Green Roofs - Living Architecture Monitor Winter 2020 - 20

METAL BALLS DROPPED ON GREEN ROOFS
SIMULATE THE IMPACT OF HAIL

Photo courtesy Leila Tolderlund

a rapid return on investment.
The direct value of many of
the aforementioned benefits
can be difficult to measure for
the individual developer or
building owner.
When looked at for an
extended 60-year life-cycle,
green roofs have the ability
to offset their own initial
investment cost, by protecting
and prolonging the life of the
roof membrane it sits on. This
return on investment over 60
years also includes projected
costs for maintenance and
irrigation over the life of the
green roof. The payback will
shorten significantly in case of
a severe hailstorm hitting anytime within that time frame.
There are few publications
on the subject of green roofs
ability to mitigate hailstorm
damage. It has not been particularly relevant for insurance
companies to consider (or

promote) the added benefits
of green roofs in the past. On
the contrary, green roofs might
have been (and to some degree
still are) a perceived factor of
risk for insurance companies.
Yet, as the green roof industry
continues to grow in North
America, and requirements
such as for example, the Green
Building Ordinance (I-300;
CB18-1134; 2018) for the City
of Denver takes effect, building owners across all sectors
in the industry along with city
officials are beginning to better understand the integrated
and holistic benefits associated
with green roofs.
During the costliest hailstorm in the Denver Metro
area in May, 2017, developer
Zeppelin discovered that two
of his buildings with green
roofs were left intact with no
damage. Buildings immediately
adjacent without green roofs

LIVING ARCHITECTURE MONITOR / WINTER 2020 / 20

received severe damage. The costly replacement and repairs
on one of his buildings turned out to be more expensive than
an initial green roof installment. Observing that the areas of
roofs protected by green roofs were left intact, made developer
Zeppelin realize the benefit of the upfront cost and investment
in green roofs. 'An unseen upside...', Kyle Zeppelin said, that
'...more than outweighed the upfront cost [for the green roofs].
Additionally, he said, this is likely not the last hailstorm - so
there is also that advantage'. And he is probably right. Adding
a green roof to a low slope building in the 'Hail Alley' region
will more than likely protect roof surfaces more than once in
its 60-year life cycle. In 2019 alone, the US was hit with over
5,000 major hailstorms according to the NOAA's Severe Storms
database.
Accumulative insurance premium discounts, if green roofs are
approved as a Class 4 category roofing material, have the potential to be a pivoting factor in making green roofs a cost-efficient
choice for low-slope roofs. The significant savings associated
with adding green roofs to low slope buildings can help grow
a new shared interest between property owners and insurance
agencies in regions prone to hailstorm damage.
Research on green roofs ability to mitigate hail damage on
low-slope roofs was done by Assistant Professor (CTT) Leila
Tolderlund LEED AP, GRP, Research Assistants Martin Egan,
GRP and Adam Bosco, and Professor Peter Jenkins PhD, University of Colorado Denver.

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Green Roofs - Living Architecture Monitor Winter 2020

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