The five main ADU types — and which one suits your property.

Market
Written by AB

Most homeowners begin with one question: "Can I add an apartment?"


A better question is:
"Which type of ADU best fits my property?"

There are five common ADU types to consider.

  • 1.Internal ADU. Built within the existing home. Feasible if the house has enough legal floor area, proper access, and a layout that allows the new unit to be separated from the main living space.

  • 2.Basement or cellar ADU. Appealing because the space already exists, but it must meet strict safety standards. Under NYC's Appendix U, basement and cellar ADUs need a minimum clear ceiling height of 7 feet in habitable rooms — plus requirements for light, air, egress, and fire separation.

  • 3.Garage conversion. Sounds straightforward — but you need to confirm whether the garage is detached, attached, located in the rear yard, shared with a neighbor, or integrated into the main structure.

  • 4.Attached addition. Expands the existing house.

  • 5.Detached backyard ADU. Typically depends on lot depth, rear-yard requirements, access, and separation from the main house.

Don't get attached to one ADU idea too early. First, determine which type your property can realistically support.

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