Don't Forget the Green Benefits of Accessory Dwelling Units

Margaret Morales details an under-appreciated benefit of Accessory Dwelling Units (which are sometimes known by other names, like garden suites, mother-in-law apartments, backyard cottages, or casitas). Accessory dwelling units (ADUs), argues Morales, "are a tool in the fight against climate change."

While ADUs have been commonly touted as a tool for easing the housing affordability crisis in many cities—not to mention the entire state of California, which approved ADU-enabling legislation last year—the green building angle inherent in ADU construction isn't as frequently cited.

According to Morales, "the compact size of these unassuming homes makes them remarkably energy efficient, cutting lifetime CO2 emissions by as much as 40 percent as compared with medium sized single-family homes." Moreover, "[t]hat’s far beyond the benefits of almost any other green building practice, including using green building materials, state of the art insulation, and best practices in building material waste disposal."

Morales is citing data from a 2010 Oregon Department of Environmental Quality report, which "found that a typically sized new single-family home (defined as about 2,300 square feet) built to industry standards uses nearly 60 percent more energy than a home approximately half its size [pdf[ over the course of an average 70-year home lifespan, from construction to demolition."

Morales cites all these green reasons to support and enable ADU construction as an appeal to cities and communities in the Pacific Northwest. Supply of ADUs is limited in cities like Seattle, due to regulatory hurdles, according to Morales, despite increasing interest in the option.