Extensive or Intensive? Green Roofs Explained

There are two general types of green roofs: extensive and intensive systems. Intensive green roofs, commonly thought of as “garden roofs,” are the more complex of the two, exhibiting much greater plant diversity, and a greater need for design expertise. Planting media for intensive green roofs are a foot deep at minimum, and have saturated weights ranging from 80 to 120 pounds per square foot, depending on type and depth of planting medium and the type of plants. Almost always used for new construction, intensive green roofs can be anything from a public garden to an entire park — as is the case with the world’s largest green roof, Millennium Park in Chicago, which is 24.5 acres of landscaping on top of two subterranean parking garages.

Extensive green roofs, with a saturated weight of 12 to 50 pounds per square foot, are the most common. With planting media of 1 to 5 inches thick, most extensive green roofs aren’t designed for public access or to be walked on any more than a typical membrane roof would. Several modular extensive green roof products have emerged in the last few years that allow plants to be grown at the factory prior to being installed on a roof. We’ve found that these products allow the opportunity to pre-grow the roof so that it can be laid out like a giant jigsaw puzzle when the roof is ready for installation, so you get an “instant green roof.”

Dealing with Complexity
Whether the roof is intensive or extensive, you should consider the details of green roof design and construction carefully. There are a few more layers of complexity with a green roof than with traditional construction. That complexity, as well as cost, and the misperception that green roofs are more leak-prone, are the main reasons many don’t seriously consider green roofs for commercial projects.

However, there is no evidence to suggest that green roofs are more leak-prone. In fact, green roofs should be better at preventing leaks because the membrane is more protected from the elements. Still, we caution that a green roof is only as watertight as its design, which is why it’s even more critical on a green roof to have a good contractor like RAMCON and make sure the roof is designed properly from the outset.

With a strong understanding of the considerations that go into a green roof project and RAMCON at your side, you’ll be in the best position to ensure success. For more information about vegetative roofing systems, contact RAMCON at (877) 726-2661 or visit www.vegetativeroofing.com