Dollar & Sense of Green Roofs

The Dollar and Sense of Green Roofing

Written by Brian Lambert - Garland Marketing Manager
Published by The Royal Architectural Institute of Canada - Fall 1999

Everyone knows that conserving natural resources makes good sense. But good sense solutions are rarely adopted until dollar and cents benefits are clearly in sight.

That reality can be disheartening at times for architects, designers, and engineers committed to environmental responsibility and building sustainability. The growing popularity of green roofing solutions in North America is largely attributable to the fact that their track record in Europe has demonstrated significant benefits -- not only for the natural ecology, but for building owners and managers.

How Green Roofing Works

• Beneath every green roof, a roofing membrane provides the critical waterproofing layer.
• A unique, root-resistant compound prevents plant roots from penetrating beneath this waterproofing membrane.
• A drainage layer draws excess moisture away from the roofing membrane.
• Lightweight, specially formulated soil absorbs and retains water in a controlled manner to nourish the plant life.
• A surface layer of plant life is customized to meet specific functional and aesthetic requirements of individual applications.

When evaluating the variances in performance among green roofing systems, here are a few things to keep in mind:


Effective Waterproofing
It is the roofing membrane that is the heart of any green roof. Only a proven, high-performance waterproofing and reinforcement layer can ensure that your green roofing solution is both ecologically sound and economically efficient.

Ideally, the system solution will provide the multi-ply protection of a Styrene Butadiene Styrene (SBS) modified bitumen that offers exceptional tensile strength, puncture resistance, and elongation characteristics, plus optional performance enhancements such as fire-resistance. The Garland® modified bitumen roof system that protects our GreenShieldTM green roof system incorporates post-consumer recycled tires into the waterproofing membrane.
Modified bitumen membranes have been field-proven to last 25 years or more in urban environments fully exposed to the challenges of UV, hail, snow, wind, and routine foot traffic. It is anticipated that the protective barrier provided by plant life will significantly extend the life cycle of underlying membranes in green roofing systems.


Building Sustainability
A surface covering of plant life reduces the intense thermal radiation that typically occurs on the black roof surfaces commonly used in cities. By extending the insulating properties of the waterproofing layer, green roofs can reduce energy consumption in hot urban environments significantly.

Because the leaf surface of plants is evaporative, a significant amount of the sun's radiation on a green roof is put to work evaporating the moisture in the plants. The larger the total leaf area on a green roof, the greater this natural cooling effect.

Although trees and shrubs provide greater cooling than ground covers, they also require greater soil depths, imposing higher loads on the roof deck. Structural load limitations will ultimately determine how much energy reduction is possible.

Typically, green roofing systems use thin layers of specially formulated lightweight soil, in combination with multi-ply roofing membranes, over steel or concrete decks. This type of configuration enables the user to select plant life with a large enough leaf surface area to positively impact thermal radiation. With lightweight metal or wood decks, or when considering larger plantings that require greater soil depths, a structural engineer should be employed to thoroughly evaluate load considerations.

Storm Water Management
Another benefit of green roofs is their ability to reduce storm water run-off. Instead of draining off the roof, where it can become a burden to a city's infrastructure and ecosystem, a significant portion of storm water is absorbed by the soil and, in turn, by the plant life.
John W. White, Ph.D., Professor Emeritus, Pennsylvania State University, and Horticultural Consultant to The Garland Company explains: "Thirty to fifty percent of the incoming sun's radiation is used to evaporate the water in plants. This process of evapotranspiration, which produces a cooling benefit, also slows down and in some cases can eliminate storm water run-off."

Many municipalities are restricting new construction or mandating the creation of freestanding reservoirs to deal with excessive storm run-off. Overbuilding, particularly in areas with high water tables, can result in overburdening urban sewer systems when high volumes of rain fall.
Since storm water run-off from an urban roof is typically hotter than the river or lake it eventually drains into, overbuilding can also have an adverse effect on fish and their food supply.

The ability of green roofs to reduce rainwater run-off is enabling new construction in areas with high water tables. Green roofs are also being used to improve ecosystems in communities concerned about the adverse effects of "heated" rainwater traveling from urban roofs into our natural waterways.

Additional Ecological Benefits
One square meter of leaf surface supplies enough oxygen, through photosynthesis, to supply one person's requirements for an entire year. Since the foliage in plants binds dust, all green roofing solutions further improve air quality by reducing dust.

The StressPly® modified bitumen membrane is the primary waterproofing component of the GreenShieldTM system. It incorporates post-consumer recycled rubber in its underlying membrane, providing an additional improvement in the natural ecology by reducing scrap tire waste.

Quality of Life
Perhaps the most important benefit of environmentally friendly green roofing is its positive impact on the quality of life in urban environments. Since plant life actively suppresses noise, presenting a barrier to sound vibration, green roofs reduce the noise-related stress of urban environments. Health care facilities, hotels, public buildings, and even urban condominium communities are embracing the aesthetic and recreational benefits of green roofs.

Adjacent patios and other architectural features are being designed into new buildings to take advantage of the natural beauty of green roofing solutions. In the future, we may see herb gardens on the roofs of urban restaurants, secured gardens on the roofs of rehabilitation hospitals, and fenced-in vegetable plots on the roofs of public housing projects.

Summary
By conserving our natural resources while providing quantifiable, life-cycle economies, green roofing is providing an aesthetically pleasing, highly functional alternative to conventional roofing solutions.

History of Green Roofs
Types of Green Roofs
Benefits of Green Roofs
Garland's GreenShield System
Dollars and Sense of Green Roofs


Green Roofs
ENERGY STAR®*/Cool Roofs
Recycled/Recycleable Systems
Solar Roof Systems
Sustainable Links
Title 24

*ENERGY STAR® is a registered trademark of the U.S. government. The ENERGY STAR Program represents a voluntary partnership between businesses and organizations and the federal government to promote energy efficiency and environmental activities.