ADU Construction: What to Expect from Start to Finish

Expand Your Home with Professional ADU Construction

Families in San Jose, CA are discovering that adding an accessory dwelling unit is one of the most rewarding investments they can make. ADU construction creates a versatile 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 integrity.

The interest in ADU construction has surged in recent years, and it's not hard to see why. California state law has streamlined permitting for homeowners to construct these secondary units, and local municipalities like San Jose have supported 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 draw on extensive hands-on experience to every ADU construction project. Our team knows the San Jose building codes, the engineering requirements, and the aesthetic decisions that make an ADU truly livable. When you're ready to explore what ADU construction could look like on your property, this guide will walk you through 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 complete living space — including a kitchen, bathroom, sleeping area, and its own entryway — that exists on the same lot as a primary residence. ADU construction includes various structural types, including detached backyard units, attached additions, garage conversions, and even interior space reconfigurations.

Mechanically, the work starts with a comprehensive review of your lot, where our professionals evaluate property boundaries, available square footage, and infrastructure capacity. 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 encompasses site preparation, framing, HVAC, drywall, flooring, and exterior finishes. The result is a fully functional living unit connected to or independent of your main home.

What sets quality ADU construction apart is the level of craftsmanship at every stage. Products need to be chosen to align with the neighborhood's character. Systems like plumbing and electrical must be sized for independent daily use. Brother & Brother Builders handles every ADU construction job with the same high standards we use on major custom home projects.

Key Advantages ADU Construction

• Higher Resale Potential — ADU construction delivers real market value to your property, often generating strong equity gains 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, providing a consistent income stream for the homeowner.
• Space for Loved Ones — ADU construction provides adult children a comfortable home of their own without leaving the property.
• Personalized Layouts — From open-plan one-bedrooms, ADU construction may be customized to the intended occupant's lifestyle.
• Faster Permitting in California — Recent state legislation has cut down the permitting obstacles associated with ADU construction, creating a path that is faster and more cost-efficient than ever before.
• Efficient Use of Your Lot — Building an ADU maximizes the land you already own instead of expanding urban sprawl, which supports broader sustainability goals.
• Independent Living Areas — Unlike a bedroom addition, ADU construction creates a truly separate unit where occupants have full privacy.
• Lasting Financial Benefit — A well-built ADU continues to produce returns for decades, providing both usable housing and equity growth.

The ADU Construction Journey Step by Step

1. Initial Property Assessment and Feasibility Review — Our team visits your property to evaluate setbacks, lot coverage limits, and utility connections. This stage clarifies exactly what's possible before any time is invested in drawings.
2. Architectural Drafting and Space Planning — Our design team create precise architectural drawings based on your goals. Layouts are carefully considered to optimize daily use.
3. Filing for Building Permits — ADU construction in San Jose requires submitting plans to the city's building department for sign-off and verification. Our team handles all submissions on your behalf, resolving any revision requests promptly.
4. Site Preparation and Foundation Work — Once permits are issued, physical construction begins. This involves leveling and prepping the ground, completing foundation work, and running initial plumbing and electrical conduits.
5. Framing, Roofing, and Exterior Work — The structural frame is erected followed by roofing, siding, windows, and exterior doors. At this stage, the ADU becomes recognizable as a structure.
6. Mechanical, Electrical, and Plumbing Installation — Certified technicians install the plumbing lines, electrical wiring, and HVAC systems that make the ADU fully functional. Inspections are completed at each code checkpoint throughout ADU construction.
7. Finishes, Fixtures, and Final Walkthrough — Trim, appliances, tile, and lighting are fitted and completed to the approved plan. A final city inspection grants legal occupancy status 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 recognizable groups. If you are a homeowner with available square footage under zoning rules, you're already a strong candidate. Homeowners looking to generate income through rental are among the most motivated ADU construction clients, along with families supporting elderly parents.

ADU construction also suits someone who works from home and wants a separate office or studio space that is distinct from your family's daily life. Property investors and rental owners who already own residential properties are also well suited for ADU construction, since the long-term value is proven.

Homeowners who may want to pause and evaluate include sites with unusual utility access challenges. Very small lots or properties with easements may require additional review. Our experts will evaluate each property individually and honestly to provide realistic options.

ADU Construction Common Questions Answered

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

The total process for ADU construction usually runs between six to fourteen months, based on the project scope and how quickly approvals come through. Permitting alone can take two to four months in San Jose, so starting early is important. Smaller detached units can move faster, while larger new construction ADUs require more time.

What does ADU construction typically cost?

Budget requirements differ based on project complexity and finishes selected. For most projects in this region, ADU construction generally falls between $150,000 to $400,000 or more for a standalone backyard unit. Attached ADU additions often come in under, sometimes in the $80,000 to $150,000 range. An accurate budget can only be developed after a full site assessment.

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

The level of disruption depends on whether you're converting existing space or building new. Standalone ADU projects are typically less disruptive, since the crew operates at a distance from your living areas. Garage conversions or attached additions may involve some shared wall work during certain phases of construction. Brother & Brother Builders keeps you informed about upcoming work and timelines.

Do I need to vacate the property during ADU construction?

In most cases, you won't have to vacate your house during ADU construction. Most job sites are set up to let you stay in your primary unit throughout the build. Exceptions may arise if interior conversion work touches shared systems in ways that require short-term access disruption. Our construction supervisors will walk you through any potential disruptions during the pre-construction consultation.

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

An ADU constructed with quality materials can be expected to last as long as any standard residential structure — typically 50 years or more. How long it lasts comes down to the systems installed, how well routine maintenance is performed, and how proactively issues are resolved over time. Our builds use commercial-grade materials and follow all code requirements to protect your investment for the long haul.

ADU Construction for San Jose Homeowners

The communities throughout San Jose provide a variety of property types that are ideally positioned for ADU construction. Homeowners in the Willow Glen neighborhood often discover their properties accommodate detached backyard units nicely. Communities around the Capitol Expressway corridor are increasingly popular for ADU construction as multigenerational living becomes more common. If you're located closer to Evergreen, our team has likely worked nearby.

The City of San Jose's building department applies particular standards for ADU construction that our team navigates routinely. Location near major arterials like Story Road or Tully Road can affect how quickly permits are approved for a given ADU project. Our familiarity with these local conditions means more accurate timelines and budgets from design through the final walkthrough.

Book Your ADU Construction Consultation Today

When you want to add an ADU to your property, Brother & Brother Builders is ready to guide you. Our builders provide years of hands-on experience in ADU construction across a wide range of project types — from simple garage conversions to large custom detached cottages. Our approach opens with a comprehensive site assessment where we listen to your goals and give you a realistic picture of what ADU construction on your property will look like.

Get in touch with our office to set up your consultation. No matter where you are in the decision-making process, our team is happy to discuss timelines, costs, and design possibilities and make sure you feel confident before committing. Building an ADU is a major decision — and we're committed to helping more info you get it right.

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