With the design community more focused than ever on sustainable infrastructure, coupled with the re-emergence of DIY urban farming, “green roofs” are experiencing somewhat of a renaissance in cities across the globe. After all, what city dweller wouldn’t want a lush garden retreat atop their facility?
Besides the obvious amenity of your own park-like setting in which to grow and harvest a small field of fruits and veggies, green roofs provide a number of proven benefits to the environment, including reducing the urban heat island effect, significantly reducing the amount of stormwater that runs off into city sewer systems, improving air quality, reducing heating and cooling costs for entire buildings, noise reduction, added fireproofing, and potential educational opportunities for others.
IS A GREEN ROOF RIGHT FOR MY BUILDING?
Green roofs can be wonderful installations for certain clients, but our experience has taught us that they’re not necessarily the best solution for every building. Before jumping into such a project, we highly recommend an introductory meeting with a licensed landscape architect in order to assess your goals and challenges. Before you make that leap, here are thoughts to consider about green roof technology.
First off, it’s important to understand that there are essentially three categories of green roofs.
1. Extensive Green Roof: The name is slightly misleading. The word extensive has nothing to do with area, but the overall depth of the green roof system, including the planting medium and water retention drainage layer. They’re lighter and require less soil than the other forms of green roofs, but the disadvantage is that they can only support a limited number of perennials and herbs, and no shrubs.
2. Semi-Intensive Green Roof: These roofs systems are deeper and require greater structural support, as well as regular watering. However, they can grow vegetation that the extensive green roof cannot.
3. Intensive Green Roof: The intensive green roof system is meant to support a lot of weight – this is the kind of roof you may see dotted with small trees, shrubs, lawns, large scale agricultural ventures, and decorated with rock gardens and water features. But as the name says, an intensive roof is the most expensive to install, and requires a full-time green thumb to maintain.
Regardless of which model you go with, a green roof overburden system can be used to protect waterproofing membranes. Many roofing manufacturers provide complete waterproofing and green roof systems to protect and extend the lifespan of the roof. Overburden systems add between $50-120 per square foot to the cost of construction on average.
The type of roof you select, along with your preferred plants you want to grow will depend upon the weight-bearing abilities of your building. Of course, there are ways around these structural inferiorities provided money isn’t an obstacle.