b'Proper Locationwater vapor from. I[]n fu order to prevent theI passing through the wall, itnecessary to,iurIL is install a vapor retarder at the proper location inis nearpossible to the the wall, whichas orthe wallas warmroom side ofsoto stop the moisture before it reaches the colder sections of the wall. Asvaporbe a general rule,retarders should consideredforusewhenbothofthe following conditions are anticipated: outside average January temperature The is below 40F. Theexpectedwinterinteriorrelative humidity is 45 percent or greater. As stated, this is a general rule.Detailed research results can be found in WayneThe CRCA\'s 8th Annual Trade Show ribbon cutting ceremony on February 27, 1991. Tobiasson\'s paper,Vapor Retarders for MembraneRoofing Systems,which was presented at the 9th ConferenceRoofingCRCA8th on Technology, co-sponsored by the National InstituteStandards andandAnnual Trade Show a Success ofTechnology theNationalRoofingContractors Association. TheChicagoRoofingContractors\'of roofingsystems.The CRCA Trade The effectiveness of avapor retarder isAssociation (CRCA) opened its 8th AnnualShow offers an opportunity for contractors measured by its The porosityTrade Show at the Drury Lane Conferenceandarchitects to obtain clarification of perm" rating. Center in Oakontechnical details and specifications from ofofisBrook, Illinois,February material to the passagewater vapor measured in perms.This is defined as the27, 199}, with a ribbon cutting ceremony.the leading material suppliers. numbergrains of(7,000the ribbon cutting ceremony Participants in ofwater vaporper included (from leftright)Mr.C.Mr.LarryWolfe,Presidentof CRCA, pound) that will pass through 1 square foottoRichard Rosenow, President Elect ofcommentedthat,"OurAssociationis of materials in one hour when the vaporthe National RoofingContractorsAssociation,Mr.determinedtechnical pressure differentialsidesto make the very best between the two LarryWolfe,Presidentof CRCA,Mr.information availableall of our ofto 1 inchmercurytomembers. the material is equalof WilliamO\'Brien, Chainnan ofWe (0.49 psi).E.the Tradefeel that this knowledge, along with the Show, and Mr. Harlan L. Hanson, Presidenteducation program for our workmen, will oftheMidwestRoofingContractorsinsure quality roofs forcustomers. We To be classifiedas avapor retarder,aour Association.are pleased with the huge tum outroofing material should have aperm rating notof exceeding 0.50 perms.Perm ratings areprofessionals to the Trade Show." establishedpublished by the AmericanTheTradeShowattractedover1,800 and Society for Testing and Materials (ASTM).roofing contractors, architects, specifiers,For informationabout the CRCA1992 Laboratories such as Factory Mutual andconsultants, material manufacturers, andTrade Show, please contact: Underwriters Laboratories that issue labelsroofing material distributors. for material approvals do not test vaporPatricia H. Keating The purposetheExecutive Manager permeability characteristics.ofTrade Show is to bring together alltheinChicago Roofmg Contractors\' Association ofprofessions interested (ReprintedpermissionContractorslearning more about the complexities of4415 W. Harrison Street - 242C withof installing a quality, long lastingforHillside, Illinois60162 Guide magazine.)roofthe roof owner.The two day Trade Show is(708) 449-2933 alsoan opportunity for contractorsand architects to discuss technical aspects of roofing construction with each other and with material manufacturers.The roofing industry has seen aproliferation of new products during the last ten years which not areeasily understood by the purchaser Page3'