Concerned with the aesthetic
and functionality of a building, designers are
usually apprehensive behind piles of drawings in
attempt to discern the best floor plan layout,
despising the number of levels of a building.
When it comes to the roof, however, it
seems that not much consideration is necessary and
typically a plain flat slab is the best solution
to all modern, and even “sustainable”
buildings.
Roofs are the
most exposed surface of a building, receiving
direct sunlight and rain all year long.
With such a large impervious cover area,
they can certainly have a great impact (positively
or negatively) on the city’s environment.
Thus, particularly in dense cities, why not
make the roof vegetated and useful?
“Green
roofs,” which is a general term for roofs that
in some way improve the building’s self
sufficiency, offer several advantages for their
diverse design solutions. Some of the several
benefits include the encouragement of native
plants; the improvement of life span of roof; the
reduction of urban heat island; the possibility of
storm water management, and the addition of
accessible green areas.
The
Encouragement of Native Plants
By designing
vegetated roofs, the use of local plants and
biodiversity can be greatly encouraged.
Obviously, not any plant is suitable for
roofs. Besides
the load-bearing capacity of the roof, the climate
conditions must also be considered.
The plant selection is usually based on
adaptability and performance since vegetated roofs
varies in soil depth from approximately 18 inches
to 4 feet. Native plants have the advantage of not
threatening the biodiversity and of being easily
adaptable to the local climate, since that is
their natural habitat; but at an efficient and
economical point of view, native plants are the
ideal solution; they are drought tolerant and
require less watering, therefore reducing the
water consumption of the building.
The
Improvement of Life Span of Roof
Contrary to
what may be thought, green roofs do extend the
life span of the roof significantly.
Plants and other layers within the green
roofs assembly such as soil, gravel and asphalt,
help protect the roof membrane from extreme
temperatures, absorbing some of the ultraviolet
light and other environmental factors to protect
the roof surface from weathering; it also extends
the life of the roof to 40 years (compared to 10
to 15 years for a regular roof).
Although the initial cost of installing a
vegetated roof may be higher than traditional roof
systems, its cost can be partially compensated in
the long term.
In addition, as vegetated roofs become more
popular in the
US
, the initial cost is most likely to be reduced.
The
Reduction of Urban Heat Island
The heat
island effect, which is the difference in
temperature between urban areas and the adjacent
countryside, is created when vegetation is sparse
and an abundance of reflective surfaces and
impervious areas exist.
By implementing vegetated roof in
buildings, the effect could be noticeable not only
with the building itself but with the city as a
whole. Besides
reducing the electricity consumption of the
building due to its effective roof insulation, the
vegetated roof, if taken to a larger scale, can
also improve the air quality of city and reduce
the urban temperature; according to studies,
vegetated roofs can be up to 80ºF cooler than
buildings with traditional roofs.
Vegetated roofs, therefore, can play a
crucial role in improving the cooling and shading
areas of dense cities.
The
Possibility of Storm Water Management
Besides
vegetated roofs, other types of green roofs are
those that efficiently and effectively make use of
rainwater. Traditional
roofs (with shingles) can also be designed in a
“green” way, by collecting storm water in
cisterns to be used externally (i.e. plant
irrigation) or internally (i.e. toilet flush).
In addition, green roofs can also capture
rainwater while still keeping vegetating roofs;
the plants and other layers within the green roof
can act as a filter and can improve the quality of
the rainwater runoff.
Furthermore, in large commercial buildings,
partial roofing can be designated for vegetated
roof while the other portion can be mainly set
aside for storm water collection.
In fact, fresh
water is becoming scarcer due to population growth
and consumption rates per capita.
Therefore, the importance of capturing this
“taken-for-granted” and “free” water is
growing substantially; this is crucial for the
building’s economy as well as for the
environment itself.
The
Addition of Accessible Green Area
In addition to
all of the economical and environmental
advantages, green roofs can also be seen as an
“urban oasis.”
Packed with growing high-rises, modern
cities are urging for green, open spaces. A
Starbucks in
Austin
,
TX
, for instance, is becoming more popular by
providing a view to a green roof.
It is clearly more pleasant to look out at
a green, livable roof than at a standard, lifeless
roof. And
especially those roofs that are public accessible,
the vegetated roofs can provide enjoyable outdoor
space that help build a sense of community and
improved quality of life.
With only a
few of the advantages of green roofs mentioned
above, it is surprising to see that many of the
so-called “green” buildings have not yet
considered green roofs as a solution.
In fact, green roofs can greatly contribute
toward several LEED points.
If the landscaped roof covers at least 50%
of the roof area, for instance, the design can
earn points for Site Credit (7.2 Heat Island
Effect). An
efficient green roofing system can also contribute
to the Water Efficiency Credit (1.1 Water
Efficient Landscape) as well as to the Energy
& Atmosphere Credit (1 Optimize Energy
Performance).
Therefore, it is ironic to see that not all
“green” designers are using this feature
towards their own benefit.
Although
useful and livable roofs may not be widely
designed yet, there will hopefully come the time
when the uncertainty of going for green roofs will
not longer be questionable.
Ana
P S Beckner is a student at the University of
Texas at Arlington, and wrote this article as part
of a course curriculum focusing on sustainability.
All
comments are the sole responsibility of the
author.
This
article was originally posted 9/12/06.
