Photo by atomicShed on Flickr.

Washington, DC may adopt a “Green Area Ratio” requirement for multi-family and commercial buildings in its new zoning code. It’s an attempt to promote sustainable practices in large projects, but its ultimate effect might just be to make environmentally friendly urban living more expensive with limited actual benefits.

The newly-released draft of the zoning code contains very promising changes, like reducing parking requirements and allowing homes on narrow alley streets after a decades-long ban.

It also introduces “Green area Ratio,” modeled on similar laws in European cities such as Berlin and Malmö. Seattle has already implemented a version of the same idea, called the “Green Factor,” 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.

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 bioswales and rain gardens, as useful as these may be, but window boxes, hanging pots, climbing vines and clay urns:

Eguisheim, Alsace, France. Image by Ela2007 on Flickr.

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.

Cross-posted at Old Urbanist.