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Green Roofs, Green Buildings

Posted by Matt Lee, Guest Columnist

Jan 3, 2017 12:08:17 PM

Vegetative roof systems are one of the most sustainable options available in commercial roofing today.

Vegetative or green roof systems are being seen on commercial buildings around the world. This innovative system uses actual, living plants, which grow above a waterproofing membrane on top of a commercial building where a roof would normally be found. In addition to being beautiful and to increasing the aesthetics of the building itself, vegetative roof system have a number of benefits, all of which add up to one, very attractive roofing option.

Parts of a Vegetative Roof System

Every vegetative roof system begins with a waterproofing membrane spread out onto the roof itself. This membrane is important because one of the things a vegetative system does is help to prevent water runoff from the roof. On top of the membrane is a protective surface to help prevent damage to the roof or building due to the roots or moisture from the vegetation on top.

Above this surface is a root break to help prevent the roots from going too deep into the system, along with insulation and drainage paneling. This is all topped with growing media – such as soil – and a thin layer of vegetation measuring anywhere from 3- to 6-inches in depth. The ultimate depth of the vegetation depends largely on what type of plants grow in your climate, and how deep you want the roof to be.

Vegetative Roof System

Less Run Off

The first major benefit to using a green roof system is the fact that the plants help filter rainwater, absorbing a large amount of it, and preventing it from reaching the storm drains. According to a study published by EPA, a vegetative roof can contain roughly 50% of the precipitation that falls onto it. Because so many commercial buildings are surrounded by impervious surfaces, such as asphalt, a vegetative roof can help prevent overwhelming of storm drain systems. At the same time, the vegetation helps filter what water does run off, providing cleaner, less polluted water back into the drainage systems so there is less need of water treatment.

Cooler Roofs

The many layers of vegetation, growing media, insulation, and waterproofing membrane create a very dense, lush insulating layer on top of your building’s roof. This is turn means that the roof itself will stay cooler, resulting in lower energy bills for the upper floors of the building.

This insulation also works both ways; buildings lose less heat through the roof during the colder months because of this thicker layer of roofing material. This means that year-round utility bills for the building can be kept lower than on buildings with more traditional flat roofing materials installed. In fact, a study done at Columbia University on several different roofing types found that a typical commercial building that has a vegetative roof installed will see a reduction in heating bills of roughly $400 a year, and a reduction in cooling bills of roughly $200 a year.

At the same time, there are fewer temperature fluctuations within the building itself, as well as a slower change in temperature overall. So while you’re keeping energy bills down, you’re also keeping the building as a whole more temperate and comfortable in temperature for those indoors. This means less adjustments of the thermostat, which can help prevent smaller power spikes throughout the day.

Better Air Quality

As more commercial buildings in larger cities begin to adopt the vegetative roof system, another benefit is beginning to emerge that benefits not only the building itself, but also the surrounding area. The vegetation on top of the roof cleans the air, reducing CO2 levels and producing better quality air for the surrounding area. As many commercial buildings are located in areas of dense population, green roofs can help reduce airborne contaminates that are common in these areas. Studies carried out on green roofs in Chicago found that they reduced air pollution by 1675 kg. At the same time, oxygen levels were increased for the same area, and green roofs were found to be equal to urban planting in terms of improving city air quality.

This in turn means that not only does the entire area get to breathe easier, businesses can spend less on air filtering systems indoors. This further translates into an energy savings both from the filtering standpoint, and from the fact that cleaner ducts and HVAC systems do not need to work as hard to circulate air. This both extends their lifespan and helps keep utility bills down overall.

Prolonging the Life of the Roof

Studies done on vegetative roofing systems have found that they last significantly longer than traditional flat roofing material. This is due in part to the number of layers that make up the green roofing system, which helps prevent things like moisture and UV light from affecting the roof and causing it to break down. In fact, green roofs are estimated to last roughly twice as long as other commercial roofs, with some estimates going as high as a 50-year lifespan.

In addition, a well maintained green roof will sustain itself long term, which means that the roof itself will need less maintenance and fewer replacements over the lifetime of the building in contrast to a commercial building with a traditional flat roofing material installed. Therefore, while a green roof may be more costly to install, between energy and maintenance savings, a green roof comes out ahead in the long term. According to Corrie Clark from the University of Michigan “Annual benefits for the green roof are broken into economic value realized from stormwater reduction, energy savings, and air pollution reduction under (a) the high valuation and (b) the low valuation of the contribution of NO2 reduction to public health.” “Annual benefits for the green roof system in this scenario are $2740 (2006$) per year.”

Quieter Roof

The insulating properties of the vegetative roof system go beyond thermal benefits; the vegetation helps insulate for sound as well. Top floors of buildings with a green roof system are quieter, have less ambient noise, and more comfortable to work in than buildings with traditional flat roofs installed. During a study carried out by Dr. ir. Timothy Van Renterghem in Belgium, it was discovered that green roofs absorb street sounds by up to 10 dBA – a significant reduction in sound for those inside the building.

Go Green

Vegetative roof systems are one of the most sustainable options available in commercial roofing today. They have numerous benefits both for the building itself and for the environment around it. Make the switch to a green roof to find out how much your building could save.








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