roofs can mean more than the typical covering that provides shelter
from the environment. With the advent of new materials and
thoughtful planning, today's roofs can be more than just a cover
to protect what is inside. They can increase a building's
energy efficiency, reduce storm water retention, extend the service
life of waterproofing, reduce the urban heat island effect, improve
the air quality around us, and reduce noise infiltration.
Green roofs can be divided into (3) basic types:
"Extensive" which are typically low parapet roofs that
require minimal maintenance and have a shallow depth growth medium
of 3"-6" with a localized mix of vegetation. Planting
materials could include mosses, sedum, succulents and grasses.
"Intensive" green roofs are higher parapet roofs with
a growing depth of 8" to 5" or more. This roof includes
a larger variety of plants such as perennials, bulbs, annuals, shrubs
and trees. These roofs are often accessible to pedestrians
and can include such things as walk paths, streams, waterfalls,
and sitting areas. This type of roof often includes complex
irrigation and drainage systems and has a much higher weight per
square foot adding to a possible increase in the supporting structure.
A "Semi-Intensive" green roof combines features of both
the "Intensive" and "Extensive" green roof.
When deciding which roof to incorporate there are several factors to consider: If you are working with an existing building the weight carrying capacity of the roof will most likely require the installation of an Extensive roof. Before deciding which green roof to install, a structural engineer should be consulted. Is it going to be used by the buildings occupants or viewed from adjacent structures? Will your roof be in a prevailing wind or tucked behind other structures? Will the roof garden be exposed to direct light reflecting off an adjacent building? All of these issues can be solved with well thought out planning beforehand.
One very important consideration is what will a
green roof mean to your roof system warranty? Most of today's
manufacturers have design standards that allow for some form of
green roof but be sure to check first so as not to void your warranty.
By planning ahead a well thought out design can be achieved that
can meet both the economic and aesthetic benefits of a green roof.