Beefing up R-values and reducing air leaks are the twin rallying cries of builders focusing on energy efficiency. Regardless of the particulars of the house design, more insulation and fewer air leaks make houses more comfortable, more durable, and less expensive to heat and cool.
No one seems to argue that point. But Al Cobb wonders which is more significant.
“My real goal is to find the tipping point when a leaky building loses more energy via air changes then via the insulated envelope,” he writes in GBA’s Q&A forum. “I’ve had many answers where the losses from air leakage have been as low as 10% or as high as 50%.”
Cobb believes home buyers have been “brainwashed” into thinking only about R-values, as energy codes give short shrift to the importance of airtightness. Energy modeling is especially frustrating, he says, because it asks for highly specific information on R-values but only broad generalizations when it comes to airtightness.
“Therefore, I’m looking for a study or analysis of homes (real or not) that have been modeled to the extent that heat loss from conductive and air infiltration losses are clearly defined,” Cobb adds. “It only makes sense that as leakage rates increase, the decision to ignore air-sealing can be shown as a critical mistake.”
Ain’t no such animal
Good luck and God speed, suggests Robert Riversong: “Your question is similar to, ‘What’s the difference between an apple?’,” he writes. “The answer could range from near zero to near 100%, and is entirely dependent on whole-house R-value and whole-house air exchange rate during normal operation (not under blower door testing). If you’re asking about ‘average’ existing housing, there is some data on that. If you’re asking about a particular new construction project, you have to do the…