b'Use of Cover Boards Over Polyisocyanurate Roof Insulation NRCA BULLETIN 2000-3, MARCH 2000 The(NRCA) has received aproblems experienced in the field, N recomw that designers specify National Roofing Contractors Associationsig RCAends nificant number of reports of problems associated with the use of polyisocya cover board over polyisocyanurate insulation in a low-slope membrane roof ll nurate roof insulation, although it is import to note that the vast maiority ofsystems.of ashould help to reduce problems whether The usecover board roof assemblies thatpolyisocyanurate insulation have performed suc directly related to the manufacturing process or due to other causes. include cessfully. However,reported problems often involve large roofwhereFurther, polyisocyanurate roof insulation is often specified because of its thearea, remedies can be quite expensive. The majority of the reported problems havefire-resistance properties. There are occasions, however, when the use of a occurred inmembrane roof assemblies where arlayercover board may be required to achieve are-resistance classification for a low-slopecove bo1rdfiof insulation was not included indesign.roof assembly, and the use of certain types of cover boards can generally the According to the Polyisocyanurate Insulation Manufacturers Associationimprove the fire-resistance properties of roof assemblies that include poly(PIMA), more than 4.5 billion board feet of polyisocyanurate foam insulationisocyanurate insulation. reasonableminimum were produced in the United States in 1999. Aestimate is that atInsulation cover boards should be a"(13mm) thick and be least 2.5 b lion board feet were installed in low-slope membrane roof assem composed of any of the followinil g: blies, which represents, according to NRCA market survey data, about 55 perGlass-faced s n ed gypsum ilico iz board cent of the market for insulation used in low-slope membrane roof systems Perlboard ite Polyisocyanurate roof insulation can exhibit problems in several different Wood-fiber board ways. T e Glass-fiber board hes include:Facer-sheet delamination Mineral-fiber boardEdge cavitationWhen selecting afic suitable cover board,should consider speci designersCupping or bowingthe characteristics of the specific roof assembly, and take into account theShrinkagecover board\'s compatibility with the assembly.Crushing or powderingUsing acover board over polyisocyanurate insulation in low-slop~ suitable These characteristics are discussed more fully in an attachment to this bul membrane roof assemblies provides the following attributes:./ letin. It separates the membrane from the polyisocyanurate in tion, reducing sulaNRCA has previously recommended the use of cover boards over polyiso the possible effects of facer-sheet delamination, edge cavitation, cupping cyanurate insulation where hot-applied b minous membranes are installed.or bowing, shrinkage and crushing or powdering of the polyisocyanurate ituT recommendation is included in The NRCA Roofing and Waterproofinginsulation. he Manual, Fourth Edition, and was the subject of NRCA Technical Bulletin 9,It allows forllation of the insulation board layers with staggered board insta"NRCAStatement on Pofyisocyanurate,Polyurethane and Phenolic Foamjoints, aknown to reduce stresses on the membrane and improve practice expandingroofce. Root Insulations," dated September 1988. NRCA is nowits rec aassembly\'s overall thermal performanommendation for the use of cover boards to include alother low-slope memIt may be required to achieve aclassification for a Ifire-resistanceroof brane roof assemblies, including thermoset and thermoplastic single-ply roofassembly. assemblies inlasted, mechanically attached and fully adhered configurations.bal Attachment toTechnical In addition, NRCA has separately reported (in aissued May 24, report 1999) concerns with theU.S.material standardfor polyisocyanurate roofBulletin 2000-3,March 2000 1289, insulation, ASTM C"Standard Specification for Faced Rigid Cellular Polyisocyanurate Thermal Insulation Board."For example, the standard doesCharacteristics ofReported with Polyisocyanurate Problems not establish a requirement for curing time prior to shipment, andNRCARoof Insulation believes that improperlypolyisocyanurate insulation is more prone toFacer-Sheetis the separation of the facer sheet, which is curedDelaminationtypexperience problems. Similarly,NRCA hasrecommended changesin theically roofing felt made with glass fibers or composite materials, from the standard\'sfor compressive strength, dimensional stability and R-valuepolyisocyanurate foam core. This can result from the manufacturing process values the determination.if the foam is off proper ratio;foam eel Is can become elongated and thereNRCA has had aof discussions with polyisocyanurate insulationfore not as strong as cellswith proper ratios.-sheet delaminumberproducedFacermanufacturersandPIMA addressingtheseissues.NRCAhasa beennation can also result from concentrated and/or repetitive traffic on the insulso actively working to improve ASTM C1289, and intends to continue to do so,lation\'s surface.Facer-sheet delamination causedby concentrated and/or by working, where appropriate, in cooperation with individual polyisocyanu repetitive facer-sheet delamination is caused by concentrated and/or repetirate insulation manufacturers and with PIMA.tive traffic;affected area generally will be limited to the traffic area(s)on(J the Given NRCA\'s concerns with shortcomings in ASTM Cand reportedand notportions of the roof. 1289other'