Green Roof Systems

A Guide to the Planning, Design, and Construction of Landscapes over Structure

Susan Weiler, Katrin Scholz-Barth

• Publisher: Wiley
• Year: 2011
• Print ISBN: 9780471674955
• eBook ISBN: 9781118174463
• Edition: 1
• Topic: Architecture
• Subtopic: Urban Planning & Landscaping

Green Roof Systems goes beyond the fashionable green roof movement and provides solid information on building accessible space, often as important public space, over structure. It offers brief coverage of the entire process, including planning and collaboration, and focuses on the technical aspects of these roof systems, their components, and their applications.

Chapter 1

Replenishing Our Diminishing Resources: Integrating Landscape and Architecture

The world is a glorious bounty.

—Ian L. McHarg, Design with Nature

The technology and materials for vegetating roofs and creating usable open spaces over structure have been known for centuries. Since 4000 BC, practitioners of building and agriculture have utilized the knowledge and materials of their time to construct sacred places such as ziggurats, simple vegetated roofs, and remarkable gardens over elevated surfaces.

The building green movement is not new, nor is the practice of using natural resources responsibly to sustain life and encourage the regeneration of natural resources.

In the last five years, the term green roof has taken on ecological and social significance beyond its seemingly simplistic description. As commonly understood, the term has become an epithet for the reduction of pollution and urban heat islands, for large-scale mitigation of stormwater runoff, and for maximum utilization of urban land.

Justifiably, the concept of the green roof as a way to add pervious surface and usable open space without taking up additional land is easy to understand and should be equally easy to implement. Consequently, many clients, municipalities, architects, landscape architects, and planners have come to consider them as an integral element of sustainable building practice.

More recently, many European municipalities have mandated the incorporation of green roof systems as standard building practice. Even without legislative mandate, landscape architects and architects have, with the personal will and mandate of their clients, successfully built numerous green roofs as stormwater management systems and as comfortable, accessible, open spaces over structure. This has happened without fanfare, perhaps because many of these spaces have been imperceptibly integrated with the architecture and surrounding urban fabric, and perhaps because much of what sustains green roof functionality is invisible to the user.

Most roofs as we know them, however, are not invisible, and as cities grow so do the number and sizes of rooftops. So too does the amount of land used for roads, parking lots, and pavement. At issue is the fact that conventional rooftops and paved surfaces are impermeable, which in turn affects the quality of our water and air. The use of more and more land for building affects the way we live. As our cities grow we need to be thoughtful about how we use our limited natural assets.

FIGURE 1-1 Gardens at the United Nations, viewed from the East River, illustrate extensive portions built over the FDR Drive.

One of many strategies for replenishing our diminishing resources and integrating landscape and architecture is the green roof, and its wide-scale utilization is the focus of this book.

FIGURE 1-2 Outside Geneva, Switzerland, where vast meadows grow over the roof of a reservoir, a rich palette of plants provide a diversity of habitats for insects and small animals, as well as nesting places for birds.

FIGURE 1-3 Even a small individual effort can help ameliorate the negative impacts of unplanned development and urban growth in the Netherlands. (Photo: Joyce Lee)

This book aims to provide a comprehensive, systems-based approach to understanding, designing, and constructing green roof systems in an urban environment. The following chapters will:

• Broaden the reader’s understanding of the deleterious effects that conventional roofs can have on the environment

FIGURE 1-4 West Ferry Circus, a lush garden of canopy trees, shrubs, lawns, and walkways, is one of the numerous interconnected open spaces at Canary Wharf in London. This part of the project was built over a highway, service roads, mechanical equipment rooms, and major utilities. Other open spaces were built over three to five stories of parking, a shopping center, and a tube stop.

• Challenge conventional thinking about the design and development of our built environment and foster innovative solutions that change the perception, appearance, and use of roofs for the benefit of our natural and cultural environment
• Identify the environmental, social, and economic benefits of turning the under-explored surfaces of roofs into multifunctional systems for stormwater management and the creation of usable landscapes over structure
• Provide detailed insight into their design, construction, and maintenance

Defining and Redefining the Roof: Traditional Roofs and Green Roof Systems

In traditional building terms, the roof is considered the lid or top of a habitable structure that keeps the unwanted weather elements outside and helps maintain the most comfortable conditions and temperatures for human habitation inside. For as long as there have been humans seeking shelter beyond a cave or a tree canopy, some type of protective weatherproofing material was overhead to provide protection from the sun, wind, rain, and snow. This has evolved from natural materials such as leaves, thatch, and sod to more durable materials such as slate, wood shingles, asphalt shingles, EPDM (ethylene propylene diene monomer) membranes—and contemporary green roof systems.

