The term ‘green’ roofing can be used in a few ways. Any kind of highly reflective roof membrane is considered ‘green’. Roof membranes composed of recycled materials can also be considered ‘green’. But the true exemplification of ‘green’ roofing originated hundreds, if not thousands of years ago, and involves actual ‘green’ (and other colored) vegetation. This is the original method of creating thermal mass at the top of built structures to maintain an homeostatic and insulated interior environment.
1) Can vegetative roofing earn LEED building credits?
YES. Site Credit 6: Stormwater Management (1 point), Site Credit 7: Landscape and Exterior Designs To Reduce Heat Islands (up to 4 points), Materials Credit 4: Recycled Content (up to 4 points).
2) What are the benefits of a vegetative roof system?
There are numerous benefits to having a vegetative roof system installed on your commercial or residential structure. The first benefit is that, by increasing the thermal mass on top of your structure, you decrease heating and cooling costs, and also reduce the Heat Island Effect. Vegetative roofs also decrease storm water runoff. Ordinarily, rainwater and snow melt leave the roof surface through drains or gutters. Eventually it all ends up absorbing into the soil, thereby contaminating the lawns we, and our animals play on, and the below ground aquifer that provides us with our drinking water.
Vegetative roofing also fills in the building footprint that removed virgin land during construction. Once a vegetative roof is installed, it becomes part of our living ecosystem that not only functions as all other vegetation does by sequestering carbon from the atmosphere, but provides an environment for other living organisms to inhabit. Vegetative roofing systems (from root barriers, to vegetation, and everything in between) are also made of recycled, AND 100% recyclable materials.
3) Vegetative roofing sounds like it would be difficult to maintain. Is it maintenance intensive, and what would I have to do to maintain it?
A common misnomer about having vegetation on your rooftop is that it would require a lot of maintenance. On the contrary, it is a living, and self-sustaining, self-maintaining, part of our environment like anything else. Particularly living in the northeastern United States, our temperate climate provides a perfect balance of sunlight, rain, and warm weather days to allow vegetation to live and grow.
In the winter, because native plants and succulents will be used on your rooftop, they will adapt accordingly and lie dormant, but not die. When spring arrives, your vegetation will begin flourishing again. It is important to note that no matter the season, vegetative roofing still maintains it’s thermal mass value. Because of this, your residential or commercial structure will reap the heating and cooling benefits year round. In locations where lack of precipitation is a concern, irrigation systems can be integrated within, or above, your vegetative system.
4) How are roof leaks handled when there is a vegetative system installed above my waterproofing membrane?
A service called Vector Mapping is available to handle possible waterproofing membrane compromises. This process uses electronic sensors to pinpoint leaks or membrane breaches in the roof. It is less expensive, faster, safer, and more reliable testing than conventional methods. This allows your roofer to find the origin of a leak in your home or business, carefully remove a small section of your vegetative roofing, and replace it once the membrane is repaired and made water tight.
5) I’ve seen very extravagant vegetative designs on rooftops before. What are the different types, and are they available for my building?
There are 3 types of vegetative roofing. They are known as extensive, semi-intensive, and intensive. Extensive is comprised of a 3” + growing medium, and low-lying grasses that adds the least amount of weight to your rooftop load. Semi-intensive systems are made up of a deeper growing medium, and make use of larger native plants and possibly small bushes.
Intensive systems are made up of the thickest growing medium because they are composed of large shrubs, bushes, trees, benches, and other things that enable the building occupants to use the rooftop space as a recreational, or other “livable area”.
The ability of your structure to support the various systems must be determined by a structural engineer. Homes and businesses can also be retro fitted to support the extra loads that vegetative roofing add. It is important to note that in most cases, existing homes and commercial structures are already designed to support the load of an extensive vegetative roof system.
6) Can fruit, vegetables, and herbs be grown on a vegetative roof?
Absolutely! Vegetative roofs are living ecosystems, just like your home garden or a farm. Anything that can be grown on the ground in your region, can also be grown on your vegetative rooftop garden. In fact, there are restaurants around world that are now seizing this opportunity to maximize their building space by growing the fresh food they serve on top of their business.
7) What about my carbon footprint, and the energy I could save by installing a vegetative roof system on my home or commercial structure?
When a home or commercial building is created, the size of that structure is the amount of natural environment that is lost. By installing a vegetative system on your rooftop, the entire natural environment is replaced. In addition, by increasing the thermal mass (R-value) of your roof, the savings on your home heating and cooling costs could be 20-30%.
-FAQ section above contributed by Noel Ciota, Director of Sustainability for Division7Inc.