ADU Construction: What to Expect from Start to Finish

Expand Your Home with Quality ADU Construction

Homeowners across San Jose, CA are realizing that adding an accessory dwelling unit is one of the most practical investments they can make. ADU construction creates a flexible new living space on your existing property — whether you want to house get more info a family member. Brother & Brother Builders has supported hundreds of local homeowners bring these projects to life with craftsmanship and integrity.

The demand for ADU construction has surged in recent years, and it's easy to understand why. California state law has simplified the process for homeowners to add these secondary units, and local municipalities like San Jose have embraced 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 offers greater control over how your property functions.

At Brother & Brother Builders, we draw on extensive hands-on experience to every ADU construction project. Our team is familiar with city and county requirements, the engineering details, and the design choices that make an ADU functional. 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 planning, approving, and constructing 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 entrance — that exists on the same lot as a primary residence. ADU construction comes in multiple configurations, including detached backyard units, attached additions, garage conversions, and even below-grade dwelling units.

Mechanically, everything kicks off with a detailed site assessment, where our builders evaluate property boundaries, available square footage, and infrastructure capacity. From there, architectural drawings 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 completely finished 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 match the primary home's aesthetic. Systems like plumbing and electrical must be sized for independent daily use. Brother & Brother Builders treats each project with the same professional rigor we bring to full custom home projects.

Key Benefits ADU Construction

• Increased Property Value — ADU construction adds measurable 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, providing a consistent income stream for the homeowner.
• Space for Loved Ones — ADU construction gives aging parents a private, independent living space without leaving the property.
• Customization Options — From open-plan one-bedrooms, ADU construction can be tailored to your household's priorities.
• Simplified Regulatory Path — Recent state legislation has reduced the permitting obstacles associated with ADU construction, creating a path that is faster and more affordable than ever before.
• Efficient Use of Your Lot — Building an ADU maximizes the land you already own instead of consuming open land, which contributes to sustainability goals.
• Privacy for All Residents — Unlike a bedroom addition, ADU construction delivers a genuinely independent unit where occupants have full privacy.
• Long-Term Investment Security — A well-built ADU holds its value for decades, providing both usable housing and equity growth.

The ADU Construction Procedure Step by Step

1. Initial Property Assessment and Feasibility Review — Our experts review your property to determine what type of ADU is allowed and where it can be placed. This stage clarifies exactly what's possible before any time is invested in drawings.
2. Architectural Drafting and Space Planning — Our design team 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 review and approval. Our team handles all submissions on your behalf, resolving any revision requests promptly.
4. Site Preparation and Foundation Work — Once permits are granted, physical construction begins. This involves leveling and prepping the ground, laying the structural base, and setting up utilities.
5. Shell Construction and Exterior Finishing — Framing is completed followed by roofing, siding, windows, and exterior doors. This phase, the ADU takes its visible shape.
6. Mechanical, Electrical, and Plumbing Installation — Skilled tradespeople install the heating, cooling, drainage, and power infrastructure that make the ADU fully functional. Every system is reviewed at designated stages throughout ADU construction.
7. Interior Completion and City Sign-Off — Countertops, hardware, finishes, and fixtures are placed and inspected to your specifications. A final city inspection confirms the unit is code-compliant and the ADU is ready for use.

Who Is a Right Fit 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 in a good starting place. Homeowners wanting to add a revenue stream through rental are among the most common ADU construction clients, along with families supporting elderly parents.

ADU construction also suits someone who runs a small business and wants a separate office or studio 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. Very small lots or properties with easements may face additional constraints. Our team can assess each property on its own merits to advise you on what's feasible.

ADU Construction Frequently Asked Questions

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

The total process for ADU construction usually runs between six to fourteen months, based on the project scope and local permitting timelines. Permitting alone can take several months in San Jose, so beginning the process sooner rather than later is wise. Smaller detached units can move faster, while multi-room detached cottages fall toward the upper end of the timeline.

What does ADU construction usually run in terms of budget?

Costs vary widely based on whether it's a conversion or new construction. In the San Jose area, ADU construction typically ranges from $150,000 to $400,000 or more for a standalone backyard unit. Attached ADU additions are generally priced lower, sometimes in the $80,000 to $150,000 range. An accurate budget can only be given after completing a full site assessment.

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

The day-to-day impact depends on where the ADU is being built. New construction in the rear yard are usually easier to live alongside, since the crew operates at a distance from your living areas. Projects that connect to the main structure 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 vacate the property during ADU construction?

For the majority of homeowners, you won't have to vacate your primary residence during ADU construction. Most job sites are set up to let you continue living in the home throughout the process. There are edge cases if major utility upgrades affect the main house in ways that require short-term access disruption. Our construction supervisors will flag these situations during the pre-construction consultation.

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

An ADU constructed with quality materials 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, how well routine maintenance is performed, and whether systems like roofing and plumbing are serviced regularly. Our builds use residential-grade products rated for longevity and follow all code requirements to ensure lasting performance.

ADU Construction for San Jose Homeowners

Residential areas across San Jose present a diverse mix of property types that are ideally positioned for ADU construction. Homeowners in the Willow Glen neighborhood have found their lots accommodate detached backyard units nicely. Neighborhoods near Blossom Hill Road are seeing more homeowners add secondary units as housing demand rises. Whether your property is near downtown San Jose, our team knows the permitting landscape well.

Local regulatory bodies in this area applies particular standards 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 the San Jose permitting environment means fewer surprises from the first meeting to the final inspection.

Schedule Your ADU Construction Consultation Today

If you're ready to explore what an ADU could look like on your lot, Brother & Brother Builders is here to help. Our builders provide proven skills in ADU construction across a wide range of project types — from small attached additions to multi-room backyard residences. Every project starts with a comprehensive site assessment where we listen to your goals and provide an honest assessment of what ADU construction on your property will look like.

Reach out to our team to schedule a site visit. Even if you're just exploring the idea, we're glad to walk through your options, review completed projects and make sure you feel confident before committing. ADU construction is a significant investment — and we're committed to helping you get it right.

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