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Study: All Insulation Performs Equally

Tuesday, August 18, 2015

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A recent study of several insulation types suggests that no single type of insulation offers better performance than others when all are properly installed.

The report—"Thermal Metric Summary Report"—was released July 22 by the North American Insulation Manufacturers Association (NAIMA). It provides the result of a test designed to examine how walls insulated with different materials perform with air movement and at different temperatures: from 144 degrees Fahrenheit to -18 degrees Fahrenheit.

Setting Up the Tests

Researchers at the Building Science Corporation (BSC) tested fiber glass batts, cellulous and closed cell spray polyurethane foam and foam sheathing on a baseline set of walls.

The walls included six that used 2x4 construction, one with 2x6 construction, five different stud cavity insulations and one exterior insulation application.

They also tested open cell spray polyurethane foam, but discovered that the wall on which it had been sprayed had defects that prevented them from certifying those results, the final report said.

© /  kevinjeon00

Among other findings in a recent study, Building Science Corp. discovered that, when properly installed and air sealed, all insulation types perform about the same.

NAIMA and its funding partners—Dow Building Solutions, Honeywell, Huntsman Polyurethanes, Icynene, and Greenfiber—originally sought to come up with a new metric for thermal performance.

However, that metric, which industry partners had hoped would take into account heat flow with air movement at a range of operating temperatures, has not yet been developed as a result of the research.

Summary of Findings

The report did find that when walls are constructed to the same R-value (a measure of thermal resistance) and air sealed correctly, all insulation types perform basically the same.

Some of the other findings of the study were:

  • Air sealing is required for all insulation types, and that no insulation product alone provides a sufficient, whole-house air sealant;
  • Large voids left during open cell spraying can affect that type of insulation’s performance;
  • All insulation types lose energy because of thermal bridging (about 15 percent);
  • The energy impact of airflow depends on the flow path, the interaction between the air and the solid materials in the assembly, and the installed R-value of the assembly;
  • Conventional energy models might over-predict the negative energy impact on walls that have a significant interaction effect (for example, those walls where a lot of air moves through the insulation); and
  • All insulation materials showed temperature-dependent thermal performance (for example, changes in insulation R-value with changes in mean temperature).

Study Response

In responding to the study, the American Chemistry Council's Center for Polyurethanes Industry noted, "The report confirms what the building community has known for years: air sealing and R-value are critical factors to consider when designing an energy efficient home or building."

The ACC further maintained the energy efficiency of spray polyurethane foam as an air barrier and insulation solution.


Tagged categories: Building Envelope; Building Science Corp.; Coatings under insulation; Corrosion Under Insulation (CUI); Dow Building Solutions; Honeywell; Huntsman; Icynene; Insulation; North America; Roof insulation; Thermal emittance

Comment from Charles Brown, (8/18/2015, 8:58 AM)

Key words; "when all are properly installed." I'm comfortable saying 90% of insulation is not properly installed - at least in the southeast. Energy codes and awareness like your blog are helping.

Comment from Tom Schwerdt, (8/19/2015, 10:24 AM)

Charles, that's a good point along with "air sealed correctly" - separate air sealing is typically NOT performed. When there is no separate air sealing, closed cell foam and wet-sprayed cellulose do a much better job at air sealing than something like fiberglass batts. This has been shown in prior full-wall studies. It would be interesting to see what the difference in temperature dependent thermal performance is between insulation types. Sure, they all change - but if one loses 10% of R value with a 20 degree temperature drop and another loses 50% - that's some critical information for predicting real-world performance.

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