Some insulation basics

According to www.usainsulation.com, there are five main types of insulation on the market: foam insulation, batts, rolls, loose-fill and rigid foam boards. The insulation utilized depends on local codes and type of application.

Insulation is rated in terms of thermal resistance, called R-value. “R” means “resistance,” as in resistance to heat flow. The higher an insulation’s R-value, the greater its effectiveness at insulating. To be even more specific, there are two types of R-value: Center-of-Cavity is the R-value estimation at a point in the wall’s cross-sectional R-value containing the most insulation; Clear wall R-value is the estimation for the exterior wall area containing only insulation and necessary framing materials for a clear section with no fenestrations, corners, or connections between other envelope elements such as roofs, foundations, and other walls.

According to the Oak Ridge National Laboratory, unfortunately, wall energy efficiency is usually marketed solely by the misleading “clear wall” R-value (exterior wall area containing only insulation and necessary framing materials for a clear section with no fenestrations, corners or connections between other envelope elements such as roofs, foundations and other walls), or even worse “center-of-cavity” R-value (R-value estimation at a wall cross-sectional point containing the most insulation), which converts to a 0-percent framing factor and does not account for any of the framing material thermal shorts through the insulation. For information on Oak Ridge’s proposal for a nationally accepted consensus methodology for estimating the whole opaque wall R-value, visit www.ornl.gov/roofs+walls/articles/wallratings/index.html.

Universal thermal value

Oak Ridge proposes a Whole-wall R-value: R-value estimation for the whole opaque wall including the thermal performance of not only the “clear wall” area, with insulation and structural elements, but also typical envelope interface details, including wall/wall (corners), wall /roof, wall/floor, wall/door, and wall/window connections. The lab reports that the most commonly used calculation procedures for conventional residential wood-frame construction tend to overestimate the actual field thermal performance of many of today’s popular housing designs, which feature large fenestration areas and floor plans with many exterior wall corners. This leads to the need for a thermal performance indicator to represent the whole wood-frame wall including thermal shorts created at wall interfaces with other envelope components. The Oak Ridge proposal is very thorough and interesting and may arm contractors with extra data to help sell a customer.

In last month’s metal framing issue, I mentioned the challenges of metal framing’s thermal performance. An article in this issue, “An End to Exfiltration,” addresses this topic.

The winner of the Redo Your Crew contest has been selected. See page 66 for the lucky crew!