Everything You Need to Know About ADU Construction

Expand Your Home with Quality ADU Construction

Families in San Jose, CA are discovering that adding an accessory dwelling unit is one of the smartest investments they can make. ADU construction provides a flexible new living space on your existing property — whether you want to generate rental income. Brother & Brother Builders has helped hundreds of local homeowners turn these plans to life with skill and transparency.

The interest in ADU construction has increased significantly in recent years, and it's not hard to see why. California state law has simplified the process for homeowners to add these secondary units, and local municipalities like San Jose have supported 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 provides increased control over how your property works.

At Brother & Brother Builders, we apply deep hands-on experience to every ADU construction project. Our team understands the local permitting process, the engineering considerations, and the planning steps that make an ADU truly livable. If you've been thinking about what ADU construction could look like on your property, this guide covers 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 fully independent living space — featuring a kitchen, bathroom, sleeping area, and its own entrance — that sits on the same property as a primary residence. ADU construction includes various structural types, including detached backyard units, attached additions, garage conversions, and even interior space reconfigurations.

Mechanically, everything kicks off with a thorough property evaluation, where our professionals evaluate lot dimensions, existing structures, soil conditions, and local code requirements. From there, blueprints are prepared and submitted to the local building department. Once the paperwork is cleared, ADU construction enters the physical build phase — which covers everything from foundational work, framing, HVAC, drywall, flooring, and exterior finishes. The result is a fully functional living unit attached to or separate from your main home.

The difference between a good and a great ADU build is the level of craftsmanship at every stage. Materials must be selected to match the primary home's aesthetic. Systems like plumbing and electrical must be built for long-term residential demand. Brother & Brother Builders handles every ADU construction job with the same high standards we apply to large-scale custom home projects.

Key Reasons to Choose ADU Construction

• Higher Resale Potential — ADU construction contributes significant market value to your property, often increasing appraised value substantially when it's time to sell.
• Revenue Generation — 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 self-contained residence without losing proximity to the family.
• Personalized Layouts — From modern studio layouts, ADU construction can be tailored to your household's priorities.
• Streamlined Approval Process — Recent state legislation has reduced 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 works within your current footprint instead of consuming open land, which supports broader sustainability goals.
• Separate Entrances and Spaces — Unlike a bedroom addition, ADU construction delivers a genuinely independent unit where residents have their own space.
• 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

1. Initial Property Assessment and Feasibility Review — Our team visits your property to evaluate setbacks, lot coverage limits, and utility connections. This step tells you exactly what ADU types will work before any time is invested in drawings.
2. Architectural Drafting and Space Planning — Experienced draftspeople create comprehensive blueprints reflecting your priorities. Layouts are carefully considered to maximize function and livability.
3. Permit Submission and Municipal Review — ADU construction in San Jose requires submitting plans to the city's building department for sign-off and verification. We manage this entire process on your behalf, resolving any revision requests promptly.
4. Excavation and Foundation Installation — Once permits are issued, physical construction begins. This involves leveling and prepping the ground, pouring the concrete foundation, and establishing utility connections.
5. Framing, Roofing, and Exterior Work — Walls and roof systems go up followed by roofing, siding, windows, and exterior doors. During this step, the ADU takes its visible shape.
6. Interior Systems and Infrastructure — Licensed subcontractors install the heating, cooling, drainage, and power infrastructure that make the ADU operationally complete. All work is inspected at each code checkpoint throughout ADU construction.
7. Interior Completion and City Sign-Off — Countertops, hardware, finishes, and fixtures are placed and inspected to the agreed design. A last official inspection confirms the unit is code-compliant and the ADU is ready for use.

Who Is a Strong Candidate for ADU Construction?

Property owners who are best suited from ADU construction typically fall into a few clear categories. If you have a residential property with enough lot space to meet setback requirements, you're already a strong candidate. Homeowners hoping to offset mortgage costs through rental are among the most financially driven ADU construction clients, along with families navigating multigenerational living situations.

You may also be someone who works from home and wants a detached creative or business space that is distinct from your family's daily life. Landlords and real estate investors who are building a portfolio are also prime candidates 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 team can assess each property individually and honestly to recommend the right path forward.

ADU Construction Common Questions Answered

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

The complete duration for ADU construction commonly spans six to fourteen months, influenced by the type of unit being built and city review schedules. The approval phase alone can take two to four months in San Jose, so beginning the process sooner rather than later is wise. Simpler garage conversions often finish in the lower end of the range, while custom detached builds fall toward the upper end of the timeline.

What does ADU construction cost in San Jose?

Budget requirements differ based on whether it's a conversion or new construction. For most projects in this region, ADU construction typically ranges from $150,000 to $400,000 or more for a standalone backyard unit. Interior conversion projects tend to cost less, sometimes between $75,000 and $140,000. A precise cost projection can only be produced following a full site assessment.

Is ADU construction intrusive while it's underway?

The level of disruption depends on whether you're converting existing space or building new. Detached backyard builds are typically less disruptive, since work happens away from the main house. Interior conversions may create short-term inconveniences during certain phases of construction. We provide advance notice about upcoming work and timelines.

Do I need to vacate the property during ADU construction?

Generally speaking, you are not required to vacate your house during ADU construction. The vast majority of projects are set up to let you continue living in the home throughout the construction timeline. Certain situations could require a brief departure if significant structural connections require temporary shutoffs in ways that briefly affect habitability. 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 remain in good condition?

Any ADU built to code with professional oversight should last as long as any standard residential structure — indefinitely with proper upkeep. Durability depends to the systems installed, how consistently minor repairs are addressed, and whether systems like roofing and plumbing are serviced regularly. Our builds use high-quality components and follow all code requirements to deliver a structure that stands the test of time.

ADU Construction for San Jose Homeowners

Residential areas across San Jose present a diverse mix of property types that are well suited for ADU construction. Residents in the Rose Garden district have found their lots work well for both attached and detached projects. The Berryessa area are increasingly popular for ADU construction as housing demand rises. If you're located closer to Evergreen, our team knows the permitting landscape well.

San Jose's permitting office follows defined procedures for ADU construction that experienced builders know well. 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 the first meeting to the final inspection.

Book Your ADU Construction Planning Session Today

When you want to move forward with ADU construction, Brother & Brother Builders is here to help. Our builders provide proven skills in ADU construction including all types of project types — from simple garage conversions to multi-room backyard residences. Our approach opens with a detailed, no-pressure consultation where we understand your vision and share clear expectations of what's achievable.

Contact Brother & Brother Builders to set up your consultation. No matter where you are in the decision-making process, we're glad to answer questions, share examples of our work and make sure you feel confident before committing. ADU construction is a significant investment — and we want to make sure it's adu construction San Jose the right one for you.

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