30 APRIL 2019 COMMERCIALARCHITECTUREMAGAZINE.COM
V
egetative roofs are not a new concept, but it is new to many
architects and designers who are approaching their first
planted-roofing project. These green roofs are progressively
catching on with building owners, as they offer a variety of benefits.
Here are several reasons to pursue a vegetative roof.MANDATED/EXTERNAL REASONS
Various cities, such as Toronto and San Francisco, require or heavily
incentivize vegetative roofs to deal with larger problems affecting the
area, such as excessive stormwater runoff or urban heat-island effects.- Stormwater runoff is a major issue in municipalities where aging
sewer systems can be overwhelmed and chemicals/waste can end up in
waterways. Some sewer districts tax stormwater runoff as a result, and
cities sometimes require new buildings to have water-retaining roofs to
mitigate the problem. Vegetative roofing not only slows the rate of
runoff during storms but can remove as much as 95% of heavy metals
in rainwater.- Urban heat islands, where cities become especially hot when sun-
light is absorbed into hard, dark surfaces, are another long-standing
problem. Planted roofs alleviate this by absorbing sunlight instead of
reflecting is as happens with nonporous surfaces. Vegetative roofs typ-
ically emit a temperature of only 95 F on a 90 F day. A traditional roof
might exceed 160 F. - Green roofs can also help combat CO 2 and smog levels, actively
converting CO 2 to O 2 to improve air quality.
BUILDING-SPECIFIC REASONS
In other cases, a building owner might choose a green roof because of
the benefits such a system grants to the owner.- A vegetative roof can help save energy by absorbing sunlight that
Here are factors to consider when specifying planted-roof systems.
Finding The Ideal Vegetative Roof
PROJECT | exteriors
The functional design of a rooftop makes
a difference not only in the sort of mate-
rials used to construct the space, but in
the types of plants installed. For exam-
ple, will a patio, garden, or other usable
space be incorporated?