How Big Can an ADU Be in California?
Understanding Popular ADU Sizes in California
Each ADU size serves a unique purpose - from compact studios to family-ready second units. Here's a quick look at what’s possible:
Great for: Open-concept studios, simple living, or a backyard retreat.
This ultra-compact size fits well in small lots and usually includes a kitchen, bath, and open living area.
Perfect for: A little more breathing room.
It works well for an office with a bathroom or a cozy rental. Can comfortably accommodate a compact bedroom and living area.
Perfect for: Studio-plus or one-bedroom ADU.
This size allows for distinct zones - kitchen, living, and sleeping - without feeling cramped.
Perfect for: Comfortable one-bedroom units.
Popular among homeowners balancing affordability and space. It often includes full kitchens and laundry setups.
Works well for: A roomy one-bedroom setup or adding a small den.
Extra square footage means a more spacious layout, ideal for long-term living or rentals.
Perfect for: Hitting the rent-friendly sweet spot.
This size is often the maximum allowed on smaller lots and still offers full-sized living comforts.
Suited for: Building to the full permitted size of a detached ADU.
With full-size appliances and rooms, it’s a go-to option for families or rental income.
Perfect for: Two-bedroom units or luxury one-bedrooms.
Great for families needing space or multi-generational living, with plenty of room for storage.
Perfect for: Spacious two-bedroom living.
Frequently used as an additional home on-site. Some cities allow this for attached ADUs.
Detached vs. Attached ADU Sizes in California
In most areas of California, detached ADUs can be up to 800 square feet by right. That means you won’t need a special permit or hearing to build up to that size. Attached ADUs can sometimes be larger - up to 1,000 sq ft ADU or even 1,200 sq ft - depending on your main house size and local rules. Height, lot coverage, and setbacks can also affect how big your ADU can be.
The real answer to “how big can an ADU be in California?” depends on where you live, your lot size, and how your city enforces state ADU laws. But with expert planning, you can often get more space than you think.
Average Cost of an ADU in California
Understanding the cost of an ADU helps you budget smarter and avoid costly surprises. Here’s why it matters:
- Helps You Choose the Right Size
Each square foot adds cost. Knowing average prices guides size decisions that match your budget. - Avoids Unnecessary Delays
Miscalculating expenses could slow down permits or delay funding. Clarity helps keep your project moving. - Shapes Long-Term Value
Knowing what most homeowners spend helps you invest in an ADU that adds long-term resale or rental value. - Guides Financing Options
Accurate cost estimates help you explore loans, grants, or home equity options with confidence.
How ADU Scale Can Help
From dream to doorstep, we make building your ADU hassle-free. Here’s how we help:
- Free Property Assessment
We evaluate your lot and tell you what size ADU in California you can build. - Custom Floor Plans
Choose from ready-made layouts or let us design something unique to fit your goals. - Permit Management
We handle all the paperwork with your city to avoid delays. - Transparent Cost Breakdown
You’ll see a clear cost estimate based on your ADU size, location, and design. - Construction Management
We manage the build from start to finish, using vetted local contractors. - Move-In Support
Final inspections, utility connections, and finishing touches - all taken care of.
Ready to Build the Right-Sized ADU?
Now that you know how sizes vary and how big an ADU can be in California, you're one step closer to building smart. Whether you're adding rental income, housing family, or expanding your home, the size of your ADU can shape its function - and its future.
Have questions? Want help estimating the average cost of an ADU in California based on your preferred size? Finding the right fit for your property and budget is our priority.