Accessory Dwelling Units as Mansionization Control

Sarah Anne Lloyd reports on Seattle's efforts to tweak its ADU laws to make the buildings, also known as mother-in-law units or granny flats, to reduce the prevalence of McMansions.

Legislation that would reform ADU regulations is still taking shape, but some councilmembers are pushing for a version of reform that would reduce floor-area ratio (FAR) as a method to reduce the incentives for building large, bulky mansions on single-family lots.

Lloyd explains:

Single-family zoning in Seattle is currently extremely permissive. While it has height limits (25 to 30 feet), there’s no limit to FAR, as long as the giant home that results is only one home. This is how you get giant, out-of-scale houses in single-family neighborhoods: They’re built to maximize square footage under height limits.

The ADU legislation, in an effort to incentivize both building new homes and keeping older homes around, would set an FAR limit at 0.5 for the main home on a single-family lot, whether the home has ADUs or not.

ADU legislation has been in the works in Seattle for years now, so it might still be some time before the City Council produces a final action. ADUs were intended as a key component of affordability measures recommended by the city's Housing Affordability and Livability committee (HALA) in 2015.