In most cities, adding a second house to a single-family lot would be illegal or would set off an epic battle with the neighbors that could drag on for years. But not in Portland, Ore.

There, this kind of housing — referred to officially as “accessory dwelling units,” but better known as granny flats, garage apartments or alley houses — is being welcomed and even encouraged, thanks to friendly zoning laws. And additional living spaces are springing up everywhere, providing affordable housing without changing the feeling or texture of established neighborhoods the way high-rise developments can.

In the southeastern part of town, Jen Wantland, 40, and Bryan Scott, 37, converted their two-car garage into a 480-square-foot home using mostly salvaged materials, for about $60,000. Then they moved in and rented out their four-bedroom house, which more than covers their living expenses. They’re delighted to talk about how fabulous downsizing feels and how it allows them to work less and play more.

Stephanie and Sam Dyer, who are both 34 and live in the coveted Boise neighborhood, built a 342-square-foot version of their bungalow so their parents could have somewhere to stay when they visit. The rest of the time, the couple have been steadily recouping their $110,000 investment by renting out the little house through sites like Airbnb and VRBO.