ADU Construction Arcadia

Single Family Properties: Your Main Paths To An ADU

Own a single-family lot with an existing or concurrently built primary dwelling? Arcadia lets you choose one path:

One attached ADU; or

One detached ADU or one JADU; or

One detached ADU plus one JADU together.

Conversion of ADUs from existing permitted enclosed spaces is also allowed, and you enjoy relaxed setbacks when you keep the footprint. citeturn1view1turn1view2

Key Dimensional Checks

Detached or attached units over 800 square feet trigger a Zoning Clearance. Adding an ADU cannot push the total floor area ratio above 45 percent, lot coverage above 50 percent, or reduce the required open space below 50 percent. Maintain at least 6 feet of building separation eave to eave between a detached ADU and the main house. These are objective measures that the City will verify during review. 

Setbacks

State law limits side and rear setbacks for new attached or detached ADUs to 4 feet. No new setback is required when you convert an existing permitted living area or accessory structure in place, unless needed for fire safety. Arcadia guidance mirrors these rules. 

Multi-Family And Mixed-Use Lots: Hidden Capacity

If you own apartments or a mixed use property, Arcadia gives you two choices, pick one: create interior ADUs in unused spaces such as storage rooms up to 25 percent of the existing unit count, or build up to two detached ADUs, each limited to 800 square feet, one story, and 16 feet in height, with 4 foot side and rear setbacks. 

Parking Made Easier

Parking rules no longer block backyard projects. California limits parking to one spot per ADU or bedroom, whichever is less, allows tandem parking on existing driveways, and prevents cities from requiring parking replacement when garages are converted or demolished for ADUs. Many ADUs qualify for zero parking, especially if near transit, inside the existing home, in historic districts, or near car share vehicles.

No Owner Occupancy Needed

California law forbids local agencies from requiring owners to live on-site for ADUs. You can rent out both your main home and ADU long-term. Junior ADUs have different rules, so check before you start.

Faster Permits Than You Think

 ADU permits are ministerial, with agencies required to approve or deny within 60 days of a complete application. They have 30 days to request corrections, and if they miss deadlines, your permit is deemed approved. Getting plans right upfront protects your timeline.

Pre-Approved Plans Save Time and Money

Arcadia offers a Pre-Approved ADU Program where professionals submit detached ADU designs for city pre-review. Homeowners choosing these plans skip Planning review, save about $700 in fees, and get faster building plan checks. These approvals stay valid until code updates.

Budget Reality for Southern California ADUs

Custom ADUs usually cost $100,000 to $350,000+, while prefab options range from $90,000 to $180,000 before upgrades. Costs break down roughly into design (8-12%), permits (5-10%), site prep (5-15%), utilities (5-10%), construction (45-60%), finishes (10-15%), and contingency (10-15%). Units under 750 sq ft may qualify for fee waivers, so right-sizing can save you money.

Design Tips That Work in Arcadia

Match your ADU’s roof and exterior materials to your home for a seamless look. Use sliding or pocket doors to save space. Place windows for privacy and garden views, not into neighbors’ homes. A small porch facing the yard improves livability and rental appeal. Durable, mid-grade finishes photograph well if you plan to rent. Standardized sizes that fit typical Arcadia yards speed permits through pre-approval.

Financing Your ADU

Options include home equity loans, cash-out refinancing, construction-to-perm loans, and some state or local grants. California programs like CalHFA and SB13 impact fee waivers for small units help lower entry costs. Be sure to check current availability when budgeting.