If It Ain't Broke, Why Fix It?

May/June 2009
A version of this article appears in the May/June 2009 issue of Home Energy Magazine.
Click here to read more articles about Building Envelope
May 06, 2009
Something old and a few things new in the choices of insulation material and installation.
In the last two decades there has been tremendous growth in the variety of insulation products, and in our understanding of those products. This has accompanied a boost in fraudulent and near-fraudulent claims (for example, that reflective foils are a good alternative to wall or subslab insulation). There are also new types of insulation that are better suited for some installations than for others. Most importantly, the development of building science and sophisticated measurement tools has allowed the shortcomings of standard insulation methods to be better understood. It is important to understand that the published R-value of an insulating material is based on laboratory testing. This testing does not take into account the degrading effects of air infiltrating through the building envelope, which can increase heating-and-cooling costs by up to 40%. Most insulation works by trapping pockets of air (or other gases) to retard the conduction of heat. For this reason, any batt insulation can be a reasonable insulator if it is properly applied with no voids, and if the cavity is airtight. But the real world of construction is rarely airtight, and fiberglass batting with air passing through it loses R-value. With this in mind, it is easy to see ...

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