b'ENERGY EFFICIENCYWHAT IS THE ENERGY RESISTANCE OF COMMERCIAL ROOFS?BY SUDHAKAR MOLLETI & BAS BASKARANT heenergyefficientdesignofpresentsimplifiedapproachestodeter- Towardstheeffortsofenhancing roofs involves the use of thermalmine the thermal transmittance (U value)theenergyefficiencyofthecommer-insulationwiththeprimaryof the roof assembly, which is limited tocial roofing systems and determining its purposetoreduceheatingandopaque roof assemblies with continuousenergy resistance, the National Research coolingcostsandmaintaininteriorinsulation. The definition of continuousCouncil Canada (NRC) developed the comfort. Properly designed roof systemsinsulationaccordingtoASHRAE90.1industry consortium Energy Resistance contribute to increased energy efficiencyis, insulation that is uncompressed andof Commercial Roofs (ERCR). Partners of the building. The factors that affect thecontinuous across all structural membersinclude the National Roofing Contractors thermal performance of roofing assem- withoutthermalbridgesotherthanAssociation (NRCA), Canadian Roofing bliesarethethermalresistanceofthefastenersandserviceopenings.WhatContractorsAssociation(CRCA), insulation,variabilityinthermalresis- can be inferred from this definition is thatRoofingContractorsAssociationof tanceofinsulationwithtemperature,thermal bridging resulting from fastenersBritishColumbia(RCABC),Roofing thermalbridgingduetofastenersandor any rooftop penetrations is not signifi- Consultants Institute (RCI now IIBEC), rooftop penetrations, thermal bypass duecant and is negligible.Sika,Trufast,EPSIndustryAlliance, to gaps between the insulation boards, airCodesandstandardshavemainlyRockwool,Soprema,2001Company, intrusion and moisture migration. Eachfocused on the insulation requirementsand Natural Resources Canada - Program of these factors has a different magnitudeinroofthermaldesignomittingtheof Energy Research and Development. of influence on the thermal performanceimpactofthermalbridgingonenergyThis consortium embarked on a three-of the roof assembly. loss (Figure 1). Reasons for the omissionyear project that started in 2016 and was Buildingenergycodes,suchascould include the absence of codifiablecompleted in 2019.ASHRAE90.1,InternationalEnergydata that could determine the impact ofTheERCRconsortiumproject ConservationCode(IECC),andthethermal bridging on the holistic thermalhadtwomajortasks.InTask1,36 NationalEnergyCodeofCanadaforperformanceoftheroofingassembly.roofingassembliesrepresentingseven Buildings(NECB)provideminimumNowthequestionis:dothecurrentclimaticzonesinNorthAmerica performance requirements for the designapproaches of roof thermal design mani- weredesignedandtestedtoevaluate of energy-efficient roofs. The codes alsofests its actual energy performance? theireffectivethermalresistanceand Figure 1: Thermal bridging of roofing fasteners32lROOFINGBC l FALL 2019'