San Francisco leadership is supporting the growth of accessory dwelling units (ADUs) to solve for the city's housing affordability challenges. The major issue so far happens to be zoning, which has been evolving and could be creating a model for the rest of the country to take notes on.

Despite its place as the proverbial battleground between pro-development YIMBYs and anti-development NIMBYs, the literal backyard is, increasingly, common ground.

For many years, backyard cottages — also known as granny flats, mother-in-law suites or accessory dwelling units (ADUs) — were treated as nuisance uses, outlawed in urban and suburban zoning codes around the country. But as affordable housing becomes ever more scarce, cities are beginning to look at liberalizing rules for building ADUs, as a way of adding cheaper, more diffuse housing supply in tight markets.

San Francisco passed a local ordinance in 2014 that allowed owners to legalize one accessory unit per residential lot. The practice of converting garages or basements into rentable units was already common despite being illegal, the planning department acknowledged at the time. A few years later, the city created a neighborhood pilot program to legalize and streamline the construction of new ADUs — including backyard cottages as well as converted garages or basements. The program later became citywide, and was followed up with statewide laws aimed at achieving the same ends.

This year, San Francisco earned a National Planning Achievement Award for its efforts around ADUs. In the award announcement, the American Planning Association noted that ADUs in San Francisco generally cost less than $150,000 to construct, and typically rent for about a third of the rate of units in other types of new development.

Gina Simi, the communications manager for the San Francisco Planning Department, confirms via email that there are currently around 1,200 ADUs in the construction pipeline. Since they’re permitted in all residential zoning districts, the proposed ADUs are spread around the city and don’t seem to be clustering in any particular neighborhood, Simi says. According to the planning department, 685 permits have been submitted to legalize pre-existing ADUs so far, and 166 units have been legalized.

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