Expert ADU Builders in Napa & Sonoma Valleys

At JS Design + Build, we simplify Accessory Dwelling Unit (ADU) construction by managing every part of your project under one roof — from initial design concepts to the final walkthrough.

Based in Napa and serving St. Helena, Calistoga, and our neighbors in Sonoma, Solano, and Green Valley, we’re a full-service ADU builder with the experience to navigate local codes, streamline approvals, and deliver exceptional results. Our in-house team of designers, builders, and project managers ensures seamless communication, consistent quality, and on-time, on-budget completion.

Whether you’re adding an income-generating rental, creating a private guesthouse, or expanding space for family, we provide the expertise and accountability you need for building an ADU successfully.

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Our Comprehensive ADU Building Services

From design to permits to construction, we handle every detail so you can focus on the possibilities.

Custom ADU Design

Creating the best ADU designs to maximize space and match your vision.

Garage Conversions

Transforming garages into beautiful, livable units.

Prefabricated ADUs

Faster, cost-efficient factory-built ADU solutions.

ADU Construction & Project Management

Quality is managed by our in-house team from start to finish.

Interior Design & Finishing

Complete move-in-ready spaces with custom finishes

Permit & Zoning Assistance

Expert handling of permits, zoning, and compliance

Why work with JS Design + Build

Accountability

Our team takes ownership of the project from day one of the design process to the final construction clean up. No excuses, no finger pointing - just accountability.

Expertise

Designing for over 45 years and building for over 20, we have always maintained focus on a high level of craftsmanship. Having solid experience in-house allows us to recognize and solve potential issues before they start.

Integrity

Earning our good reputation did not come easily. We take your trust seriously and do the right thing when no one is looking.

ADU Construction FAQs

How much does an ADU cost?

ADU costs typically range from $285,000–$400,000+, depending on size, complexity, and finishes. Garage conversions are often less expensive, while detached units with full utilities can cost more.

What types of ADU do you build?

We build many different types of ADU including Detached ADUs, Custom ADUs, Tiny Homes, Secondary Units, In-law Suites, Guest Houses and more.

How long does it take to build an ADU?

Most projects with custom ADU builders take 6–12 months,including design, permitting, and construction. Prefabricated units and garage conversions may be completed faster, while custom detached units may take longer.

Do I need a permit for an ADU?

Yes, ADUs in Napa / Sonoma / Solano counties all require building permits and must follow local zoning regulations. We handle all permitting to ensure your project meets municipal codes.

Can I rent out my ADU?

In most areas, ADUs can be rented out for additional income. Some jurisdictions (such as Napa County) have restrictions on short-term rentals, and we’ll help you understand the rules in your area.

What size ADU can I build?

ADUs typically range from 400–1,200 square feet, depending on local zoning and lot size. Our site evaluation will determine your maximum allowable size.

Will an ADU affect my property taxes?

Yes, adding an ADU usually increases your property assessment and taxes. However, the added value and rental income often outweigh the additional costs.

Do ADUs require separate utilities?

This depends on local codes and your preferences. We can design either shared utility connections with the main house or separate meters for the ADU.

Ready to Build Your ADU? Let's Get Started Today.

Your dream ADU is closer than you think, and as your trusted ADU contractor, our team is here to make the process smooth and stress-free. Contact us today for a free consultation and take the first step toward building your perfect ADU.