Not quite measuring up
Polyisocyanurate insulation thicknesses seem to vary
NRCA has received a limited number of reports of faced, rigid board polyisocyanurate insulation with thicknesses less than what was specified and indicated on the insulation's package labeling being delivered from manufacturers to distributors and job sites. Following is information about these reports, as well as information about recognized allowable thickness tolerances and NRCA's recommendations to roofing contractors for monitoring this situation.
NRCA has received reports of new, uninstalled polyisocyanurate insulation being received directly from polyisocyanurate insulation manufacturers with thicknesses notably less than nominal dimensions. Reports have been received from the East Coast to the Rocky Mountains and as far north as Wisconsin and south to Texas.
Reports have been received about various specified nominal thicknesses of polyisocyanurate insulation; however, the problems appear to be more common with thicker polyisocyanurate insulation products than thinner ones. For example, NRCA has received multiple reports of 3 1/2-inch nominal thickness polyisocyanurate insulation measuring less than 3 1/2 inches thick at board edges.
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