Size is one of those things that can be measured but is still very subjective. A child might think their teacher is tall, even though he’s only 5 feet 6 inches, while Manute Bol might think someone who stands 6’6: is short. The size of back yard cottages or laneway housing can determine their acceptance or rejection in single family neighborhoods—but, again, size is in the eye of the beholder.

Height, bulk, and scale of buildings can make or break a project or proposal. But, when does a building get too tall or too bulky? When does a house become a McMansion? What factor decides whether my neighbor and I can agree on a house that’s just right? What size is right depends on who you talk to.

So, to help us decide the right size for new housing options, the most important questions to ask focus on the outcomes we want—for families, neighborhoods, the environment.

  • There seems to be some consensus that backyard cottages are a good idea. In hours of discussion on laneway housing (called backyard cottages or detached accessory dwelling units—DADUs—in the US) in Vancouver and at the most recent hearing about it in Seattle, most of those who testified spoke in favor and cited affordability, flexibility as the main reasons cottages make sense. Cottages combine easy access for an aging family member with cost-savings, independence, and privacy, for example.

    Portland has again demonstrated its progressive mindset in this area. Unlike Seattle, Portland has allowed detached accessory dwelling units for years in all parts of the city. Seattle, on the other hand, is proposing a rather modest 50 DADUs beginning sometime in the next year, in addition to the less than 2 dozen built under a pilot program started a few years ago.

    Portland is also decoupling the size of the DADU from the size of the existing home. According to Eric Engstrom, Principal Planner at the Bureau of Planning and Sustainability, this limitation would often require home owners to seek variances from the code because they could only build a DADU 1/3 the size of the existing house. This just isn’t big enough to make many projects worth doing. The Portland planning commission is considering a recommendation that would simply limit all DADUs to 800 square feet. Vancouver allows 750, and Seattle’s proposal is currently at 800 square feet as well.

    But some Seattle city councilmembers expressed concerns about the size of cottages at the recent hearing. Sally Clark, the chair of the Council’s land use committee felt that the height, massing, and size of the cottages were bigger than anticipated, maybe too big. However, the Seattle planning commission has wisely recommended keeping the cottage proposal at 800 square feet and removing the limit on permits. So while Portland is moving toward bigger, Seattle is considering going smaller. Again, the subjective nature of size makes this a tricky political issue. Some neighbors wouldn’t be pleased with a cottage even it was Lilliputian. How can policy makers make find a middle ground?

    One option would be to try and outsmart themselves by developing yet another seemingly objective formula of height bulk and scale like the one proposed by architect Seymour Auerbach, called the Bulk Factor. The Bulk Factor is an invention that Auerbach suggests would get around the problem of personal taste or fears of overbuilding.  The Bulk Factor establish a ratio of volume to lot size to determine how big new buildings should be. This approach would establish the appropriate ratio based on a comparison with existing buildings. Auerbach’s Bulk Factor would create regulation based on the ratio to limit the size of DADUs. I think this would just lead to yet another formula, like the one Portland is dispensing with, that would stymie good projects.  

    Size Matters Bulk Factor

    How about a solution that is more performance-based, like the standard that Jason McLennan of the Cascadia Green Building Council suggests?

    In the natural world, it is commonly understood that are limits to the density of any one species on a given area of land. These limits are never hard and fast rules, but are based on the carrying capacity of the land that varies through time and location. Too many of one animal in any one place results in less than ideal conditions for the whole. There are limits, but we believe our cleverness removes these rule on our behalf.

    Now, McLennan is writing about the ‘sweet spot’ of mixed use buildings, which he places at 4 to 8 stories and densities of 30 to 100 dwelling units per acre.

    Size Matters alt Sweet Spot

    McLennan’s excellent article, Density and Sustainability, is focused on a different type of development, but his point applies to cottages too. Building tall doesn’t automatically lead to sustainability. But McLennan’s fundamental performance-based question, “what building heights and urban densities result in the maximum benefits to culture, society and the environment?” is the right one to be asking when the size question comes up. True, culture, society and environment are pretty slippery terms, but a community could reach consensus on public benefits like access for families, and affordability. Hearing real people talk about the positive difference right sized backyard cottages would make for elderly family members or young families just starting out is convincing.

    It is much easier for bureaucrats to administer a formula like the Bulk Factor. But looking for solutions that focus on outcomes makes more sense. One case study that is worth reading was put together by a team at Weber Thompson architects who created a site plan for Fairhaven Heights in Bellingham that all at once reduced the footprint of a proposed development, increased protections for critical areas, increased density and avoided height increases.

    Size Matters Fairhaven Different Format.png

    The newer proposal for Fairhaven Heights kept the same number of units, 739, and created a smaller foot print without increasing height. This was largely accomplished by reducing th
    e number of detached single family units.

    Size matters, but so does context. It’s our job to ask first what outcomes we want from rules governing land use.

    Thanks to Joshua Curtis of the Seattle Great City Initiative and to Weber Thompson for background on Fairhaven Heights.