by Lisa Murphy
Often times urban landscapes can seem like an endless expanse of skyscrapers and
other man-made materials, with a horrific lack of wildlife for as far as the eye can see.
One burgeoning trend in building planning and renovating is trying to change that. The
trend is that of “green” or “living” roofs. Basically a green roof is where vegetation is
planted on building rooftops and allowed to grow.
Green roofs aren’t a new idea; they have been around for hundreds of years. Sod
roofs, as well as roofs made from other living and growing vegetation, were quite
common in Norway (and other parts of Europe) in the 18th century.
other man-made materials, with a horrific lack of wildlife for as far as the eye can see.
One burgeoning trend in building planning and renovating is trying to change that. The
trend is that of “green” or “living” roofs. Basically a green roof is where vegetation is
planted on building rooftops and allowed to grow.
Green roofs aren’t a new idea; they have been around for hundreds of years. Sod
roofs, as well as roofs made from other living and growing vegetation, were quite
common in Norway (and other parts of Europe) in the 18th century.
Photo Credit: http://www.homesresult.com/tag/green-roofs/
The relatively
recent popularity of living roofs was started in Germany in the 1960s, and
while the United States has greatly embraced the practice of green roofing, it
is still most popular in Europe.
Photo Credit: City of Chicago
Photo Credit: City of Portland
One of the largest living roofs in the world is in Dearborn, Michigan at Ford Motor
Company’s Rogue River Plant. Over 42,000 square meters are covered in sedum and
other plants.
Company’s Rogue River Plant. Over 42,000 square meters are covered in sedum and
other plants.
Photo Credit: Ford Motor Company
At this point you may be thinking: “Sure, plants on top of buildings seems like a good
thing, but is it worth the effort?” The answer is that numerous studies have shown very
interesting and important benefits of living roofs.
termed the “carbon economy.” This involves many global entities trying to lower, and
cap, carbon emissions. Within the new carbon economy, these entities buy and sell their
shares of “carbon” to show how Eco-conscious they are and to make an effort to lower
and control carbon emissions. This economy also involves taking preventative measures
that do lower carbon emissions, or that can at least help to combat carbon emissions in
different ways. Living roofs are one such way to combat carbon emissions.
Living roofs help to mitigate the negative effects of buildings’ carbon footprint by
recreating green space at the roof level. Healthy, growing vegetation on rooftops can
help store and retain CO2 and other pollutants in urban environments. Simply storing
carbon is an asset to an urban environment, but living roofs provide even more ecosystem
services. Along with filtering air and pollutants, green roofs are fantastic for storm water
management. The roofs are designed to filter and sometimes retain storm water. When the
water is released the runoff is far cleaner than if it had come off a regular city roof.
thing, but is it worth the effort?” The answer is that numerous studies have shown very
interesting and important benefits of living roofs.
The Pros:
All over the world corporations, cities, and nations have begun dealing in what istermed the “carbon economy.” This involves many global entities trying to lower, and
cap, carbon emissions. Within the new carbon economy, these entities buy and sell their
shares of “carbon” to show how Eco-conscious they are and to make an effort to lower
and control carbon emissions. This economy also involves taking preventative measures
that do lower carbon emissions, or that can at least help to combat carbon emissions in
different ways. Living roofs are one such way to combat carbon emissions.
Living roofs help to mitigate the negative effects of buildings’ carbon footprint by
recreating green space at the roof level. Healthy, growing vegetation on rooftops can
help store and retain CO2 and other pollutants in urban environments. Simply storing
carbon is an asset to an urban environment, but living roofs provide even more ecosystem
services. Along with filtering air and pollutants, green roofs are fantastic for storm water
management. The roofs are designed to filter and sometimes retain storm water. When the
water is released the runoff is far cleaner than if it had come off a regular city roof.
Another benefit of green roofs is that they help to combat the Urban Heat Island
Effect. Studies have shown that most common materials in cities (metals, concrete,
cement, asphalt, ect.) absorb UV radiation and heat during the day and make cities up
to 4ºC hotter than surrounding areas. Even after the sun has gone down these urban
materials continue to radiate heat, so cities do not cool down at night as much as they
naturally should. Large scale studies in Chicago and Washington D.C. have shown that
the microclimates of green rooftops are as much as 4.4ºC cooler than traditionally roofed buildings. Researchers even went as far as to estimate that if all roofs in a major city
were greened, urban temperatures could be reduced by as much as 7ºC. That is a large
difference in temperature, and not only can it have a significant effect on human comfort
and well-being, but it can drastically affect wildlife within cities and near city limits.
