Greenroof professionals and enthusiasts alike will be delighted with the easy reading and scope of content offered in "Planting Green Roofs and Living Walls" by Nigel Dunnett and Noël Kingsbury. Very well organized, the book's forte and major value is as an essential resource - especially in terms of plant description, characteristics and specification. It's also a great bargain in that the book is filled with color photos, drawings, charts and reference material. This indispensable hard cover reference guide contains a truly massive collection of appropriate plant information, and perhaps most importantly, extensive plant directories are provided for both greenroofs and façade greening.
Organic Architecture with Plants
Greenroofs, living walls, and various other bio-engineering techniques are introduced and the authors cite the associated benefits and reasons why we should be integrating these measures of organic architecture into our built environments. The authors refer to current international research and technology; background and history are touched on; and benefits and applications of these "ecotechnologies" are discussed at length. Yet, a "How-To Build" book this is not; basic principles are set out and tools for further research are provided.
Benefits at a Range of Scales
The section "Why Build Green Roofs?" explores hard evidence and the various benefits operating at a range of scales from amenity and aesthetic values to economic and environmental aspects. Increased roof life, insulation and energy efficiency, green building assessment and public relations, biodiversity and wildlife value, water management, air pollution, and fire prevention and risks are discussed with supporting evidence.
Although previously well known, the biodiversity and wildlife value of greenroofs is expanded upon here, including the new British models of "brown" or "rubble" greenroofs - those which recreate the thin, infertile landscapes of disturbed brownfield sites. Spontaneous colonization is presented as an important natural occurrence.
A Vast Array of Planting Opportunities
The authors rightly note that "The majority of guides to green roofs and roof greening concentrate on the technical and construction aspects but have relatively little to say about planting opportunities - mainly because most authors are not plant specialists." Well, Noël - a well known writer of plants and gardens, and Nigel - a senior lecturer in the Department of Landscape at the University of Sheffield, most certainly are plant experts, and an entire 47-page chapter is devoted to the wide range of planting opportunities for extensive greenroofs, beyond the ubiquitous albeit hugely successful use of Sedum species.
Prevailing site conditions will always dictate the plant selection, so designers need to know what plant species will not only survive but thrive in extreme local conditions. Desirable physical attributes of plants and how they may be established and managed are presented. Considerations of monocultures, single plant combinations and mixtures, and plant communities are useful as planting design tools. The form and physiology of suitable greenroof plants are nicely covered from a botanical as well as functional and aesthetic perspective. Issues of viewing considerations are pondered and design solutions are offered relating to the roof function and visual criteria. "Methods of vegetation establishment" is particularly detailed and thus extremely valuable. The authors point out, however, that current research is insufficient to show how long each species will live and how each species will interact over the years atop roofs.
The very important aspect of different growing medium properties and functions is addressed in-depth, and comments are provided about particular types of materials, substrate depths, and accompanying vegetative possibilities. Maintenance issues and requirements are briefly noted, touching on feeding, plant protection, drainage, and weeding.
Considerations of Natives and Introduced Species
The unexploited opportunities of testing and using native vegetation are explored, in terms of increasing biodiversity and aesthetic benefits. Regionally native plants should be tested for many reasons, including ecological restoration. Non-native plant species with invasive tendencies can be a problem, therefore careful selection is critical to maintain healthy ecosystems. Yet many introduced species are appropriate, and there are many circumstances where non-natives offer considerable local wildlife value.
Certain natural plant communities and their soil types are explained and presented as an argument for further study as suitable models for successful roof plantings. Trialing of appropriate local plant communities is therefore recommended and encouraged so as ultimately to be able to introduce more natives into the greenroof matrix of plant species.
"The natural habitats of potential roof-greening plants" explores the potential to discover and trial the world's flora found in similar harsh habitats. Mountain, high latitude, coastal, limestone, sclerophyllous woody vegetation, semi-desert environments, and species whose plants are exposed to climatic extremes are regions with potential for testing of new roof greening plants.
The Task Has Just Begun
Philosophy and advice to greenroof plant enthusiasts can be summed up with these reflections by the authors: "With roof greening becoming an important part of the new built environment, it is increasingly important that more attention is paid to sourcing new plant material from habitats in the wild where conditions approximate those on rooftops and other problem urban situations...The task of selecting suitable plant species for roof greening has arguably just begun, and it offers potentially enormous rewards."
They are quick to point out that the globalization of our knowledge base and the ready availability of certain aggressive species can threaten entire ecosystems, and care must be provided to the selection of greenroof environments (just as at ground level) so as to avoid invasive and potentially destructive non-natives or introduced species.
Façade Greening and Living Wall Structures and Surfaces are the final two chapters of the book, offering both visual and ecological climbers, clingers, ramblers and scramblers. New support structures, materials, technologies and details provide practical and interesting information for this older yet equally fascinating design element of green architecture. The authors examine how the design of façade greening can equally disguise unattractive features while at the same time enhance existing surfaces. In either case, education and care are necessary to promote vigorous growth that is supported by a variety of vertical and/or horizontal structures.
At the end of the book, 49 pages are devoted to the Roof-Greening and Façade-Greening Plant Directories, listed by botanical names, common names, cultivars and related species. The horticultural and cultural aspects are presented with definitions and listings of many specific plant characteristics.
A minor grumbling on my part about the book is the absence of identifying greenroof project photo captions for the geographic locations and the building application types. It would be beneficial to know not only where each is located, but also whether the project is commercial, industrial, residential, etc.
A Dovetailing of Living Plants, the Building, and Its Human Users
Whereas Ted Osmundson's excellent 1999 "Roof Gardens: History, Design, and Construction" is considered the bible for the intensive greenroof crowd, Nigel Dunnett and Noel Kingsbury's "Planting Green Roofs and Living Walls" is simply a must have for extensive and intensive greenroofers worldwide.
"Planting Green Roofs and Living Walls" is a comprehensive argument for integrating nature and architecture, and I highly recommend it. It's obvious that Kingsbury and Dunnett are first and foremost dedicated, ecologically minded plantspeople; here, then, is a very important work for those of us in the greenroof industry. ~ Linda S. Velazquez, Publisher Greenroofs.com