It’s Miller Time (Again) (Sorry)

Preamble:  Please believe me when I say that I am not obsessed with David Miller!  I am, however, hopelessly obsessed with the idea that sustainable urbanism is critical to our future.   And while I don’t doubt that Miller is a swell guy and this is nothing personal, in my view he and his cohorts are proliferating misinterpretations that will impede progress toward sustainable urbanism in Seattle.


Thank you David Miller for taking the time to respond to the Q&A, even though this is just some hack’s blog with the word “ass” in its title.   Many of your replies beg for followup, but first I should be a good sport and respond to your questions to me:

1. You obviously want to reduce the amount of SF in Seattle. How much should we have left?

By your definition, none, because I support allowing backyard cottages, a.k.a. DADUs in all single-family zones.  Assuming we’re ignoring DADUs, I cannot give you a precise number, but I assure you I am not calling for anything like the elimination of all single-family zones in Seattle.  I believe there are numerous areas in the city where strategic upzoning of single-family should be done, in particular where it is adjacent to transit corridors or stations, and the Beacon Hill light rail station area is one example.  To throw a number out, within a 10 year time frame, it would probably make sense to upzone something like 10 percent of our single-family zones to multifamily.  Not that radical.

What I am more concerned about than the exact number is the attitude among many in Seattle that single-family zones are untouchably sacred, such that the planning process hits an automatic dead end whenever the possibility of upzoning single-family is merely hinted at.  To most electeds it’s totally radioactive.  And this is the same attitude that you, David, displayed when you twice dodged my question about upzoning single family (#1 and #2).   And so I’ll ask you again:  Would you, or would you not, support any upzoning of single-family zones that are within one-quarter-mile of the Beacon Hill light rail station?  This is the kind of tough decisions elected officials have to make.

2. Given there is no convincing data showing green roof techniques can match the stormwater retention capability of conifers, plus the loss of truly permeable surfaces that inevitably result from upzoning SF to higher densities, how do you expect to upzone SF and avoid environmental damage and massive increases in Seattle’s stormwater treatment requirements? If you’re willing to sacrifice Seattle’s environment for environment elsewhere, that’s a valid answer as long as you also explain how we’ll deal with Endangered Species requirements in our urban watersheds.
3. Given the inevitable increase in stormwater treatment requirements (unless you pull a rabbit out of the hat in #2 and figure out what no stormwater expert in any jurisdiction has been able to answer for me), how will you pay for it in a way that does not hurt affordability.

I believe you are greatly overestimating the role of conifers in single-family zone hydrology.  In my Central Area single-family neighborhood I don’t see many conifers, though I realize they are more common in the north end. But let’s probe a little deeper with some math, shall we?  Tree canopy coverage in single family zones is currently 18 percent.  Assuming the tree type mix is similar to Seattle’s urban forests, conifers would make up about 15 to 20 percent of that 18 percent—or about four percent of the total land area in single-family zones.

But then we also must consider that tree cover in Seattle’s multifamily zones is currently 13 percent, which means you don’t lose all the trees going from single- to multi-family—you would expect lose a little less than a third of them.   Combining with the result above, the conifer tree cover that would be lost with a complete conversion of single-family to multifamily would be equivalent to roughly one percent of the total single-family land area.

Of course, a full zoning conversion like that will never happen—if there was a ten percent conversion as I proposed above, the conifer cover lost would on the order of a mere 0.1 percent of all single-family land.* It’s hard to imagine how that would result in a stormwater catastrophe.

Important aside: None of this is to say that urban trees don’t matter, or that conifers are not a valuable asset.  The point is we need reality-based policy.

I’ll venture to guess that the most common land cover in single-family zones is turf grass lawns, which have stormwater retention capacity significantly lower than that of conifers, and thus would be more easily replaced functionally by green roofs. And furthermore, green roofs are not the only available approach—there are many other strategies, including swales, rain gardens, rainwater harvesting, and pervious pavement. Seattle Public Utilities has been experimenting quite successfully with many of these techniques (pdf), and found them to be both effective and economical.

But listen:  I believe the answers to all of your concerns in #2 and #3 can be found in an existing multifamily development right here in Seattle:  High Point.  This development has roughly three times the density of a typical single-family neighborhood, and has a natural drainage system that eliminates runoff to the Seattle stormwater system (in all but the most extreme conditions).  And since it all drains to Longfellow Creek—a salmon-bearing stream and one of Seattle’s priority watersheds—I think it is safe to assume that it is in compliance with the Endangered Species Act.  The development also happens to provide affordable housing.

To be fair, it would be difficult to retrofit an existing neighborhood with a large-scale natural drainage system like the one at a High Point.   But on my reckoning, projects like High Point clearly demonstrate that we have the technology to economically offset the loss of pervious surface that would occur with modest single-family upzones.

(Do I even need to mention that Seattle isn’t the end of the story, that if Seattle loses 10 trees to save 100 on the urban fringe, then the region—and therefore all of us—benefit in the long run?  No, I didn’t think so.)

4. Do you agree we need to increase our urban tree canopy to 30%? If so, how would you accomplish this in a city that you believe should become more dense? Bonus points for addressing the conifers versus deciduous tree problem in your answer.

I’ll give you the answer you want:  infill in existing multifamily zones.  Did I get it?

I’m all for more trees.  But while it is true that single-family zoned land represents the biggest opportunity for increasing tree canopy in Seattle, that does not justify a moratorium on single-family upzones, as you would seem to believe.  The benefits of trees  must be measured against the benefits of density.   And there are all kinds of possibilities for increasing tree canopy in areas other than single-family if we try a little harder.  We all love trees, but policy must be based on rational, big picture assessments, not on myopic fancy.

Bonus: Deciduous are the ones that the leaves fall off of, right?  Or is it the other way around?  All I know for sure is we’ve got a deciduous conifer growing right in our traffic circle.


*This is a very loose calculation and is only meant to be an order of magnitude approximation.  The assumption that conifer cover in single-family is similar to urban forests overall is probably generous.  On the other hand, because conifers are so big they are less likely to thrive in multi-family than in single-family.