Changing temperatures is not the only affect living roofs have on wildlife. In cities
throughout the world green roofs have become vital stopovers for migrating and local
birds. Living roofs can provide important feeding and nesting habitats for endangered and
displaced birds and other wildlife. Providing habitats for animals within the city helps to
raise biodiversity within a usually sparse, human-made and human-dominated landscape.
Effect. Studies have shown that most common materials in cities (metals, concrete,
cement, asphalt, ect.) absorb UV radiation and heat during the day and make cities up
to 4ºC hotter than surrounding areas. Even after the sun has gone down these urban
materials continue to radiate heat, so cities do not cool down at night as much as they
naturally should. Large scale studies in Chicago and Washington D.C. have shown that
the microclimates of green rooftops are as much as 4.4ºC cooler than traditionally roofed buildings. Researchers even went as far as to estimate that if all roofs in a major city
were greened, urban temperatures could be reduced by as much as 7ºC. That is a large
difference in temperature, and not only can it have a significant effect on human comfort
and well-being, but it can drastically affect wildlife within cities and near city limits.
Changing temperatures is not the only affect living roofs have on wildlife. In cities
throughout the world green roofs have become vital stopovers for migrating and local
birds. Living roofs can provide important feeding and nesting habitats for endangered and
displaced birds and other wildlife. Providing habitats for animals within the city helps to
raise biodiversity within a usually sparse, human-made and human-dominated landscape.
Photo Credit: Earth Pledge. Green Roofs: Ecological Design and Construction (Atglen, PA: Schiffer Publishing), p. 77. Crerar SB419.5.G76 2005
There is even a
special kind of living roof, often referred to as a brown roof, which helps to
increase biodiversity even more. Brown roofs are important because they
specifically support rare species of plants, invertebrates, and animals. They
are made by taking locally sourced material and covering the flat roofs of new
developments, in an effort to somewhat mitigate the habitat loss caused by the
developments. The original idea was to allow the roofs to self-colonize with
plants, but they are sometimes seeded to increase their biodiversity potential
in the short term. In the UK, many of the roofs are being colonized by spiders
and insects (many of which are becoming extremely rare in the UK, especially in
developed areas) and provide a feeding site for insectivorous birds.
The Cons:
Perhaps the
largest drawback to living roofs is the start up cost. Nearly any building
(including residential homes) can be given a living roof, but some need certain
renovations to make this happen, and even when a building does not need
renovations, initial costs of these roofs can be quite high. All of the
materials needed for a green roof are highlighted in the figure below, and they
average costing about $15 per square foot on a perfectly flat roof. Costs only
increase for slanted and more complex roof designs. Then there is also the
added cost of watering and maintenance of green roofs.
Photo Credit: http://www.greenestate.org.uk/material_supply22
On the plus side, once installed most of
these roofs require very little maintenance. They usually only need to be
watered sparingly for the first year and never after that. Also, they generally
only need to be weeded 3-4 times a year, unless the roof is actually being
cultivated for gardening, which then it will have to be maintained as any
garden would. These roofs have even been shown to produce more economic
benefits than first imagined. The studies in Chicago and other major cities
discovered that living roofs are actually great insulators so in the winter
when it was cold the roofs helped to keep the buildings warm, and in the summer
they helped to keep the buildings cooler. The roofs turned out to have a rather
substantial positive effect on the cost of heating and cooling the buildings
they were on.
Another
interesting benefit was that living roofs actually help to extend the life of
the actual rooftops of buildings. Since soil, vegetation, and other living roof
matter cover the roof of the building, the materials that make the building’s
roof are actually protected from natural damaging processes such as UV
radiation and storms. Green roofs in Europe have been shown to last as long as
50 years, which is a lot longer than the average shingle roof lifespan of about
20, so longer roof life is just one more thing to offset installation and
maintenance costs.
Green roofs can do great things for biodiversity in developed areas and they are
economical. They should be implemented by more architects and city planners in the
future.
Public commentary focusing more on green roofs can be found here.
economical. They should be implemented by more architects and city planners in the
future.
Public commentary focusing more on green roofs can be found here.
References:
Czemiel Berndtsson, J., Emilsson, T. and
Bengtsson, L., 2006 The influence of extensive vegetated roofs on runoff
water quality, Science of The Total Environment, Volume 355, Issues 1–3, Pages 48–63
Gill, S.E., J.F. Handley, A.R. Ennos and S. Pauleit. “Adapting Cities for climate Change: The Role of the Green Infrastructure.” Built Environment Vol 33 No. 1, page 122-123.
Grant, G., Engleback, L., and Nicholson, B., Green Roofs: their existing status and potential for conserving biodiversity in urban areas [Report No. 498], Publisher: English Nature Reports (2003)
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