What are the different types of ADUs?

The specific type of ADU that can be built depends heavily on local regulations, lot size, and homeowner preferences. Some common types of ADUs include attached or detached structures, basement, attic, or garage conversions, junior ADUs, and SB-9 property lot splits.

ADU construction in California with architect and contractor reviewing building plans

Detached ADU: Standalone Independence

Detached ADUs are freestanding structures separate from the primary residence. They offer the greatest degree of privacy and independence, essentially functioning as miniature houses.

Advantages: Increased privacy, potential for larger size, clear separation from the main residence.
Considerations: Higher construction costs due to foundation, utilities, and separate building envelope. Zoning regulations regarding setbacks and lot coverage can be restrictive.
Location: Often situated in backyards or side yards.
Example: A small cottage or guest house built behind the main home.

Attached ADU: Seamless Integration

Attached ADUs share a wall with the primary residence, often created by extending the existing structure or converting an attached garage.

Advantages: Lower construction costs compared to detached ADUs, easier access to utilities, and seamless integration with the main house.
Considerations: Requires careful planning to ensure proper soundproofing and privacy for both the main residence and the ADU.
Location: Extensions of the main house, converted attached garages.
Example: An addition to the side of a house with a separate entrance.

Basement ADU: Utilizing Existing Space

Basement ADUs transform underutilized basement space into self-contained living units.

Advantages: Lower construction costs, as the foundation and roof are already in place. Can significantly increase property value.
Considerations: Requires careful attention to waterproofing, ventilation, and natural light. Egress windows and proper ceiling height are essential for safety and code compliance.
Location: Basements of existing homes.
Example: A finished basement with a separate entrance, kitchen, and bathroom.

Garage Conversions: Transforming Functional Space

Garage conversions transform existing garages into ADUs. This is a widespread method, especially in areas with large numbers of homes with garages.

Advantages: Relatively cost-effective, utilizes existing structure, can be completed faster than new construction.
Considerations: Requires addressing insulation, plumbing, electrical, and structural integrity. Significant upgrades are often required to meet habitability standards, and parking issues must be addressed.
Location: Converted garages.
Example: A detached garage transformed into a small apartment.

Junior ADU (JADU): Compact Living

Junior ADUs are smaller ADUs, typically limited to 500 square feet or less. They are often created within the existing footprint of a single-family home.

Advantages: Lower construction costs and a faster permitting process can be created within existing structures.
Considerations: Size limitations, may require shared utilities with the primary residence and often require owner occupancy of either the principal residence or the JADU.
Location: Within existing homes, such as converted bedrooms or small additions.
Example: A converted portion of a house with a kitchenette and bathroom.

Senate Bill 9 (SB-9): California's Density Initiative

California's Senate Bill 9 (SB 9) allows homeowners to split their single-family lots and build up to two primary dwelling units, in addition to one ADU and one JADU, on each resulting lot. This is a significant change to single-family zoning.

Advantages: Increased density, potential for multiple housing units, greater flexibility in land use.
Considerations: Subject to specific requirements regarding lot size, setbacks, and local regulations. Can significantly alter the character of single-family neighborhoods.

Key Considerations

Understanding the different types of ADUs and their associated considerations is essential for homeowners looking to expand their living space and maximize their property's potential. Careful planning, adherence to local regulations, and professional guidance are crucial for a successful ADU project.

Local Zoning Regulations: ADU regulations vary significantly between cities and counties. It is crucial to consult your local planning department for specific requirements.
Building Codes: All ADUs must comply with local building codes, including safety, electrical, plumbing, and structural requirements.
Permitting: Obtaining the necessary permits is essential before starting any ADU construction.

TIP: Use our ADU Equity Growth Calculator to help estimate your property's value increase with an ADU.