A new book suggests Accessory Dwelling Units – ADUs – are going to become more common in the United States:

Eight years later, Peterson works full-time helping others build ADUs, preaching the granny-flat gospel via classes for other Portland homeowners. The number of ADU permits the city issues has risen dramatically; in 2016, it was 615. In Vancouver, Canada—an ADU pioneer—more than 2,000 ADUs have been built citywide in the last decade. But for most cities in North America, steep legal barriers are preventing this form of housing from taking off: Many cities ban them outright, and those that don’t often have severe restrictions on size, owner occupancy, and parking. Only a handful of cities have adjusted their regulations to encourage more ADUs—mostly on the West coast, where severe housing affordability is a growing problem. But Peterson and other ADU advocates are predicting that the country is on the verge of welcoming more of them.

And a short portion from the interview with Peterson regarding the benefits of ADUs:

ADUs allow people housing flexibility over time. You can design an ADU in which to age in place, and then rent out your main house, allowing you to stay in your neighborhood as you grow older, and at less cost. Parents, caregivers, or adult children can also live in ADUs.

ADUs use fewer resources like gas and electricity due to their size, and because they’re often built in walkable and bikeable areas, their residents generate less of an environmental impact that way as well. They also reduce the per capita residential footprint. This is important because there are a lot of one- and two-person households in cities, but not the housing to match that demographic. ADUs can help fill this need.

And ADUs generally don’t have a significant infrastructural impact on a city, in contrast to, say, a 400-unit apartment building. They bring more housing to an area organically, and the city doesn’t have to build new infrastructure to accommodate it.

If these do catch on, in which neighborhoods would be become most popular? I would guess they would be most attractive in working-class and up-and-coming neighborhoods where homeowners are looking to generate extra income and where they are more open to having close neighbors. In contrast, I think it would be more difficult for these to catch on in wealthier neighborhoods. After all, don’t Americans tend to think that one of the benefits of having a larger and more expensive home is the ability to be separate from other people?