Green Roofs - Living Architecture Monitor - Winter 2015 - 29

Tool (LAPT) is to align with
municipal stormwater management goals and create metrics
and test methods to clearly quantify and ensure a base level of
performance. That way, instead
of evaluating applications on a
case-by-case basis, municipalities
can have a tool they can rely on
to help determine anticipated
rainwater attenuation (and other
benefits) from green roofs, and
can provide incentives in line
with the public benefits created.
An important discussion
during the workshop revolved
around the use of annual or
event-based stormwater metrics.
Both approaches have value; they
are simply measuring rainfall
attenuation in different contexts.
Annual metrics, such as 50%
retention of annual rainfall,
reflect the unique hydrology of
green roofs and ensure that their
high performance during smaller

rain events is aggregated and
quantified. Event-based metrics,
such as capturing the first 1" of
rain or the volume of rain from
a 90th percentile rain event,
align with what policy makers
are already using and help fulfil
the goal of complying with EPA
consent decrees by reducing
CSO events. They are however,
more theoretical because
antecedent moisture can vary
the water holding capacity of
green roofs. For example, three
consecutive days of rain will
likely diminish the water holding
capacity of a green roof. Green
roofs also delay stormwater that
does leave the roof, an important
performance contribution that
neither metric captures.
After much deliberation, the
consensus among workshop participants was that the future success of the LAPT is dependent
on aligning with the needs of

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policy makers. It also needs to be
supportive of, and inform, other
rating systems commonly in use,
like LEED, as well as emerging
performance rating systems such
as SITES. LEED and SITES
currently use event-based metrics
and targets to measure stormwater management performance. If
the LAPT uses a standard that
dependably articulates how to
measure the stormwater management performance of green
roofs, it could simplify policy and
be adopted by both incentive
programs and rating systems.
Green roofs have a myriad
of benefits, but their dynamic
nature, variability, and complexity make it difficult to create a
standardized, accurate quantification of these benefits. The
purpose of the LAPT is simple:
make it easier to measure the
performance benefits of living
architecture, and watch the mar-

ket take off in North America as
we have seen happen elsewhere.
With your support, we will continue to work on the LAPT, with
the goal of releasing a complete
draft framework at CitiesAlive
2016 in Washington D.C.
Rohan Lilauwala is a Senior Researcher at Green Roofs for Healthy
Cities. David Yocca is the Principal
Landscape Architect/Planner at
Conservation Design Forum and CoChair of the LAPT Committee..

FIND OUT MORE

Learn more about the Living
Architecture Performance tool
at http://greeninfrastructurefoundation.org/lapt. If you have
questions or would like to get
involved in the development of
the program, contact rlilauwala@
greenroofs.org

http://greeninfrastructurefoundation.org/lapt http://www.iranalyzers.com

Table of Contents for the Digital Edition of Green Roofs - Living Architecture Monitor - Winter 2015