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Prefab ADU in San Mateo County

Abodu makes and installs prefab homes for play, passive income and possibility in as little as 6 months.

About San Mateo County

With various custom finishes and floor plan configurations, an Abodu prefab ADU in San Mateo County can maximize your residential property’s living potential. An accessory dwelling unit is a versatile solution for homeowners looking to expand their living spaces or generate reliable rental income.

Completing construction off-site, Abodu precisely tailors prefab ADUs to suit your unique preferences and lifestyle. Whether you’re in the market for a cozy in-law unit or a two-bedroom granny flat, Abodu’s range of detached ADUs can accommodate any property layout.

What are the benefits of having an ADU?

Given the high demand for affordable housing in the San Francisco Bay Area—from Berkeley to Palo Alto—a prefab ADU in San Mateo County offers a tried-and-true way to earn extra cash if you rent it out. By adding a custom ADU to your property, you could also boost your real estate’s overall value, potentially leading to a higher resale value in the future.

Alternatively, the secondary unit provides incredible versatility and can be turned into a personal gym, dedicated home office, or creative workshop. A detached ADU is also an ideal living space for family members enjoying their golden years. The secondary unit offers independence and privacy, while keeping loved ones close.

Plus, prefab ADUs are often more budget-friendly and sustainable than constructing a brand-new home, which is a win for your wallet and the environment. Built in a controlled factory setting, a prefab ADU reduces construction waste and minimizes unexpected expenses. This efficiency translates into saved time and money—and you won't have to deal with the hassles of traditional on-site construction.

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San Mateo County ADU requirements

To streamline ADU projects, the San Mateo County Planning and Building Department outlines the essentials of ADU construction, including the permitting process, building codes, and financing options.


How much does an ADU unit cost in San Mateo County?

The cost of constructing an ADU in San Mateo County can vary significantly based on several factors, such as the unit's square footage, material choices, and its specific location within the county.

You can estimate the cost of building a modular home by using the ADU calculator tool, which was developed by the county planning department’s Second Unit Resources Center. According to the calculator, a premium 750-square-foot modular studio in San Carlos or Redwood City could cost around $331,000 to build.

Building Permits

How do I get an ADU permit in San Mateo County?

The permitting process for building an ADU involves submitting detailed plans and documentation—such as floor plans, energy calculations, and engineering data—to the county planning department for review. The office will permit the homeowner or ADU company if the plans comply with local building codes and regulations.


What are the top ADU requirements in San Mateo County?

Since ADUs are functional living spaces separate from the primary residence, California state law requires secondary units to have access to basic utilities like water, sewage, and electricity. Additionally, each city within the county has specific requirements for ADU utilities like fire sprinklers and water meters.


How do I finance an ADU in San Mateo County?

When financing your ADU, there are multiple options. One of the most common approaches is to take out a home equity line of credit (HELOC), where you can borrow up to a certain amount, then repay it over time.

There’s also cash-out refinancing, where homeowners refinance their existing mortgage for a higher amount than the current outstanding loan balance, allowing them to turn their equity into cash. For short-term financing, a construction loan could provide a credit line for ADU construction, but interest rates may be higher than other options.

FAQs: Prefab ADUs in San Mateo County

Fee schedules for ADU permits in San Mateo County vary by city and unit size, but you can expect to pay a few thousand dollars. For example, the Atherton ADU planning fee is roughly $1,380 for a secondary unit up to 1,199 sq. ft. The permit fees vary based on the ADU value.

California state law mandates a minimum distance of 4 feet between the ADU and a homeowner’s property line.

Size restrictions on a prefab ADU in San Mateo County differ based on municipality. The city of San Mateo has a maximum of 1,200 sq. ft. for detached ADUs. However, other cities may limit units depending on the lot size.

ADUs often come equipped with several essential appliances, including, but not limited to:

  • Stove or cooktop

  • Refrigerator

  • Oven

  • Dishwasher

  • Washer and dryer

  • Water heater

  • HVAC system

These appliances enhance the comfort and functionality of any living space.

A prefab ADU is a secondary dwelling unit designed for existing residential properties, often smaller in size and subject to specific zoning regulations for accessory dwellings. On the other hand, a modular home is a standalone residential structure that serves as a primary residence, typically in compliance with broader building codes.

Learn more about Abodu Prefab ADUs

With a focus on quality craftsmanship and sustainability, Abodu prefab ADUs combine modern comfort with environmental responsibility. Take advantage of a hassle-free experience with upfront pricing and a streamlined building and installation process. After you design your custom unit, a dedicated Abodu project manager will handle the rest of the ADU project, from securing permits to delivering your new prefab ADU by crane. Embrace the future of affordable housing with Abodu, where design meets function and sustainability meets style.

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All-in-One Service

Featuring an impressive selection of pre-approved plans, Abodu streamlines the process of building and installing premium built-to-order ADUs.

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Unparalleled Design

Each floor plan showcases timeless designs using sustainable, high-quality materials—all with upfront pricing.

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Committed to delivering a straightforward, hassle-free experience for California homeowners, our efficient approach to prefab ADUs lets you enjoy your newly added living space as soon as seven months after signing on the dotted line.

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A Great Investment

Take advantage of an exceptional return on investment with an Abodu ADU.

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