Why do SIP built structures outperform stud framed buildings with the same R-Value factor?
R-Value factors tell only a portion story relating to the thermal properties of a given building material or structure. R-Value ratings measure the resistance to heat loss that is attributable to conduction. This measurement was not intended to rate the thermal efficiency of a particular material or wall assembly, as other forms of energy loss besides conduction can come into play, namely convection, radiation and infiltration (leakage). For instance, approximately 40% of the energy loss of a conventional stud framed structure with batt insulation is lost to air leakage/infiltration; in contrast, a properly constructed SIP building experiences virtually no air leakage.
