Green Roofs - Living Architecture Monitor - Fall 2019 - 34

ON SPEC

WHY DOESN'T BOSTON USE GREEN
ROOFS TO COMBAT FLOODING?
BY OSCAR WARMERDAM, PRESIDENT, SEMPERGREEN

oston is in trouble, and
they know it. Massive
tidal shifts of 10-14 feet
in the Boston Harbor
mean that every time a North
Eastern storm coincides with
high tide, the excess stormwater cannot readily flow into the
harbor. The result is flooding.
Boston expects this to happen
every year as tidewater is
expected to rise to street level
in the next 15 years.
The resulting economic
damages climb into billions of
dollars lost. AI simulator software technology maps these
impacts, as cities struggle to
understand flooding complexity to see what happens how,
to whom, when, and at what
cost. This software deploys a
diverse collection of stormwater solutions... but not green
roofs!
What the flood? Why
not? If roofs cover 50 per cent
of downtown Boston, why are
green roofs not considered
part of the solution?

Green Roof Diagnostics
(GRD), is a $400.000 green
roof laboratory built by a
consortium of Sempergreen,
Knauf, Hydrotech, and
GRSP. We confirmed that
stormwater retention based
solutions are indeed awesome
and even civil engineers can
agree that green roofs are
great as volume reduction
tools, but at the peak of
the storm... does the civil
engineer see a green roof a
primary peak flow reduction
tool? Aaaahhhh... not so
much.
As an industry, we proudly
state annual retention rates
of 40-50 per cent. As a result,
the size of 'retention cups or
sponges' are our collective
bragging rights. My cup (or
sponge) is bigger than yours!
Yet, civil engineers don't care.
Let me re-phrase because
this statement causes industry
riots. Retention is great... unless the cup/sponge was filled
with yesterday's rain.

LIVING ARCHITECTURE MONITOR / FALL
FALL 2019
2019 // 34
34

RETENTION COMBINED WITH TRUE DETENTION CAPACITY
IS THE ULTIMATE VALUE POTENTIAL OF A GREEN ROOF

Few green roofs can deliver this. Charlie Miller's unique award
winning green roof designs provided both. He has been saying
this out loud for 20+ years. If it were not for Charlie, Joshua
Robinson and Brad Garner , software engineer, from Green Roof
Diagnostics we would never have solved that problem for our
clients. Brad rebuilt the GRD laboratory in 2017 to emphasize
True Detention based testing. He also built the Evapotranspiration calculator in 2018 that clearly show that most storms come
in clumps of 2-3 days in a row (see https://purple-roof.com/
model) Simply put, on the first and or second day, the rain fills up
the retention capacity of the green roof, and then it releases water
as fast as it rains on the 3rd day. The re-charge rate of a retention
based green roof is simply too slow (7-21 days), and because of
this, software engineers prefer alternatives that re-charge quickly.
...any solution with a cup or sponge that does not re-charge
within 24 hours ...does not qualify as True Detention.

TRUE DETENTION IN GREEN ROOFS SHOULD BE THE FOCUS

Detention is focused on peak flow reduction, and peak flow delay. If
we want cities like Boston to use green roofs as primary stormwater
management tools, and True Detention is what software engineers
are looking for, this is what we as an industry need to provide.
Yours truly,
Oscar Warmerdam
CEO Sempergreen USA
CEO Purple-Roof
LIVINGARCHITECTUREMONITOR.COM

https://www.purple-roof.com/ http://www.LIVINGARCHITECTUREMONITOR.COM

Green Roofs - Living Architecture Monitor - Fall 2019

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