Saving Energy With Insulation: How Much is Best?
Insulation is widely accepted as the best method to capture roof-related energy savings. Right-sized insulation provides an R-value sufficient to limit the escape of heated and cooled indoor air, as well as prevent outside air from penetrating. When this happens, HVAC systems must compensate for the heating/cooling loss by operating more than necessary.
It seems simple; the more insulation the better, right? Not necessarily. There are numerous factors that influence what the right R-value is for a facility and when it’s cost effective to increase the amount of insulation.
Adding insulation isn’t right for every building. D. C. Taylor Co.’s Vice President National Account Manager Ben Fashimpaur explains, “In the food industry, they are engaged in operations that produce heat and don’t necessarily wish to trap it.” This is just one example of how a building’s function will influence insulation levels.
Energy codes provide a minimum requirement for thermal insulation and are typically adopted and implemented on a state-by-state basis, and can even vary by city. To find out what energy codes are applicable where you are, visit the National Roofing Contractor Association’s (NRCA’s) database of energy codes by state. Most states have adopted some version of the International Energy Conservation Code (IECC). This code is typically updated every three years. Work with an experienced roofing contractor who understands the state and local energy code requirements, what it takes to comply, and how to address situations when variances to the code are desired.
Decisions about insulation could also be driven by your insurance company – specifically Factory Mutual (FM) Global Insurance Company, which runs the non-profit engineering and research affiliate FM Global Research. “They restrict insulation usage to only those assemblies that have been tested and passed,” adds Fashimpaur. Every year, FM Global issues Property Loss Prevention Data Sheets and a list of approved products (including insulation); compliance means lower insurance rates.
“Programs exist where you enter in the factors – the desired interior temperature, the energy costs (kilowatt-hours and natural gas cost per therm) for the building – to figure out what the cost savings are for one assembly vs. another,” says Fashimpaur. One such program is the NRCA’s EnergyWise Roofing Calculator; this tool can help you evaluate virtual roof assemblies for thermal efficiency and estimate the heating and cooling cost reductions resulting from each option.
Impact to/on Roof Elements
If you thought a return on investment calculation was simply a matter of weighing the expense of more insulation against how much energy it would save, you’re wrong. Adding insulation can have other cost implications. When you add insulation, you’re often increasing the roof’s volume. Fashimpaur warns, “Additional roof height can cause additional expense. Maybe now all of your fan curb heights have to be raised. Industrial piping also may have to be raised. What is the cost of adding additional wood blocking at the roof’s edge? How is drainage impacted?” An experienced roofing contractor will consider the impact an increase in roof insulation will have on the project costs, as well as long-term energy reduction.
Installation & Roof Maintenance
Once you’ve zeroed in on the right R-value, consider how it will be achieved. While staggered joints, a tight fit, and workmanship with no significant gaps is standard practice, using multiple plies of insulation isn’t. “When insulating, you want to avoid thermal short, which is a direct conduit of cold and hot.
Use of staggered layers should be considered. Some contractors will reach R-20 by having a single layer of 3-inch of isocyanurate. It’d be better to have two staggered layers of 1.5 because it eliminates the thermal short.”
When the installation is complete, keep people off the roof (especially if cover board was not installed) and fix leaks promptly. The thermal efficiency of wet and compressed insulation is severely diminished.