Dan Bertolet writes for the Sightline Institute on a certain kind of density infill.  We call these “basement suites”, “granny flats” and “laneway houses”.


ADUs are relatively modest apartments or cottages integrated into single-family properties, and they come in two flavors: physically attached to the main house (AADU), or detached in a structure separate from the single-family house on the same lot (DADU). Most fall in the moderate affordability range—$1,200 to $1,800 per month for a one-bedroom unit in Seattle—and offer a housing option in single-family neighborhoods for residents who cannot afford a single-family house.

Known as “granny flats” for a reason, ADUs work well for multigenerational families. And they are particularly well-suited for young children, because they tend to be relatively large (at least for a rental), provide direct access to outdoor yards, and are often located in neighborhoods well served with schools and parks.


And why does Vancouver have lots of these type of dwellings?  What does the rest of Cascadia need to do?

Myriad regulatory barriers currently litter the law books of Cascadian cities, clogging the ADU pipeline. Vancouver’s success in building more than 26,000 ADUs has been all about undoing those restrictions. Starting in the late 1980s, the city legalized thousands of existing, but illegal, ADUs. Over time, it eliminated the most counterproductive barriers. Vancouver, unlike many Cascadian cities:

  • does not require an off-street parking spot for each ADU
  • does not require the owner to live on site
  • allows single-family lots to host both an AADU and a DADU
  • awards additional occupancy limits for each dwelling on a property, and
  • provides great latitude to property owners in terms of size, height, and placement of each ADU.