An ADU, or Accessory Dwelling Unit, is a secondary dwelling built on a single-family property. These are especially popular in California as they do not require buying additional land and can be built without a lot of additional infrastructure.
ADUs are typically built for additional family members or guests staying long-term on the property. Most homeowners that build ADUs go forward with construction because the additional square footage, bedrooms, and bathrooms are added to the overall appraisal of the property for valuation purposes.
Maximum and Minimum ADU Sizes in California
In California, as of 2023, the minimum size of an ADU is 150 sq ft, the maximum size for an ADU is 1200 sq ft.
According to AB 58, passed in 2023, you are allowed to build an ADU with a maximum size of 1200 sq ft with 4-ft setbacks. Single family properties can also build an additional Junior ADU (JADU) up to 500 sq ft.
The old laws in California stated if the ADU would cause you to exceed your floor-area ratio (FAR), the maximum size was 800 sq ft with a 16-ft height restriction and a 4-ft setback requirement.
The FAR is the usuable square footage of housing divided by the lot size. Multi-story floor plans count towards usuable square feet. The new laws relaxed requirements on ADUs.
Attached ADUs must have a square footage that is no more than 50% of the main property’s square footage, while conversion ADUs are usually not limited by any size restrictions.
Under AB 68, municipalities are required to approve:
- For single-family lots: One ADU (attached or detached) up to 1200 sq ft and one JADU up to 500 sq ft.
- For multi-family lots: Multiple ADUs attached to the existing multifamily structures and two detached ADUs.
Types of ADUs
These are some of the different types of ADUs.
- Accessory Dwelling Unit (ADU): Any attached or detached residential dwelling unit providing independent living facilities on a lot that already has a primary residence.
- Detached ADU: An ADU that is separated from the primary structure.
- Attached ADU: An ADU attached to the primary structure.
- Converted Existing Space aka Converted ADUs: Space already on the lot converted to an independent living unit, such as a garage conversion or storage shed converted to an ADU.
- Junior Accessory Dwelling Unit (JADU): An ADU of no more than 500 square feet, created by converting existing space within the single-family residence. Space cannot be created by converting a garage or utility building.
An Interesting Rule About Detached ADUs
In California, if you convert an existing structure, like a barn, storage shed, or garage, there is no size restriction. However, you may be required to pay fees if the ADU is larger than your primary residence. In practice, you could convert a 2500 square foot barn into an ADU.
Best Size for ADUs in California
An ADU just smaller than 750 sq ft is the best size to build in California.
The reasons for selecting this number are myriad, but these are the main reason is ADUs below 750 square feet are exempt from impact fees.
California ADU law states that impact fees should be charged “proportionally in relation to the square footage of the ADU to the square footage of the primary dwelling unit” for any ADU over 750 square feet. In all cases, the impact fee for the ADU must be less than the fee for the primary dwelling on the lot.
As a result, some of the most popular ADU floor plans are less than 750 square feet.
Summary of ADUs in California
These are the main types of ADUs in Sacramento and California.
1. Detached ADU
A detached ADU can be a newly built construction, a container home, a backyard cottage, or other small building. California allows up to 1200 square feet, with 4-foot setbacks, due to new regulations passed in 2023.
2. Attached ADU
Attached ADUs are usually garage conversions or basement apartments. They cannot exceed 50% of the square footage of the main dwelling and cannot exceed the height of the primary house.
3. Conversion ADU
A conversion ADU is created from an existing structure, such as a garage, shed, barn, or attic, and they have no maximum size limit if the structure already exists. If the structure is converted to a Junior ADU, it must be no more than 500 square feet and attached to the main house.
4. Internal ADU
Internal ADUs can sometimes be a Conversion ADU. An Internal ADU is part of the main dwelling that is partitioned off to become it’s own dwelling space. It can be an attic, basement, part of a floor, or an entire floor. These generally have fewer regulations than external ADUs.
Make the Most of Space in Your ADU
No matter how big or small your ADU is, you can make the most of the space by planning ahead.
1. Use Windows to Your Advantage
Windows are a vital component in making your ADU feel like home. In addition to bringing in light, providing ventilation, and creating a bright illuminated space, they can be energy efficient, helping you save money on electricity bills.
2. Plan Ahead for Storage Space
With any living space, storage is a priority. In an ADU, even more so than normal. Plan out how you will use cabinets, drawers, shelves, closets, entertainment centers, and any other storage capacity.
3. Declutter on a Regular Basis
To keep your ADU looking spacious and tidy, regularly declutter your space. Minimizing the items you collect and using storage effectively will help you keep your living area clean and organized.
Need an ADU for Your Sacramento or Roseville Property?
If you’re a homeowner in the Sacramento region and you need an ADU, room addition, or garage conversion, give our team a call at (916) 862-1444. Our experienced Sacramento remodeling company has helped hundreds of homeowners with kitchen renovations, bathroom remodeling, and general contracting.
ADUs can help you increase the value of your property, and give you more room for family members and guests. We can work with you through every step of the process, from planning to completed construction.
Call Sacramento Remodeling Group at (916) 862-1444 for your Free Consultation with an AD Building expert, or fill out our contact form.
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