Everything You Need to Know About ADU Construction

Expand Your Home with Expert ADU Construction

Property owners throughout San Jose, CA are finding read more that adding an accessory dwelling unit is one of the smartest 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 helped hundreds of local homeowners see these visions to life with precision and care.

The popularity of ADU construction has increased significantly 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 address housing needs. Whether you're building a detached backyard cottage, a garage conversion, or an attached addition, ADU construction offers greater control over how your property functions.

At Brother & Brother Builders, we draw on extensive hands-on experience to every ADU construction job. Our team understands the local permitting process, the engineering considerations, and the planning steps that make an ADU beautiful. Should you want to learn about what ADU construction could mean for your property, this guide covers everything you need to know.

What Is ADU Construction?

ADU construction refers to the process of designing, permitting, and building an accessory dwelling unit on a residential property. An accessory dwelling unit is a complete living space — including a kitchen, bathroom, sleeping area, and its own access point — 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 thorough property evaluation, where our team evaluate setbacks, zoning, utility access, and structural feasibility. From there, architectural drawings are prepared and submitted to the city for permit approval. Once the paperwork is cleared, ADU construction enters the physical build phase — which includes foundation work, framing, mechanical systems, weatherproofing, and interior finishing. The result is a move-in-ready living unit adjacent to or detached from your main home.

What separates excellent ADU construction from an average project is the attention to detail at every stage. Materials must be selected to match the primary home's aesthetic. Systems like wiring and water supply must be built for long-term residential demand. Brother & Brother Builders approaches every build with the same high standards we use on major custom home projects.

Key Advantages ADU Construction

Increased Property Value — ADU construction delivers real market value to your property, often returning more than the build cost when it's time to sell.
Revenue Generation — A completed ADU can be rented as a long-term rental or short-term vacation unit, providing a consistent income stream for the homeowner.
Multi-Generational Living — ADU construction offers family members a private, independent living space without losing proximity to the family.
Design Flexibility — From open-plan one-bedrooms, ADU construction can be tailored to your specific needs.
Streamlined Approval Process — 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.
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 tenants live autonomously.
Long-Term Investment Security — A well-built ADU continues to produce returns for decades, providing both functional space and financial upside.

The ADU Construction Procedure Step by Step

Site Evaluation and Zoning Analysis — Our builders assess your property to determine what type of ADU is allowed and where it can be placed. This stage clarifies exactly what ADU types will work before any money is spent on design.
Custom Design and Architectural Planning — Licensed architects and designers create comprehensive blueprints tailored to your needs. Space is thoughtfully allocated to maximize function and livability.
Filing for Building Permits — ADU construction in San Jose involves filing drawings to the city's building department for sign-off and verification. Brother & Brother Builders coordinates the permitting on your behalf, resolving any revision requests promptly.
Ground Prep and Structural Base — Once permits are approved, physical construction begins. This covers land preparation, pouring the concrete foundation, and running initial plumbing and electrical conduits.
Structural Framing and Weatherproofing — The structural frame is erected followed by weatherproofing and exterior finish materials. At this stage, the ADU takes its visible shape.
Interior Systems and Infrastructure — Skilled tradespeople install the plumbing lines, electrical wiring, and HVAC systems that make the ADU fully functional. Inspections are completed at required milestones throughout ADU construction.
Interior Finishing and Final Inspections — Trim, appliances, tile, and lighting are installed and finished to the approved plan. A final city inspection grants legal occupancy status and the unit is officially approved for use.

Who Is a Strong Candidate for ADU Construction?

Property owners who are best suited from ADU construction generally fit within a few common profiles. If you have a residential property with available square footage under zoning rules, you're already in a good starting place. 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 needs a dedicated professional workspace and wants a separate office or studio space that is distinct from your family's daily life. Real estate-minded homeowners who want to maximize their land are also well suited for ADU construction, since rental income frequently offsets build costs.

Situations where ADU construction may not be the best first step include lots that are below minimum size thresholds. Very small lots or properties with easements may require additional review. Our team can assess each property on its own merits to recommend the right path forward.

ADU Construction Frequently Asked Questions

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

The full timeline for ADU construction commonly spans six to fourteen months, based on the project scope and how quickly approvals come through. The approval phase alone can take two to four months in San Jose, so planning ahead matters. Straightforward interior conversions may complete more quickly, while multi-room detached cottages take longer to complete.

What does ADU construction typically cost?

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. Attached ADU additions are generally priced lower, sometimes starting around $80,000 depending on scope. A precise cost projection can only be developed after a formal feasibility evaluation.

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

The level of disruption depends on where the ADU is being built. New construction in the rear yard are typically less disruptive, since the construction zone is separate. 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 what to expect at each stage.

Do I need to vacate the property during ADU construction?

For the majority of homeowners, you do not need to vacate your house during ADU construction. The vast majority of projects are set up to let you stay in your primary unit throughout the construction timeline. Exceptions may arise if major utility upgrades affect the main house in ways that briefly affect habitability. Our project managers will discuss these scenarios during the kickoff meeting.

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

A well-built ADU is designed to last as long as your primary home — indefinitely with proper upkeep. Durability depends to the systems installed, whether the unit is properly cared for, and whether systems like roofing and plumbing are serviced regularly. Brother & Brother Builders specifies high-quality components and build to current California residential standards to deliver a structure that stands the test of time.

ADU Construction for San Jose Homeowners

San Jose's neighborhoods offer a wide range of property types that are perfectly suited for ADU construction. Property owners near the Almaden Valley area often discover their properties work well for both attached and detached projects. Communities around the Capitol Expressway corridor have seen growing ADU activity as housing demand rises. If you're located closer to Evergreen, our team has likely worked nearby.

Local regulatory bodies in this area applies particular standards for ADU construction that our team navigates routinely. Location near major arterials like Story Road or Tully Road can influence utility connection requirements for a given ADU project. Our familiarity with this region's building landscape means fewer surprises from kickoff through certificate of occupancy.

Schedule Your ADU Construction Consultation Today

Should you be thinking about how to add an ADU to your property, Brother & Brother Builders is ready to guide you. We bring proven skills in ADU construction for many different project types — from small attached additions to multi-room backyard residences. Our approach opens with a comprehensive site assessment where we understand your vision and give you a realistic picture 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, we enjoy 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're committed to helping you get it right.

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