Everything You Need to Know About ADU Construction

Transform Your Property with Expert ADU Construction

Families in San Jose, CA are realizing that adding an accessory dwelling unit is one of the most practical 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 guided hundreds of local homeowners bring these projects to life with precision and care.

The interest in ADU construction has increased significantly in recent years, and it's not hard to see why. California state law has streamlined permitting for homeowners to build these secondary units, and local municipalities like San Jose have embraced the trend as a way to increase density responsibly. Whether you're building 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 apply deep hands-on experience to every ADU construction project. Our team understands the local permitting process, the engineering requirements, and the design choices that make an ADU truly livable. 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 refers to the process of planning, approving, and constructing an accessory dwelling unit on a residential property. An accessory dwelling unit is a complete living space — equipped with a kitchen, bathroom, sleeping area, and its own entrance — 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 below-grade dwelling units.

Mechanically, the process begins with a detailed website site assessment, where our team evaluate setbacks, zoning, utility access, and structural feasibility. From there, design plans are prepared and submitted to the relevant municipal authority. Once approvals are in place, ADU construction transitions to the physical build phase — which covers everything from foundational work, framing, mechanical systems, weatherproofing, and interior finishing. The result is a completely finished living unit adjacent to or detached from your main home.

What sets quality ADU construction apart is the depth of planning at every stage. Materials must be selected to align with the neighborhood's character. Systems like HVAC and drainage must be sized for independent daily use. Brother & Brother Builders handles every ADU construction job with the same technical discipline we use on major custom home projects.

Key Reasons to Choose ADU Construction

• Boosted Home Equity — ADU construction contributes significant market value to your property, often increasing appraised value substantially when it's time to sell.
• Rental Income Potential — A completed ADU can be rented as a long-term rental or short-term vacation unit, creating ongoing passive income for the homeowner.
• Space for Loved Ones — ADU construction offers family members a private, independent living space without losing proximity to the family.
• Customization Options — From modern studio layouts, ADU construction is adaptable to your specific needs.
• Streamlined Approval Process — Recent state legislation has minimized the red tape associated with ADU construction, creating a path that is faster and more affordable than ever before.
• Efficient Use of Your Lot — Building an ADU works within your current footprint instead of requiring new development, which aligns with sustainability goals.
• Separate Entrances and Spaces — Unlike a bedroom addition, ADU construction creates a truly separate unit where residents have their own space.
• Durable Return on Investment — A well-built ADU continues to produce returns for decades, providing both usable housing and equity growth.

The ADU Construction Process Step by Step

1. Initial Property Assessment and Feasibility Review — Our team visits your property to determine what type of ADU is allowed and where it can be placed. This phase answers exactly what ADU types will work before any money is spent on design.
2. Custom Design and Architectural Planning — Experienced draftspeople create detailed floor plans based on your goals. Space is thoughtfully allocated to optimize daily use.
3. Permit Submission and Municipal Review — ADU construction in San Jose requires submitting plans to the city's building department for review and approval. Brother & Brother Builders coordinates the permitting on your behalf, responding to review feedback promptly.
4. Ground Prep and Structural Base — Once permits are issued, on-site work kicks off. This covers land preparation, pouring the concrete foundation, and setting up utilities.
5. Shell Construction and Exterior Finishing — Framing is completed followed by insulation, sheathing, and exterior cladding. During this step, the ADU becomes recognizable as a structure.
6. MEP Systems Rough-In — Skilled tradespeople install the water supply, drain lines, and electrical panel that make the ADU operationally complete. Inspections are completed at required milestones throughout ADU construction.
7. Interior Completion and City Sign-Off — Countertops, hardware, finishes, and fixtures are placed and inspected to the agreed design. A closing municipal review issues the certificate of occupancy and the ADU is ready for use.

Who Is a Right Fit for ADU Construction?

Property owners who are best suited from ADU construction often belong to a few recognizable groups. If you have a residential property with enough lot space to meet setback requirements, you're already a strong candidate. Homeowners wanting to add a revenue stream through rental are among the most common ADU construction clients, along with families navigating multigenerational living situations.

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 are building a portfolio are also well suited for ADU construction, since the return on investment is well-documented.

Homeowners who may want to pause and evaluate include lots that are below minimum size thresholds. Sites with underground infrastructure conflicts may need a modified approach. Our experts will evaluate each property individually and honestly to provide realistic options.

ADU Construction FAQ

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

The total process for ADU construction usually runs between six to fourteen months, based on the project scope and city review schedules. Permitting alone can take two to four months in San Jose, so starting early is important. Straightforward interior conversions can move faster, while custom detached builds take longer to complete.

What does ADU construction usually run in terms of budget?

Costs vary widely based on whether it's a conversion or new construction. For most projects in this region, ADU construction generally falls between $150,000 to $400,000 or more for a standalone backyard unit. Attached ADU additions often come in under, sometimes between $75,000 and $140,000. An accurate budget can only be developed after a formal feasibility evaluation.

Is ADU construction intrusive while it's underway?

The day-to-day impact depends on whether you're converting existing space or building new. New construction in the rear yard are typically less disruptive, since work happens away from the main house. Interior conversions may create short-term inconveniences during specific stages like framing or MEP rough-in. Our team communicates clearly about what to expect at each stage.

Do I need to move out during ADU construction?

For the majority of homeowners, you are not required to vacate your house during ADU construction. The vast majority of projects are structured to allow you remain on the property throughout the construction timeline. Certain situations could require a brief departure if interior conversion work touches shared systems in ways that require short-term access disruption. The team at Brother & Brother Builders will flag these situations during the kickoff meeting.

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

Any ADU built to code with professional oversight can be expected to last as long as the main residence — typically 50 years or more. Durability depends to the standard of construction, how consistently minor repairs are addressed, and whether systems like roofing and plumbing are serviced regularly. Our builds use commercial-grade materials and build to current California residential standards to deliver a structure that stands the test of time.

ADU Construction for San Jose Homeowners

Residential areas across San Jose present a variety of property types that are perfectly suited for ADU construction. Homeowners in the Willow Glen neighborhood frequently see their parcels are well configured for ADU builds. Neighborhoods near Blossom Hill Road are seeing more homeowners add secondary units as housing demand rises. If you're located closer to Evergreen, our team has likely worked nearby.

San Jose's permitting office follows defined procedures for ADU construction that experienced builders know well. Access to infrastructure along thoroughfares like Monterey Road can influence utility connection requirements for a given ADU project. Brother & Brother Builders' experience across these local conditions means fewer surprises from kickoff through certificate of occupancy.

Book Your ADU Construction Planning Session Today

When you want to add an ADU to your property, Brother & Brother Builders is here to help. We bring licensed expertise in ADU construction across a wide range of project types — from small attached additions to fully independent secondary homes. Every project starts with a thorough and honest property review where we listen to your goals and share clear expectations of what the project will involve.

Reach out to our team to set up your consultation. No matter where you are in the decision-making process, our team is happy to discuss timelines, costs, and design possibilities and give you the clarity you need to move forward. Building an ADU is a major decision — and our goal is to ensure it delivers real value.

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