ADU Construction: What to Expect from Start to Finish

Transform Your Property with Quality ADU Construction

Families in San Jose, CA are realizing that adding an accessory dwelling unit is one of the most rewarding investments they can make. ADU construction creates a powerful new living space on your existing property — whether you want to generate rental income. Brother & Brother Builders has guided hundreds of local homeowners turn these plans to life with precision and care.

The interest in ADU construction has increased significantly in recent years, and it's easy to understand why. California state law now makes it easier for homeowners to add these secondary units, and local municipalities like San Jose have supported the trend as a way to increase density responsibly. If you're planning a detached backyard cottage, a garage conversion, or an attached addition, ADU construction gives you more control over how your property functions.

At Brother & Brother Builders, we draw on extensive hands-on experience to every ADU construction project. Our team is familiar with city and county requirements, the engineering requirements, and the aesthetic decisions that make an ADU beautiful. When you're ready to explore what ADU construction could look like on your property, this guide explains everything you need to know.

What Is an ADU Build?

ADU construction refers to the process of engineering, filing for, and completing an accessory dwelling unit on a residential property. An accessory dwelling unit is a fully independent living space — featuring a kitchen, bathroom, sleeping area, and its own access point — that sits on the same property as a primary residence. ADU construction includes various structural types, including detached backyard units, attached additions, garage conversions, and even below-grade dwelling units.

Mechanically, the process begins with a thorough property evaluation, where our professionals 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 transitions to the physical build phase — which encompasses site preparation, framing, roofing, plumbing, electrical, insulation. The result is a move-in-ready living unit connected to or independent of your main home.

What sets quality ADU construction apart is the level of craftsmanship at every stage. Components should be specified to complement the existing structure. Systems like HVAC and drainage must be designed to handle full-time occupancy. Brother & Brother Builders handles every ADU construction job with the same high standards we use on major custom home projects.

Key Reasons to Choose ADU Construction

• Increased Property Value — ADU construction adds measurable market value to your property, often returning more than the build cost when it's time to sell.
• Revenue Generation — A completed ADU may be listed as a long-term rental or short-term vacation unit, providing a consistent income stream for the homeowner.
• Space for Loved Ones — ADU construction provides adult children a private, independent living space without moving to another neighborhood.
• Design Flexibility — From modern studio layouts, ADU construction is adaptable to your household's priorities.
• Faster Permitting in California — Recent state legislation has minimized the red tape associated with ADU construction, creating a path that is faster and less expensive than ever before.
• Efficient Use of Your Lot — Building an ADU uses your existing lot instead of requiring new development, which contributes to sustainability goals.
• Separate Entrances and Spaces — Unlike a bedroom addition, ADU construction delivers a genuinely independent unit where tenants live autonomously.
• Durable Return on Investment — 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 builders assess your property to determine what type of ADU is allowed and where it can be placed. This stage clarifies exactly what can be built before any money is spent on design.
2. Custom Design and Architectural Planning — Experienced draftspeople create detailed floor plans tailored to your needs. Space is thoughtfully allocated to create practical, comfortable living.
3. Filing for Building Permits — ADU construction in San Jose demands documentation to the city's building department for inspection and clearance. Our team handles all submissions on your behalf, resolving any revision requests promptly.
4. Ground Prep and Structural Base — Once permits are granted, on-site work kicks off. This covers land preparation, pouring the concrete foundation, and running initial plumbing and electrical conduits.
5. Structural Framing and Weatherproofing — The structural frame is erected followed by weatherproofing and exterior finish materials. During this step, the ADU transforms from a concept to a building.
6. Interior Systems and Infrastructure — Skilled tradespeople install the plumbing lines, electrical wiring, and HVAC systems that make the ADU fully functional. Every system is reviewed at designated stages throughout ADU construction.
7. Interior Completion and City Sign-Off — Countertops, hardware, finishes, and fixtures are fitted and completed to your specifications. A last official inspection issues the certificate of occupancy and the unit is officially approved for use.

Who Is a Strong Candidate for ADU Construction?

Homeowners who benefit most from ADU construction often belong to a few common profiles. If you own a single-family home with available square footage under zoning rules, you're already in a good starting place. Homeowners looking to generate income through rental are among the most common ADU construction clients, along with families supporting elderly parents.

Another strong candidate is someone who works from home and wants a private work environment that is distinct from your family's daily life. Property investors and rental owners who already own residential properties are also a natural fit for ADU construction, since rental income frequently offsets build costs.

Those who should discuss alternatives first include lots that are below minimum size thresholds. Sites with underground infrastructure conflicts may face additional constraints. Our team can assess each property case by case to provide realistic options.

ADU Construction FAQ

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

The complete duration for ADU construction commonly spans six to fourteen months, depending on design complexity and city review schedules. City review on its own can take two to four months in San Jose, so planning ahead matters. Smaller detached units may complete more quickly, while multi-room detached cottages require more time.

What does ADU construction usually run in terms of budget?

Pricing depends on many factors based on the type and size of the ADU. For most projects in this region, ADU construction typically ranges from $150,000 to $400,000 or more for a fully custom construction. Attached ADU additions tend to cost less, sometimes between $75,000 and $140,000. A precise cost projection can only be produced following a formal feasibility evaluation.

Is ADU construction intrusive while it's underway?

The day-to-day impact depends on the project's location on your property. New construction read more in the rear yard are generally the least intrusive, since the construction zone is separate. Projects that connect to the main structure may create short-term inconveniences during specific stages like framing or MEP rough-in. We provide advance notice about upcoming work and timelines.

Do I need to vacate the property during ADU construction?

For the majority of homeowners, you are not required to vacate your house during ADU construction. Most builds are designed so that you remain on the property throughout the construction timeline. Certain situations could require a brief departure if major utility upgrades affect the main house in ways that require short-term access disruption. The team at Brother & Brother Builders will discuss these scenarios during the pre-construction consultation.

How long will an ADU built through professional ADU construction hold up?

Any ADU built to code with professional oversight is designed to last as long as your primary home — typically 50 years or more. Longevity is tied to the quality of materials used, how consistently minor repairs are addressed, and how proactively issues are resolved over time. We select high-quality components and follow all code requirements to ensure lasting performance.

ADU Construction for Local Homeowners

San Jose's neighborhoods offer a diverse mix of property types that are perfectly suited for ADU construction. Property owners near the Almaden Valley area often discover their properties accommodate detached backyard units nicely. Communities around the Capitol Expressway corridor have seen growing ADU activity as housing demand rises. From neighborhoods near the Guadalupe River Park corridor to those near Branham Lane, our team knows the permitting landscape well.

San Jose's permitting office has developed specific protocols for ADU construction that our team navigates routinely. Location near major arterials like Story Road or Tully Road can affect how quickly permits are approved for a given ADU project. Our team's knowledge of the San Jose permitting environment means more accurate timelines and budgets from kickoff through certificate of occupancy.

Start Your ADU Construction Consultation Today

If you're ready to explore what an ADU could look like on your lot, Brother & Brother Builders is here to help. Our experts offer licensed expertise in ADU construction including all types of project types — from simple garage conversions to fully independent secondary homes. Every project starts with a thorough and honest property review where we learn what you're trying to accomplish and provide an honest assessment of what ADU construction on your property will look like.

Contact Brother & Brother Builders to schedule a site visit. Whether you're in the early stages of planning, we enjoy answer questions, share examples of our work and help you take the next step. ADU construction is a significant investment — and we're committed to helping you get it right.

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