lbmjournal.com – A new study from Building Science Corporation (BSC) demonstrates that all insulation products perform equally well when properly installed and air sealed. The Thermal Metric Summary Report concludes a multi-year collaborative research project that examined the thermal performance of typical walls with air moving through them. The report provides the results of testing designed to examine how walls insulated with different materials perform with air movement at a wide range of temperatures – between 144°F and -18°F.
This research project headed by BSC and funded by a group of industry partners, including NAIMA, sought at the onset to develop a new metric for the thermal performance of walls that better accounts for heat flow with air movement at a range of operating temperatures. At this stage of the research project, the industry partners have not proposed a new metric for quantifying the thermal performance of insulation beyond conventional R-value and the report does not include any recommendations for a new metric.
Given the substantial cost advantage that fiber glass delivers to the market, there are a number of key takeaways from this report that argue strongly for choosing fiber glass batts. Among the relevant findings:
• R-value is R-value. When walls are constructed to the same R-value and properly air sealed, all insulation types perform essentially the same.
• Air sealing is required for all insulation types to provide the optimal performance. No insulation product alone provides a sufficient whole-home air sealant.
• During decommissioning of the open cell spray foam wall, the researchers confirmed there were areas where the foam did not adhere to the OSB sheathing, resulting in large voids. These gaps can affect performance.
• Energy losses due to thermal bridging occur with all insulation types and has the same effect on all insulation types.
• The R-15 fiber glass batt wall was among the better-performing assemblies tested and all of the fiber glass walls with air-sealing were among the top performers.
• All of the insulation materials showed temperature-dependent thermal performance (i.e., changes in insulation R-value with changes in mean temperature).
Fiber glass has yet another advantage that merits consideration. Based on a comparison of fiber glass, cellulose and spray foam insulation being installed at a 3.5 inch thickness, a National Association of Home Builders report (Air Infiltration of Wood Framed Walls) determined that at cost per square foot, fiber glass had the lowest installed cost. In an informal survey, an insulation contractor estimated the cost of insulating and air sealing a new 2,300 square foot home in Climate Zone 4 to 2012 International Energy Conservation Code specifications comparing fiber glass batts, cellulose, blown-in fiber glass, open-cell spray foam and closed-cell spray foam. Fiber glass batts showed installed costs lower than the other products. These estimates may vary regionally among contractors.
The results of this research clearly demonstrate that there is no single “best” insulation material and that all insulation materials perform equally well when properly air sealed and installed, debunking the claims that spray foam insulation performs better than other insulation types and provides air sealing for the whole building.