Everything You Need to Know About ADU Construction

Transform Your Property with Quality ADU Construction

Property owners throughout 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 flexible new living space on your existing property — whether you want to house a family member. Brother & Brother Builders has helped hundreds of local homeowners bring these projects to life with precision and care.

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

At Brother & Brother Builders, we draw on extensive hands-on experience to every ADU construction build. Our team is familiar with city and county requirements, the engineering details, and the aesthetic decisions that make an ADU truly livable. Should you want to learn about what ADU construction could look like on your property, this guide covers everything you need to know.

What Is an ADU Build?

ADU construction describes 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 — equipped with a kitchen, bathroom, sleeping area, and its own entrance — that exists on the same lot as a primary residence. ADU construction can take several forms, 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 professionals evaluate property boundaries, available square footage, and infrastructure capacity. From there, blueprints are prepared and submitted to the local building department. Once the paperwork is cleared, ADU construction transitions to the physical build phase — which includes foundation work, framing, HVAC, drywall, flooring, and exterior finishes. The result is a completely finished living unit adjacent to or detached from your main home.

What sets quality ADU construction apart is the level of craftsmanship at every stage. Products need to be chosen to complement the existing structure. Systems like HVAC and drainage must be built for long-term residential demand. Brother & Brother Builders treats each project with the same professional rigor we apply to large-scale 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, generating steady monthly revenue for the homeowner.
• Multi-Generational Living — ADU construction gives aging parents a comfortable home of their own without losing proximity to the family.
• Design Flexibility — From modern studio layouts, ADU construction can be tailored to your household's priorities.
• Streamlined Approval Process — Recent state legislation has minimized the red tape associated with ADU construction, making the process 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 contributes to sustainability goals.
• Separate Entrances and Spaces — Unlike a bedroom addition, ADU construction produces a fully self-contained unit where residents have their own space.
• Lasting Financial Benefit — A well-built ADU remains an asset for decades, providing both functional space and financial upside.

The ADU Construction Process Step by Step

1. Initial Property Assessment and Feasibility Review — Our builders assess your property to evaluate setbacks, lot coverage limits, and utility connections. This phase answers exactly what's possible before any resources go toward planning.
2. Blueprint Development and Layout Design — Our design team create precise architectural drawings reflecting your priorities. Every square foot is planned 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 inspection and clearance. Our team handles all submissions on your behalf, addressing any city comments promptly.
4. Ground Prep and Structural Base — Once permits are issued, on-site work kicks off. This includes grading the site, laying the structural base, and setting up utilities.
5. Framing, Roofing, and Exterior Work — Walls and roof systems go up followed by roofing, siding, windows, and exterior doors. During this step, the ADU transforms from a concept to a building.
6. MEP Systems Rough-In — Certified technicians install the heating, cooling, drainage, and power infrastructure that make the ADU ready for occupancy. Every system is reviewed at required milestones throughout ADU construction.
7. Interior Completion and City Sign-Off — Flooring, cabinetry, fixtures, paint are installed and finished to your specifications. A final city inspection grants legal occupancy status and the ADU is ready for use.

Who Is a Right Fit for ADU Construction?

Homeowners who benefit most from ADU construction often belong to a few clear categories. 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 motivated ADU construction clients, along with families navigating multigenerational living situations.

You may also be someone who works from home and wants a separate office or studio space that doesn't interfere with your family's daily life. Real estate-minded homeowners who want to maximize their land are also well suited for ADU construction, since the return on investment is well-documented.

Those who should discuss alternatives first include sites with unusual utility access challenges. Sites with underground infrastructure conflicts may face additional constraints. Our team can assess each property on its own merits to recommend the right path forward.

ADU Construction FAQ

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

The total process for ADU construction commonly spans six to fourteen months, depending on design complexity and city review schedules. Permitting alone can take several months in San Jose, so planning ahead matters. Simpler garage conversions may complete more quickly, while custom detached builds require more time.

What does ADU construction cost in San Jose?

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 fully custom construction. Garage conversions often come in under, sometimes starting around $80,000 depending on scope. A detailed estimate can only be given after completing a thorough property review.

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

The day-to-day impact depends on where the click here ADU is being built. Standalone ADU projects are typically less disruptive, since work happens away from the main house. Garage conversions or attached additions may involve some shared wall work during certain phases of construction. We provide advance notice about any phases that may affect your routine.

Do I need to leave my home during ADU construction?

In most cases, you won't have to vacate your main home during ADU construction. Most builds are structured to allow you remain on the property throughout the build. Certain situations could require a brief departure if significant structural connections require temporary shutoffs in ways that briefly affect habitability. The team at Brother & Brother Builders will flag these situations during the kickoff meeting.

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

An ADU constructed with quality materials should last as long as the main residence — indefinitely with proper upkeep. Longevity is tied to the quality of materials used, how consistently minor repairs are addressed, and how proactively issues are resolved over time. Brother & Brother Builders specifies residential-grade products rated for longevity and follow all code requirements to protect your investment for the long haul.

ADU Construction for Local Homeowners

Residential areas across San Jose present a diverse mix of property types that are ideally positioned for ADU construction. Residents in the Rose Garden district have found their lots are well configured for ADU builds. Neighborhoods near Blossom Hill Road are increasingly popular for ADU construction as multigenerational living becomes more common. Whether your property is near downtown San Jose, our team has project experience in the area.

Local regulatory bodies in this area has developed specific protocols for ADU construction that require a builder familiar with local expectations. 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 these local conditions means fewer surprises from the first meeting to the final inspection.

Start Your ADU Construction Consultation Today

When you want to explore what an ADU could look like on your lot, Brother & Brother Builders is here to help. We bring proven skills in ADU construction including all types of project types — from small attached additions to large custom detached cottages. Every project starts with a detailed, no-pressure consultation where we learn what you're trying to accomplish and provide an honest assessment of what's achievable.

Get in touch with our office to set up your consultation. No matter where you are in the decision-making process, we're glad to walk through your options, review completed projects and give you the clarity you need to move forward. This type of project is a meaningful commitment — and our goal is to ensure it delivers real value.

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