b'Figure 1. A Fall of 2016 roof installation in the Midwest. The knit lines on these polyisocyanurate boards are clearly visible at installation. The adhered membrane, to be installed, will most likely telegraphs these through. Knit lines will then be visible on the installed roof. .T&R UPDATE FIELD VERIFY THE PHYSICAL CONDITION OFPolyisocyanurate Board Shipmentsby Rene Dupuis PhD PET his technicalinsulation board products.The most8.1 Dimensional Tolerances and article iswidely used polyisocyanurate board forSection 8.5 Face Trueness, which are about aroofing application is Type II, Classgiven below.growing concern about physical dimensional issues with bundled polyisocyanurate insulation board products, delivered to the roof.As will be explained below, two issues may be of concern to you as the installer and provider of these products to the building owner.The first more troubling issue is knit line cavitation.We have seen this occur with polyisocyanurate insulation board products since 2010.The problemFigure 2. A view of a polyisocyanurate board sample is appearing to be more widespreadthat has undergone ASTM C1289 conditioning. Note the today.The second issue is boarddimensional stability and amplification of the knit lines.thickness.If you have taken delivery of bundles or truckloads, we would recommend you check board thickness8.1 Dimensional TolerancesThe on at least 10 different boards, in each1 which has a reinforced celluloselength and width tolerances shall shipment. mat facer; further the board can havenot exceed +/-inch (6.4 mm), the For the record, we are dealing with aa minimum specified compressivethickness tolerance shall not exceed product manufactured to meet ASTMstrength of 16 psi for Grade 1, 20 psi1/8 in. (3.2 mm) when measured in C 1289-16 Faced Rigid Cellularfor Grade 2 and 25 psi for Grade 3. accordance with Test Method C303.Polyisocyanurate Thermal InsulationOf special note in ASTM C 12898.5 Face TruenessThe thermal Board.This ASTM standard dealsis Section 8 -Dimensions, which hasinsulation boards shall not depart from with 18 different polyisocyanuratetwo subsections of interest.Section 28 www.mrca.orgMidwest Roofer'