ADU Construction: What to Expect from Start to Finish

Unlock New Space with Expert ADU Construction

Families in San Jose, CA are realizing that adding an accessory dwelling unit is one of the smartest investments they can make. ADU construction provides a versatile new living space on your existing property — whether you want to generate rental income. Brother & Brother Builders has supported hundreds of local homeowners bring these projects to life with craftsmanship and integrity.

The interest in ADU construction has grown rapidly in recent years, and it's easy to understand 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 expand the housing supply. If you're planning a detached backyard cottage, a garage conversion, or an attached addition, ADU construction provides increased control over how your property serves your household.

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 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 the ADU Construction Process?

ADU construction describes the process of planning, approving, and constructing an accessory dwelling unit on a residential property. An accessory dwelling unit is a self-contained living space — including a kitchen, bathroom, sleeping area, and its own entryway — that is located on the same parcel as a primary residence. ADU construction can take several forms, 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 team 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 the paperwork is cleared, ADU construction moves into the physical build phase — which covers everything from foundational work, framing, HVAC, drywall, flooring, and exterior finishes. The result is a completely finished living unit website adjacent to or detached from your main home.

What sets quality ADU construction apart 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 sized for independent daily use. Brother & Brother Builders treats each project with the same high standards we bring to full custom home projects.

Key Advantages ADU Construction

• Boosted Home Equity — ADU construction contributes significant market value to your property, often returning more than the build cost when it's time to sell.
• Monthly Cash Flow — A completed ADU may be listed 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 moving to another neighborhood.
• Personalized Layouts — From two-bedroom configurations, ADU construction is adaptable to the intended occupant's lifestyle.
• Simplified Regulatory Path — Recent state legislation has minimized the permitting obstacles associated with ADU construction, creating a path that is faster and more cost-efficient than ever before.
• Responsible Property Development — Building an ADU uses your existing lot instead of consuming open land, which aligns with sustainability goals.
• Privacy for All Residents — Unlike a bedroom addition, ADU construction delivers a genuinely independent unit where occupants have full privacy.
• Long-Term Investment Security — 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. 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 resources go toward planning.
2. Blueprint Development and Layout Design — Licensed architects and designers create precise architectural drawings tailored to your needs. Layouts are carefully considered to create practical, comfortable living.
3. Permitting and City Approval — ADU construction in San Jose involves filing drawings to the city's building department for inspection and clearance. Brother & Brother Builders coordinates the permitting on your behalf, responding to review feedback promptly.
4. Site Preparation and Foundation Work — Once permits are approved, the build starts. This includes grading the site, pouring the concrete foundation, and setting up utilities.
5. Shell Construction and Exterior Finishing — Walls and roof systems go up followed by roofing, siding, windows, and exterior doors. At this stage, the ADU becomes recognizable as a structure.
6. Interior Systems and Infrastructure — Licensed subcontractors install the heating, cooling, drainage, and power infrastructure that make the ADU fully functional. Every system is reviewed at each code checkpoint throughout ADU construction.
7. Interior Finishing and Final Inspections — Flooring, cabinetry, fixtures, paint are installed and finished to the approved plan. A final city inspection grants legal occupancy status and the ADU is ready for use.

Who Is a Good Candidate for ADU Construction?

Property owners who are best suited from ADU construction typically fall into a few recognizable groups. If you own a single-family home with a backyard, garage, or basement that could be converted, you're already well-positioned. Homeowners looking to generate income through rental are among the most financially driven ADU construction clients, along with families supporting elderly parents.

ADU construction also suits someone who needs a dedicated professional workspace and wants a detached creative or business space that doesn't interfere with your family's daily life. Real estate-minded homeowners who want to maximize their land are also a natural fit for ADU construction, since the return on investment is well-documented.

Those who should discuss alternatives first include properties with significant setback limitations. Sites with underground infrastructure conflicts may face additional constraints. Our experts will evaluate each property case by case to advise you on what's feasible.

ADU Construction Frequently Asked Questions

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

The total process for ADU construction typically ranges from six to fourteen months, influenced by the type of unit being built and how quickly approvals come through. The approval phase alone can take two to four months in San Jose, so starting early is important. Simpler garage conversions can move faster, while multi-room detached cottages require more time.

What does ADU construction typically cost?

Budget requirements differ 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 detached new build. Interior conversion projects are generally priced lower, sometimes starting around $80,000 depending on scope. A detailed estimate can only be developed after a thorough property review.

Is ADU construction disruptive while it's underway?

How much the build affects daily life depends on where the ADU is being built. Standalone ADU projects are usually easier to live alongside, since work happens away from the main house. Garage conversions or attached additions may involve some shared wall work during certain phases of construction. Brother & Brother Builders keeps you informed about any phases that may affect your routine.

Do I need to leave my home during ADU construction?

Generally speaking, you do not need to vacate your house during ADU construction. Most builds are structured to allow you continue living in the home throughout the construction timeline. Exceptions may arise if interior conversion work touches shared systems in ways that briefly affect habitability. The team at Brother & Brother Builders will discuss these scenarios during the planning phase.

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

A well-built ADU is designed to last as long as the main residence — typically 50 years or more. Durability depends to the standard of construction, whether the unit is properly cared for, and whether systems like roofing and plumbing are serviced regularly. We select residential-grade products rated for longevity and comply with all local building codes to ensure lasting performance.

ADU Construction for Local Homeowners

Residential areas across San Jose present a variety of property types that are perfectly suited for ADU construction. Property owners near the Almaden Valley area frequently see their parcels accommodate detached backyard units nicely. The Berryessa area are increasingly popular for ADU construction as families expand. If you're located closer to Evergreen, our team has project experience in the area.

San Jose's permitting office follows defined procedures for ADU construction that our team navigates routinely. 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 the San Jose permitting environment means more accurate timelines and budgets from design through the final walkthrough.

Schedule Your ADU Construction Planning Session Today

Should you be thinking about how to explore what an ADU could look like on your lot, Brother & Brother Builders is the team to call. Our builders provide years of hands-on experience in ADU construction across a wide range of project types — from modest studio builds to multi-room backyard residences. The process begins with a detailed, no-pressure consultation where we learn what you're trying to accomplish 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. Whether you're in the early stages of planning, our team is happy to answer questions, share examples of our work and make sure you feel confident before committing. 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