When “cool” roof requirements were first introduced into energy standards like ASHRAE 90.1, contractors and specifiers were allowed to use less insulation if a reflective roof was installed.
In contrast, most industry associations recommend that the maximum amount of insulation that can be justified be used on a low-slope roofing project. Then, give the roof in question the extra energy efficiency boost that a cool roof may provide.
“Many roofs in California still have very little insulation,” said James R. Kirby, AIA and vice president of sustainability for the Center for Environmental Innovation in Roofing, based in Washington, D.C. “Changing roof color from dark to light on a building located in a cooling climate zone makes sense. But that doesn’t translate to all geographic locations, building types and roofing systems.” Kirby advocates for a holistic approach, combining the benefits of cool roofing and insulation.
Some roofing contractors may be opposed to adding extra insulation on a re-roofing project due to the added expense of the new insulation, raising curbs to accommodate it, etc. Due to these increased costs, some contractors fear the property owner will cancel the reroofing project or use a lower bidder.
On the other hand, adding extra insulation involves additional labor, which should generate a greater profit for the roofing contractor. It also enables the building owner to meet energy code requirements and overall is a more responsible approach to the environment. Even when a design professional is involved with a project, it is generally the roofing contractor’s responsibility to ensure the new or reroofing system meets code requirements.
“We need to get back to thinking about the basics of building science,” said Kirby. “Roof color depends on location, building proportions and the amount of insulation in the roof system. If that’s how we start the decision-making process on roof color, then the answers should come easily.”
Roof insulation also works in all International Energy Conservation Code (IECC) Climate Zone Maps (1-5). It works all the time; not just when the sun is shining, because it stops all mechanisms of heat flow – radiation, convection and conduction – from entering or exiting the building.
When attempting to calculate optimum roof insulation levels through a life-cycle analysis, the “cost” line increases as the insulation level rises. When creating a chart based on life-cycle costing, the lowest life-cycle cost value is where the insulation level and energy cost lines cross; in most cases this at a roof insulation level of R-20. Of course, these values depend heavily on climate, building type and location, and the costs of energy and insulation in the area.
Most industry associations — including SPRI, which represents sheet membrane and component suppliers to the commercial roofing industry — recommend that roofing contractors and specifiers use the level of insulation required by the most current version of the IECC. One of the reasons for this is that the IECC conducts an optimum insulation analysis to ensure its recommendations are cost-justified with regard to insulation expenditures.
“That’s why SPRI and other industry organizations do not recommend using ‘tradeoffs’ between insulation levels and light-colored, reflective roof membranes to meet energy efficiency requirements,” said SPRI Technical Director Mike Ennis.
In summary, it’s important for both contractors and specifiers to strive for synergy between reflective roofing technology and roof insulation in most climate areas.