Up on the Roof

You could hold a big party up on the new roof of 636 I Street NW in Washington DC -- headquarters of the American Society of Landscape Architects (ASLA).

The plants are still growing in, but you can see the greenery from street level, and tours will soon be underway by appointment. ASLA unveiled the 3300 square foot project this week and hopes it will inspire others to plant their roofs as well.

Nancy Somerville, ASLA's Executive Vice President/CEO, said green roofs in general have positive environmental benefits in cities "where green space is at a premium."  While she admitted that this one roof "is not going to make a dent" in DC's air quality, she said planted roofs can reduce roof temperatures by 90 degrees, reduce heating and air conditioning costs, improve storm water retention, and make roof replacement unnecessary for 40 years or more. And, if enough owners put green roofs atop their buildings, they together could have a significant impact.  DC currently ranks second in green roofs in the United States, just behind Chicago.

This roof was designed by Michael Van Valkenburgh Associates Inc., of Cambridge, MA and New York City. Landscape architect Chris Counts said the designers wanted to use the roof as an educational tool and also take the concept a step further to "what the next generation of green roofs would be like."  He said it was "quite a challenge" to come with a design that had "a spatial quality" in the flat, 38 x 82 foot space. You have to acknowledge the solution is very ingenious.

(photo left: Courtesy Michael Van Valkenburgh Associates, Inc)
(click on images for larger view)

From the entrance to the roof, you step out onto a wooden deck.  On either side is a large green mound (or wave) covered with plants.  Straight ahead, there's a metal grid -- plants coming up through it -- and walkways made of the same material.  The landscape architects craftily planted low-growing sedums (Sedum spurium, Sedum reflexum, Sedum kamtschaticum) below the grates that will self-prune as people walk over them. Various parts of the roof demonstrate different planting techniques for green roof systems.

The north and south waves have 4 to 6 inch soil depths to support "extensive" plantings -- plants that survive on rainwater alone once they're established. Aside from a variety of sedums, the waves are planted with prickly pear cactus (Opuntia humifusa), black-eyed susans (Rudbeckia hirta), prairie dropseed (Sporobolus heterolepsis) and many other ornamental grasses and perennials.  Landscape architect Stephen Noone said visitors will see a "mosaic of grasses and succulents" that one might find in a prairie environment.

Atop the staircare and elevator shafts are "intensive" plantings with deeper soil (12-24") that can support shrubs and small trees.  These areas are planted with native roses (Rosa carolina), New Jersey Tea (Ceanothus americanus), Flame Sumac (Rhus copallina) and 'Madame Galans' trumpet vine (Campsis radicans) that will eventually cover a metal trellis above the entryway.

And here's a very special added extra -- track the progress of this project through ASLA's green roof webcam.

(Image right: Courtesy Michael Van Valkenburgh Associates, Inc)
(click on images for larger view)