Everything You Need to Know About ADU Construction

Unlock New Space with Professional 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 provides a versatile new living space on your existing property — whether you want to create a private workspace. Brother & Brother Builders has supported hundreds of local homeowners bring these projects to life with craftsmanship and care.

The interest in ADU construction has increased significantly in recent years, and it's no mystery. California state law has simplified the process for homeowners to build these secondary units, and local municipalities like San Jose have supported the trend as a way to increase density responsibly. If you're planning a detached backyard cottage, a garage conversion, or an attached addition, ADU construction provides increased control over how your property works.

At Brother & Brother Builders, we bring years of hands-on experience to every ADU construction job. Our team understands the local permitting process, the engineering considerations, and the design choices that make an ADU beautiful. 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 describes the process of designing, permitting, and building an accessory dwelling unit on a residential property. An accessory dwelling unit is a fully independent living space — featuring a kitchen, bathroom, sleeping area, and its own access point — that sits on the same property 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 process begins with a comprehensive review of your lot, where our builders evaluate setbacks, zoning, utility access, and structural feasibility. From there, design plans are prepared and submitted to the city for permit approval. Once permits are secured, ADU construction enters the physical build phase — which covers everything from foundational work, framing, roofing, plumbing, electrical, insulation. The result is a completely finished living unit adjacent to or detached from your main home.

What sets quality ADU construction apart is the attention to detail at every stage. Components should be specified to match the primary home's aesthetic. 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 apply to large-scale custom home projects.

Key Reasons to Choose ADU Construction

• Increased Property Value — ADU construction delivers real market value to your property, often generating strong equity gains when it's time to sell.
• Revenue Generation — A completed ADU can be rented as a long-term rental or short-term vacation unit, creating ongoing passive income for the homeowner.
• Multi-Generational Living — ADU construction provides adult children a self-contained residence without losing proximity to the family.
• Design Flexibility — From two-bedroom configurations, ADU construction is adaptable to your specific needs.
• Simplified Regulatory Path — Recent state legislation has reduced the barriers and delays associated with ADU construction, resulting in a timeline that is faster and more affordable than ever before.
• Efficient Use of Your Lot — Building an ADU maximizes the land you already own instead of consuming open land, which supports broader sustainability goals.
• Privacy for All Residents — Unlike a bedroom addition, ADU construction delivers a genuinely independent unit where tenants live autonomously.
• Long-Term Investment Security — A well-built ADU holds its value for decades, providing both usable housing and equity growth.

The ADU Construction Process Step by Step

1. Site Evaluation and Zoning Analysis — Our builders assess your property to analyze zoning rules, slope conditions, and available square footage. This step tells you exactly what's possible before any money is spent on design.
2. Blueprint Development and Layout Design — Licensed architects and designers create comprehensive blueprints reflecting your priorities. Every square foot is planned to maximize function and livability.
3. Permitting and City Approval — ADU construction in San Jose demands documentation to the city's building department for review and approval. We manage this entire process on your behalf, responding to review feedback promptly.
4. Excavation and Foundation Installation — Once permits are issued, the build starts. This includes grading the site, completing foundation work, and setting up utilities.
5. Shell Construction and Exterior Finishing — Walls and roof systems go up followed by insulation, sheathing, and exterior cladding. This phase, the ADU takes its visible shape.
6. Interior Systems and Infrastructure — Licensed subcontractors install the water supply, drain lines, and electrical panel that make the ADU ready for occupancy. All work is inspected at each code checkpoint throughout ADU construction.
7. Finishes, Fixtures, and Final Walkthrough — Trim, appliances, tile, and lighting are installed and finished to the agreed design. A final city inspection confirms the unit is code-compliant and the unit is officially approved for use.

Who Is a Good Candidate for ADU Construction?

Homeowners who benefit most from ADU construction typically fall into a few common profiles. If you have a residential property with enough lot space to meet setback requirements, you're already in a good starting place. Homeowners hoping to offset mortgage costs through rental are among the most motivated ADU construction clients, along with families accommodating adult children who need housing.

ADU construction also suits someone who runs a small business 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 prime candidates for ADU construction, since the return on investment is well-documented.

Homeowners who may want to pause and evaluate include properties with significant setback limitations. Sites with underground infrastructure conflicts may require additional review. Brother & Brother Builders reviews each property on its own merits to recommend the right path forward.

ADU Construction Frequently Asked Questions

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

The full timeline for ADU construction usually runs between six to fourteen months, depending on design complexity and how quickly approvals come through. The approval phase alone can take two to four months in San Jose, so beginning the process sooner rather than later is wise. Straightforward interior conversions can move faster, while multi-room detached cottages require more time.

What does ADU construction cost in San Jose?

Budget requirements differ based on the type and size of the ADU. In the San Jose area, ADU construction generally falls between $150,000 to $400,000 or more for a fully custom construction. Garage conversions tend to cost less, sometimes in the $80,000 to $150,000 range. An accurate budget can only be produced following a thorough property review.

Is ADU construction disruptive while it's underway?

How much the build affects daily life depends on whether you're converting existing space or building new. Standalone ADU projects are typically less disruptive, since the construction zone is separate. 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 move out during ADU construction?

In most cases, you won't have to vacate your main home during ADU construction. The vast majority of projects are set up to let you remain on the property throughout the build. Certain situations could require a brief departure if major utility upgrades affect the main house in ways that require short-term access disruption. Our project managers will walk you through any potential disruptions during the planning phase.

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

Any ADU built to code with professional oversight is designed to last as long as any standard residential structure — indefinitely with proper upkeep. Longevity is tied to the systems installed, how well routine maintenance is performed, and how proactively issues are resolved over time. Our builds use high-quality components and build to current California residential standards to ensure lasting performance.

ADU Construction for Local Homeowners

The communities throughout San Jose provide a variety of property types that are ideally positioned for ADU construction. Property owners near the Almaden Valley area have found their lots are well configured for ADU builds. Communities around the Capitol Expressway corridor are seeing more homeowners add secondary units as families expand. From neighborhoods near the Guadalupe River Park corridor to those near Branham Lane, our team has project experience in the area.

The City of San Jose's building department 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. Brother & Brother Builders' experience across these local conditions means more accurate timelines and budgets from kickoff through certificate of occupancy.

Start Your ADU Construction Assessment Today

When you want to move forward with ADU construction, Brother & Brother Builders is here to help. We bring licensed expertise in ADU construction for many different project types — from modest studio builds to large custom detached cottages. Our approach opens with a comprehensive site assessment where we learn what you're trying to accomplish and give you a realistic picture of what's achievable.

Reach out to our team to begin the conversation. Even if you're just exploring the idea, we're glad to walk through your options, review completed projects and make sure you feel confident before committing. ADU construction is a significant investment — and we want to make sure it's the more info right one for you.

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