Understand the challenges of installing and maintaining a green roof
Components of a Vegetative Roof
Before addressing any of the benefits and challenges of
vegetative roofs, it is important to identify their components.
Vegetative roofs require adequate structure to support the
roof’s weight and specific materials to properly maintain the
ecosystem and capitalize on the main benefits for a long period. No matter the type of application, you need to consider
these components of a vegetative roof.
■ Starting at the bottom is the structural roof deck. It’s most
likely metal, but it also could be structural concrete, which
might be better because of the weight of the vegetative roof.
■ Above the roof deck, you need a waterproofing membrane
that is covered by other materials and potentially in contact
with water a high percentage of the time. This will often
be different from a conventional roof membrane, although
many of the same products are used for both applications.
Use fully adhered or mechanically attached membranes that
are reinforced so you won’t have ballooning issues that can
displace the vegetative materials. You can choose between
PVC, TPO, liquid-applied (rubberized asphalt), asphaltic
(BUR, modified bitumen and rubberized asphalts) and
■ The root barrier is required in some systems and includes
not only the barrier to keep roots from damaging the membrane but also insulation. It is optional depending on membrane type, with asphaltic materials requiring some sort of a
■ The retention or drainage sheet is basically a thin plastic
molded sheet that is dimpled and is similar to waterproofing
in walls. The retention/drainage sheet can retain rainwater
for plant use on drier days, as it will fill up in the low spots
and water can later diffuse into the growing media.
■ Above the retention/drainage sheet is the filter layer or a
filter fabric that keeps the growing medium above it from
clogging the drainage system.
■ The growing media is not soil, so you shouldn’t dig up top
soil from the ground and bring it up to the roof to grow your
plants in. This is a manufactured blend of materials to let the
plants grow in.
■ Of course, the vegetation is on top.
Improving Your Building and the
Beyond the clear aesthetic benefits to vegetative roofs, they
provide extensive benefits to facilities. The first and perhaps
Is a Vegetative Roof
Right for Your Building?
Building owners are
always looking for new
ways to bolster their green
credentials, and many have
turned to vegetative roofs as a
means to improve building
performance and display an
Green roofs will do just that, but
they come with a set of distinct
challenges for retrofits. Would
your building be a good fit for a
TECH DECK IN MOUNTAIN VIEW, CA, received a 2016 Award
of Excellence for its intensive green roof from Green Roofs
for Healthy Cities, a non-profit organization that supports the
green roof industry in North America.
BY TED MICHELSEN