Does a guest house or garage apartment count as square footage?
Published August 27, 2026
No, not as part of the house. A guest house, casita, or apartment over a detached garage is a separate structure under ANSI Z765. Its finished area is measured and reported on its own line, never added to the main house's gross living area. If the garage is attached and the apartment is reached through finished space in the house, it is a bonus room and can count.
How it is valued
As an accessory building or unit, based on what buyers in the market pay for one, not on a per-square-foot GLA rate. A 600 sq ft casita with a kitchen and bath can add far more than 600 sq ft of GLA would; it just shows up on a different line. If it has its own kitchen and entrance, it is really an ADU, and the same reporting applies.