Study: In a Perfect World, All Insulation Performs About the Same

The report, sure to be controversial among insulation manufacturers, is not as radical as it sounds. The key to high-performance insulating has long been in the details.

The catch line "why pay more?" is the phrase that's sure to irk makers of pricier insulating products such as spray foam. But our experience building VISION house show homes across the country has taught us that contractors pay more for certain insulation materials for a good reason: because achieving a "perfect" insulating job requires three things that are often in short supply: time, experienced labor, and communication among the trades.

A new report from Building Science Corp. aims, according to its authors, to assess "the adequacy of R-value as a metric for the thermal performance of enclosure assemblies." The highly technical report does fill in some gaps in understanding of how insulating materials perform in homes. And it incorporates newer products, such as spray foam, ICFs and hybrid systems. But these results should not be oversimplified. The various insulating products have their place, especially given what is arguably the toughest variable in the insulation equation: quality of installation.


Nonetheless, here are some of the observations reported by the researchers:

  • When walls are constructed with the same installed R-value in the stud space, and are air sealed
    both inside and outside (i.e. there is effectively zero air leakage through the assembly), they
    exhibit essentially the same thermal performance regardless of the type of insulation material
  • *All of the tested wall assemblies were subject to thermal bridging regardless of the type of
    insulation material used in the stud space. Thermal bridging through the framing resulted in a
    roughly 15% decrease in thermal performance.
  • Commercially available 2D and 3D heat transfer models provided good predictions of the
    thermal bridging in the assemblies tested, as did the parallel path method described in the
    ASHRAE Handbook of Fundamentals and other texts.
  • All of the insulation materials exhibited temperature-dependent thermal performance (i.e.
    changes in insulation R-value related to changes in mean temperature). The mechanisms that explain
    this phenomenon are well understood; however, there is a lack of relevant material property
    information (i.e. measurements of insulation R-value at different temperatures).

Despite its limitations, the report is still valuable, as an academic exploration of just how important insulating details can be. It also suggests that so-called hybrid systems may have the right idea: a way to balance installation surety with cost.