Article #141 - Compliance for Metal Buildings
Most energy codes with prescriptive compliance options state that each building component must meet the minimum values specified and that the insulation cannot be compressed. Metal buildings are typically insulated by draping batt-type insulation over the structural supports and attaching the metal panels, compressing the insulation at the supports. The fasteners or connectors provide a "thermal short circuit" (known as thermal bridging) through the compressed insulation, significantly reducing the overall thermal performance and thus the full R-value of the insulation. For example, R-19 insulation installed using this technique yields an effective R-value of approximately R-11.
A thermal bridge is a component or assembly of components in a building envelope through which heat is transferred at a substantially higher rate than through the surrounding envelope area.
One solution to thermal bridging, which is an improvement to the "over-the-purlin" technique, is to use insulating spacers to provide thermal isolation or a thermal break between the panels and purlins. Batt insulation remains uncompressed by installing the spacers between the purlins. R-19 insulation installed using this technique yields an effective R-value of approximately R-14.