work, and setting up utilities.
5. Framing, Roofing, and Exterior Work — Framing is completed followed by insulation, sheathing, and exterior cladding. During this step, the ADU transforms from a concept to a building.
6. Mechanical, Electrical, and Plumbing Installation — Skilled tradespeople install the plumbing lines, electrical wiring, and HVAC systems that make the ADU fully functional. Every system is reviewed at required milestones throughout ADU construction.
7. Interior Finishing and Final Inspections — Countertops, hardware, finishes, and fixtures are placed and inspected to your specifications. A final city inspection grants legal occupancy status and the ADU is ready for use.

Who Is a Good Candidate for ADU Construction?

Homeowners who benefit most from ADU construction typically fall into a few clear categories. If you have a residential property with a backyard, garage, or basement that could be converted, you're already a strong candidate. Homeowners looking to generate income through rental are among the most financially driven ADU construction clients, along with families accommodating adult children who need housing.

ADU construction also suits someone who runs a small business and wants a private work environment that is distinct from your family's daily life. Property investors and rental owners who are building a portfolio are also well suited for ADU construction, since rental income frequently offsets build costs.

Homeowners who may want to pause and evaluate include lots that are below minimum size thresholds. Sites with underground infrastructure conflicts may require additional review. Our experts will evaluate each property on its own merits to provide realistic options.

ADU Construction Common Questions Answered

How long does ADU construction typically take from start to finish?

The total process for ADU construction commonly spans six to fourteen months, based on the project scope and how quickly approvals come through. City review on its own can take a significant portion of the overall timeline in San Jose, so planning ahead matters. Simpler garage conversions often finish in the lower end of the range, while custom detached builds require more time.

What does ADU construction typically cost?

Pricing depends on many factors based on whether it's a conversion or new construction. For most projects in this region, ADU construction commonly costs $150,000 to $400,000 or more for a detached new build. Interior conversion projects are generally priced lower, sometimes between $75,000 and $140,000. A detailed estimate can only be developed after a full site assessment.

Is ADU construction difficult to live through while it's underway?

How much the build affects daily life depends on the project's location on your property. New construction in the rear yard are usually easier to live alongside, since the crew operates at a distance from your living areas. Projects that connect to the main structure may involve some shared wall work during certain phases of construction. Brother & Brother Builders keeps you informed about upcoming work and timelines.

Do I need to move out during ADU construction?

In most cases, you are not required to vacate your house during ADU construction. Most builds are structured to allow you stay in your primary unit throughout the construction timeline. Exceptions may arise if major utility upgrades affect the main house in ways that require short-term access disruption. Our construction supervisors will flag these situations during the kickoff meeting.

How long will an ADU built through professional ADU construction last?

An ADU constructed with quality materials is designed to last as long as your primary home — typically 50 years or more. How long it lasts comes down to the standard of construction, whether the unit is properly cared for, and whether systems like roofing and plumbing are serviced regularly. Our builds use residential-grade products rated for longevity and follow all code requirements to protect your investment for the long haul.

ADU Construction for San Jose Homeowners

Residential areas across San Jose present a diverse mix of property types that are perfectly suited for read more ADU construction. Property owners near the Almaden Valley area often discover their properties are well configured for ADU builds. Communities around the Capitol Expressway corridor have seen growing ADU activity as multigenerational living becomes more common. If you're located closer to Evergreen, our team has project experience in the area.

The City of San Jose's building department follows defined procedures for ADU construction that experienced builders know well. Proximity to transit corridors can influence utility connection requirements for a given ADU project. Our familiarity with the San Jose permitting environment means fewer surprises from design through the final walkthrough.

Book Your ADU Construction Assessment Today

If you're ready to explore what an ADU could look like on your lot, Brother & Brother Builders is ready to guide you. Our builders provide proven skills in ADU construction for many different project types — from simple garage conversions to large custom detached cottages. Our approach opens with a comprehensive site assessment where we learn what you're trying to accomplish and share clear expectations of what the project will involve.

Contact Brother & Brother Builders to schedule a site visit. No matter where you are in the decision-making process, our team is happy to walk through your options, review completed projects and give you the clarity you need to move forward. Building an ADU is a major decision — and we want to make sure it's the right one for you.

Brother & Brother Builders | 3109 Stevens Creek Boulevard | San Jose CA 95117 | (888) 412-2632