What Exactly Is an ADU? (And Why They’re Transforming Bay Area Homes)
If you live in the Bay Area, you’ve probably heard the term ADU thrown around a lot- especially in real estate listings, contractor estimates, and neighborhood discussions about adding space.
But what exactly is an ADU, and why are so many homeowners in San Francisco and Marin County building one?
Let’s break down what ADUs are, what they can be used for, and why they’ve become one of the smartest property investments in California.
ADU Defined: Accessory Dwelling Unit
An ADU (Accessory Dwelling Unit) is a secondary living space built on the same property as a primary home.
It’s a self-contained unit – meaning it has its own entrance, kitchen, bathroom, and living area, but it shares the lot with the main house.
They’re sometimes called:
- Granny flats
- In-law units
- Backyard cottages
- Garage conversions
- Basement apartments
ADUs can be attached, detached, or converted from an existing space like a garage or lower level.
Types of ADUs
Here are the most common styles we build or remodel for Marin County and SF clients:
1️⃣ Detached ADU
A separate structure built in your backyard: ideal for rental income, a guest suite, or an office space.
➡️ Example: A 400–800 sq. ft. cottage behind a primary home.
2️⃣ Attached ADU
Connected to your main home, often sharing one wall.
➡️ Example: A side addition that includes a small kitchen, bath, and bedroom.
3️⃣ Garage or Basement Conversion
Turns underused square footage into a livable space.
➡️ Example: Converting a San Francisco garage into a studio apartment.
4️⃣ Junior ADU (JADU)
A smaller version – typically 500 sq. ft. or less – that may share a bathroom with the main home.
➡️ Example: A converted guest suite with a kitchenette and private entry.
Why ADUs Are So Popular in the Bay Area
California’s housing shortage and high property values have made ADUs a practical and legal solution for adding livable space.
Recent state laws (SB 9 and AB 68) have simplified the approval process, so homeowners can now add ADUs faster and with fewer local restrictions.
Top reasons homeowners build ADUs:
- Rental income or Airbnb
- Space for adult children or parents
- Home office or creative studio
- Long-term property value
- Increased resale potential
ADUs are also a sustainable way to build, using existing land and infrastructure, reducing commute time for family or renters, and often increasing energy efficiency compared to older structures.
What’s Involved in Building an ADU
Building an ADU involves a few key steps:
- Design + Feasibility: Determining placement, size, and style (while following zoning rules).
- Permitting: Coordinating with your city for design review, setbacks, and utility tie-ins.
- Construction: Foundation, framing, utilities, interior finishes.
- Final Inspection: Ensuring code compliance and safety before occupancy.
At Home Team Services Remodeling, we guide clients through this entire process- from initial design discussions to permits and build-out. Our team has experience navigating the requirements of San Francisco, Marin County and other Bay Area municipalities.
How Much Value Does an ADU Add?
According to real estate data from Northern California, a well-designed ADU can increase property value by 20–35%, depending on location, size, and quality.
Even more importantly, it provides flexibility ( income today, living space tomorrow).
An ADU isn’t just an addition- it’s a strategic investment in flexibility, family, and financial growth.
Whether you’re looking to create a rental unit, home office, or guest cottage, an ADU offers lasting value and freedom without needing to leave your neighborhood.
At HTS Remodeling, we help homeowners design, permit, and build ADUs that fit beautifully with the architecture of their existing home- built to last, and built to feel like home.