Insulation innovation holds promise for true energy efficiency
03.07.2008 04:00
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- Source: Home Envy
There's something less than ideal about the way new Canadian homes are insulated, and drywallers see it more clearly than most. The surprising, hidden fact is that if it weren't for sheetrock, the inside surfaces of exterior walls in many code-compliant houses would be coated in frost and ice during cold, windy winter weather. In fact, many are, though homeowners never see it. One experienced drywaller I know brings a windshield scraper with him on wintertime jobs, just so he can brush the ice off the plastic vapour barrier before he puts up wallboard in fully heated houses. This happens even in lavish, expensive custom-built projects, too. The energy waste is as dire during summer weather, you just can't see it. So what's going on? How can this possibly be? New houses are required to have walls with an insulation rating of R-20, yet my own real-world observations suggest something far less than R-20 performance. Discrepancies like this put me on a quest for answers, and what I've found raises serious questions about the value of the fiberglass insulation that's routinely used in three-quarters of all new Canadian homes. 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 2x6 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. New building technologies that include closed-cell foam insulation instead of fiberglass are code-approved and field proven. Trouble is, few are making it onto homebuilding sites in a big way because most prospective homeowners don't know enough to ask for them. At least not yet, anyway. We Canadians need to become much better energy stewards than we are right now. To make that happen we need to support builders that use proven homebuilding innovations, while re-examining all building traditions in light of what makes sense today. And who knows? If we do things right, maybe my drywaller friend won't have to bring his ice scraper with him any more when he puts up sheetrock.
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