Although gaining more popularity in cities and towns across the country over the last decade, green roofs are not a new concept. Evidence of green roofs can be found on historical structures throughout Europe, and the first modern green roof in the United States was installed in Rockefeller Center over 85 years ago.
A green roof is simply a roof that allows for the growth of vegetation, from grass to trees. The modern green roof is constructed of a waterproofing layer, a root barrier, a drainage system, and a growing medium for plants.
There is scale of green roof styles, based on the depth of the medium and plant types. An intensive green roof, also often called a “roof garden”, can be accessible and include larger plants and even water features. The soil medium is thicker and requires increased structural support. They are typically found on very flat roofs.
An extensive green roof, on the other hand, is a thinner, lighter, version that looks more similar to a standard roof. It can be sloped to a degree or flat. Often it will be planted with sedum or other low-lying, lightweight plants. In between these two types are “semi-intensive” green roofs, which can be home to an array of plant species, including native grasses and flowers.
There are a wide variety of benefits for installing a green roof. Green roofs can help save on utilities by protecting the home from direct solar heat in the summer and minimizing heat loss through the roof during winter. Green roofs can also help with stormwater management, with the growing medium and plants retaining rainwater. Even water that leaves the roof is cleaner than traditional roof runoff and is delayed by traveling through the green roof system, easing stress on stormwater infrastructure and sewers. Lastly vegetated rooftops can serve as habitats for a variety of native species.
A common reason homeowners and builders give for not installing a green roof is potential leaks. However, a leaky roof is independent of whether it’s a green or a traditional roof. It has to do with the installation and design specification of the structure. All roofs must have a proper waterproofing membrane, whether green roof or not. In fact, green roofs can even help protect the waterproof membrane from ultraviolet sunlight, which may help provide a longer life cycle, with the plants and substrate acting as a natural barrier to weathering.
Others cite the cost and complexity of irrigating the green roof as a reason to not install one. However, using native species, especially drought-tolerant ones, can require no irrigation except in the beginning while the roots are being established. Mixing water-storing plants with other types of vegetation, such as native grasses, can create beautiful sceneries hardy enough to stand up to the tough conditions of a roof.
Photo of Lebanon Hills Visitor Center rental building in Eagan Minnesota with gardens and green roof in bloom
When it comes to the overall costs of installing green roofs, the Environmental Protection Agency estimates the cost at $10 to $25 per square foot. This price is highly variable, depending on location, accessibility of the roof, and green roof type. The warranties on building products used in a green roof are similar to those for all of the other building products in a home. They must be installed according to the manufacturer’s specifications by a qualified professional.
So for your next project, consider installing a green roof. Work with your builder, structural engineer, architect, and installer to ensure a high-quality roof that can help reduce your utilities, and provide an oasis on top of your home.
