b'Investigating Plywood Roof Decking byBobLacosse, CAEdecking such as oriented strand board and waferboard with thicknesses of 15/32-inch At the annual convention of the Nationalinstead of 1/2-inch. Roofing Contractors Aswciation (NRCA)\'-.J ininIt was the reports of excessive deflection February 1990San Diego, a contractor specialty session was held titled "When isand fastenerpulloutfromthesethinner a Wood Deck No Longer a Wood Deck?"veneer and non-veneer decks that resulted in the formation ofin early the task force The title of this session was "catchy," but1989. it raised a lot of questions on the type of roofUsing fourteams,thefieldinspections decks that presently are being installed. It also questioned what type ofwereconducted on both low-sloped and veneer or non-veneer roof decks will be installed insteep roofing in the Phoenix, Ariz., area, the future because ofproblems presentlynorthern and southern California, Oregon theandWashington. being reported. The ses,sion had seven speakers includingAs aresult of the investigations,it was Bob LaCosse, CAEshown clearly that in Frank Lawson Jr. of the Lawson Roofingmost cases, the veneer Co.,San Francisco,who alsowastheand non-veneer decking was installed poorly session\'s moderator.Toe main thrust ofby the deck applicators before the membrane the session involved reports on the field"The title ofwasor shingles were applied. this session inspectionsthat wereconductedby the joint task force on plywood problems.\'catchy\', but it raised a lot ofA definite pattern of the decking material showed through the membrane and shingles. questions on the type ofWhenthemembrane or shingleswere roof Thetaskforceiscomprisedof representativesthe NRCA, the Americandecks that presently are beingremoved, not enough fasteners were holding ofdown the panels. Plywood Association (APA), the Asphaltinstalled." RoofingManufacturersAssociation (ARMA) and the Western States RoofingOn oneparticularproject,many of tbe Contractors Association(WSRCA).buildingsbad theorientedstrandboard applied temporarily with nails. Then whe; Speakers included Lawson, Ken Andreason excessive deflections of the deck;a separate crew came later to complete] ofAPJay Bligh of Bligh Roofing Co., fastenerpullout;fasten the panels with power- driven staples, A, SantaSprings, California, Dwain Bouton corrosion of fasteners;spacingswerefoundfarbeyondthat Ferecommended by the AP of ConsolidatedFiberGlassProducts, buckling and bowing of the deck;A Bakersfield,California, and Ray LaTonachipping and splitting of the deck; of Simpson GumpertzandHeger,Sanpoor deck design;Also,manyof thefastenersmissedthe Francisco. warping at edges of sheets;rafters and were exposed below the decking.worker& slippingdecks installed wrongthe panels were bowed Therefore, many of on Inaddition, Jerrold Winandy ofside up.upwardbecausethefastenerswerenot the Forestdriven into the rafters. Madison, Products Laboratory inWisconsin, reportedon fire-retardanttreated(FR1)Inthe Beginning plywood (to be covered in a future article)Nominimum1/8-inch spacewas left between the ends and sides of and Steve Phillips ofTheconcerns started in 1983 whenthethe panels to Hendrick, Spanos &plywoodindustryreducedtheminimumallows for expansion as recommended by Phillips, Atlanta, reported on the contractorsnominal thickness oftheAThe vast majority of liability involving veneer and non-veneerveneer plywood fromAPthe panels plywooddecking.1/2-inch to 15/32-inch for roof decking.were butted together and showed buckling. This was a follow-up to a session held atAll approvals published by UnderwritersAlso, it was found that the deflections that theWSRCA annualconventionin JuneLaboratories(UL)forfire-ratedroofresulted in buckling and bowing of some 1989 titled "WoodDeck Controversyassemblies at that time were based uponof thepanelswereduetomoisture Roofthe use of a1/2-inch minimum thicknessimpregnating themwhen exposed to the - Toe Good, the Bad and the Ugly."weather for an extended period of time. plywood. ofTests then were conducted on Thereasonsforconductingthefieldthese thinner (15/32-inch) panels, and they investigations stemmed from the problemswere found to be a suitable substitute forFurther investigations by the task force are reported at the June 1989programthe1/2-inchmaterialforfire-ratedroofcontinuing asaresult of thereportson WSRCAbucklingandbowingof thepanels and also in reports submitted by contractorsassemblies. themselves and also the reports of to theNRCA andtheWSRCA.Thesefastener~ included the following problems on bothThen in 1985, veneer plywood began to beContinued on page 4 low-sloped and steep roofing:replaced extensively by oon-veneer plywood Page 2'