Why do SIPs insulate better than their relative R-value rating?
Air tightness is the main factor, setting up a chain of thermal characteristics. Air movement through an insulation member tears away thermal value. SIPs are 15 times more air-tight than a framed assembly. High efficiency is attained through a combination of the solid EPS insulation without air spaces and the air-tightness created by the urethane glue film and the EPS foam. Ratings of fiberglass R-value are done in static air conditions -not with the reality of the applications. Wind movement on a building creates significant pressure differentials across the wall section and literally sets up a ‘wind’ in the wall. Also -air voids and channels form at all edges & corners in stud frame with fiberglass batt-insulation systems. This network of voids of insulation are air conduits, allowing the colder air within the stud frame walls to drop to the bottom of the wall cavity which is the starting point for condensation and molds. Further, in terms of comfort, the temperature gradient created
