by Brianna Crandall — November 6, 2013—Building Science Corporation (BSC) has released a report detailing the results of a multi-year insulation research project. The most significant finding from the report is that sealed walls of the same R-value perform equally well regardless of the type of insulation used. The North American Insulation Manufacturers Association (NAIMA) defines the R-value as the ability of insulation to slow the transfer of heat (the higher the R-value, the better).
BSC’s Thermal Metric Summary Report entailed a baseline set of seven test walls using various insulation types, including fiber glass, cellulose, spray foam and extruded polystyrene.
Among other findings of the report are:
- 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 used.
- All of the reference test wall assemblies were subjected to significant temperature differences. Natural convective looping was not noted in any of the wall assemblies.
- Conventional energy models may over-predict the negative energy impact on walls that have a significant interaction effect (e.g. air moving through insulation).
- All wall assemblies experienced a loss in thermal performance due to air movement through the assembly. This is true for all of the assemblies tested, regardless of the type of insulation material used (e.g. cellulose, fiber glass, open cell spray foam, closed cell spray foam or extruded polystyrene).
- Commercially available 2D and 3D heat transfer models provided good predictions of thermal bridging in the assemblies tested, as did the parallel path method described in the ASHRAE Handbook of Fundamentals and other texts.
- Thermal bridging through the framing resulted in a roughly 15 percent decrease in thermal performance regardless of the type of insulation material used in the stud space.
Energy cost and security issues have generated demand for building enclosures that exhibit higher levels of thermal performance. R-value has long been the industry standard for assessing the thermal performance of insulation materials. The findings of this report clearly demonstrate that sealed walls with the same R-value perform equally well regardless of the type of insulation used, whether fiber glass, cellulose, spray foam or extruded polystyrene.
