The proper performance of any insulation system is directly dependent on the product being installed according to manufacturer’s recommendations.  However, some insulation systems also rely on contractors following standard building practices and nominal framing patterns when constructing the building envelope.  Studies(1) have indicated that between 30% and 40% of residential structures do not follow nominal framing patterns.  This will have an impact on not only the framing factor, but will also increase the chance of installation deficiencies with cavity insulations such as fiberglass since custom cutting and fitting will be required.  This will potentially introduce air/moisture infiltration and thermal short-circuiting.

Although it seems insignificant, installation deficiencies can lead to a major decline in thermal performance of a building envelope.  Studies completed by ORNL(2) concluded that the performance of what we think is an R-19 fiberglass wall can be further degraded from R-13.6 to R-11 when common installation factors (interface details, piping, wiring, etc) are considered.

(1) “How the Same Wall Can Have Several Different R-Values: Relations Betyween Amount of Framing and Overall Thermal Performance in Wood and Steel-Framed Walls”, Jan Kosny, David Yarbrough, Phillop Childs, Syed Azam Mohiuddin(2)Energy Design Update, vol. 19, no 9, September 1999 “How Thermal Shorts and Insulation Flaws Can Degrade an “R-19″ Stud Wall to a Measly “R-11″