Seattle Sets a New Standard for Residential Zoning

Seattle has approved a landmark law that would both allow the developments of accessory dwelling units and limit the size of single-family residential projects. Planetizen referred to the law in May as ADUs for mansionization control, and a "two-birds-with-one stone" situation.

Dan Bertolet and Margaret Morales broke the news shortly after the Seattle City Council unanimously approved the law yesterday, and provide the context to appreciate the scope of Seattle's legislative accomplishment for the potential of adding new residential density to the city:

The adopted changes amount to the most progressive ADU policy in the US. By boosting the addition of ADU homes in the three-quarters of Seattle’s residential land reserved for expensive, single-detached houses, the new rules will lower the invisible walls of economic exclusion, and make the city greener too. 

Bertolet and Morales also describe the effect of the law at the other end of the spectrum:

The legislation’s house size limit of 2,500 square feet on a typical lot will make it more attractive to add ADUs to existing houses instead of tearing those houses down. And when teardowns inevitably occur—as they already do under the status quo—the size cap will provide a new incentive to build ADUs along with the new house. Neighborhoods will see fewer teardowns replaced by McMansions and more modest, mixed-income options. 

The article also details the political process that yielded the final law, which includes last-minute deal making and a four-year build up. The article also expresses support for the new law, listing the potential affordability and environmental benefits of the additional density enabled by the law. Despite calling the new law "the best" ADUs regulations in the country, Bertolet and Morales still share a few tweaks that could make the law "even better."

The news from Seattle comes shortly after Oregon passed landmark legislation that ends single-family zoning in most cities in the state, allowing duplexes, triplexes, and fourplexes for all properties zoned for single-family residential in cities over 25,000.