SpecTopics: Roof Gardens – The Embodiment of Sustainability

With sustainability at the forefront of every architect’s mind, choosing the most environmentally friendly products can seem daunting. In the commercial roofing and building envelope industry, a holistic approach should be taken to ensure the products chosen will maximize the building’s sustainability while also maintaining or improving long-term performance. It is important to consider the products’ life cycle, recyclability, environmental and human health benefits, and resiliency as well as the manufacturing process.

When it comes to low-slope roofing, roof gardens check all the sustainability boxes. The following list highlights some of the sustainability attributes of roof garden systems.

Stormwater Retention and Detention: Out of all their benefits, the main driving factor for many of the mandates and incentive programs is roof gardens’ ability to retain and detain stormwater. This is especially beneficial in cities, where there is often a lack of natural green space to absorb rainwater, which can lead to flooding. Roof gardens act like a sponge on top of the roof, combining multiple products such as moisture retention mats, engineered growth media, and vegetation to not only hold rainwater but also delay runoff. This makes roof gardens ideal for stormwater management – they do so in a much more cost-effective way than building up gray infrastructure, while also providing a multitude of additional environmental and building performance benefits.

Oxygen Production: By design, roof gardens are covered in vegetation to make use of the absorbed stormwater and to enhance aesthetics. Like all other vegetation, roof garden plants help to sequester carbon dioxide while producing oxygen at the same time. This is obviously very important everywhere but especially in cities where there is dense human population producing CO¬2 and little natural vegetation to offset it.

Increased Biodiversity: Roof gardens help to increase biodiversity, providing a habitat for bees, birds, butterflies, beetles, and fungi. Roof gardens can also provide a welcoming, useable amenity space that allows building occupants to enjoy the outdoors. This is especially beneficial for healthcare settings and nursing and assisted living facilities where roof gardens can be used as healing gardens, helping to reduce anxiety and increase patient recovery times by providing access to nature.

Urban Heat Island Reduction: Vegetation’s natural cooling process (called evapotransporation) helps to cool the surrounding environment. This makes roof gardens especially beneficial in city and urban environments where there is a need to reduce temperatures to those of a more natural, rural environment. Vegetation’s evapotransportive cooling is so efficient that it has been shown to reduce city-wide ambient temperatures by up to 5 degrees Fahrenheit, minimizing the urban heat island effect.

Thermal Mass: In addition to the cooling effect of the vegetation itself, a roof garden helps to reduce the cooling load on the building through its thermal mass. Although there isn’t an exact insulative R-value you can put on a roof garden due to water retention, the thermal mass of a roof garden will help to protect the building from extreme temperatures and provides thermal inertia.

Physical Protection: It is imperative that all roof garden systems be installed over a properly designed, installed, and inspected roof system. That means creating a robust roof system that can withstand the added weight of the overburden components using cover boards as well as fully adhered and thicker membranes with seam enhancements. Once the roof is topped with a roof garden, it will be protected from damaging UV exposure, temperature fluctuations, and physical abuse caused by hail, wildlife, building occupants, and tradespeople. This physical protection adds resiliency to the building, extending the life of the roofing system beyond the standard 20-30 years and reducing the number of re-roofs required over the lifetime of the building. Therefore, roof gardens directly contribute to a reduction in landfill waste.

Carlisle offers a full range of roof garden products and systems eligible for single-source overburden warranties. For more information on Carlisle’s Roof Garden systems, visit the Roof Garden page on the website.

For more information on how roof gardens help to contribute towards green building standards, refer to Carlisle’s Product Sustainability Reference Guide.