b'Mounting Problems with Equipment byCAE Bob LaCosse,InrJc MRCA Technical Advisorall cases, the necessary installation woshould beL,J done by and under the supervisiofAmong Asa result of continued problems withskilled and qualified personnel. water leaks coming from air conditioningthe criteria for roof-mounted equipment is that the top ofelfter equipmentonlow-slopedroofs,the curb should be lev arepresentativesof the National Roofinginstallation. Contractors Association (NRCA) met in 1982withrepresentativesoftheAirThecurbandequipmentshouldbe Conditioning and Refrigeration Institutestructurallycapableofsupportingthe (ARI)todiscusstheproblemsbeingintended loads and should be designed so encountered by roofing contractors.that no penetration for drains, power lines or anything else will be sent through the Inuproof flashing. a follow- meeting, the two groups met with representativesthe Sheet Metal and of AirConditioningContractorsNationalThe curb should be furnished with a wood Bob Lacosse, CAEnailerthatprovidesaminimum of 31h Association(SMACNA)to discusstheMRCA Technical Advisor standards on ducts for both low and highinches of nailingsurface.It should be velocity as well as duct liner applications.mounted at the top of the curb to permit vAs mentioned above, inofmechanicalattachmentof theflashing the majority It was quite apparent from the meetingscases where leaking units were installedmaterial. that the equipment manufacturers were notbecause the equipment manufacturers were aware of theleaking problems fromairunawareoftheproblems,roofingCaution should be used when considering conditioning equipment because the ownercontractors werethe firstones called tothe use of wood that has been treated with make the necessary repairs.an would calltheroofingcontractor,whooil-borne preservative for wood nailers. would do the necessary repairs to fix theTheoilthatisusedinmanylumber leak.Guidelinestreatments can act as a solvent on roofing can materials andcause bitumen drippag As a result ofofby these But intwo yearseffort\'\'\' most cases it was difficult to do thethree groups, a joint brochure was finalizedWhen nailers constructed of repairs below the equipment because ofwood that has and the NRCA released itAugust 1985been treated with an oil-borne preservative little clearance between the bottom ofin thewiththetitleof "GuidelinesforRoofare used, a barrier of unit and the roof membrane.rosin-sized sheathing MountedOutdoorAirConditionerpaper orshould be placed similar material At the same time, according to a poll ofInstallations."It includes 10 details forbetween the membrane and the nailer. roofing contractors, the most frequent callsmountingrooftopequipment,duct to repair a leak in a roof involved rooftopinstallation, conduit and piping through theCounterflashing equipment.Also,asthethreegroupsroof. examined the situation, they found that:Thecurbshouldprovideaminimum The24-pagepamphletdescribesgoodclearance of 10 inches betweene top of thvCurbing for the units normally is installedconstructionpracticesfortheinterfacethe finished roofthe top of the surface and by the mechanical contractor before thebetween the roof membraneand theairwood nailer and be continuous around the roofisapplied.Buttheactualairconditioning units\' piping, electrical wiringcurb base.In no case should the curb be orsheetmetalductworkwhentheseless than 14 inches in conditioningequipmentisnotinplaceheight. before the roof is installed.elements pass through the roof. Ifthecurbdoesnotincludea vGenerally,thecurbingusedisnot.addition, the pamphlet gives guidelines Incounterflashingreceiver,aseparate provided by the equipment manufactur~r,for curbs, roof penetrations and seals.Incounterflashing receiver should be attached and problems in curbing design orpractice, the guidelines supplement the airbeforetheequipmentisinstalled.All assemblyconditioning unit manufacturer\'s specificreceiversshouldbeofwatertight sometimesmakewaterproofinginstallation instructions.construction. impossible. vDesign problems usually appear withinAlso, the pamphlet gives general advice,The metal counterflashing should extend the first few months after installation., whilewhile the specific requirements of eachdown over thebaseflashing sothatno problems causedabusedamage showinstallationwilldependonthecomposition material is exposed, therd byorcircumstances,jobconditionsandreducing the danger of up much later.foot abuse. manufacturer\'s specifications. Page2(Continued on page 3)'