Green
roof, eco-roof, nature roof or green roofing system
are general terms referring to vegetated roof
coverings consisting of a thin layer of living
vegetation installed on top of a modified conventional
roof system with significant changes. Modern green
roof systems replace traditional rooftops; flat
or angled up to 45 degrees, with a series of carefully
engineered layers. A water and root- repellent
membrane is installed on top of a reinforced roof
structure. A filter layer is placed between the
base membrane and a layer of soil as thin as 1.2
inch thick. Finally the soil layer is seeded with
varieties of simple durable plants- sedums, perennial
grasses and other "rock garden" plants.
Within a short period of time the entire rooftop
is covered with a solid layer of dense vegetation
forming an ecologically friendly environment where
a potentially harmful one existed. The new roof
will perform its intended design functions in
an excellent manner, as well as, deliver a multitude
of additional benefits.
The
green roof concept is akin to the popular, but
traditionally heavy and difficult to maintain
roof garden found atop buildings worldwide. Roof
gardens are nothing new. Gardens for the enjoyment
and relief of city dwellers have existed atop
buildings for decades. Such roof gardens are expensive
to build, often require modification of the structural
system of the building to support the increased
load and are fairly high in maintenance requirements.
When
it comes to roofing, concern for the environment
isnt new either. For decades roofing choices have
had an environmental and energy impact on civilization.
Today, energy efficient and environmentally friendly
roof designs are growing in popularity, as even
more and more building owners become aware of
how much their roofing choices can affect the
environment as well as their pocketbooks. Modern
green roof systems generally fall into two categories,
extensive or intensive, depending on the type
of landscape structural burden. Extensive green
roof systems are designed for lightweight planting
burden construction on flat or sloped roofs. Intensive
green roof systems are intended for heavier landscape
construction for flat roofs and landscape planters.
There are distinct differences in the application
and design criteria for the load requirements
of each system.
Extensive
systems may be installed over any properly designed
deck, including Concrete, wood and steel. Typically
a vapor barrier or vapor retarder is installed
over the deck depending on occupancy and local
conditions. Over the vapor retarder or substrate
a layer(s) of (optional)thermal insulation is
installed. Mechanical fastening of the insulation
may be required depending on wind uplift conditions,
slope, building height and local codes. The waterproofing
membrane and metal flashings are installed to
complete the watertight envelope. Decks with slopes
of 8 degrees or more may require the installation
of landscape retainers at the roof membrane elevation.
Intensive systems may be installed over decks
designed to accommodate the added load. Typically,
concrete decks are the best design choice.
Eco-roofs
are becoming fairly common in parts of Europe,
principally in Germany and the Netherlands, where
green roof technology is well researched and a
green roof industry is well developed. The Amsterdam
airport has incorporated a sloped green roof into
the design of its terminal building. Some cities
in Germany now require green roofs on flat-roofed
buildings; by 1996 over 3.2 million square feet
of green roofs had been constructed in Germany
alone.
Green
roof technology explores and promotes interest
in viable solutions that are aesthetically, functionally
and environmentally friendly. It addresses the
urgent ecologically demanding issues of air and
water quality and storm water management. Green
roofs help to invest in the protection of our
environment by diminishing developmental impact
on our communities while providing a fresh approach
with visually appealing organic architecture.
The new paradigm, variously known as eco-roofs,
green roofs or extensive roof gardens, typically
cover the entire roof of a building with a continuous
thin growing medium that supports low vegetation.
Eco-roofs are lightweight, modern versions of
he sod roofs that are a centuries-old tradition
in Scandinavia. Because of their light weight
eco-roofs require little additional load-bearing
capacity from a buildings structural systems;
in many cases they may be installed on existing
buildings with no structural modification. They
do not require flat roofs as do conventional roof
gardens but may be installed on roofs with slopes
of up to forty-five degrees if provided with a
raised grid structure to hold the growing medium
in place. Additionally eco-roofs typically require
little of no irrigation or fertilizer.
Green
roofs create buildings and developments that heal
rather than harm the environment. Green roof structures
can become net producers of energy, clean water
and air, as well as part of healthy human and
biological communities.
