Monday, February 13, 2012

Greening the DC Zoning Code?

The newly released draft of Washington DC's zoning code, as reported by Greater Greater Washington, contains promising changes, including reduced parking requirements and the allowance, after a decades-long ban, of homes on alleys.  Also new to the code is the proposed "Green Area Ratio," a regulation that is molded on similar laws found in European cities such as Berlin and Malmo.  A version of the same idea, the so-called "Green Factor," has already been implemented in Seattle, where it has drawn praise and some criticism

The basic idea of the GAR is this: in order to address a perceived imbalance of paved/built to green space in urban areas, the zoning code must mandate dedicating a certain proportion of each lot to landscaping or permeable surfaces.

 According to its proponents, the GAR will push buildings to better treat stormwater, improve air quality and reduce urban "heat islands." However, the draft regulations do not appear to contain any standards to determine whether landscaping elements actually aid in stormwater retention or treatment. Nor is there information about whether the estimated benefits are large enough to matter regionally or city-wide.

Existing research also raises potential concerns that nobody will monitor the environmental performance of these features once built. George Washington University professor Melissa Keeley, whose work the draft documents cite, sounds a cautionary note about "policy deficits and the lack of adequate outcome monitoring" in her 2011 study of Berlin's green ratio.

Some of the benefits seem questionable, like the statistic that "1,000 square feet of green roof can supply 110 people with oxygen." While this is beneficial, that the carbon monoxide-emitting motor vehicle creates much more pollution in urban areas than the lack of landscaped surface.

Berlin's air quality, which some sources estimate is the cleanest in Europe, largely owes its success to car restriction zones and policies that encourage traveling by foot, bicycle and mass transit. Cities are unlikely to substantially improve air quality without confronting the role of the car.

Additionally, GAR does not appear to distinguish between non-green ground coverage. An asphalt-covered surface parking and a 10-story apartment building with no parking and which covers its entire lot both receive a GAR of zero. On the other hand, it appears that the same apartment building with a 160-car garage but with a green roof could earn a high GAR.

The most notable element of the GAR is, perhaps, what it does not include. Single-family homes receive a special exemption from the proposed regulations because, the hearing report states:
Implementing this standard would impose an undue financial and logistical burden upon homeowners. Properties with one-family dwellings typically maintain higher standards of landscaping and retain more green area.
Imposing expensive mandates on multifamily housing while exempting single-family homes from regulation creates a perverse outcome in which dense, space-efficient housing suffers penalties for being environmentally unfriendly, while low-density homes occupying a small portion of their lot enjoy rewards for "retaining more green area." While the GAR is compatible with high density urbanism, regulations which apply differently to various densities can make some types of housing more expensive, especially small apartment buildings.

The proponents of the New Urbanism, meanwhile, have been working to address stormwater management from an unapologetically pro-urban perspective, recently engaging the EPA in a discussion over existing stormwater standards that may inadvertently penalize density and enourage sprawling development.   Laurence Aurbach's article Dense and Beautiful Stormwater Management discusses these issues in depth, suggesting that planners and regulators accept density as a best management practice for stormwater.

Ultimately, certain landscape elements, green roofs and other innovations may have an important role to play in Washington, but residents deserve to learn more about the long-term costs and benefits of such a large scale, mandatory and relatively untested regulation before adopting it as part of the zoning overhaul.

In old cities, the highest art is often maximizing visible greenery while minimizing GAR. That creates streetscapes of intense greenery at low cost. The tools of this approach are not swales and rain gardens, as useful as these may be, but window boxes, hanging pots, climbing vines and clay urns:

Eguisheim, Alsace

Taipei, Taiwan.

Cagliari, Sardinia.


  1. When I saw that note about "Green Area Ratio" in the DC planning documents, I nearly went nuts. This is straight up Radiant Garden City nonsense, disguised as "sustainability". How perverse!

  2. ^
    Agreed. Once you strip away all the fancy language, how is this really different from the open space + minimum lot size + berm + setback requirements in so many suburbs?

    We are sooo lost when it comes to "green design." "Greening" a city does not necessitate smearing it over with plant matter AT ALL (though plants are obviously a nice thing to have). Otherwise Siena and Florence would be terribly unsustainable hellholes, which they are not.

