Green Roofs - Living Architecture Monitor Winter 2020 - 6

The Benefits and Challenges
of Green Roofs on Public and
Commercial Buildings

A Report of the United States General Services Administration
MAY 2011

tion guidelines. That will stimulate interest
in the market and build capacity in the
industry so that a mandate has more chance
of succeeding.
SWP: What has surprised you most during your
research and analysis on green roofs?
KW: The study we did for Walmart about
10 years ago generated a few results that
run counter to popular assumptions about
green roofs. My favorite, I think, related
to maintenance. People often talk about
green roofs being high maintenance, but
for Walmart, the green roofs actually saved
money on maintenance compared to their
standard roofs. There are two main reasons
for this. First, Walmart's roofs are flat and
they see a lot of traffic - technicians are
up there regularly maintaining the HVAC
equipment. Combine that with the daily
thermal expansion and contraction experienced by any exposed roof membrane, and
you get wear and tear. With a green roof, the

LIVING ARCHITECTURE MONITOR / WINTER 2020 / 6

membrane is buffered from foot traffic and
thermal expansion and needs less repair. The
second factor is the plant composition. When
green roofs have high maintenance costs, it's
usually because the owner is trying to maintain an exacting aesthetic. Walmart (along
with designer and maintenance provider,
Roofmeadow) went with a more natural look
and were willing to allow for some drift in
the rooftop plant species, so their maintenance costs were correspondingly lower.
I guess the other thing that can sometimes be surprising is just the sheer number
and range of the benefits that green roofs can
provide. When I review the laundry list of
benefits and the magnitude of the value with
a client or audience, it sometimes seems a
little crazy that one building system can do so
much: energy savings, heat island and climate
change mitigation, stormwater attenuation,
roof longevity, biodiversity, wellbeing and
productivity, real estate value, green jobs, etc,

etc - it's a lot! But when you consider that a
green roof in concept is really a little slice of
nature lifted up onto a building, it all begins
to make sense. What other than nature can
provide all the things people need, and in
such a beautiful package?
Kirstin Weeks kirstin@bio.studio
More Information
SF cost-benefit study https://default.sfplanning.
org/Citywide/livingroof/SFLivingRoofCostBenefitStudyReport_060816.pdf
GSA https://www.gsa.gov/cdnstatic/The_Benefits_and_Challenges_of_Green_Roofs_on_Public_and_Commercial_Buildings.pdf
Walmart
https://cdn.corporate.walmart.com/95/ab/
ecb63ba44f51bec6f9aa42c73a9e/walmart2013-green-roof-report.pdf

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https://default.sfplanning.org/Citywide/livingroof/SFLivingRoofCost-BenefitStudyReport_060816.pdf https://www.gsa.gov/cdnstatic/The_Benefits_and_Challenges_of_Green_Roofs_on_Public_and_Commercial_Buildings.pdf http://cdn.corporate.walmart.com/95/ab/ecb63ba44f51bec6f9aa42c73a9e/walmart-2013-green-roof-report.pdf http://www.archatrak.com http://www.LIVINGARCHITECTUREMONITOR.COM

Green Roofs - Living Architecture Monitor Winter 2020

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