Green roofs in the United States are a nascent technology. They may be a common site in parts of Europe (especially Germany), where the technology has been around for decades, but here they can be a risky venture. With only about a decade of use in the U.S. and with their lengthy establishment time (they need at least a few growing seasons to reach a mature state), there is still a lot of trial and error in their design and installation. While it may be true that they are installed with greater certainty in Europe since they’ve been around there longer, European models can’t be directly imported here due to climatic and biotic differences.
The new technology of extensive green roofs differs significantly from the traditional landscape form of rooftop gardens. Green roofs are installed not necessarily for their aesthetic value (though some argue they should be), but to add a variety of architectural and environmental services such as reduced stormwater runoff and prolonging the life of the building's roof membrane. In cities they can be particularly beneficial, given their diminishment of stormwater runoff and their lesser contribution to the urban heat island effect when compared with traditional roof finishes.
In The Green Roof Manual: A Professional Giude to Design, Installation, and Maintenance (2010, Timber Press. 296 pages, $29.95), authors Ed Snodgrass and Linda McIntyre are primarily concerned with the nitty gritty details of design and installation. While they note that green roofs can and have been built with usable space in mind, they spend little time on it, instead focusing on establishing a working green roof with little additional embellishment. Their aim is to help establish a baseline standard for a green roof industry in the U.S. One of their concerns is that over enthusiasm (even if well-intentioned) can distract people from genuine technological concerns or that overselling can lead people to believe that green roofs are a panacea to environmental ills when there is really a short list of environmental services they can provide. Add to that the relative inexperience of most involved in the industry in America, and there can be a genuine problem with green roof failure. In other words, “let the buyer beware.”
These days you can find a lot of literature rhapsodizing about how wonderful and environmentally friendly green roofs are and how sustainable design can save the planet and even the distressed economy. But it will take more than feel good slogans to bring about the widespread adoption of green roof technology... - Snodgrass and McIntyre, The Green Roof Manual
In The Professional Design Guide to Green Roofs (2013, Timber Press, 300 pp., $39.95), co-authors Karla Dakin, Lisa Lee Benjamin, and Mindy Pantiel take a slightly different approach. As the title would suggest, they look at green roofs through the lens of design. Their concern, almost the opposite of Snodgrass and McIntyre, is that green roofs might get short shrift from potential builders and users if they are seen as strictly functional and not necessarily aesthetically pleasing. While attempting to inspire their readers and make green roofs an element of high design, they go over not just their technological details but spend a lot of time on the process of design itself. In other words, their text is as likely to contain a reference to a Cezanne painting as it is to get into substrate details.
It may sound like the two books and their sets of authors are almost in direct opposition with one another, but that isn’t entirely accurate. In fact, it may be better to conceive of the two texts as complementary opposites that make up a whole. Their points of emphases may be different, but they do cover a lot of the same ground. Manual’s technical prowess is found in the text of the Design Guide, and the latter’s emphasis on designing usable spaces is found to a lesser degree in the former. Design Guide also goes a little further on the ecological end of the scale than does Manual, such as with a section on green roofs as restorative habitats.
As a result, those interested in green roofs may find both of the books useful, albeit for different reasons. If you are a neophyte with green roofs or are a potential builder, looking for a frank, nuts and bolts guide to installation, Manual will definitely be the better choice. If you already have some experience with green roofs, or are interested more in aesthetics or the ecological function of green roofs, Design Guide may be the book that’s right for you.