b'Clean EnergyWind Design vs. Resistance of By Sudhakar Molleti and Mauricio ChavezPhotovoltaic Roof Assemblies (PVRA)Clean energy andThisarticleoriginallyappearedinploresthesetwoparameterstoStep 2: Determine the Fall 2020 issue of Roofing BCprovidesomedirectionontheReference Velocity magazine and is reprinted with thepractical design of PVRA.permission of the Roofing ContractorsPressure, q, and the green initiatives Association of BC. represent- NBCC Wind Design of Roof- Factors, C e , C tand I W in C ommercial rooftops providemounted Solar Panels was lit- These parameters are obtained extensiveareasFor many years, therefromtheStaticProcedure ing the desired platform totle guidance on determining theNBC Article 4.1.7.3. And again, install Photovoltaic (PV) systems.windloadsonrooftopPVsys- those familiar with Part 4 of the Roof assemblies, with or withouttems. With the efforts of SEAOCNBCC will notice that these pa-thePVsysteminstalled,mustand numerous wind tunnel stud- rameters are the same in the roof fulfill various standard and func- ies conducted by reputed labs, thecladding design.tional requirements. The combi- designmethodologyfordeter- Referencevelocitypressure nation of a roofing assembly andmining wind loads on PV systemsNBC table C-2PV system is termed as Photovol- has been established, and this has-Exposurefactor(NBC taicRoofingAssembly(PVRA).become part of the American So- clause 4.1.7.3.(5)(b))As PVRA become more common,ciety of Civil Engineers (ASCE)-Topographicfactor(NBC it is essential for the roofing and7-16 and National Building Codesentence 4.1.7.4.(1))solar industries to work togetherof Canada (NBC) 2015. -Importance factor (normal, to ensure that PVRA integrity isNBCCintroducedthewindNBC table 4.1.7.3)maintainedandthePVperfor- loads on roof-mounted solar pan-mance is optimized. els in the User GuideNBC 2015Step 3: Calculate the The wind dynamics on a low- StructuralCommentaries(Users GuideNBC 2015:Part 4 of Divi- Tributary Area of the slope roof-mounted array dependsion B). Sections 56 and 57 in theArray Normalized by the on the winds characteristics, the buildingsgeometry,thePVar- guideprovidetheproceduretoBuilding Size raysaerodynamicpropertiesdetermine the net design pressureThe equation represents it:and the array layout on the roof.on solar panels. This procedure is Wind flowing over the PV arraylimited to low-slope roofs (up to exerts pressure or suction on theseven degrees) but is applicable to surface of the array. This pressureall building heights.transmits forces onto the clamp- For simplification, the process ing fasteners, the racking systeminvolvedindeterminingthenet and eventually to the roof assem- design pressure can be categorizedWhere:Commercial and Residential Roofing bly.ThePVsystemmusthaveinto five simple steps as follows: A N= normalized tributary, Trinity Roofing Ltd. specializes in a variety of roofing applications and enough resistance to resist the ex- Step 1: Determine theA = dimensional tributary area,pected wind loads. Not only that,for the array component under waterproofing for residential, commercial and institutional buildings. but the roof assembly should alsoRoof Zones consideration, andPhone: 416-630-9213URL: www.trinitycanada.comwithstandthetransmittedloadIn this step, the size of the roofL b= normalized building length =Fax: 416-630-1722 Email: info@trinitycanada.comwithoutcompromisingitsstruc- corner,edgeandfieldzonesaremin[0.4(hW L )0.5,h,W S ], tural,thermalandwaterproofingdetermined.Figure1(referencedwherefunctionalities. Before a PV systemas Figure I-8 in the guide) provides W=widthofthebuildingonits REMY CONSULTING ENGINEERS LTD. is installed on a building, a localthe zone dimensions correlated toLbuilding code official must verifythe roofs mean height. This figurelongest side, andEngineering Services For: theinstallationswindintegrity.applies to solar installations on any Roofing W= widthofthebuildingonits Parking Garages & Balconies They will need two parameters toheight of the building. Those famil-S Building Envelope validatethewindperformance:iar with roof cladding wind designshortest side.Windows & DoorsAsphalt & Concrete Pavements the design load and the resistance.will notice significantly larger edgeThepressure-gustcoefficients 75 Westmore Drive,Toronto,Ontario,M9V 3Y6The PV systems resistance needswidth dimensions, which increased(CgCp) n inFigure1aredevel-www.remyeng.com905-794-2911 to meet or exceed the design loadsfive-fold from 0.4h for roof clad- oped from wind tunnel test data. forpotentialinstallationonthatding to 2h for the roof that will beThis data applies to all building particular building to demonstrateinstalled with solar panels (where hheights. The concept of normal-code compliance. This article ex- is a buildings height). izedareaisusedtonotover-24ONTARIO ROOFING NEWSISSUE 2 2021 THE ONLY SOURCE FOR PROFESSIONAL ICI ROOFING CONTRACTORS IN ONTARIO ORN'