Green Roofs - Living Architecture Monitor - Spring 2018 - 6

"I BELIEVE THE GI WILL CONTINUE TO GAIN IN POPULARITY,
PARTICULARLY IN URBAN AREAS WHERE SPACE IS
LIMITED, AND COST OF LAND PROHIBITS BUILDING LARGE
STORMWATER PONDS OR OTHER LARGE FOOTPRINT BMPS."
- MIKE HARDIN
EFB: The primary advantage
of a green roof is that it is
a self-mitigating surface
with respect to stormwater.
Green roofs prevent runoff
generation, or minimize it
to a trickle, for the majority
of day-to-day storm events.
They can be effective even in
winter, with dormant plants.
If there is no runoff, there is
no problem. Among all other
stormwater management
tools, green roofs offer more
ancilliary benefits. Where
designed appropriately, we
can provide amenity space,
habitat, and reduce energy
demand at the site-scale.
MH: There are several pros
but the big one is turning a
stormwater generator into a
stormwater sink. Implementation of green roofs allows for
more developable or revenue
5. What are the pros and cons, from generating land or minimizing
the amount of land needed to
your perspective, of using green
meet stormwater management
roofs to meet stormwater managerequirements. This is espement requirements?
achieved with shallow-depth,
reasonably low weight green
roofs if materials and plants are
appropriately specified.
MH: I think rain gardens and
bio-swales are the most accepted GI. They are relatively
low risk and low cost. The
maintenance of these systems
is well understood by the
engineering community and
easy to relate to municipal or
regulatory enforcement personnel. It should also be noted that
municipalities struggle with
ensuring that the final property
owner performs the necessary
maintenance to keep GI performing properly, making them
more likely to encourage simpler systems that they are more
familiar with in case they need
to provide some training to get
the GI operating properly.

cially true if a cistern or other water storage is used in conjunction with green roofs to capture and reuse green roof runoff,
which frequently results in a significant water quality benefit
due to the significant volume reductions. The biggest cons are
the initial cost of green roofs, building code impediments, and
lack of an in-depth understanding of the technology in the
general engineering community.
6. There are some green roof configurations that are more like blue/green
roofs, designed to retain more water than typical systems? What do you
think are the most promising new approaches to building-based stormwater management?
EFB: On-site runoff management provides the most technically
effective opportunities for minimizing stormwater impacts to the
environment and infrastructure.
MH: I think that blue/green roof projects that incorporate stormwater and grey water capture and reuse are the most fascinating and
promising approaches to whole building water management. As
fresh water supplies continue to be stressed, designs will more and
more need to manage water in a more holistic fashion to preserve
supplies. I see blue/green roofs, stormwater harvesting, and grey
water reuse as being integral to this process.
7. Which models are best able to address the contribution green roofs make
to stormwater management and why?
EFB: Stormwater regulations carry quantitative objectives. Civil
engineers must be able to calculate runoff quantities and quality
under a variety of scenarios. Of utmost importance is to accurately
quantify the effect of a green roof, and to be able to integrate that

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LIVING ARCHITECTURE MONITOR / SPRING 2018 / 6

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Table of Contents for the Digital Edition of Green Roofs - Living Architecture Monitor - Spring 2018