The competitiveness of the real estate market in California’s Wine Country coupled with recent ADU-friendly legislation from the state government has paved the way for a significant increase in demand for ADUs in Wine Country including Napa, Somoma, Santa Rosa, and Petaluma. Accessory Dwelling Units (ADUs) are small, residential units that can be placed on an individual’s property in addition to their primary residence as a way of increasing the amount of livable space. Also known as granny flats, in-law suites, or secondary dwellings, ADUs can either be attached or detached from the primary residence. In our guide to buying an ADU in California Wine Country, we cover areas such as Napa, Sonoma, Santa Rosa, and Petaluma, and address key questions you may have while considering if an ADU is right for you such as “Why should I build an ADU” and “What companies build ADUs in my area?”

What is an ADU?

An ADU is a secondary dwelling unit that is located on the same property as the primary residence. These units can either be attached to the primary home, above the garage for example, or act as standalone units. It is important to note that ADUs are tied to the building lot and primary residence, meaning that an ADU cannot be sold separate from your main home.  A common use for these secondary units is as a rental property as it affords homeowners an alternative stream of income. Whatever your indented purpose is, we’ve got you covered when it comes to buying an ADU in Wine Country like Napa, Sonoma, Santa Rosa, and Petaluma.

Why Might You Want an ADU?

• Additional living space - with quick construction times and relatively little site work, ADUs are a straightforward solution to increasing the amount of livable space on your property

• Alternative form of income - ADUs are an increasingly popular way to earn secondary income. Since ADUs can be built separate from the main residence, once permitted, the extra space can be rented out and generate additional income for homeowners

• Favorable State Legislation - new state legislation aimed at simplifying the process of building an ADU requires jurisdictions to approve/reject permits in under 60 days, eliminates minimum lot size and owner-occupancy requirements, prohibits jurisdictions form setting maximum size restrictions under 850 square feet or 1,000 square feet for units with 1 or more bedrooms

Key Decisions

• Size - California state regulations require ADUs to be larger than 150 sqft and block any local restrictions on building an ADU under 800 sqft. For larger ADUs, local ordinances may apply but require cities to allow studio ADUs of at least 850 sqft or 1,000 sqft for ADUs with 1 or more bedrooms.

• Local Ordinances:

If you live in an area other than the ones listed above, you can contact us here and we will gladly assist you in finding the appropriate information.

• Standard vs. Custom - Many prefab manufacturers offer pre-designed models small enough to qualify as an ADU. However, there are many custom ADU builders that operate in Northern California, and Wine Country in particular; this is particularly beneficial if you live in an area where standard design options may be limited due to a small work area or sloped lot

Common Questions

• How long does it take to build an ADU?

  • ADU construction times are significantly less than the 1-2 years it takes to construct a standard prefab home. Some ADU manufacturers have installation times as quick as 6 weeks from the time the deposit is received

• How much does an ADU cost?

  • While variables such as location, manufacturer, and lot-specific conditions may change your exact cost, an ADU will likely cost between $250-$500 per square foot.

• Can I finance my ADU construction?

  • Yes, though financing an ADU may be slightly different from financing a primary residence. Whereas, buyers interested in financing a traditional prefab build might want to consider a construction loan or a temp to perm loan, individuals interested in an ADU may have a more advantageous financing options. Because ADUs are often less expensive than traditional homes, borrowing options can be expanded to include financing such as a personal loan or Home Equity Line of Credit or Home Equity Sharing. 

  • With a personal loan:

    • Many personal lenders allow you to borrow up to $100k with no down payment

    • These loans are typically amortized over a shorter period than mortgages (up to 12 years)

    • These loans typically don’t underwrite the property and instead underwrite you as a borrower

    • Many of the best personal lenders are online and serve almost the entire country

    • The time to get approved for a personal loan is generally pretty fast (as little as a day to up to a couple weeks)

• With Home Equity:

• You must have enough “equity” built up in your current home

• Also considered “second mortgages”

• Home Equity Sharing

  • Not considered a loan

  • Allows individuals to access unconditional cash in exchange for a share of equity in their primary residence

  • Read our full review of Home Equity Sharing

Reputable Companies that Build ADUs in California’s Wine Country:

• KitHaus

  • Make 4 models of modern tiny-homes perfect for use as an ADU

  • All-in-cost: $330-$550 per sq ft

• Bay Modular

  • Offers 3 models of modern, turn-key ADUs up to 640 sqft

  • All-in-cost: $275 - $335+ per sqft

• PrefabADU

  • Offers 9 models of ADUs with the ability to customize exteriors to match your primary residence

  • All-in-cost: $345 - $405 per sqft

• Studio Shed

  • Have 3 models of environmentally friendly and partially-customizable ADUs

  • All-in-cost: $200 - $300+ per sqft

• Digz2Go

  • Specializes in fully-custom ADUs and is based in the SF Bay Area

  • All-in-cost: $400 - $450 per sqft

Or, for a more complete list, see our list of the Best ADU builders in The Bay Area