A green roof system is green both because it’s planted with all sorts of vegetation and because it harbors many environmental benefits. The soil or other growing medium insulates the roof, slowing the loss of conditioned air from inside the home to the outside. It also absorbs the sun’s heat, keeping the inside space underneath cooler in the summer. The growing medium absorbs rain water, reducing the amount of water the roof sends through gutters and into the storm system (the plants use this water so rarely does a green roof have to be irrigated). The plants provide habitat for birds and butterflies, help clean the air, and can even be a source of vegetables and herbs. The assembly can have a lifespan of up to 50 years when installed properly. While green roof systems aren’t that common (yet) atop houses, they are quickly gaining popularity in commercial and institutional buildings.
There are some green roofs in our neighborhood, however.
In 2006 Jane and Rick Rutherford decided to install a green roof system atop a portion of their Hill row house. Through contacts at local nonprofit DC Greenworks, the Rutherfords were able to hire a contractor to make some structural modifications to their home and ready the roof for planting. Using sedums and herbs from Emory Knoll Farms in Maryland, the roof was covered with a special planting soil and covered with 350 small plants. Sedums are drought-tolerant plants that can survive up to 80 days without water—perfect for planting in places that can’t be hosed down easily. The installation was complete in April 2008.
While Jane didn’t mention it in our conversations, please note that normal green roof systems also include a waterproofing membrane, water-retention layer, and sometimes a root-barrier membrane that prevents plant roots from getting into cracks and crevices of the roof structure. These layers are placed under the soil to prevent water infiltration (leaks).
Three years later, the Rutherfords report their roof “has held up beautifully.” Maintenance on the roof is minimal. Jane reports cutting back the herbs (a type of chive) in the fall and having to weed the roof “a couple of times,” to rid it of the plants the birds bring when they drop seeds. The biggest benefit they report is the reduction in water runoff. After a moderate shower there is hardly a trickle of water coming off the roof. The greatest benefit, however, may be the toughest to quantify: the green roof is visible from Rick’s home office as well as some of the neighbors’ homes and provides a pleasant view amid all the other asphalt and rubber roofs on the block.
When it’s time to replace your home’s roof, consider greening up the neighborhood with a green roof system.