b'PMRATable 2: PMRA design configurations.Roof Assembly Minimum EffectiveDesign ConfigurationR-Value, (ft 2 Fhr)/Btu) Insulation ThicknessR36 3 in. + 4 in. Source 1, two layers,(35, 40, 60 psi) 35 psi boards tested with and without drainage channel on bottom board.R41 4 in. + 4 in. (35 psi), Source 2, two configurations testedtwo layers and 3 in. + 3 in. + 2 in. three layers. For the 40 & 60 psi configurations, the (40 & 60 psi) top board has ribs or grooves.R47 3 in. + 3 in. + 2 in. Source 3, three layers, no drainage channels or ribs.(35, 40, 60 psi)assembly in real-world conditions is consid-erably more complex. This is primarily due to the presence of dynamic environmental factors that influence heat transfer, such asmoistureabsorptionbytheroofing materialsandheatlossassociatedwith precipitation events. These thermal impact factors can significantly alter the effective insulating properties of the assembly over time, making it challenging to predict long-termperformancebasedsolelyonstaticU-value specifications.Tobetterreflectreal-worldperfor-mance,theeffectsoffactorslikemois-tureandheatlossfromrainshouldbe included by adding an adjustmentcalled a surchargeto the standard U-value oftheroof.TheU-valuenormally represents how well the roof resists heat flow,butitdoesntalwaysaccountfor changing weather conditions or how mate-rials behave when they absorb water. By adding this surcharge, we can more accu-rately estimate how the roof will perform ineverydayconditions,leadingtobetter energy efficiency predictions and smarter design choices.Theactualthermaltransmittanceis calculated using Equation 1:U= U+ UORPMRA base PMRAR= R- R (1)PMRA base PMRAU= U+ U (3)PMRA LTC rainWhere Uis change relating to long LTCterm water absorption TRS BUILDING U rainis the change due to ENVELOPE CORP.precipitation heat lossUnder Task 2, the thermal effect factor,TOMTAR ROOFINGU LTC , was evaluated for PMRAs designed& SHEET METAL LTD.for three out of the six climate zonesZones 5, 6 and 7A with minimum effec- Unmatched Industry Experience.tive R-Values of R36, R41 and R47 (RSI 6.4, 7.2 and 8.3) (Table 2). The PMRAsServing the Interior & Western CanadaweredesignedwithXPSinsulation www.rcabc.orgl19'