ADU Construction: What to Expect from Start to Finish

Expand Your Home with Quality ADU Construction

Property owners throughout San Jose, CA are finding that adding an accessory dwelling unit is one of the most rewarding investments they can make. ADU construction opens the door to a powerful new living space on your existing property — whether you want to generate rental income. Brother & Brother Builders has helped hundreds of local homeowners see these visions to life with skill and care.

The demand for ADU construction has grown rapidly 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 embraced 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 works.

At Brother & Brother Builders, we apply deep hands-on experience to every ADU construction build. Our team is familiar with city and county requirements, the engineering requirements, and the planning steps that make an ADU truly livable. If you've been thinking about what ADU construction could do for your property, this guide will walk you through everything you need to know.

What Is ADU Construction?

ADU construction involves 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 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 below-grade dwelling units.

Mechanically, the process begins 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 city for permit approval. Once permits are secured, ADU construction moves into the physical build phase — which covers everything from foundational work, framing, mechanical systems, weatherproofing, and interior finishing. The result is a move-in-ready living unit adjacent to or detached from your main home.

What separates excellent ADU construction from an average project is the depth of planning at every stage. Products need to be chosen to complement the existing structure. Systems like wiring and water supply 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 contributes significant market value to your property, often returning more than the build cost when it's time to sell.
• Rental Income Potential — A completed ADU may be listed as a long-term rental or short-term vacation unit, generating steady monthly revenue for the homeowner.
• Housing for Extended Family — ADU construction offers family members a self-contained residence without losing proximity to the family.
• Personalized Layouts — From modern studio layouts, ADU construction may be customized to the intended occupant's lifestyle.
• Simplified Regulatory Path — Recent state legislation has minimized the red tape associated with ADU construction, resulting in a timeline that is faster and more cost-efficient than ever before.
• Efficient Use of Your Lot — Building an ADU uses your existing lot instead of requiring new development, 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 the long haul by offering both livable square footage and monetary benefit.

The ADU Construction Procedure Step by Step

1. Site Evaluation and Zoning Analysis — Our team visits 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. Custom Design and Architectural Planning — Our design team create comprehensive blueprints based on your goals. 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, addressing any city comments promptly.
4. Site Preparation and Foundation Work — Once permits are granted, physical construction begins. This includes grading the site, laying the structural base, and running initial plumbing and electrical conduits.
5. Framing, Roofing, and Exterior Work — Framing is completed followed by weatherproofing and exterior finish materials. At this stage, the ADU transforms from a concept to a building.
6. Mechanical, Electrical, and Plumbing Installation — Certified technicians install the plumbing lines, electrical wiring, and HVAC systems that make the ADU fully functional. All work is inspected at required milestones throughout ADU construction.
7. Finishes, Fixtures, and Final Walkthrough — Countertops, hardware, finishes, and fixtures are placed and inspected to the agreed design. A final city inspection grants legal occupancy status and the unit is officially approved for use.

Who Is a Strong Candidate for ADU Construction?

Property owners who are best suited from ADU construction generally fit within a few recognizable groups. If you own a single-family home with available square footage under zoning rules, you're already a strong candidate. Homeowners looking to generate income through rental are among the most common ADU construction clients, along with families supporting elderly parents.

Another strong candidate is someone who runs a small business and wants a separate office or studio space that doesn't interfere with your family's daily life. Landlords and real estate investors who want to maximize their land are also well suited for ADU construction, since the return on investment is well-documented.

Those who should discuss alternatives first include properties with significant setback limitations. Very small lots or properties with easements may need a modified approach. Our team can assess each property individually and honestly to advise you on what's feasible.

ADU Construction FAQ

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

The full timeline for ADU construction typically ranges from six to fourteen months, based on the project scope and local permitting timelines. The approval phase alone can take two to four months in San Jose, so planning ahead matters. Simpler garage conversions can move faster, while larger new construction ADUs require more time.

What does ADU construction typically cost?

Pricing depends on many factors based on the type and size of the ADU. For most projects in this region, ADU construction typically ranges from $150,000 to $400,000 or more for a detached new build. Attached ADU additions tend to cost less, sometimes in the $80,000 to $150,000 range. An accurate budget can only be given after completing 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. Detached website backyard builds are usually easier to live alongside, since work happens away from the main house. Garage conversions or attached additions may require temporary access during key milestones. Brother & Brother Builders keeps you informed about upcoming work and timelines.

Do I need to move out during ADU construction?

Generally speaking, you are not required to vacate your main home during ADU construction. Most builds are structured to allow you remain on the property throughout the build. Certain situations could require a brief departure if significant structural connections require temporary shutoffs in ways that temporarily impact livability. Our project managers will flag these situations during the planning phase.

How long will an ADU built through professional ADU construction last?

An ADU constructed with quality materials should last as long as your primary home — often several decades with routine maintenance. Durability depends to the standard of construction, how well routine maintenance is performed, and if mechanical components are maintained on schedule. Our builds use residential-grade products rated for longevity and build to current California residential standards to ensure lasting performance.

ADU Construction for Local Homeowners

San Jose's neighborhoods offer a diverse mix of property types that are well suited for ADU construction. Homeowners in the Willow Glen neighborhood frequently see their parcels are well configured for ADU builds. Neighborhoods near Blossom Hill Road have seen growing ADU activity as families expand. From neighborhoods near the Guadalupe River Park corridor to those near Branham Lane, our team knows the permitting landscape well.

San Jose's permitting office has developed specific protocols for ADU construction that require a builder familiar with local expectations. Access to infrastructure along thoroughfares like Monterey Road can impact the design approach for a given ADU project. Brother & Brother Builders' experience across these local conditions means fewer surprises 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 the team to call. Our builders provide proven skills in ADU construction including all types of project types — from simple garage conversions to fully independent secondary homes. The process begins with a comprehensive site assessment where we listen to your goals and give you a realistic picture of what the project will involve.

Contact Brother & Brother Builders to schedule a site visit. Even if you're just exploring the idea, we enjoy discuss timelines, costs, and design possibilities and make sure you feel confident before committing. 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