Green Roofs: Planting More Than Just a Roof
After becoming popular in Europe, green rooftops have made their way across the Atlantic Ocean to the U.S. as an attractive, sustainable solution for commercial buildings. The North American green roof industry experienced an estimated 10-percent growth in 2016 over 2015, according to the 2016 Annual Green Roof Industry Survey. Commercial building owners and property managers are discovering there are many benefits to choosing a green roof over a conventional system.
Also known as an eco-roof or garden roof, a green roof is a layered roofing system that grows practically maintenance-free plant life on its flat or slightly-sloped waterproofed substructure.
When compared to traditional roof systems, green roofs have a longer lifespan, cut down on energy costs due to its natural insulation, improve air quality, and absorb storm water. These advantages make the need for complex drainage systems unnecessary and help with managing the Urban Heat Island Effect, which is where a metropolitan area is warmer than the surrounding rural areas, created by caused by pavement and dark man-made structures that heat up quickly and cool down quickly.
Storm Water Management
When examining absorption of storm water, traditional roofs create a large amount of runoff while a green roof collects and holds the water. Eco-roofs manage drainage with a waterproof membrane and keep the building protected from the wear and tear from the weather. The green roof’s growth media and water retention layers act as a sponge and absorbs up to one gallon of water per cubic foot of media. This makes green roofs particularly useful in urban areas where storm water management options are limited.
Eco-roofs have many other benefits besides storm water management. Having plant life on a roof can also lower a building’s noise levels and energy usage. Green roofs provide a high sound absorption, especially when compared to typical roofs. The soil, plants and trapped layers of air can act as a noise insulation barrier. Green roofs can also reduce annual heating and cooling costs. They can significantly reduce energy use in buildings that have poor insulation when it comes to both cooling in the summer and heating during the winter.
When looking at longevity, green roofs protect the roof membrane from harsh weather and UV rays, therefore, they can last much longer than traditional roofs.
Intensive Versus Extensive
When installing a new green roof, there are typically three options: extensive, intensive or modular trays. Intensive green roofs are similar to traditional landscaping. They have deep soil and most often an irrigation system that leads to more favorable conditions for deep-rooted plants, such as trees, shrubs and prairie grasses. A wide variety of habitats are sustainable on these roofs. However, intensive green roofs are more expensive than extensive green roofs because they typically require an irrigation system, have more media to install resulting in more labor, and have a wider variety of plants.
Extensive green roof and modular tray systems usually do not include rooftop gardens, have thin soil and little to no irrigation systems, and require low maintenance of the vegetation. Due to these conditions, there is a limited type of foliage that can be grown, which is traditionally of a sedum variety, a type of succulent. When comparing the different green roof techniques, the lightweight extensive green roofs are a lower maintenance and less expensive option than intensive green roofs, and modular trays are typically the least expensive.
Depending on design integration with other building systems, green roofs can also help improve the LEED rating of a building. It can contribute as many as 15 credits under the system, according to Green Roofs for Healthy Cities. In some instances, green roofs may not contribute directly to achieving points under the system, but they contribute to earning LEED credits when used with other sustainable building elements.
When constructing or renovating a building, one benefit of green roofs not always considered is its increased marketability for the building. Adopting a sustainable roof shows that the building is part of the green building movement, which can serve as an incentive to someone who is interested in the energy-saving benefits of being ecologically responsible.
With the popularity of green roofs growing, more commercial roofing companies are adding them to their repertoire of services. For property managers and building owners, it is important to use a commercial roofing contractor who provides turnkey green roof capabilities. Commercial roofing contractors should be able to coordinate waterproofing, irrigation, storm water management, media selection, load requirements, plant selection and more. Other services suitable commercial roofing contractors provide includes operational expertise related to these unique systems.