    I think Charlie's suggestion for traditional, fine-grained "greening" - individuals embellishing their homes with planters, urns, vines, etc. - makes far more sense and that it even turns out to be more pleasant and endearing in the long run. Another useful tool - porous paving! (Which goes by the traditional names of "bricks" or "cobblestones.") Rather than relying on mandated rainwater-absorption lawns, wouldn't cobblestone streets + plazas-as-parking-lots do a better job of absorbing rainwater than asphalt streets and parking lots? You'd also get the benefit of better speed/traffic control on residential side streets.

    Swales and swathes of lawn are useless in an urban setting - this is just more of the rampant urban ruralization we've been desperately engaging in ever since Olmsted. (Not surprisingly, it hasn't worked.)

    BTW Duany made some great points on the absurdities of urban ruralization well before the LU fad cropped up, even. He cites Portland as a prime example of ruralization gone awry:

    As for the other proposed zoning changes, I think DC is moving in the right direction, though I still think the current revisions are too timid. Why not scrap parking requirements altogether - let the developer respond to perceived market demand and put in as much (or as little) parking as he/she thinks is needed for his/her building to be appropriately saleable/rentable?

    And loosen up on those corner stores already! The many thousands of surviving examples show us that the world will not end if a corner store is open to 10pm!

    Good summary! I think this zoning revision is a good start, but it doesn't go far enough.

  3. BTW: I haven't yet seen a clear answer to this:
    The zoning revisions will allow for the addition of alley houses along some existing alleys, but will it allow for the construction of *new* alleys/narrow streets complete with housing and commerce?

  4. @Marc: I'm afraid I can't clear that up, either. My hunch is that existing street width standards have not changed, though. The basics should not be so difficult to figure out, but with 458 pages just for the first third of the draft, clarity and simplicity were evidently not the primary objectives.

    Also, as far as the "open space + minimum lot size + berm + setback requirements," your point (and Matthew's) are well taken. Introducing greenery as a cure for the perceived ills of the city has been a theme of American urbanism for well over 150 years now. Only the justifications have changed to track the prevailing political climate (e.g. decongestion in the 1930s, "green urbanism" in the 2000s).

    Great presentation by Duany, also. He's not afraid to call Landscape Urbanism (or its antecedents) like they are.

  5. I missed this the first go-around, but this quote from a planning memo helps to show the thinking here:

    "In developing the GAR system, it is generally assumed that the environmental performance of a forested or meadow lot not impacted by human intervention would have the highest possible environmental performance, and an entirely asphalt paved lot would have the lowest. Generally the data shows that lower lot occupancy equates to higher existing GAR."

    That is the opposite of the definition for a "green" city given in, for instance, "Green Metropolis," as GAR does not distinguish between a surface lot and a lot entirely covered by a building. Even LEED, for all its shortcomings, is farther sighted and more holistic than this.

  6. Judging by the posted draft regulations, the purpose of the GAR is primarily aesthetic. It's about promoting a citywide green image rather than achieving measurable environmental performance. Any green planting would qualify for the GAR, whether or not it has any stormwater management function. The GAR could be satisfied by a renewable energy installation, no matter how little energy it actually generates.

    More importantly, the draft GAR lacks the flexibility that is needed to support dense urban development. One presentation says the goal is to eliminate lots that are 100% covered by nonpermeable surface. Buildings with 100% lot coverage will have to install green roofs. Green roofs can be very good, but they are not appropriate, desirable, or feasible for every building that occupies all of its lot. To reduce the heat island effect, "cool roofs" (light-colored roofs) can have equal performance at lower cost.

    The CNU Rainwater-In-Context page has numerous articles and resources that discuss these issues and describe alternative solutions and best practices. See

  7. "In developing the GAR system, it is generally assumed that the environmental performance of a forested or meadow lot not impacted by human intervention would have the highest possible environmental performance, and an entirely asphalt paved lot would have the lowest. Generally the data shows that lower lot occupancy equates to higher existing GAR."

    Unbelievable! So by their logic, it makes sense for DC to raze rowhouse and apartment block neighborhoods for dispersed "cottage homes" (ranch houses) if it wants to become more "sustainable."

    I have less and less patience with the greenies with every passing day. The fact that they talk about "forest" and "meadow" lots shows that they're inappropriately striving to "violate the transect" as a New Urbanist would say, or in other words, to transplant the rural environment and superimpose it on the city to cure its supposed "environmental" ills. Lower lot occupancy = sprawl and bread-and-butter suburbia, *not* an ecotopia! Sheesh!

