Technology Snapshot & Benefits:
Green roofs are roofs on which plants are grown. The roofs are extensions of
existing roofs that are suited with waterproofing systems, fiber cloth, drainage
systems, irrigation systems, and soil to keep the roof safe while providing an
environment where plants can grow. These roofs are beneficial in a variety of
ways. The evaporative cooling of the plants and heat reduction from the added
thermal resistance of the plants can help reduce monthly cooling costs. This
reduction is even more significant in urban areas where the roofs can also help
combat "heat island effect," which is caused by reflections off buildings and
cars in urban areas and often contributes to high cooling costs. Because of
this, the size of heating, ventilation, and air conditioning (HVAC) systems on
the roof can also be reduced in new or remodeled homes, which can save money.
For homes or businesses with solar heating systems mounted on the roof, this
cooling helps increase the efficiency of the solar units. Green roofs also
extend a roof's lifespan an average of 20 years by reflecting UV rays and
preventing the roof from experiencing extreme temperature changes. Because the
plants and soil act as insulators, homes with green roofs require less
traditional insulation. Green roofs act as a fire retardant and reduce noise
pollution by buffering the roof. The buffering also eliminates nearly all
electromagnetic penetration, which can be important in buildings with
telecommunications equipment mounted on the roof.
Evidence has shown green roofs contribute to personal and societal well-being.
Studies also show that green roofs help reduce stress, stress-related illness,
and patient healing times. Food and flowers that can be sold or consumed by the
homeowners can be grown on the roof. The plants on the roof help filter CO2 out
of the atmosphere and other pollutants out of the rainwater. Having largely
biodegradable roofs helps reduce the amount of roof waste filling landfills.
They can also provide a habitat for small wildlife in urban or suburban areas.
The work necessary to maintain, design, produce, and install green roofs can
create much-needed jobs. Additionally, green roofs may be fashioned for specific
purposes, such as playgrounds, day cares, or recreational/leisure areas that
would provide additional outdoor community space.
Estimated Cost Savings:
Estimated cost for green roofs is $8-25 per square foot, depending on the type
of roof (extensive or intensive; see "Issues" and "Installation"), soil and
vegetation desired, and location of the home or business. Costs may be higher in
urban areas because of traffic costs, or in areas where materials aren't readily
available. Savings for the homeowner on monthly cooling costs vary depending on
climate, building type, and typical building use; however, according to a 2002
Canadian Research Council study, green roofs can reduce peak energy demands up
to 75%, but the average homeowner utilizing a green roof reported 20-25%
reduction in heating and cooling costs. Some insurance companies, such as State
Farm, are also offering a reduction in home insurance costs of up to 33% for
installing green roofs. Companies installing green roofs could also potentially
gain emissions trading credits or LEED points. It should be noted that the cost
of replacing or fixing a green roof is usually higher than that of replacing or
fixing an ordinary roof, but the savings due to the extended lifetime of green
roofs will counterbalance these costs in most cases.
There are several legal issues associated with green roofs. The homeowner or
business owner is usually liable if there is any roof damage due to leakage or
roots; therefore, it is very important that green roofs are properly installed
and maintained. There is a time commitment for the homeowner or a hired
caretaker of the roof, although this commitment can vary greatly. There are two
types of green roofs: extensive and intensive. Intensive roofs can support a
wider variety of plant life, even small trees, and are labor-intensive,
requiring a lot of maintenance. Extensive roofs are much less demanding and are
set up to be basically self-sustaining, needing only to be weeded once or twice
a year. The time that is available for one to care for the green roof should be
taken into account when deciding what type of roof to get and what time of
plants to grow.
If the roof is being used for recreation, there are obvious potential personal
injury issues, so safety must be carefully considered. Another tip for those
looking to install green roofs is to set up a system that can collect rainwater
or runoff and use that water to irrigate the roof. This keeps water bills lower
and is another easy way to recycle resources.
Reduction in heating and cooling costs from green roofs is dependent on original
demand, which is in turn dependent on local climate. Areas with more extreme
temperatures are likely to see the most benefit.
In very dry regions, green roofs require more irrigation. Local weather, such as
high winds, should be taken into account when choosing which type of plants to
install and how to install them. Pollution reduction is most apparent in heavily
Green roofs must be installed by a professional. Installation involves
installing structural support, a vapor control layer, thermal insulation, a
waterproof membrane, a drainage layer, a filter membrane, a growing medium
(usually soil), and any desired vegetation. Installation of intensive green
roofs is more expensive, typically $15-25 per square foot, than extensive green
roof installation, typically $8-20 per square foot.
Green roofs can be installed in new or old homes. It is highly recommended or
necessary (depending on the roofing company's policy) to consult a structural
analyst before installing a green roof to ensure that the roof is tailored to
work with a specific roof.
Videos On This Topic:
Green Roofs 101 (4:50)
- GreenRoofs.com - Find out what green roofs are, how they are installed, and
how they can impact our environment and energy savings.
(6:21) - Green Energy TV -
Green roofs are
being installed in buildings across the globe, from Germany to the US to
Australia to Japan. In this video, listen as Dr. Patrick Dixon, "Europe's
leading futurist" and authority on global trends, discusses various
implementations of this technology and what it means for the environment,
building temperatures, and finances.
Green Roofs Project
in Nebraska (5:19) - Backyard Farmer -
function not only as a temperature barrier, but as a solution to the problems
caused by storm water run-off. Watch this video to find out more about what
green roofs are, what they're made of, and how the different types of plants
work to help improve home surroundings.
Intro to Living Roofs/Green
Roofs (2:09) - Building Green TV -
Green roofs are a
great way to make use of empty space while decreasing a home's temperature and
increasing drainage and structural support. To learn more about the basics of
green roofs (what they are, how they're built, and why they're so beneficial),
watch this short video from PBS's Building Green TV.
Green a Roof, Cool a City (4:59) -
In New York City,
plants are often overwhelmed by concrete as buildings expand and urban
structures consume the landscape. An innovative way to counter the
disappearance of these plants is to install green roofs on new and existing
buildings like Silver Cup Studios did recently. In this video, find out more
about their project as well as the benefits of green roofs, what they�re made
of, and how they are constructed.
On This Topic:
Building Materials Guide"
"Green Roofs: Building the Future"
"Green Roofs: Building the Future"
Water Institute Green Roof Project: "Green Roof Installation"
Roofs.com: "The Greenroof Industry Resource Portal"
Roofs for Healthy Cities"