Calculating the R-value of manmade insulating materials is a straightforward process. For green roofs—not so much.
“The equations that describe energy transfer through evaporation, reflection, convection, and thermal mass can get ugly,” says Chris Wark, Senior Energy Analyst, Viridian Energy & Environmental. That’s because a green roof isn’t a static object. It is alive.
“A green roof does not just sit there resisting heat flow, it is an active energy device, literally collecting, processing, and releasing energy according to its immediate need, just like all other living things, including people,” Wark points out. “Now for a good rhetorical question: What is the R-value of a human?”
Projecting future energy savings from the installation of a green roof is not something for the average human, Wark says, no matter what his or her R-value. For an accurate estimate, hire an energy analyst who understands green roof thermal properties to model the building and conduct a proper roof treatment study, he recommends.