Backyard cottages are being built far beyond Portland’s hipstervilles.

Almost every Portland neighborhood that has single-family homes has added one or more “accessory dwelling units,” as the city calls them, in the last 16 years. The above map, prepared last week by the Portland Bureau of Planning and Sustainability, shows us where they are.

Some neighborhoods, like Woodlawn and Concordia in the northeast, average about one ADU per block.

But some are everywhere. Parkrose Heights also has five of the little homes. Maplewood has 14. Powellhurst-Gilbert, in the far southeast, has 30.

An ADU at SE 136th Avenue and Rhone Street. Image: Google Street View.

The 1,599 new homes mapped above are, of course, tiny additions to a city that has added 30,000 households since 2000 — only enough for nine months’ worth of population growth over 15 years, even if every one of them were being offered as long-term housing.

And in Portland, ADUs top out at 800 square feet, so some households might not find them large enough for their needs.

But these homes do share one thing: They reduced the city’s housing shortage without creating new sprawl and without significantly altering their neighborhoods.

Many of these homes were possible because Portland doesn’t require ADUs to have on-site parking spaces — a 2014 survey found that ADU tenants are significantly less likely to own cars than tenants in full-size homes — and because in 2010, the city started waiving ADU development fees in an effort to encourage their construction.

It worked.

Data: Portland Bureau of Planning and Sustainability. Some ADUs are built without permits, and some permitted ADUs are never built.

The development fee exemption, worth $12,000 to $20,000 per home as of last year, is set to expire in July 2018. And though that’d make ADU building less financially viable, the city does theoretically have room for a huge number of the units: an analysis from Portland State University’s Institute for Sustainable Solutions found that 70,863 home lots are “prime” ADU candidates.

Portland currently allows one ADU per lot, maximum, and forbids them on most lots with duplexes. After Portland fully approves its Residential Infill Project, an ongoing code reform whose broad outlines were approved last fall by the city council, at least some parts of the city will be allowed to have a second ADU per lot: one attached (or interior) and one detached. Duplexes could also have one on-site ADU.

Image: Courtney Ferris.

It’s not yet clear, though, where exactly those extra ADUs will be allowed. Some are urging it to be an option only within a block or two of a frequent transit line; others say any neighborhood should have the option to add so-called “gentle infill,” which was banned in 1959.

The city is currently writing the code that’ll settle this question, among others, and expects to make a draft public later this year. You can follow the process by subscribing to Portland for Everyone’s campaign updates.

Update Aug. 2018: An earlier version of this article gave the wrong year for the start of Portland’s ADU fee wavier.

Portland for Everyone supports abundant, diverse, affordable housing. This is a reported blog about how to get more of those things. You can follow it on Twitter and Facebook or get new posts by email a few times each month.