Everything You Need to Know About ADU Construction

Unlock New Space with Quality ADU Construction

Families in San Jose, CA are realizing that adding an accessory dwelling unit is one of the most practical 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 helped hundreds of local homeowners see these visions to life with skill and care.

The popularity of ADU construction has grown rapidly in recent years, and it's no mystery. California state law has streamlined permitting for homeowners to add these secondary units, and local municipalities like San Jose have supported the trend as a way to increase density responsibly. Whether you want to build a detached backyard cottage, a garage conversion, or an attached addition, ADU construction gives you more control over how your property works.

At Brother & Brother Builders, we apply deep hands-on experience to every ADU construction project. Our team knows the San Jose building codes, the engineering details, and the design choices that make an ADU functional. If you've been thinking about what ADU construction could look like on your property, this guide explains everything you need to know.

What Is ADU Construction?

ADU construction describes the process of designing, permitting, and building an accessory dwelling unit on a residential property. An accessory dwelling unit is a complete 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 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 builders evaluate setbacks, zoning, utility access, and structural feasibility. From there, architectural drawings are prepared and submitted to the local building department. Once the paperwork is cleared, ADU construction transitions to the physical build phase — which covers everything from foundational work, framing, mechanical systems, weatherproofing, and interior finishing. The result is a completely finished living unit adjacent to or detached from your main home.

What sets quality ADU construction apart is the level of craftsmanship at every stage. Products need to be chosen to complement the existing structure. Systems like wiring and water supply must be designed to handle full-time occupancy. Brother & Brother Builders handles every ADU construction job with the same high standards we use on major custom home projects.

Key Benefits ADU Construction

• Higher Resale Potential — ADU construction adds measurable market value to your property, often increasing appraised value substantially when it's time to sell.
• Rental Income Potential — A completed ADU is leasable as a long-term rental or short-term vacation unit, providing a consistent income stream for the homeowner.
• Housing for Extended Family — ADU construction provides adult children a self-contained residence without losing proximity to the family.
• Design Flexibility — From modern studio layouts, ADU construction is adaptable to your household's priorities.
• Streamlined Approval Process — Recent state legislation has reduced the red tape associated with ADU construction, creating a path that is faster and more affordable than ever before.
• Sustainable Land Use — Building an ADU works within your current footprint instead of expanding urban sprawl, which supports broader sustainability goals.
• Separate Entrances and Spaces — Unlike a bedroom addition, ADU construction produces a fully self-contained unit where occupants have full privacy.
• Long-Term Investment Security — A well-built ADU continues to produce returns for the long haul by offering both livable square footage and monetary benefit.

The ADU Construction Procedure Step by Step

1. Property Walkthrough and Feasibility Check — 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 resources go toward planning.
2. Architectural Drafting and Space Planning — Experienced draftspeople create precise architectural drawings tailored to your needs. Every square foot is planned to maximize function and livability.
3. Permit Submission and Municipal Review — ADU construction in San Jose demands documentation to the city's building department for review and approval. Brother & Brother Builders coordinates the permitting on your behalf, addressing any city comments promptly.
4. Excavation and Foundation Installation — Once permits are granted, on-site work kicks off. This includes grading the site, laying the structural base, and setting up utilities.
5. Shell Construction and Exterior Finishing — Walls and roof systems go up followed by insulation, sheathing, and exterior cladding. During this step, 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. Every system is reviewed at each code checkpoint throughout ADU construction.
7. Finishes, Fixtures, and Final Walkthrough — Trim, appliances, tile, and lighting are placed and inspected to your specifications. A last official inspection grants legal occupancy status and the ADU is ready for use.

Who Is a Strong Candidate for ADU Construction?

Homeowners who benefit most from ADU construction typically fall into a few clear categories. If you have a residential property with a backyard, garage, or basement that could be converted, you're already a strong candidate. Homeowners hoping to offset mortgage costs through rental are among the most common ADU construction clients, along with families accommodating adult children who need housing.

ADU construction also suits someone who needs a dedicated professional workspace and wants a detached creative or business space that remains away from your family's daily life. Landlords and real estate investors who want to maximize their land are also well suited for ADU construction, since rental income frequently offsets build costs.

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 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 typically ranges from six to fourteen months, influenced by the type of unit being built and local permitting timelines. The approval phase alone can take a significant portion of the overall timeline in San Jose, so starting early is important. Straightforward interior conversions often finish in the lower end of the range, while larger new construction ADUs fall toward the upper end of the timeline.

What does ADU construction usually run in terms of budget?

Budget requirements differ based on the type and size of the ADU. Locally, ADU construction generally falls between $150,000 to $400,000 or more for a standalone backyard unit. Interior conversion projects often come in under, sometimes in the $80,000 to $150,000 range. An accurate budget can only be given after completing a thorough property review.

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

How much the build affects daily life depends on whether you're converting existing space or building new. New construction in the rear yard are typically less disruptive, since the construction zone is separate. Interior conversions may create short-term inconveniences during specific stages like framing or MEP rough-in. Brother & Brother Builders keeps you informed about any phases that may affect your routine.

Do I need to move out during ADU construction?

Generally speaking, you are not required to vacate your primary residence during ADU construction. Most builds are designed so that 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 require short-term access disruption. Our project managers will discuss these scenarios 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 is designed to last as long as your primary home — typically 50 years or more. How long it lasts comes down to the systems installed, whether the unit is properly cared for, 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 Local Homeowners

The communities throughout San Jose provide a wide range of property types that are well suited for ADU construction. Property owners near the Almaden Valley area have found their lots are well configured for ADU builds. Neighborhoods near Blossom Hill Road are increasingly popular for ADU construction as housing demand rises. If you're located closer to Evergreen, our team knows the permitting landscape well.

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 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 design through the final walkthrough.

Book Your ADU Construction Assessment Today

When you want to add an ADU to your property, Brother & Brother Builders is ready to guide you. Our experts offer years of hands-on experience in ADU construction for many different project types — from modest studio builds to large custom detached cottages. Our approach opens with a detailed, no-pressure consultation where we understand your vision and provide an honest assessment of what ADU construction on your property will look like.

Contact Brother & Brother Builders to set up your more info consultation. No matter where you are in the decision-making process, we enjoy answer questions, share examples of our work and give you the clarity you need to move forward. Building an ADU is a major decision — 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