ADU Education

What's an ADU?

An Accessory Dwelling Unit is a secondary home on the same lot as a primary residence. Here are the most common types you'll encounter.

Detached ADU - standalone backyard cottage

Detached ADU

Also known as: Backyard Cottage, Granny Flat, Casita

A standalone structure separate from the main house, typically built in the backyard with its own entrance and utilities.

Best For

  • Maximum privacy for occupants
  • Rental income potential
  • Lots with adequate backyard space

Common Constraints

  • Often requires setback from property lines
  • Typically has height limits (varies by municipality)
  • May require separate utility connections
Attached ADU - addition connected to main house

Attached ADU

Also known as: Addition, Attached Suite, Bump-out

A new living space added directly onto the existing home, sharing at least one wall with the primary residence.

Best For

  • Aging family members who want proximity
  • Smaller lots with limited yard space
  • Shared utility efficiency

Common Constraints

  • Must often maintain architectural harmony
  • Setback requirements still typically apply
  • Fire separation requirements vary by code
Garage conversion ADU

Garage Conversion

Also known as: Garottage, Converted Garage

Converting an existing garage (attached or detached) into a livable dwelling unit with bedroom, kitchen, and bath.

Best For

  • Faster, often lower-cost conversion
  • Existing structure reduces new construction
  • Properties with street parking alternatives

Common Constraints

  • May require replacement parking in some areas
  • Foundation & ceiling height must meet code
  • Insulation and egress upgrades often needed
Basement conversion ADU - finished lower level living space

Basement Conversion

Also known as: Basement ADU, Lower-level Unit

Converting existing basement space into a separate dwelling unit, often with a separate exterior entrance.

Best For

  • Homes with existing full basements
  • No yard space impact
  • Natural temperature regulation

Common Constraints

  • Ceiling height minimums (often 7'–7'6")
  • Egress window requirements for bedrooms
  • Moisture and waterproofing considerations
Above-garage or attic ADU

Above-Garage / Attic

Also known as: Carriage House, Over-garage Suite

A unit built above an existing or new garage, or a conversion of attic space into a separate dwelling.

Best For

  • Preserving yard/ground space
  • Added privacy with separate entrance
  • Properties with tall garage structures

Common Constraints

  • Height limits may restrict feasibility
  • Structural support upgrades often required
  • Stairway access and fire egress codes apply
Internal ADU - converted interior space

Internal ADU

Also known as: In-law Suite, Junior ADU, JADU

A conversion of existing interior space (spare rooms, unused area) within the home's current footprint into a separate unit.

Best For

  • Lowest construction cost option
  • No exterior changes required
  • Homes with underutilized square footage

Common Constraints

  • May require separate exterior entrance
  • Kitchen requirements vary (efficiency vs. full)
  • Shared or separate utilities depending on code
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