ADU Construction: What to Expect from Start to Finish

Expand Your Home with Professional ADU Construction

Homeowners across San Jose, CA are discovering that adding an accessory dwelling unit is one of the most practical 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 see these visions to life with craftsmanship and integrity.

The interest in ADU construction has surged in recent years, and it's easy to understand 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 address housing needs. Whether you want to build a detached backyard cottage, a garage conversion, or an attached addition, ADU construction offers greater control over how your property serves your household.

At Brother & Brother Builders, we draw on extensive hands-on experience to every ADU construction build. Our team knows the San Jose building codes, the engineering requirements, and the aesthetic decisions that make an ADU functional. When you're ready to explore 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 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, and even basement or interior conversions.

Mechanically, everything kicks off with a detailed site assessment, where our team evaluate lot dimensions, existing structures, soil conditions, and local code requirements. From there, design plans are prepared and submitted to the relevant municipal authority. Once the paperwork is cleared, ADU construction enters the physical build phase — which covers everything from foundational work, 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. Materials must be selected to complement the existing structure. Systems like wiring and water supply must be sized for independent daily use. Brother & Brother Builders approaches every build with the same high standards we apply to large-scale custom home projects.

Key Reasons to Choose ADU Construction

• Boosted Home Equity — ADU construction delivers real market value to your property, often increasing appraised value substantially 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, generating steady monthly revenue for the homeowner.
• Multi-Generational Living — ADU construction gives aging parents a private, independent living space without moving to another neighborhood.
• Personalized Layouts — From modern studio layouts, ADU construction can be tailored to the intended occupant's lifestyle.
• Simplified Regulatory Path — Recent state legislation has reduced the red tape associated with ADU construction, creating a path that is faster and more affordable than ever before.
• Efficient Use of Your Lot — Building an ADU works within your current footprint instead of requiring new development, which aligns with sustainability goals.
• Independent Living Areas — Unlike a bedroom addition, ADU construction delivers a genuinely independent unit where occupants have full privacy.
• Lasting Financial Benefit — A well-built ADU remains an asset for many years and generates both usable housing and equity growth.

The ADU Construction Journey Step by Step

1. Initial Property Assessment and Feasibility Review — Our experts review your property to evaluate setbacks, lot coverage limits, and utility connections. This stage clarifies exactly what ADU types will work before any time is invested in drawings.
2. Architectural Drafting and Space Planning — Experienced draftspeople create detailed floor plans tailored to your needs. Layouts are carefully considered to maximize function and livability.
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, addressing any city comments promptly.
4. Excavation and Foundation Installation — Once permits are approved, on-site work kicks off. This includes grading the site, pouring the concrete foundation, and running initial plumbing and electrical conduits.
5. Structural Framing and Weatherproofing — Walls and roof systems go up followed by insulation, sheathing, and exterior cladding. This phase, the ADU takes its visible shape.
6. MEP Systems Rough-In — Certified technicians install the plumbing lines, electrical wiring, and HVAC systems that make the ADU operationally complete. Every system is reviewed at designated stages throughout ADU construction.
7. Interior Completion and City Sign-Off — Countertops, hardware, finishes, and fixtures are fitted and completed to your specifications. A closing municipal review issues the certificate of occupancy and your new space is cleared for use.

Who Is a Strong Candidate for ADU Construction?

Property owners who are best suited from ADU construction often belong to a few clear categories. If you are a homeowner with a backyard, garage, or basement that could be converted, you're already in a good starting place. Homeowners looking to generate income through rental are among the most motivated ADU construction clients, along with families accommodating adult children who need housing.

Another strong candidate is someone who works from home and wants a separate office or studio 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 long-term value is proven.

Those who should discuss alternatives first include lots that are below minimum size thresholds. Sites with underground infrastructure conflicts may need a modified approach. Our experts will evaluate each property on its own merits to recommend the right path forward.

ADU Construction Common Questions Answered

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

The total process for ADU construction commonly spans six to fourteen months, influenced by the type of unit being built and local permitting timelines. The approval phase alone read more can take two to four months in San Jose, so planning ahead matters. Straightforward interior conversions may complete more quickly, while custom detached builds require more time.

What does ADU construction typically cost?

Pricing depends on many factors based on whether it's a conversion or new construction. For most projects in this region, ADU construction commonly costs $150,000 to $400,000 or more for a standalone backyard unit. Garage conversions tend to cost less, sometimes in the $80,000 to $150,000 range. An accurate budget can only be produced following a formal feasibility evaluation.

Is ADU construction intrusive while it's underway?

The level of disruption depends on the project's location on your property. New construction in the rear yard are typically less disruptive, since the crew operates at a distance from your living areas. Garage conversions or attached additions may require temporary access during key milestones. Brother & Brother Builders keeps you informed 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 house during ADU construction. Most builds are designed so that you continue living in the home throughout the build. Exceptions may arise if significant structural connections require temporary shutoffs in ways that require short-term access disruption. The team at Brother & Brother Builders will walk you through any potential disruptions during the kickoff meeting.

How long will an ADU built through professional ADU construction remain in good condition?

Any ADU built to code with professional oversight can be expected to last as long as your primary home — indefinitely with proper upkeep. Durability depends to the quality of materials used, how well routine maintenance is performed, and if mechanical components are maintained on schedule. Our builds use commercial-grade materials and comply with all local building codes to deliver a structure that stands the test of time.

ADU Construction for Local Homeowners

The communities throughout San Jose provide a wide range of property types that are ideally positioned for ADU construction. Homeowners in the Willow Glen neighborhood frequently see their parcels accommodate detached backyard units nicely. Neighborhoods near Blossom Hill Road 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 our team navigates routinely. Access to infrastructure along thoroughfares like Monterey Road can influence utility connection requirements for a given ADU project. Brother & Brother Builders' experience across these local conditions means smoother project delivery from design through the final walkthrough.

Schedule Your ADU Construction Assessment Today

Should you be thinking about how to explore what an ADU could look like on your lot, Brother & Brother Builders is ready to guide you. Our builders provide licensed expertise in ADU construction including all types of project types — from small attached additions to multi-room backyard residences. The process begins with a detailed, no-pressure consultation where we learn what you're trying to accomplish and share clear expectations of what ADU construction on your property will look like.

Contact Brother & Brother Builders to begin the conversation. Even if you're just exploring the idea, we're glad to discuss timelines, costs, and design possibilities and make sure you feel confident before committing. ADU construction is a significant investment — 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