Areas we serve

Alameda County

Build a Custom Prefab ADU or Home in Alameda County

Whether you're planning an ADU for family, creating rental income, supporting multigenerational living, or building a new single-family home, Perpetual Homes designs and builds highly customizable prefab homes throughout California. Our streamlined process combines expert planning, engineering, permitting, and construction to make building simpler from start to finish.

ADU Regulations & Permitting in Alameda County

Types & Quantity

  • Standard ADUs: Up to two new detached ADUs and/or converted spaces within existing buildings—even for multifamily properties (e.g., duplexes may add up to one ADU; a 20-unit apartment building could potentially add five ADUs, two of which may be detached).
  • Junior ADUs (JADUs): Allowed only in R‑1 zones, within an existing home (≤ 500 sq ft) and combined with at most one detached ADU (800 sq ft max).

Parking requirements

  • No extra parking if the ADU is within ½ mile of transit, within a historic district, built inside existing space, street permits are restricted, or there's a car-share nearby.
  • For new attached/detached ADUs, one parking spot per unit or per bedroom is required.

Other development rules

  • Detached ADUs must be behind the primary dwelling (75 ft from front property line or rear half), unless in agricultural zones.
  • Interior access and compatibility with existing building aesthetics are required.
  • Rentals must be for ≥ 30 days; cannot sell or separate the ADU from the main residence.

Permitting & fees

  • Ministerial (no discretionary review). Requires building permit; additional permits (sewer, fire, grading, etc.) may apply.
  • ADUs within existing structures and under 750 sq ft may be exempt from County planning fees; larger ones may incur park dedication and impact fees.

Support & guidance

  • The County offers "HelloADU" technical assistance, a detailed guidebook, permitting flowcharts, calculators, and a “Can I Build?” tool for addresses.

Ongoing compliance

  • These interim regulations align with State law as of January 2023, pending potential updates.

Planning an ADU or Home in Alameda County

Create space for family, plan for the future, or increase your property's flexibility with a prefab ADU, duplex, or single-family home can be a smart long-term investment. Backed by more than 40 years of California development experience, Perpetual Homes ADU helps Alameda County homeowners build with confidence.

Our 10-Step Process

Areas We Serve Throughout Alameda County

We are proud to build high-quality prefab ADUs and homes across Northern California and beyond.
Don't see your city listed? Contact us for a free virtual assessment and explore what's possible on your property.

  • Unincorporated Communities: Ashland  •  Castlewood  •  Castro Valley  •  Cherryland  •  Fairview  •  Happy Valley  •  Hillcrest Knolls  •  San Lorenzo  •  Sunol

Place an ADU on Your Lot

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prefab ADU models fit your California property. You can drag, rotate, and compare backyard homes to confirm the right size and placement before starting your project.

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Why Homeowners Choose Perpetual Homes ADU

Experienced California ADU & Home Builder

One of California's largest family-owned prefab ADU and home builders, helping homeowners navigate the building process with confidence.

Highly Customizable Floor Plans

Choose from ADUs, duplexes, and single-family homes with flexible floor plans, designer finishes, and energy-efficient features.

Full-Service Design & Permitting

From site evaluation and engineering to permitting and construction, our experienced team manages every step of your project.

Transparent Pricing & Peace of Mind

Financing resources, a 7-year warranty, and recognized as the 2026 Prefab ADU Development Company of the Year by Construction Business Outlook.

Find the Perfect Home for Your Lifestyle

Browse our collection of prefab ADUs, duplexes, and single-family homes designed for residential properties throughout California. Compare floor plans, personalize finishes, and discover home designs that fit your property, budget, and lifestyle.

Frequently Asked Questions

  • What are Accessory Dwelling Units (ADUs)?

    ADUs are separate housing units built on existing single family residential properties. ADUs are also known as secondary dwelling units, guest houses, backyard cottages, mother-in-law units and granny flats.


    There are many different types of ADUs, including both separate structures located in back or side yard (detached) and conversions of existing spaces such as basements, attics and garages.

  • How do I know if my property is suited for a Perpetual Home?

    Many different types of properties will accommodate an ADU. In most cases, properties with a flat backyard with few obstructions, and where an open space with minimum dimensions of 45′ x 25′ can be created, will work. If you aren’t sure, contact us and we’ll review property information online and even perform a site visit to determine if your property is suitable for a Perpetual Homes.

  • What amenities does Perpetual Homes offer?

    ADUs are separate housing units built on existing single family residential properties. ADUs are also known as secondary dwelling units, guest houses, backyard cottages, mother-in-law units and granny flats.


    There are many different types of ADUs, including both separate structures located in back or side yard (detached) and conversions of existing spaces such as basements, attics and garages.

  • What is the cost of a Perpetual Homes to a homeowner?

    Perpetual Homes sells fully installed ADUs in the California market starting in the mid price of $100,000’s. This price includes all permits, installation costs, utility connections, appliances, and landscaping. Perpetual Homes is one of the most affordable but high-quality options for a detached ADU.


    Because of the variability of site characteristics, Perpetual Homes' fixed price will not cover the cost of removing existing structures, large trees, underground storage tanks, cesspools, and other impediments to installing an ADU, nor will Perpetual Homes cover the cost of non-standard installations or utility connections, or upgrading utility service to a property to serve the ADU. In addition, impact fees can vary, these costs are passed through to the homeowner.

Ready to Get Started?

Have questions about building a prefab home in Alameda County? Schedule a free consultation with the Perpetual Homes ADU team to discuss your property and explore your options.

Disclaimer: The information on this page is provided for general informational purposes only and is not legal, zoning, or permitting advice. Requirements vary by jurisdiction and may change over time. Always verify current regulations with your local Planning Department before beginning your project.