Glimmerings

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July 27, 2008

Insulation innovation holds promise for true energy efficiency

Owens Corning developed fiberglass in 1932, and since then fiberglass batts have become a standard feature of Canadian homes. The design and insulation of wall frames hasn't changed much in many years, so no one questions it. But the fact is, fiberglass is really a rather poor insulator when you look at its real-world performance. The open structure and low density of this material allows air to move right through, sapping energy performance enough to foster frosty walls and some pretty scary, real-world energy stats. To discover just how wide the discrepancy is between actual thermal performance and theoretical energy ratings of fiberglass, you need to take a look at two pivotal research studies.

The first comes from the Roof Research Center at the Oak Ridge National Laboratory in Tennessee. Scientists there discovered that fiberglass attic insulation delivers only 50% of its rated thermal performance at -28º C. As cold, dense air makes its way into the vented attic space, it moves down through the fluffy fiberglass in a way that doesn't happen when batts are rated in the lab. And the colder the air gets, the worse fiberglass performs.

Another study is Canadian, conducted by Dr. Tony Shaw at Brock University. He analyzed the energy consumption of two nearly identical, new homes built side-by-side to code standards. The only difference between the two structures was the walls. One had 2×6 wall studs insulated with R-19 fiberglass batts, and the other had walls built with structural insulated panels (SIPs) rated at R-17. Under actual wintertime field conditions, the walls of the SIPs home delivered exactly what they were rated to - R-17. The internal, closed-cell foam insulation in these panels isn't subject to air infiltration, so thermal performance remained high and consistent.

The walls of the fiberglass-insulated, stud-frame home, on the other hand, performed at an actual level of only R-4 because of the inevitable air movement within the hollow wall cavities. Hard to believe, but true. You can put all the building wrap and siding you like around the outside of a house, but air still wafts through wall cavities, carrying energy with it. In the Brock study, the code-built, stud-wall home lost over 60% more energy than the SIPs home, while the SIPs structure cost less than 5% more to build.

http://www.homeenvy.com/db/8/1018.html

Posted by thdyck on July 27, 2008

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