    Again, I think it'd be easier for DC to reach that vaunted ecotopia status if it worked to remove/narrow asphalt roads and parking lots rather than apparently mandating a reduction in building density. But taming oversized roads/parking lots is a big no-no right now.

    This GAR notion is the result of the kind of destructive thinking you get with hyperspecialists. They only see the world through an extremely narrow, oversimplified, technocratic lens:

    Jane Jacobs, on the other hand, was truly an urban generalist.

  8. I blame politicians more than technocrats. Single family homeowners tend to vote, and aren't fans of taxes/regulations being placed on their home expansion plans.

    Mutltifamily and office buildings, on the other hand, are the purview of developers. And developers, like leprechauns, have an endless supply of hidden gold/ability to shoulder taxes and regulation.

    I'd expect this from suburban nation, but what's surprising to me is that this mindset exists in DC.

  9. It's interesting that they even mentioned oxygen production as a benefit... I don't think there is any less oxygen in cities than elsewhere. I'm pretty sure air quality problems in cities are due to other gases like carbon monoxide, low altitude ozone, nitrous oxides, various particulates, etc.

    @Laurence: interesting point about cool roofs. Would rooftop terraces which often have light coloured wood be considered cool roofs?

    I also wonder how much of an effect painting all our roads white would have on the urban heat island.

  10. @John: I agree with your point – there are hints in the released materials that suggest the planners would have preferred to include single-family homes as well, but that this was not politically feasible, at least at present. The regulatory costs are easier to conceal by pinning them on developers, who will simply pass them on to the buyer.

    @Laurence: thanks for commenting, and for sharing that link. It is great to see CNU again out there in front addressing these critical but overlooked issues like EPA stormwater regulations. I agree with your take on the GAR -- to some extent LEED appears to share many of these same issues, with an emphasis on the installation of visibly "green" features, yet (until recently) little or no monitoring of outcomes. In what circumstances, I wonder, would a green roof be inappropriate or not feasible?

    @Marc: great points! The Seattle Green Factor really emphasizes the transect confusion: there are bonus points awarded for incorporating "food cultivation," and another stated benefit is providing habitat for "birds and beneficial insects."

  11. Unfortunately, today's "green" advocates are motivated by roughly the same notions as the "huge street" advocates of the past. They just have a vague notion that a huge 19th Century Hypertrophic Street/"Green area" would be good for some unexplained reason, and then cast about for silly justifications ("heat islands"/"making U-turns with horsedrawn wagons")

    If this can be tweaked into some meaningful, positive result, it might be to aim for roughly 20% of land surface area as either "private green spaces" (yards, courtyards, gardens, etc.) and "public green spaces" (public parks and gardens). Maybe 10% private+10% public. These are all traditional elements of the Traditional City, all of them Places rather than the "green No-Place" that we suffer from today. Although the classic Italian cities show that you can have a fine result with no greenery at all, I would say that the situation is improved with about 20% (10% public/10% private) Traditional City green Places as described. Actually, it becomes quite difficult to get this if the available area is completely taken by dense private construction, because who wants to tear down high-value buildings to make a public park? So, there is some place here for advance planning of public parks and the like, done in a Traditional City context.

  12. @Nathan: I agree that park space does improve the traditional city, but even 10 percent I think might be higher than necessary. Washington DC, with all its parks and squares, only achieves 3 percent outside the Mall area. I really do think it is how you incorporate it, rather than how much you incorporate, that makes the difference. A city also needs to take into account the cost effectiveness of a park (increase in property values vs. foregone property sales, maintenance, etc.), as I've posted about before.

    Private spaces are another matter, but people do seem to instinctively "green" their surroundings even in the absence of any requirement to do so. The less space one has, the more intensively it can be greened, which I think produces these low-cost riots of vegetation that you sometimes see in traditional urban areas.

    1. Your remarks in the second paragraph makes one consider whether people actually 'internalize' the indirect benefits of 'greenery'. Might it in fact be sometimes the case that the greenery in private spaces provide public benefit to the extent that setting aside land for public parks actually results in a net loss to society? Share your thoughts.

    2. I'm not sure that private greenery alone could ever fully compensate for the absence of parks, which serve a social as well as aesthetic purpose, but it may reduce the need to some extent. Generally, I tend to think the focus on "green" is a bit misplaced. It is effective public space, green or not, that is the most essential.

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