Consider the backyard housing situation in Vancouver, B.C. and Seattle. 

In Vancouver, detached accessory dwelling units (DADUs, or backyard cottages) number about 10,000. Here in Seattle, there are only a couple of hundred. 

And it's a bit of a mystery why. After all, the basic zoning laws around DADUs are similar in both Vancouver and Seattle. Since 2009, they've been allowed in single-family zones across the city; prior to that, under a 2006 pilot program, they were only allowed in Southeast Seattle. In Vancouver, homeowners are allowed to build one DADU and one attached accessory dwelling unit (AKA a mother-in-law apartment) in their backyards. 

But there are differences that could help explain why DADUs are so much less common here. Last year, Sightline created a ranking system based on regulations on ADUs in cities across the Northwest, and rated each city by "ADU-friendliness." Vancouver scored 96, the highest in the region; Seattle scored 58, just above Eugene, OR (56) and on par with Meridian, ID.  

Among the differences between Seattle and Vancouver, according to Sightline's data, are: The fact that Seattle requires one parking space per unit (Vancouver has no minimum parking requirement); the fact that the property owner has to live on-site in Seattle, making it harder for homeowners to secure financing for a second dwelling unit (in Vancouver, the landowner can live elsewhere); the fact that Vancouver allows DADUs on much smaller lots than Seattle, where lots must be larger than 4,000 square feet; and the fact that in Seattle, unlike Vancouver, ADUs are considered part of the main house, and must share total occupancy limits (a maximum of eight unrelated people) with the main house, which can restrict their affordability and desirability.

City council land use chair Mike O'Brien says there are other factors at play as well—factors he hopes to alleviate when the city adopts a new resolution asking the city's Department of Planning and Development to put DADUs on its work plan next month. First, he says, "we can come up with a streamlined permitting process" at DPD.

Second, and more intriguingly, O'Brien says "we can maybe even have some designs that are preapproved," a list of banks that will fund DADUs, "and some prefab options. Imagine that you could go to DPD, pick up a flier" and choose an inexpensive prefab backyard cottage design that the city has already okayed, "and you can have it in six weeks." 

"When I talk to a lot of people that own single-family homes throughout Seattle, people say, I would love to do that if you make it easier for me."

Lots of local architecture firms have already done mockups of prefab backyard cottages for Seattle single-family homes.

Here's one, which Seattle's CAST architecture mocked up back in 2009:

Another, from Seattle's GroupArchitect

And another, by Paul Michael Davis Designs

 

Although we told O'Brien we thought the idea of prefab cottages seemed a bit "fantastical," the more we see the designs architects are already doing (most of them cheap compared to conventional building methods), the more we think that if Seattle can tweak its rules to allow homeowners to add this low-density pro-density option, the more we'll see them sprouting up in backyards around the city in the future.

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