Chris Kann, Product Manager, Roof Garden & Paver Systems, NVELOP, Carlisle Construction Materials
Over the last several years, the architectural community has ramped up its focus on sustainability to help reduce the environmental impact of their building designs. Unfortunately, the overuse and often incorrect use of the word “sustainable” by building product manufacturers has caused the term to fall victim to greenwashing, losing its original meaning. Many building products that claim to be sustainable may only possess one of the many attributes that sustainable building products should, causing well-intentioned architects and specifiers to be misled while perpetuating poor environmental building designs.
Sustainable building products should provide environmental, social and economic benefits while also protecting public and environmental health over their entire lifecycle. The big challenge for commercial, low-slope roofing manufacturers is creating new roofing products that check all the sustainability boxes while maintaining or improving existing performance. This is mostly due to the chemicals and raw materials that are required to achieve the weathering and performance characteristics of a roofing system. Substitute those proven and time-tested raw materials and additives with more sustainable products and you will have a more environmentally friendly and sustainable product, but at what cost? Sometimes that comes with a negative impact on performance, resulting in a roof system that needs to be replaced more often, negating their purpose altogether.
Through all the environmental and sustainability challenges that we face in the commercial roofing and building envelope industry, we can’t lose sight of the ultimate goal: designing and implementing products and systems that provide the maximum sustainability benefits while maintaining or improving performance. This means taking a holistic approach to product selection and building design. It means considering the life cycle of the products within the design, their impact on the other products being used, the environmental benefits and the resiliency of the system.
When it comes to low-slope roofing, there is no better roofing option that checks all the sustainability boxes than a green roof. Green roof’s go by many aliases including roof gardens, vegetated roofs, living roofs, eco roofs, etc. They are defined as a vegetated green space on top of a man-made structure installed above, below or at grade. In North America, the green roofing market has continued to grow over the last 20 years due to their many recognized environmental,
social and economic benefits. The benefits of green roofs have been so well recognized that many cities and municipalities throughout North America either have mandates or incentive programs in place that promote the use of green roofs.
Out of all the green roof benefits, the main driving factor for many of the green roof mandates and incentive programs is their ability to retain and detain stormwater. This is especially beneficial in cities, where there is often a lack of natural green space, instead being covered by impervious manmade structures and materials. During heavy rainfall events, which have increased in frequency across North America in recent years, stormwater runoff from impervious surfaces such as roofs can overrun a city’s stormwater system. This can lead to flooding, overworked wastewater treatment facilities and an overrun of sewer systems resulting in the release of untreated water into local rivers and streams. Green roofs act like a sponge on top of the roof, combining multiple products such as moisture retention mats, engineered growth media and vegetation designed to retain as much water as possible. Nonetheless, during heavy rainfall events, even the most well-designed green roofs can be overrun with water and runoff will occur. However, this runoff will be delayed, likely occurring after peak runoff from the other surrounding impervious surfaces. This delayed runoff is a result of a green roofs ability to retain and detain water. Retention and detention of rainwater is what makes green roofs ideal for stormwater management. Studies have shown that investing in green roofs to manage stormwater is much more cost effective than building up gray infrastructure such as additional sewer systems while, at the same time, providing a multitude of additional environmental and building performance benefits.
A green roofs’ ability to retain and detain stormwater is only the first of many environmental, social and economic benefits that it provides. By design, green roofs are covered in vegetation to make use of the absorbed stormwater and to provide aesthetics. Naturally, like all other vegetation, green roof plants help to sequester carbon dioxide while at the same time producing oxygen. This is obviously very important everywhere but is especially important in cities where there is dense human population producing CO2 and little natural vegetation to offset it.
The use of vegetation on green roofs helps to increase biodiversity, providing habitats for bees as well as other beneficial insects and wildlife such as birds, butterflies, beetles and fungi. Green roofs can also provide a welcoming, useable amenity space for building occupants to enjoy the outdoors. This is especially beneficial for healthcare, nursing and assisted living facilities where green roofs can be used as healing gardens, helping to reduce anxiety and increase patient recovery times by providing access to fresh air, daylight, vegetation and wildlife.
Green roof vegetation also helps to cool the surrounding area, which is especially beneficial in city and urban environments where there is a need to reduce temperatures to a more natural, rural environment. The reduction in the surrounding temperatures is a result of the vegetation’s evaporative cooling, called evapotranspiration. This natural cooling process is like our human perspiration, where we take in water and sweat it out. Vegetation’s evaporative cooling is so efficient that it has been shown to reduce city-wide ambient temperatures by up to 5ºF, minimizing the urban heat island effect. Although this may sound like a small number, this is a huge reduction in temperatures achieved in the most sustainable way; by adding nature back to our manmade built environments.
By providing a natural cooling effect, green roofs are a much better option than standard “cool” roofing materials designed to reflect heat away. A green roof averages 30-40ºF cooler than conventional flat roofs, resulting in reduced cooling loads for both the building it is installed on as well as the surrounding buildings. In addition to the cooling effect of the vegetation itself, green roofs help to reduce the cooling load on the building through its thermal mass. And, although there isn’t an exact insulative R-value you can put on a green roof due to water retention, the thermal mass of a green roof helps to protect the building below from extreme temperatures and provides thermal inertia.
Despite all these benefits, a green roof is only as good as the roof system installed below it. It is imperative that all green roof systems be installed over a well-designed, installed and inspected roof system. That means creating a robust roof system able to withstand the added weight of the overburden components by utilizing coverboards as well as fully adhered and thicker membranes with seam enhancements. Once the roof is topped with a green roof, it will be protected from damaging UV exposure, temperature fluctuations and physical abuse caused by hail, wildlife and building occupants or trades people. This physical protection adds resiliency to the building, extending the life of the roofing system beyond the standard 20-30 years typically expected of them and reducing the number of reroofs required over the lifetime of the building. Theoretically, a roof system protected from the elements by a green roof could last forever, as long as the flashings and other exposed elements were maintained and repaired when necessary. In fact, many roofing systems in Germany installed under green roofs have lasted more than 50 years. The prolonged life of the roof system is a sustainability benefit of green roofs that is often overlooked. However, it directly contributes to a reduction in landfill waste created by the relatively frequent reroofing required of exposed membrane systems.
When it comes to sustainable building design, a holistic approach must be taken to choose products and systems that provide the maximum sustainability benefits while maintaining or improving performance. When it comes to low-slope roofing, there is no better sustainable roofing option than a green roof. They provide environmental, social and economic benefits such as a reduction in stormwater runoff, oxygen production, reduction in solar heat gain and increased
biodiversity that our built environments so desperately need. They provide physical protection against damaging UV light, temperature fluctuations and physical damage, helping to create a more resilient, less wasteful and more environmentally friendly building.
Chris Kann has been employed at Carlisle Construction Materials since 2010. He graduated from Pennsylvania College of Technology in 2008, where he earned a Bachelor’s degree in the Science of Plastics and Polymer Engineering Technology. During his time in college, Chris worked as an intern with Carlisle Construction Materials in the R&D and analytical lab where he performed many tasks related to the testing and quality assurance of building envelope materials.
Chris’s full-time employment at Carlisle came as the Roof Garden Specialist and then Building Envelope Designer, both of which focused on assisting architects, specifiers and representatives on the design and implementation of energy conscious building designs. Currently, Chris manages multiple product lines including Roof Gardens, Paver Systems and CCM’s single-source building envelope program called NVELOP. Additionally, Chris is responsible for managing Carlisle’s Architectural Services, which focuses on outreach and continuing education of the architectural community.