Book Review: Green Roof

Green Roof - A Case Study: Michael Van Valkenburgh Associates' Design For the Headquarters of the American Society of Landscape Architects (2007) by Christian Werthmann
Princeton Architectural Press
Hardcover, 160 pages

The roof of the book's title sits atop the American Society of Landscape Architects' (ASLA) headquarters in Washington D.C. It is a relatively small roof of 3,300 sf (305 sm), but one that merits case study treatment from its design, construction, and the intentions behind these two. Designed by Michael Van Valkenburgh Associates in collaboration with Conservation Design Forum, the roof is unlike other well-known American examples like the Ford Rouge Plant or Chicago's City Hall, in that it is accessible. It is a social space as much as an ecological one. It is a roof garden as well as a green roof. This decision (and the important distinction between doing a roof garden or a green roof or a hybrid) shaped much of the design and therefore the technical considerations required to make it happen, both thoroughly presented in this book.

While certainly not new, green roofs are growing in popularity and being pushed by and to architects as solutions for primarily flat roofs for a number of reasons, some true and some not-so-true. These include: reduction of urban heat island effect, slowing of sewer runoff in urban areas, increase of the roof's insulating properties, and an increase in biodiversity, among a slew of bullet points. Regardless of criteria like these, the decision to use a green roof is also made on aesthetic grounds; they just look better than a typical flat roof. While ASLA's green roof may help convert even more people to the cause, this book illustrates a big difference between a standard flat roof and a green roof: ease of construction and maintenance, the green roof lacking ease in both respects. Sure many green roofs exist without any foresight, acts of nature and/or signs of abandonment, or what is called here "spontaneous vegetation". The pre-DS+R High Line is a great example of a raised green surface created by seeds, wind, and a lack of intervention. But most green roofs will result voluntarily, and for those willing this book is a great, though not complete resource for undertaking a green roof and/or roof garden.

Of the four major parts (historical essay, photos of the ASLA green roof, an A-Z of the roof's elements, and an interview between author Christian Werthmann and Michael Van Valkenburgh), the most valuable section is the A-Z, where pieces like air handlers (how to design a green roof around them), drainage, loads, maintenance, and plantings are explained in the context of the project. Most of these pieces can be applied to other green roofs, especially this last with its helpful color photos of the plant species used on the project. The book ends with construction documents, another helpful piece for designers wishing to tackle a green roof but lacking the representative means to know where to start, much less make it happen. This book brings architects one step closer to just such a thing, inspiring them to make their own case studies.


  1. John,

    Interesting article. We are installing a Green Roof on a project in Vancouver on a USGBC LEED Gold project.

    The area to be installed is roughly 26,000 square feet. The product we are using is a product from Xero Flor Canada Ltd. You can get particulars from Joy at

    The project is expected to be complete in November 2009.

    - Frank Soellig

  2. Chicago's City Hall roof is accessible. It may not be open to the public, but it has walking paths and they periodically give tours.


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