The green roof is a sustainable concept that is growing in popularity
By JOE WICENTOWICH
Sustainable design in single family residential construction is no longer a vernacular that is limited to construction industry professionals, as new homebuyers are increasingly pursuing green design concepts in response to their own environmental sensibilities.
One sustainable concept that is “growing” in popularity is the use of the “living roof,” or “green roof.” Many builders resist incorporating a living roof in residential construction as it is often perceived as being unproven, adding unnecessary construction costs, increasing potential for roof failure or leaks, and requiring additional maintenance. However, the benefits have been demonstrated in passive energy home design throughout Europe for many years.
A living roof is simply a system that uses natural vegetation within a thin layer of soil, combined with a drainage system that sits on top of a waterproof membrane. The entire system completely replaces traditional finish roofing materials such as asphalt, shingles, and tiles. Some advantages of the living roof include the following:
- They are natural insulators. Living roofs do an excellent job of providing additional insulation to help keep the house cooler in the summer and warmer in the winter, thus lowering energy costs.
- They help reduce the heat island effect. Heat islands affect communities by increasing summertime peak energy demand, air pollution, and greenhouse gases, due to an increase in the ambient air temperature caused by additional solar heat released from low reflective roofing. Not unlike standard “cool roof” membranes, green roofs absorb solar heat at a much slower rate. They also retain the heat longer and release the absorbed heat back into the atmosphere at a slower rate.
- They help with stormwater management. Traditional roofing sheds water at a fast rate, which requires immediate filtration at the point of discharge before it can return to the sewer system. A green roof not only retains water for a longer period of time, it provides its own irrigation before releasing the water at a slower rate. Performance data indicates that green roofs can retain up to 70 percent of collected precipitation, which is a nice benefit when a municipality charges wastewater discharge fees.
- They protect roofing membranes. Green roofs provide impact and UV damage protection to the underlying waterproof membrane, which leads to the elimination of roofing warranties. Furthermore, while hail damage can wreak havoc on a shingle system, with a green roof the homeowner will only need to worry about replacing their begonias, which will be appreciated by insurance companies.
- They can serve as ballast for solar collector systems. Many solar panel assemblies require mechanical fastening to the roof assembly, which necessitates additional waterproofing at penetrations. Living roofs can be integrated with the panel frames while acting as ballast for the panel assembly, thus eliminating membrane penetrations. There are several companies that market fully integrated solutions that combine the two systems.
- They provide a benefit to outdoor living. While roof decks are nothing new, the delightful ambient quality of natural outdoor living has often been lost. The green roof provides the missing ingredient, and there is no limit of creative ways to integrate them into an outdoor living space.
Construction costs of living roofs vary based on overall complexity, but can range from $7.50/ SF for a basic layout to $25/SF and up for complex designs. There are also a few restrictions, such as requiring a low slope roof area and involving a professional designer. However, in addition to demonstrating environmental sensitivity, it is hard to ignore the overall value of providing a beautiful outdoor experience within the footprint of the house, especially in “small lot” homes, where the ability to provide private open space is limited and difficult. In summary, it is time for builders to consider providing green roofs in response to the buyer’s quest for sustainable homes.
Joe Wicentowich, AIA, NCARB, LEED AP, is an Associate and Senior Project Manager at Danielian Associates Architecture + Planning. He can be reached at firstname.lastname@example.org