The use of live vegetation in both commercial and residential projects began in the 1980s and now has grown into a thriving industry that has developed multiple products for various project needs. Pioneered in Germany in the 1960s, a modern “living” or “green” roofing system is more than dumping soil on a roof and planting vegetation. The system is made up of a layered membrane roofing system used to support the soil for the vegetation. The systems can either be low-maintenance systems that take advantage of hardy vegetation or it can become an extension of the landscaping offering a wide variety of vegetation.
A green roofing system is a marriage of several components to get the job done. It begins with the application of a waterproof membrane to the roof decking followed by various layers of drainage channels and retention fabric to support the soil substrate. The substrate used is not actual top soil which would be to dense for a roofing system. Instead it is a mixture of mineral compounds designed to retain just enough water for the planted vegetation. The total cost of installation can range from $15 to $20 a square foot with some costing $100 per square foot. This would include installation of the waterproofing membrane to the soil substrate and planting. The installation contract general includes maintenance for the first five years also.
A basic green roof, or extensive green roof, has less than six inches of soil substrate and is designed to be low maintenance. Its primary objective is to provide energy savings and can easily integrate with solar panels. An intensive green roofing system has more than six inches of soil and includes more bio-diversity in its vegetation. This system goes beyond utilitarian goals striving to ad aesthetic value as well. These systems become gardens that can support trees creating open spaces to use and new habitats for a variety of species. However, with a green roofing system you must always keep in mind the extreme environment that the vegetation will be in and chose the vegetation accordingly. All selections should be drought-tolerant, hardy plants selected with the aid of a knowledgeable, licensed landscape professional.
Depending on use and implementation a green roof can add up to 18 points to your LEED certification score. These systems have been used to reduce the heat island effect, maximize open space, reduce potable water needed for irrigation, and restore habitat. A green roof also can reduce construction waste generated from traditional roofing systems, lower cooling costs by reducing HVAC loads, and reduce or eliminate the need for gutters and storm drains.
Green roofing systems can be used in both new construction and retrofit applications. When used in a retrofit project care should be given to installation of the waterproof membrane to reduce the chances of leaks. On average, the cost in either scenario is twice that of a traditional roofing solution. This cost increase is offset by the energy savings created, reduced costs of storm water system, and the doubling of the life expectancy of the roof itself. Because of the protection provided to the waterproof membrane, green roofing systems have a life expectancy of 30 to 50 years.
The National Research Council of Canada estimates that a green roof can reduce air conditioning loads by 75% while also providing natural habitats for local vegetation and species. In urban centers, the substrate of green roofs contains fungi that filter heavy metals from the air. Green roofs also can be used to direct rain water to graywater systems for use in toilets and irrigation along with filtering water that is returned to the local aquifer. Interior noise reduction and climate control are also benefits of a green roof. The systems are extremely durable and resilient when properly installed making them a highly sustainable system. They are also primarily made of recycled and locally sourced materials that are easily recycled at the end of usefulness. Taking all of this into account, these systems are one of the best examples of a green product on the market today.