b'PHOTOVOLTAICS theroofmembranecanreducethe effectivethermalresistanceofaroof system by as much as 20% 2 ). To improve thethermalperformanceoftheroof system,considerdesigningtheroof assembly using adhesives, or implement a hybrid securement system that incor-porates adhesives for the top materials and fasteners below the membrane and an insulation overlay (to disrupt thermal bridging). Many fully adhered and suit-able hybrid systems have been tested for windupliftresistanceandtestreports areaccessiblethroughtheAARSand PARS portals of the RPM.Insulation compressive strength is a critical factor when the PV array will be ballasted. As explained below, PV systems generatedynamicmovementthatcan affectmembranelife.Secondly,when the PV array is supported on top of the roof system membrane, the roof system must be able to support the dead loadadhered membranes and insulation over- and performance of the roof, minimize of the array, with little or no membranelays promote good thermal design. Usethenumberofpenetrationpointsfor deflection (deflection commonly resultsmechanicalfastenersinaPARSroofelectrical cabling, ensure it does not lie in ponding on conventionally insulatedsecurementdesignwherethefastenersunsupportedontheroofsystem,and systems).Finally,usehigherinsulationare located well within the roof system. direct cables into purpose-made weath-load capacities for a more resilient roofMinimizethenumberofroofer-head flashings and drooped cables so that is capable of handling anticipatedpenetrations.Everydetailpresentsathat water cant track backwards through maintenancetraffic.Additionally,usethe penetration and into the building.insulation overlays to add to the loadpotential weak point in the roof system. capacities of the roof system; overlaysClusteringpenetrationstogetheronaAdditionally, design the building elec-will also provide firm support for thecurb lifts these details out of the drainagetrical system so that conduit, boxes and membrane and add minor thermal resis- plane and, with the right approach, canother electrical installations are separated tance to the insulation assembly. promote a leak-free roof system. from the underside of the roof assembly WhilewindcangeneratenegativeProtect the roof membrane, espe- byatleast38mm(1).Manyroof (uplift) loads that threaten to lift the PVciallybeforethePVarrayisinstalled.systems use self-drilling screw fasteners to array off the roof, it can also force theInstallationactivitycanbehardonsecure materials to the roof deck. Roofing arraydownward,generatingcompres- themembrane,butdamagecanbefasteners are powerful enough to penetrate sion loads that directly impact the roofpreventedbycoveringthemembranerigid metal conduit and heavy plate steel, system. Compression loads can be hardwithprotectionmaterials.Andensureand because the placement of screws is onthemembraneasfastenersusedatthat any ballasted systems, and surface- strictlyprescribedbywind-testedroof orimmediatelybelowthemembranemounted PV support systems, are placedassembly reports, the roofer may unwit-mayprotrudeunderloadandevenon top of protection materials. tingly drill a screw right into an energized breach the membrane. To promote roofwire; occasionally, overcurrent protection systemlongevity,ensuretheinsulationDrainagepathwaysmustbefails to break the circuit, and as a result unimpededbyoverlylongorlargethe damage can go unnoticed until years inconventionalroofsystems(insu- obstructions(sleepers,forexample).later when the structure catches fire. 3Since lated below the membrane) has sufficientFurthermore,primaryroofdrains2008,theUSNationalElectricalCode compressive strength to resist anticipatedmust be located at least 300 mm (12)(NFPA 70) has included protections for compressionloads.Also,avoidroofaway from any other penetration or ancircuitsbeneaththeroofassembly(see systemsthatusemechanicalfastenersobstruction, curb or wall. Keep drainageArticle300.4(E)Cables,Raceways,orBoxes to secure the roof membrane or insu- pathways obstacle-free.lationoverlays.Assuggestedearlier, Craftasimple,effectiveandsafe3NFPA 921, 8.9 Ignition by Electrical Energy,National Fire Protection Association, 2004 2 Based on roof assembly tests performed by theelectrical connection between the PVEdition. Also see https://www.interfire. National Research Council of Canada, Energyarrayandthebuildingsownelectricalorg/features/electric_wiring_faults.asp for a Resistance of Commercial Roofs (ERCR); July 2019thorough analysis of academic research into report for the RCABC. systems.Tomaximizethedurabilityelectrical fault ignition.28lROOFINGBC l FALL 2020'