With per-square-foot prices for vegetative roofs easily reaching double digits, it’s important that contractors strengthen their selling propositions when marketing these systems.
With per-square-foot prices for vegetative roofs easily
reaching double digits, it’s important that contractors strengthen their
selling propositions when marketing these systems.
Fortunately, a recent study conducted by Oak Ridge National
Laboratory (ORNL) and SPRI shows that vegetative roofs can help reduce heat
gain and heat losses, resulting in significant energy savings in mixed climates.
The reduction in heat gain in cooling dominated periods - and
heat losses in heating dominated periods - translates into lower heating and
cooling demands for the conditioned space. However, the study notes that the
energy savings offered by vegetative roofs are climate dependent and affected
by the efficiencies of heating/cooling equipment. ORNL’s testing took place in
the mixed climate of East Tennessee.
The study also hinted at some possible roof performance
advantages of vegetative systems. ORNL reported lower membrane temperatures and
temperature fluctuations under the vegetative roofing system than in the
control black-EPDM and white-TPO roofing systems.
The ORNL research project was initiated in June 2008 by SPRI
- the association representing sheet membrane and component suppliers to the
commercial roofing industry - to quantify the thermal performance of various vegetative
roof systems relative to black and white roofs.
“As part of the effort to reduce energy use in commercial
buildings, energy codes are greatly increasing the required thermal efficiency
of roofing systems,” says SPRI Technical Director Mike Ennis. “It is important
to understand the energy savings associated with vegetative roofs so that they
can be properly credited in these codes.”
A summary of the ORNL/SPRI study written by Andre Desjarlais,
Abdi Zaltash and Jerald Atchley of ORNL and Mike Ennis of SPRI was released
earlier this year at the RCI Annual Convention.
Demand Increases for
Vegetative roof systems have enjoyed significant growth in
the last decade in the United
States. The numerous benefits that green
roofs provide have helped to fuel their resurgence in industrial and urban
settings. For these reasons, it was important that SPRI and the roofing
industry quantify the thermal performance of various vegetative roof systems
relative to black and white roofs.
In addition to energy savings, vegetative roofs offer many
environmental and economical benefits. These include:
• storm-water retention.
• reducing the urban heat island effect.
• increasing the longevity of the roofing membrane.
• adding plants that enhance biodiversity and filter air contaminants.
• beautifying the surroundings by incorporating green space.
With that said, the goal of SPRI and ORNL in this study was
to accurately measure the annual cooling and heating loads per unit area of
three vegetative roofs. The study also included side-by-side comparisons with black
and white roofing systems, as well as a test section with just the growing
media without plants.
Stay tuned for a full report on ORNL’s “Thermal Performance
of Vegetative Roof Systems” in an upcoming issue of Roofing Contractor magazine.