Green Roofs, or Vegetative Roofs, offer many benefits to the building and the environment. These include the reduction of storm water run-off, heat island effect, building heating and cooling costs; as well as extending the life of the roof’s membrane and improving air quality.
New York City has started a five-year tax abatement program.
Types of Vegetative Roofs:
Extensive Roofs are generally 2″ to 6″ deep and tend to include drought tolerant plants.
Semi-Intensive Roofs are generally 6″ to 10″ deep and can include grasses, herbs and small shrubs.
Intensive roofs are 10″ or greater in depth and may include trees and larger shrubs.
When deciding the type of Vegetative Roof system you would like, load factors are a main consideration. When building new, the necessary live loads and dead loads can be designed into the structural system. When installing a vegetative roof on an existing building, you must understand the limitations of the existing structure. Other considerations include drainage capacity, membrane selection, water test loads and wall and curb heights. Additional code considerations may include wind loads and fire ratings.
Elements of a Vegetative Roof System:
The components of a vegetative system may include the following – The waterproofing membrane, protection course, root barrier, drainage layer, moisture resistant insulation, moisture retention layer, aeration layer, reservoir layer and filter fabric. These components would be installed prior to the installation of the growing medium and selected vegetation. Timing may be critical due to growing/planting cycles.