In traditional building terms, roofs can be sloped or flat. (Flat roofs actually have a slight slope to them even though to the naked eye they appear flat.) Regardless of its overall configuration and architectural type, a sloped roof sheds rainwater, snow, and ice more quickly than a flat roof, and it is generally more suited for the application of smaller overlapping units for weather protection such as slate, wood, or asphalt shingles, clay tiles, thatch, or sheet metal. Sloped roofs, for some, have greater aesthetic appeal, which may be attributed to a more interesting architecture, size, scale, and the richness of traditional building materials used for weatherproofing.

Flat roofs are more practical for covering long spans of horizontal surfaces, but they can also be used to cover smaller structures. Because of the simpler surface configuration, weather protection for flat roofs can be accomplished more economically through using large pieces of protective membrane.

Both sloped and flat roofs become extraordinarily hot in direct sun exposure, especially in summer. The variation in temperature of the roof surface, even in moderate climates, can cover more than 70 degrees from morning till afternoon. The heat gain is more severe on flat roofs because the entire roof is exposed to the sun at all times. Even so, it is generally easier to build, inhabit, and maintain green roof systems that are constructed on flat or slightly sloped roof decks (the surface supporting the roof) than on ones with slopes because on flat roofs the loosely laid soil and vegetation layer is not subject to gravity and shear forces that pull on them. The primary advantages of constructing green roof systems on low-sloped roof decks are their applicability as stormwater retention systems, their reduction of heat gain, and their ability to be developed for usable open spaces in urban areas without taking up more land.

The technologies of each age add to our ability to live more efficiently and productively. Just as city builders of 4000 BC used the technology of their age to build beautiful rooftop gardens and other needed places, contemporary practitioners of design and building use the knowledge and materials of this time to construct our needed places.

We just need to think more carefully about how we can build our needed places and replenish our diminishing resources. This requires thinking about roofs in a different way. The roof, usually a leftover space, sitting unused and absorbing heat, can be transformed into a floor—a platform for activity—while providing insulation for the living spaces below.

Designing with Nature

In the first pages of Design with Nature, a seminal treatise on the importance of understanding and integrating natural, economic, and social systems, Ian McHarg points out that “the world is a glorious bounty” from which we benefit and for which we must serve as guardians.

Land and the natural resources it yields have enormous value, but more often they are commodities that have a price; all can be owned, bought, and sold. Land as real estate has its price, water has its price, and energy has its price.

Assigning a Value to Open Space

It is more challenging to assign a dollar value to land as open space. Whether it is under public or private ownership, open space with its intricate, interconnected elements of earth, animals, plants, water, and air provides the armature for the way we live. Well-cared-for open space is itself a valuable commodity and must be envisioned as such. It plays a pivotal role in improving water and air quality. It positively influences real estate values, and it can help to diminish energy consumption in the surrounding area. Yet we seem to take it for granted, and the responsibility for its stewardship is not always taken at individual, municipal, federal, or global levels. Globally, the amount of open space continues to shrink and our natural resources continue to be diminished in extent and quality. Ozone depletion, air and water pollution, and acid rain have caused local and, cumulatively, global environmental problems. Deforestation and desertification, ground water depletion, and degradation of other natural resources have led to a loss of habitat and biodiversity.

FIGURE 1-5 Bryant Park provides enormous value as an urban open space and has significantly increased peripheral property values. The central lawn panel is built over the stacks of the New York Public Library.

As we develop land for building, we eat up at an alarming rate valuable open space that could be used for our own recreation or for providing connected corridors of habitat and a balanced diversity of vegetation and wildlife. More importantly, we are not carefully planning for the preservation of land we need for growing food or for the replenishment of clean water and air.

Unplanned development resulting from continued population growth may be...

Table of contents

• Cover
• Title Page
• Copyright
• Dedication
• Chapter 1: Replenishing Our Diminishing Resources: Integrating Landscape and Architecture
• Chapter 2: Beyond the Property Line: Ecological, Economic, Spatial, and Social Benefits of Green Roof Systems
• Chapter 3: Envisioning Green Roof Systems: From City Scale to Project Scale
• Chapter 4: Green Roof Systems at the Project Scale: Site and Architectural Considerations
• Chapter 5: Considerations in Developing Structural Systems for Green Roof Systems
• Chapter 6: Component Parts: Inert and Dynamic
• Chapter 7: Putting the Parts Together: The Design and Documentation Process
• Chapter 8: The Bidding and Construction Process
• Chapter 9: Minimizing, Managing, and Insuring Risk
• Chapter 10: Maintenance Requirements and Performance Evaluation
• Wiley Books on Sustainable Design
• Index