Green roofs and rooftop gardens


Have you ever seen a green roof before? If you haven’t, there is still a chance you might due to its growing popularity. What is a green roof? A green roof refers to a roof covered in vegetation which is planted over a waterproofing membrane. Some green roofs will include additional layers such as root barriers and irrigation and drainage systems. Green roofs could also refer to roofs using green technology such as solar thermal collectors or photovoltaic panels. What is the purpose of a green roof and why is it becoming more popular? Green roofs serve to absorb water (which prevents runoff), provide insulation, create a habitat for wild life, lower urban air temperatures, and filter pollutants in the air such as CO2. Green roofs are claimed to also reduce urban heat island effect, which is when a city or heavily populated area absorbs and traps heat. Although green roofs cost twice as much as a conventional rooftop to build, the pay back is worth the upfront cost. Why? Because green roofs last longer than conventional rooftops by protecting the membrane of the roof from the sun’s rays and weather-related elements. 

When it comes to green roofs there are two types: intensive and extensive. Intensive rooftops serve as rooftop gardens. They are thicker, support a large variety of big and small plants, and require more maintenance. They usually hold around 80-150lbs/sq. ft. Extensive green roofs are lighter, have a light layer of vegetation, and are self-sustaining (meaning they require minimal maintenance). They usually hold about 15-50lbs/sq. ft. For those planning to grow a rooftop garden, the intensive roof would be the best choice. 

Cities and homeowners around the world are realizing the benefits from green roofs. Anyone willing and ready can put a green roof on their own house or business. At Gundersen we use green technology. For example our Integrated Center for Education building (ICE House) has a white roof which helps reflect the heat of the sun away from the building, and our new hospital has an outdoor garden that serves as a healing environment for patients and visitors. Curious as to what else we do? Check out our website on sustainable design at


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