ADU Construction Services by 9 Builders
9 Builders is an ADU contractor serving homeowners across the Bay Area, specializing in the design and construction of Accessory Dwelling Units. From backyard cottages and detached ADUs to garage conversions and attached additions, the company offers full-service ADU construction tailored to individual lots, budgets, and timelines.
An Accessory Dwelling Unit (ADU) is a secondary housing unit built on the same property as a single-family home. ADUs are commonly used to generate rental income, provide space for family members, or create a private guest suite or home office. They are self-contained units that typically include a bedroom, bathroom, kitchen, and living area. Common ADU types include:
- Detached ADU – a separate structure, often located in the backyard
- Attached ADU – an addition to the main home with its own entrance
- Garage conversion – converting an existing garage into a livable unit
- Interior conversion – transforming a basement or attic into an independent unit
9 Builders handles each of these ADU types and brings local knowledge of zoning regulations, setback rules, and building codes across Santa Clara County and the broader Bay Area.
Design, Permits, and Construction Under One Roof
One of the key aspects of 9 Builders' approach is managing the entire ADU process in-house. This includes custom design, permit submissions, construction, and final inspection. Their team navigates the permitting requirements for cities including San Jose and Los Gatos, handling every submission and revision on behalf of the homeowner.
On the design side, 9 Builders focuses on maximizing functionality within smaller footprints. Each layout is planned to make efficient use of space, with open floor plans that integrate living, dining, and kitchen areas. Design styles range from modern to traditional, with the goal of complementing the existing main residence. Where site conditions allow, outdoor features such as patios or decks may also be incorporated.
The company also incorporates eco-friendly elements into its ADU builds, including energy-efficient windows, LED lighting, quality insulation, and solar panel options. Finishes and features are selected based on the homeowner's preferences and budget, ranging from practical built-in storage to higher-end countertop materials.
9 Builders is licensed and insured, and all construction work is carried out in compliance with California building codes and energy efficiency standards.
Practical Information for Bay Area Homeowners
For homeowners considering an ADU project, here are some general facts relevant to the Bay Area and California:
- A typical detached ADU can cost between $150,000 and $350,000, depending on size, design, and site conditions
- Most ADU projects take 8 to 14 months from design to move-in, depending on permit timelines and complexity
- All ADUs in California require building permits — 9 Builders manages this process on behalf of clients
- California law permits homeowners to rent ADUs as long-term or short-term rentals, subject to local regulations
- Detached ADUs can be up to 1,200 square feet; attached ADUs can be up to 50% of the primary home's living area
- Only the new ADU construction is reassessed for property tax purposes — not the entire home
9 Builders provides detailed estimates upfront, with the aim of avoiding hidden fees or unexpected change orders. The company serves homeowners across the Bay Area and tailors each project to the specific requirements of the local city or municipality.
