would otherwise raise the temperature in the building
and tax the HVAC system, which is part of why its inclu-
sion in a design can contribute points toward LEED
credentials.
- If a building has solar panels on the roof, green roof-
ing can help the panels perform more efficiently. - Vegetative rooftops also protect the roofing mem-
brane from UV radiation, heat aging, extreme tempera-
ture fluctuation, and physical damage. - Planted roofs simply look good, making them attrac-
tive in situations where the rooftop is visible to occu-
pants or is an occupied space featuring useful overbur-
den, such as pavers, flanked by plant life.
ASK CORRECT QUESTIONS
There are a number of factors to consider when
determining the proper design and construction of a
planted roof. The following questions offer informa-
tion to aid in the selection of a vegetative-roofing solu-
tion for a variety of needs.
What is the intended use of a vegetative rooftop?
Is the rooftop going to be a generally unoccupied
space, chiefly designed to absorb rain and solar rays, or
will it have visitors? Will a patio, garden, or other usable
space be incorporated?
The functional design of the rooftop makes a differ-
ence in the materials used to construct the space and in
the types of plants installed.
Work with a landscape architect to determine which
plants are best, based on the desired use, climate, and
how much time and resources can be dedicated to
upkeep. Then, select the correct type of planted-roofing
system to meet the requirements of those plants and the
needs of the mixed-use design.What value is to be received from the planted roof?
If you simply want the rooftop to look attractive,
that is one thing. But if you want to derive more utility
from the roof design (for instance, carbon dioxide/
greenhouse-gas management or stormwater manage-
ment), that can affect vegetation choice and construc-
tion decisions.
Using a green roof for stormwater management is
partially influenced not only by the ability of plants to
soak up water through their roots, but also by structural
factors below the soil layer of a planted rooftop.
Is storage space needed that allows water to collect
below the soil level, minimizing the amount flowing off
the roof during heavy rains? The construction of the
drainage layer and choice of moisture-retention mats
will depend on the answer to this question.Based on the performance expected from the roof, is
a traditional vegetative-roof construction or a tray-
based system needed?
Traditional vegetative roofs have various layers
installed as part of their design, and the composition of
those layers depends on the performance one is seeking,
the weight-carrying capability of the roof, and other fac-
tors. Traditional vegetative-roofing constructions typi-
cally include:- Growing medium with custom soil depth on top with
plants embedded
PROJECT | exteriors
C I R C L E 211 31Work with a landscape architect to determine which plants are best based on the desired use, the climate, and how much time and resources can
be dedicated to upkeep.