The city’s own form undermines its ability to develop high-performance buildings.
In April, I called Washington, DC, the “quiet capital of sustainable design,” because it has an extraordinarily large number of exemplary green buildings. Per capita, the city has the most LEED-certified buildings and the most Top Ten Award winners from the American Institute of Architects’ Committee on the Environment. In this sense, the District of Columbia is an unparalleled leader in green building.
Yet, the city has achieved these results despite a significant barrier—namely, its own urban plan.
First, the street grid dimensions are huge. A typical block measures a tenth of a mile (526 feet), which is twice the street-to-street distance in Manhattan (264 feet) and among the largest of any American city. The 1791 L’Enfant Plan, famously inspired by Versailles, was always intended as spectacle. According to the critic Lewis Mumford, the original plan’s absurd ratio of open space to usable building lots would be justified only by a population ten times larger than the plan could actually allow. The large block size translates into large floor plates in buildings, which limits the ability of daylight to reach the middle of the building and the ability of people to see out. A University of Oregon study found that 10% of absences in the workplace can be attributed to no views, and quality views can improve office workers’ mental function and memory recall by 25%, according to the US Green Building Council.
Large floor plates are exacerbated by lower floor-to-floor heights. The federal Height of Buildings Act of 1910 mandated a maximum height of 130 feet, based on the width-to-height ratio of the street. As a result, buildings in DC tend to be large in plan but also low in height. Pancake city. New buildings therefore tend to be built with relatively short floor-to-floor heights. The lower the ceiling height, the less space that receives natural light. A window height of 12 feet can daylight a depth of 18-24 feet, while a window height of 7 feet will reach only 12-14 feet. Relying more on natural light than on artificial lighting can significantly reduce energy consumption and therefore utility costs, but it also dramatically improves the health, satisfaction, and performance of workers. So large floor plans and low ceiling heights require more energy and higher electricity costs and hinder wellness and productivity all at once.
The quantity and quality of natural light in buildings also are affected by the shape of Washington’s plan. Optimal solar orientation in buildings places most of the facades toward the south and north, with a slight tilt of up to 15 degrees in one direction or the other. This avoids low sun angles in the morning and afternoon, which can increase heat gain and thermal and visual discomfort. For a recent project, my colleagues and I calculated that turning a building toward the south could by itself reduce energy consumption by nearly 15%. Manhattan’s street grid has long blocks running east/west and short blocks running north/south, which means a large majority of building facades have nearly optimal solar orientation. In the District of Columbia, however, much of the street grid is approximately square, and many of the most prominent boulevards, such Connecticut Avenue, run on a diagonal slightly off the north axis. As a result, a large percentage of buildings, especially on major thoroughfares, face east and west.
Adding up all these challenges, the city’s basic form can deter smarter building. What can be done to alleviate this?
One option is to incentivize subdividing city blocks. For example, CityCenterDC was designed with retail-lined pedestrian alleys that the Washington City Paper has called “the best thing” about the development. Slicing east/west across the block, the mews slim up the buildings and direct the majority of facades south and north.
Raising the allowable building heights in the District would give much greater flexibility with internal floor heights. The National Capital Planning Commission (NCPC) has studied various scenarios, including increasing the maximum height to 200 feet, which could add up to 50% to the allowable space over time. As has been pointed out, taller buildings would create a more economically viable city by substantially increasing both office space and available housing. More supply can meet rising demand and improve affordability, as well. In 2014, President Obama signed an amendment to the Height Act, maintaining the current 1:1 setback but allowing occupiable penthouses at no more than one story or 20 feet, which isn’t much of an addition. Historically, the 1910 act amended an original law (1899) to raise the maximum height from 110 feet to 130, a nearly 20% increase. A similar increase today would give buildings 2-3 more floors. NCPC’s studies show a maximum width-to-height ratio of 1:1.25, which remains quite low. While such proportions offer a “sense of enclosure,” considered a fundamental principle of traditional urban design, in fact some of the most inviting streetscapes have much higher proportions, as CityCenterDC’s alleyways demonstrate.
Five years ago, the mayor’s office released “A Vision for a Sustainable DC,” a plan to become “the healthiest, greenest, and most livable city in the United States” within two decades. In 2015, the District overhauled its zoning regulations for the first time since 1958, but the changes did not address the inherent challenges to enhancing interior light, air and views. To fulfill its own vision and encourage better buildings, the city has more work to do. Washington already is a leader in sustainable design, but how much more could it accomplish?