Everything You Need to Know About ADU Construction

Expand Your Home with Expert 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 opens the door to a flexible new living space on your existing property — whether you want to create a private workspace. Brother & Brother Builders has guided hundreds of local homeowners turn these plans to life with precision and transparency.

The popularity of ADU construction has increased significantly in recent years, and it's easy to understand why. California state law now makes it easier 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 provides increased control over how your property serves your household.

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

What Is an ADU Build?

ADU construction involves 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 — featuring a kitchen, bathroom, sleeping area, and its own entrance — that is located on the same parcel as a primary residence. ADU construction includes various structural types, including detached backyard units, attached additions, garage conversions, and even below-grade dwelling units.

Mechanically, everything kicks off with a thorough property evaluation, where our team evaluate lot dimensions, existing structures, soil conditions, and local code requirements. From there, architectural drawings are prepared and submitted to the local building department. Once the check here paperwork is cleared, ADU construction moves into the physical build phase — which covers everything from foundational work, framing, HVAC, drywall, flooring, and exterior finishes. The result is a completely finished 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. Materials must be selected to align with the neighborhood's character. Systems like HVAC and drainage must be sized for independent daily use. Brother & Brother Builders approaches every build with the same professional rigor we apply to large-scale custom home projects.

Key Reasons to Choose ADU Construction

• Increased Property Value — ADU construction delivers real market value to your property, often returning more than the build cost when it's time to sell.
• Revenue Generation — A completed ADU may be listed as a long-term rental or short-term vacation unit, generating steady monthly revenue 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 open-plan one-bedrooms, ADU construction may be customized to the intended occupant's lifestyle.
• Streamlined Approval Process — Recent state legislation has cut down the red tape associated with ADU construction, resulting in a timeline that is faster and less expensive than ever before.
• Sustainable Land Use — Building an ADU works within your current footprint instead of requiring new development, which aligns with sustainability goals.
• Separate Entrances and Spaces — Unlike a bedroom addition, ADU construction creates a truly separate unit where tenants live autonomously.
• Lasting Financial Benefit — A well-built ADU continues to produce returns for many years and generates both functional space and financial upside.

The ADU Construction Process Step by Step

1. Initial Property Assessment and Feasibility Review — Our builders assess your property to evaluate setbacks, lot coverage limits, and utility connections. This phase answers exactly what can be built before any money is spent on design.
2. Architectural Drafting and Space Planning — Experienced draftspeople create comprehensive blueprints based on your goals. Space is thoughtfully allocated to optimize daily use.
3. Permitting and City Approval — ADU construction in San Jose involves filing drawings to the city's building department for review and approval. Our team handles all submissions on your behalf, responding to review feedback promptly.
4. Ground Prep and Structural Base — Once permits are issued, the build starts. This involves leveling and prepping the ground, laying the structural base, and setting up utilities.
5. Shell Construction and Exterior Finishing — The structural frame is erected followed by weatherproofing and exterior finish materials. This phase, the ADU transforms from a concept to a building.
6. Mechanical, Electrical, and Plumbing Installation — Certified technicians install the heating, cooling, drainage, and power infrastructure that make the ADU ready for occupancy. All work is inspected at designated stages throughout ADU construction.
7. Finishes, Fixtures, and Final Walkthrough — Countertops, hardware, finishes, and fixtures are fitted and completed to the approved plan. A closing municipal review grants legal occupancy status and the unit is officially approved for use.

Who Is a Right Fit for ADU Construction?

Property owners who are best suited from ADU construction typically fall into a few recognizable groups. If you own a single-family home with enough lot space to meet setback requirements, you're already in a good starting place. Homeowners looking to generate income 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 runs a small business and wants a detached creative or business space that doesn't interfere with your family's daily life. Landlords and real estate investors who are building a portfolio are also a natural fit for ADU construction, since the long-term value is proven.

Situations where ADU construction may not be the best first step include sites with unusual utility access challenges. Very small lots or properties with easements may face additional constraints. Brother & Brother Builders reviews each property individually and honestly 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 city review schedules. The approval phase alone can take two to four months in San Jose, so starting early is important. Straightforward interior 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 whether it's a conversion or new construction. Locally, ADU construction commonly costs $150,000 to $400,000 or more for a fully custom construction. Attached ADU additions are generally priced lower, sometimes starting around $80,000 depending on scope. A precise cost projection can only be given after completing a formal feasibility evaluation.

Is ADU construction disruptive while it's underway?

How much the build affects daily life depends on the project's location on your property. Standalone ADU projects are usually easier to live alongside, since work happens away from the main house. Projects that connect to the main structure may create short-term inconveniences during specific stages like framing or MEP rough-in. We provide advance notice about any phases that may affect your routine.

Do I need to move out during ADU construction?

In most cases, you are not required to vacate your house during ADU construction. The vast majority of projects are designed so that 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 require short-term access disruption. Our project managers will discuss these scenarios during the planning phase.

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

An ADU constructed with quality materials is designed to last as long as the main residence — indefinitely with proper upkeep. How long it lasts comes down to the standard of construction, whether the unit is properly cared for, and how proactively issues are resolved over time. Brother & Brother Builders specifies high-quality components and follow all code requirements to ensure lasting performance.

ADU Construction for San Jose Homeowners

The communities throughout San Jose provide a diverse mix of property types that are well suited for ADU construction. Property owners near the Almaden Valley area frequently see their parcels accommodate detached backyard units nicely. Neighborhoods near Blossom Hill Road have seen growing ADU activity as multigenerational living becomes more common. 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 applies particular standards for ADU construction that experienced builders know well. Location near major arterials like Story Road or Tully Road can influence utility connection requirements for a given ADU project. Our team's knowledge of the San Jose permitting environment means more accurate timelines and budgets from design through the final walkthrough.

Book 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 here to help. Our builders provide years of hands-on experience in ADU construction including all types of project types — from small attached additions to large custom detached cottages. The process begins with a detailed, no-pressure consultation where we understand your vision and give you a realistic picture of what the project will involve.

Reach out to our team to set up your consultation. No matter where you are in the decision-making process, we enjoy discuss timelines, costs, and design possibilities and give you the clarity you need to move forward. This type of project is a meaningful commitment — and we're committed to helping you get it right.

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