Outside the Building Envelope
Today’s energy codes require a level of insulation that is virtually impossible to achieve without a significant amount of insulation put on the exterior of a building as continuous insulation. “The whole industry is trying to recalibrate as to what the most effective, efficient way of meeting new wall R-value requirements is, and there are a lot of different ways to do it,” Dr. Hoff says. “But I also think one of the big challenges—at least in wall system design and construction—is exactly how well insulation is installed and how much that depends on very accurate installation field conditions.”
Because there are differences of opinion about application of different types of insulation, Hoff is a proponent of hiring a local consultant to oversee design and installation. “There are all these different varieties of insulation for a reason: climate differences and the needs of the building owner can be different,” he says. “To me, it’s like you can go to a doctor or you can self-medicate; I’d still recommend going to the doctor.”
To further his case, Hoff points out the design goals of a building may require different types of insulation. “There are situations where it is important to resist moisture movement within a wall or roof system and other instances when moisture should move through a system,” he says. “Roof systems offer another layer of complexity because they also have to resist roof traffic; you don’t walk on walls.”
Closed-cell foam insulations, like polyisocyanurate and extruded polystyrene, combine traffic and moisture resistance and, consequently, make up more than 80 percent of the total roofing market. In addition, moisture-resistant gypsum products are being used as cover boards to protect the insulation underneath. However, Hoff says, a highly moisture-resistant cover board will not help if it is placed over an insulation susceptible to moisture degradation. “The key issue is making the right decisions about moisture’s impact on a building, and there are a lot of different insulations that could accomplish that,” he notes. To learn more about the effects of moisture and roof traffic on roof insulations, see a new report released by the Bethesda, Md.-based Polyisocyanurate Insulation Manufacturers Association.
Hoff and PIMA also have been working to mitigate confusion surrounding R-value changes in polyiso insulation. Polyiso’s blowing agent, which is a major factor in the insulation’s performance, begins to condense as temperatures decrease. At some point, which will vary for different polyiso foam products, this condensation will result in a marginally reduced R-value. As a result, researchers have been studying whether the nominal R-value of polyiso insulation should be reduced in colder climates. Specifically, the Rosemont, Ill.-based National Roofing Contractors Association published an article using a mean reference temperature as low as 20 F to estimate R-values in cold climates.
In response, PIMA’s “Thermal Resistance and Mean Temperature: A Report for Building Owners and Design Professionals” concludes that any apparent reduction in polyiso roof insulation thermal value in colder climates is related to the use of an unnecessarily low estimate of “mean reference temperature” to calculate R-values in cold climates. Polyiso roof insulation R-values, when calculated using an adjusted mean reference temperature range indicated by analysis of North American climate data, appear to be higher than the values suggested and do not differ significantly from current PIMA member-published R-values.
“The NRCA recommendations were directionally accurate; they were talking about what is obviously a real phenomenon,” Hoff states. “But that information was, in my opinion, over-leveraged into an extreme situation that would not be suitable for judging the insulation in normal practice. My concern is looking at the extremes of temperature and not average temperatures overestimates the potential for energy savings to the building owner, so the building owner following this may think, ‘I’m getting my fair value’. However, he or she may be getting more insulation than expected while not getting the fair return off that insulation.”
If you have the luxury of re-cladding your building and are looking for a cladding and insulation product in one, insulated metal panels, or IMPs, may be the answer. Jeff Irwin, president of J.H. Irwin Consulting LLC, Canal Winchester, Ohio, is a 35-year veteran in the metal wall and roof industry, having spent 24 years focused on IMPs. Today, Irwin is director of the Chicago-based Metal Construction Association’s IMP Marketing Group, which develops market strategy for MCA’s IMP Council members.