32 APRIL 2019 COMMERCIALARCHITECTUREMAGAZINE.COM
- A drainage layer with water-retention mats underneath to let plants
absorb the needed amount of water - An insulation layer under the drainage layer to insulate the build-
ing against the elements - A root barrier designed to prevent penetration of roots into the
waterproofing membrane - A waterproofing-membrane system to protect the building.
Tray systems can be used for smaller, multifunction spaces where
water retention is less of a priority and vegetation is installed around
patios, pavers, or designated garden areas. These reportedly easy-to-
install systems, such as the Sopranature modular tray system from
Soprema Inc., Wadsworth, OH, are all-in-one systems that include a
drainage layer, filter fabric, and pre-installed vegetation. They offer
time and labor savings but are less customizable and do not fit every
application.How extensive/intensive a green- roof system is planned?
If a tray-based system is chosen, there are fewer decisions to make.
A contractor simply installs what was purchased. If the roof is a tradi-
tional approach with a built-in-place system, the consideration process
is more complex. What type of system will be created?- An extensive system is designed for projects requiring lightweight
vegetative roofing. This typically includes sedum, herbs, or other
low-maintenance plants that may not require an irrigation system and
are installed more for utility than aesthetics. - A semi-intensive system allows more plant diversity, including
small shrubs, grasses, and flowers. This design means more mainte-
nance and irrigation is needed than an extensive system but provides
better stormwater retention. - An intensive system requires the most maintenance and irrigation,
but allows the creation of on-structure landscapes with deep soil pro-
files that can sustain large shrubs and small trees. These systems are
often used to facilitate rooftop vegetable gardens or park-like spaces
for multifamily residential buildings. This sort of system can retain
the largest quantity of stormwater.
What is the real cost of the project?
Material choice is one factor infl uencing vegetative-roofi ng costs,
based on the intensity of the project and which material options are
chosen for each layer. Maintenance is another consideration, as cer-
tain plants require more care than others, especially when diverse,
intensive plantscapes are designed.
Also consider what government incentives and tax abatements
may be available. These can vary from city to city and state to state,
and there could also be federal incentives for implementing green-roof-
ing options. One can begin by reviewing some of the current offers
listed at the following link to get an idea of how net costs of imple-
menting a planted rooftop may be lower than anticipated. (http://
blog.soprema.us/vegetated-roofing-tax-incentives)DON’T FEAR COMPLEXITY
Vegetative roofi ng is, by nature, a complex topic, and there are many
resources available to ensure the correct decision is made. Begin by
considering the questions presented above, and then reach out to
professionals who can help with the details. From roofi ng-material
suppliers to landscape architects to contractors who have carried out
planted-roofi ng projects, know that the expertise is available for a suc-
cessfully completed project. CAPROJECT|exteriors
- Government incentives,
blog.soprema.us/vegetated-roofi ng-tax-incentives
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Sources listed below are linked
at commercialarchitecturemagazine.com/1904soprema.Top. Traditional vegetative roofs have
various layers installed as part of their
design, and the composition of those lay-
ers depends on the performance sought,
the weight-carrying capability of the
roof, and other factors.Above. Planted roofs help save energy
by absorbing sunlight that would other-
wise raise the temperature within build-
ings and tax the HVAC system, which is
part of why their inclusion in a design
can contribute points toward LEED cre-
dentials.