Green Roofs - Living Architecture Monitor Winter 2020 - 19

RESEARCH

GREEN ROOFS STOP COSTLY HAIL
DAMAGE TO ROOF MEMBRANES
BY LEILA TOLDERLUND, GRP, LEED AP, UNIVERSITY OF COLORADO DENVER

Hail storms result in costly damage to buildings. In some areas in the US they hit
often and they hit hard. One of the research areas I focus on at the University of
Colorado, Denver is precisely to what extent green roofs can help protect low-slope
roofs from damage caused by hail.

B

y using the recommended testing method, UL 2218
Standard for Impact Resistance of Prepared Roof Covering
Materials, my team tested impact resistance by dropping
steel balls onto unprotected and green roof surfaces from
various heights. Our research in this area shows conclusively
that both loose laid and modular green roof profiles as shallow
as four inches passed the UL2218 Class 4 requirements. Similar
to current UL 2218-rated hail resistant roof materials, with the
Class 4 rating, it is my hope that green roofs will be approved
as a roof choice qualifying for the same insurance premium
discounts. Roofs that use UL2218-rated materials enjoy up to 35
per cent savings on their insurance premiums.
The area that by far receives the most frequent and most
severe hail storms in the United States includes the states of
Colorado, Nebraska, Wyoming, Texas and Kansas. This vast
area is referred to as 'Hail Alley' because it is a prime target for
hailstorm destruction. Property damage and financial impact
due to hailstorms in the 'Hail Alley' region has been on the
increase over the past decade. The Insurance Services Office
ClaimSearch® 2019 database, one of the largest databases in
the world with detailed information about losses paid from
insurers and records of insurance premiums, reports a total
of 2,891,291 hail loss claims in the US over a 3-year period
(2016-2018). A single May 2017 hailstorm in the Denver area
caused $2.3 billion in damage from a total of 267,000 hail loss
claims, according to the Rocky Mountain Insurance Information Association.
Recent studies show that the severity of hailstorms and cost
of property damage is on the rise. This is in part due to increasLIVINGARCHITECTUREMONITOR.COM

ingly larger hailstorms, but
also due to the expansion of
urban and suburban development. Not only are hail storms
hitting harder, there are
also continuously more roof
surfaces to hit. An increase
in costly damages in decades
to come is therefore likely to
follow unless we implement
preventative measures.
Protection of properties and
reduction of insurance premiums are quite tangible continuous cost benefits that affect
the individual building owner
for the life of the roof. This is
quite relevant, as green roofs
have also proven to prolong
the life of roof membranes up
to three to five times. Especially in the Great Plains area,
where high exposure to UV
light and extreme freeze-thaw
cycles result in early wear and
tear, roof membranes exposed
to the elements only last at
best 12-15 years on average.
Roof membranes weakened

by exposure to the elements
are even more susceptible to
hail damage when larger hail
events occur. Green roofs can
protect roof membranes from
daily wear and tear from the
elements as well as during hail
events. Altogether, depending
on the membrane, green roofs
can extend the life of the waterproof membrane by 35-60
years.
Despite the multitude of
benefits (stormwater quality
and quantity management, creation of biodiversity, increase
of health and livability, cooling
and cleaning the air, growth of
urban agriculture, and increase
in real estate value, to name a
few) some building owners are
still reluctant to implement
green roofs due to their upfront costs. When considering
the upfront investment and
commitment to maintain the
life of the (green) roof, many
building owners are looking
for tangible direct value and

LIVING ARCHITECTURE MONITOR / WINTER 2020 / 19


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Green Roofs - Living Architecture Monitor Winter 2020

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Green Roofs - Living Architecture Monitor Winter 2020 - Table of Contents
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