Healthcare Design - December 2015 - 36

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In terms of the structural component,
the roof deck and support must be able
to handle the dead load weight of the
rooftop garden. Because green roof
depth can vary from 3 inches to
12 inches, the dead load can be as little
as 20 pounds per square foot to as
much as 80 pounds per square foot. For
accessible gardens, the roof must also
support the live load added by occupants. Adding a green roof to an existing
structure will require a study to understand the bearing capacity, Quirk adds.
Growth spurt
As for putting the green into these green spaces, the industry has seen significant improvement in the selection, propagation, and maintenance protocols for commonly used sedums,
expanding the plant palette available today.
Also of note, native plant species-driven by
regulatory efforts spurring stormwater management-more commonly include native grasses
and wild flowers in the rooftop mix thanks to
their water-absorbing properties. "Their root
systems are vast, soaking up large quantities
of rainwater and removing pollutants from the
resulting runoff," Uhlmann explains.
While local and federal stormwater runoff and
management requirements vary, cities located
near oceans, rivers, lakes, and subsurface
ground water are generally more regulated.
Another noted area of development is the art
and science of growing vast acres of pre-grown
mats, which are similar to sod. Here, soil blend
improvements and moisture retention fabrics-
providing more moisture control to help plants
survive heat and stress-are leading to more
reliable plant environments.
Uhlmann says that early vegetated roof irrigation systems relied on subsurface emitter
technology, which delivered moisture directly to
the plant roots and were mainly used in shallow,
extensive green roofs. Although they worked
well when installed correctly, the systems were
challenging to troubleshoot and didn't provide a
total package solution. In contrast, today's comprehensive, high-performing systems also offer
weather stations and remote operating capabilities, providing a much more reliable method
of managing hydration for hard-to-access roof
landscapes.
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HCDmagazine.com 12.15

A worthwhile endeavor
While healthcare green roofs have come a long
way in the past few years, the process is a
demanding one, requiring lots of collaboration to
make it work. "The challenges associated with
green roof design are primarily in the complexity
of the detailing, documentation, and coordination of several design and engineering disciplines, contractors, and installers," Malone says.
"Although green roofs are becoming more familiar
and understood in the realm of healthcare design
and construction, coordination throughout the
entire design and installation process is still the
most important strategy to ensure the successful
implementation of any system."
In order to achieve this, clearly delineating
which professional is detailing and specifying each
system is key. Another determination is whether to
divide or combine this information in the drawings
and specifications. "What we do as an in-house
team is combine the green roof system specification into the architectural roofing specification for
clarity, and the landscape drawings detail everything above the waterproofing," Malone says.
While not without planning, design, and maintenance challenges, healthcare green roofs come
with plenty of benefits and provide a comfortable,
quiet environment or soothing view that contrasts
with the often highly stressful clinical setting. HCD

Padded with 2 to 3 feet of
soil and hardy, heat-tolerant
vegetation, the green roof at
Virginia Tech's Carilion School
of Medicine and Research
Institute, built in 2010 and
designed by Skanska,
absorbs a significant amount
of stormwater runoff. With
easy access from the
building's lobby, occupants
frequently use the space.

Barbara Horwitz-Bennett is a contributing editor for
Healthcare Design. She can be reached at bbennett@
bezeqint.net.

MORE ONLINE For more insight on
this topic, see the latest AIA/AAH blog, "Top
Considerations for Green Roofs in Healthcare," at
healthcaredesignmagazine.com/blogs/green-roofs.

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Healthcare Design - December 2015

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