For projects with a detached accessory dwelling unit (ADU), also known as "in-law flats", how should the HSA be calculated? Should the multi-family home size adjuster be used? Does the answer change if the ADU shares systems with the main house?
Detached accessory dwelling units may be treated in one of two ways: 1) as a separate certification. In this case, the ADU will complete a separate checklist and have a home size adjuster based on the details of that unit. 2) as part of the main home. In this case, the conditioned square footage and bedrooms in the ADU should be added to the main home for the purposes of the home size adjuster, and the spaces should be included together in one energy model. The multi-family home size adjuster should not be used.
Project teams and Green Raters/Providers are given discretion about which approach to take. In cases where mechanical systems are shared, option #2 is strongly recommended but not mandated.
Ruling updated 9/5/17 for rating system version applicability.