Earth Our Only Home, Inc.
Green Roof Technology
There are three general green roof
types:  intensive, semi-intensive and
extensive.  An intensive green roof is
installed on a roof that can support at
least 60 pounds per square foot.  This
means that the planting media can be a
thickness of 9" or more and a variety of
plants, including small trees can be
planted.  The intensive green roof can
look very much like a beautiful park at
ground level, but it is atop a building.  
An extensive green roof can be likened
to a field or meadow with green plants
and wildflowers.  Generally the planting
media is shallow, between 3-5 ", on a
roof that can support at least 20 pounds
per square foot.  A semi-intensive roof
combines qualities of both intensive and
extensive green roofs with planting
media at 6-8" and the underlying roof
should support at least 40 pounds per
square foot.
This section focuses on several aspects of green roofs:  benefits of green roofs,
Karen Weber's theory on the importance of green roofs, a photo album of green
roof images, and a list of
references and links to learn more about green roofs.
Green roof technology has advanced
substantially over the past several decades.
 Germany has been installing green roofs
on many of the roof surfaces of 77 cities
since the late 1950s.  It has a wealth of
experience and research to share.  The
United States has been learning from
Germany and from various local
applications for the past 25 years.  Most
green roofs have at least the following
components in common:  a waterproof
membrane which serves as a moisture
barrier, a root barrier to prevent the roots
from penetrating the roof, a water retention
and/or drainage layer, a planting medium
or substrate, and plants.  The planting
medium is specially engineered from
regional resources to combine soil, organic
material, porous rocks (such as shale, lava
rock, pumice, etc.), and other elements to
provide an appropriate planting base that is
lightweight as well as capable of supporting
local flora.
A common plant used in green roof
applications is the sedum.  It is a hardy
succulent perennial that thrives in
sun-drenched conditions and has
beautiful blooms throughout spring,
summer and fall.  There are many other
plants and grasses that are also
available and many more being tested
for future use. About 1 ton of CO2 can
be absorbed by 23,000 sf of green roof
planted with sedums.