Expert ADU Construction Services for Homeowners

Expand Your Home with Professional ADU Construction

Families in San Jose, CA are finding that adding an accessory dwelling unit is one of the most practical 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 turn these plans to life with precision and care.

The demand for ADU construction has increased significantly in recent years, and it's no mystery. California state law now makes it easier for homeowners to build these secondary units, and local municipalities like San Jose have encouraged the trend as a way to address housing needs. 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 understands the local permitting process, the engineering considerations, and the aesthetic decisions that make an ADU truly livable. When you're ready to explore what ADU construction could do for your property, this guide covers everything you need to know.

What Is ADU Construction?

ADU construction describes the process of engineering, filing for, and completing an accessory dwelling unit on a residential property. An accessory dwelling unit is a self-contained living space — equipped with a kitchen, bathroom, sleeping area, and its own entryway — that sits on the same property as a primary residence. ADU construction comes in multiple configurations, including detached backyard units, attached additions, garage conversions, website and even below-grade dwelling units.

Mechanically, the process begins with a detailed site assessment, where our builders evaluate property boundaries, available square footage, and infrastructure capacity. From there, blueprints are prepared and submitted to the city for permit approval. Once the paperwork is cleared, ADU construction enters the physical build phase — which encompasses site preparation, framing, roofing, plumbing, electrical, insulation. The result is a fully functional living unit adjacent to or detached from your main home.

The difference between a good and a great ADU build is the depth of planning at every stage. Products need to be chosen to align with the neighborhood's character. Systems like plumbing and electrical must be built for long-term residential demand. 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

• Increased Property Value — ADU construction adds measurable market value to your property, often generating strong equity gains 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, providing a consistent income stream for the homeowner.
• Space for Loved Ones — ADU construction gives aging parents a private, independent living space without losing proximity to the family.
• Customization Options — From two-bedroom configurations, ADU construction may be customized to the intended occupant's lifestyle.
• Faster Permitting in California — Recent state legislation has minimized the barriers and delays associated with ADU construction, making the process that is faster and more affordable than ever before.
• Sustainable Land Use — Building an ADU uses your existing lot instead of requiring new development, which supports broader sustainability goals.
• Separate Entrances and Spaces — Unlike a bedroom addition, ADU construction produces a fully self-contained unit where residents have their own space.
• Durable Return on Investment — A well-built ADU continues to produce returns for many years and generates both livable square footage and monetary benefit.

The ADU Construction Process Step by Step

1. Site Evaluation and Zoning Analysis — Our experts review your property to analyze zoning rules, slope conditions, and available square footage. This step tells you exactly what can be built before any money is spent on design.
2. Blueprint Development and Layout Design — Experienced draftspeople create precise architectural drawings based on your goals. Layouts are carefully considered to maximize function and livability.
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, addressing any city comments promptly.
4. Site Preparation and Foundation Work — Once permits are granted, on-site work kicks off. This involves leveling and prepping the ground, pouring the concrete foundation, and running initial plumbing and electrical conduits.
5. Shell Construction and Exterior Finishing — Framing is completed followed by weatherproofing and exterior finish materials. During this step, the ADU transforms from a concept to a building.
6. Interior Systems and Infrastructure — Certified technicians install the plumbing lines, electrical wiring, and HVAC systems that make the ADU fully functional. Inspections are completed at required milestones throughout ADU construction.
7. Interior Completion and City Sign-Off — Countertops, hardware, finishes, and fixtures are installed and finished to your specifications. A closing municipal review confirms the unit is code-compliant and your new space is cleared for use.

Who Is a Strong Candidate for ADU Construction?

People who see the greatest return from ADU construction typically fall into a few clear categories. If you are a homeowner with available square footage under zoning rules, you're already well-positioned. Homeowners looking to generate income through rental are among the most common ADU construction clients, along with families accommodating adult children who need housing.

ADU construction also suits someone who needs a dedicated professional workspace and wants a private work environment that is distinct from your family's daily life. Real estate-minded homeowners who already own residential properties are also prime candidates for ADU construction, since the return on investment is well-documented.

Situations where ADU construction may not be the best first step include lots that are below minimum size thresholds. Sites with underground infrastructure conflicts may face additional constraints. Our experts will evaluate each property individually and honestly to advise you on what's feasible.

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, based on the project scope and local permitting timelines. The approval phase alone can take two to four months in San Jose, so planning ahead matters. Smaller detached units can move faster, while multi-room detached cottages fall toward the upper end of the timeline.

What does ADU construction usually run in terms of budget?

Pricing depends on many factors based on whether it's a conversion or new construction. In the San Jose area, ADU construction generally falls between $150,000 to $400,000 or more for a standalone backyard unit. Garage conversions often come in under, sometimes between $75,000 and $140,000. A precise cost projection can only be developed after a thorough property review.

Is ADU construction intrusive while it's underway?

How much the build affects daily life depends on where the ADU is being built. Standalone ADU projects are generally the least intrusive, since the construction zone is separate. Projects that connect to the main structure may require temporary access during specific stages like framing or MEP rough-in. Our team communicates clearly about what to expect at each stage.

Do I need to vacate the property during ADU construction?

In most cases, you do not need to vacate your main home during ADU construction. The vast majority of projects are set up to let you continue living in the home throughout the construction timeline. There are edge cases if interior conversion work touches shared systems in ways that require short-term access disruption. Our construction supervisors will flag these situations during the pre-construction consultation.

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

A well-built ADU should last as long as the main residence — often several decades with routine maintenance. Longevity is tied to the systems installed, how well routine maintenance is performed, and whether systems like roofing and plumbing are serviced regularly. We select high-quality components and comply with all local building codes to ensure lasting performance.

ADU Construction for Local Homeowners

Residential areas across San Jose present a wide range of property types that are ideally positioned for ADU construction. Homeowners in the Willow Glen neighborhood frequently see their parcels are well configured for ADU builds. Neighborhoods near Blossom Hill Road have seen growing ADU activity as families expand. From neighborhoods near the Guadalupe River Park corridor to those near Branham Lane, our team has project experience in the area.

San Jose's permitting office follows defined procedures for ADU construction that require a builder familiar with local expectations. Access to infrastructure along thoroughfares like Monterey Road can affect how quickly permits are approved for a given ADU project. Brother & Brother Builders' experience across these local conditions means smoother project delivery from design through the final walkthrough.

Start Your ADU Construction Assessment Today

Should you be thinking about how to add an ADU to your property, Brother & Brother Builders is the team to call. Our builders provide licensed expertise in ADU construction across a wide range of project types — from simple garage conversions to large custom detached cottages. Every project starts with a detailed, no-pressure consultation where we understand your vision and give you a realistic picture of what ADU construction on your property will look like.

Get in touch with our office to begin the conversation. No matter where you are in the decision-making process, our team is happy to discuss timelines, costs, and design possibilities and help you take the next step. This type of project is a meaningful commitment — 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