b'BUILDING CODEbe less than the load determined byArticle5.2.2.2isnotnewtotheload should satisfy the requirements test or analysis. Code 13 . What is new in Part 5 are theoftheCommentaryentitledLimit 4. ExceptasprovidedinSentenceoptions by which a design can conformStates Design in the Users Guide (5),thewindupliftresistanceofto these requirements. The 2012 CodeNBC 2015, Structural Commentaries membraneroofingassembliesofferednoguidance.Thedesign(Part 4 of Division B).shall be determined in accordanceauthorityknewthattheroofhadtoThetestmethoddescribedin withtherequirementsofCAN/ conform to the Code but had to lookCAN/CSA-A123.21,Dynamic CSA-A123.21,DynamicWindelsewhereforsolutions.ManydesignsWindUpliftResistanceof UpliftResistanceofMembrane- (if they even paid attention to this some- Membrane-Roofing Systems, applies RoofingSystems.(SeeNotewhatobscurerequirement)referencedonlytomembraneroofingsystems A-5.2.2.2.(4).) whatfewstandardsindustryhadtowhosecomponentsresistanceto 5. Membrane roofing assemblies withoffer, such as FM Globals design speci- wind uplift is achieved by fasteners fications and approvals. Today, the Codeoradhesives.Itdoesnotapplyto provenpastperformancefortheisspecificandoffersthreepathwaysroofingsystemsthatuseballasts, anticipatedwindloadsneednotfor compliance; none include FM stan- such as gravel or pavers, to secure the complywithSentence(4).(Seedardsortestmethods.Allareperfor- membrane against wind uplift.Note A-5.1.4.1.(5).) mance-based.Sentence(4)requires Article5.2.2.2.isnotonlyaboutarooftobedesignedusingatestedIn the case of membrane roofing roofs. It applies to any material, compo- roofassembly(TestedAssembly)systemsinwhichthewaterproof nent,assembly,ortheirconnections,(Sentence (4)). Sentence (5) permits themembrane is attached to the structural that separates environments and may beuse of a membrane system with provendeck using mechanical fasteners, the subject to wind loads. This includes wallpast performance as an alternative towind-induced forces and the roofing systemsandglazing.Nevertheless,theSentence (4). And in the Notes to Partsystemsresponsearetime-and thing to pay attention to is that envi- 5, a third way is offered, which I will dealspace-dependent and, thus, dynamic ronmental separators must be designedwithseparately.Eachofthefirsttwoinnature.Furtherinformationon to resist wind load because if they failmerits brief comments. thedesignandevaluationofsuch and breach under load, they effectivelysystems can be found in A Guide cease to function to prevent ingress offor the Wind Design of Mechanically precipitation. To put it another way, aTested Assemblies and ProvenAttached Flexible Membrane Roofs, wind-damaged roof that lets in the rainPast Performance published by NRC.no longer satisfies the Code requirementsThe term tested roof assembly refersThe wind uplift resistance obtained in Section 5.6 Precipitation and certainlytoamembraneroofthathasbeenfromthetestmethodinCAN/wont obtain the Code Objective OH1. testedinlaboratoryconditionsbyanCSA-A123.21 is limited to configura-TheinterestingrevelationarisingNRC-qualifiedfacility,usingtheCSAtionswithspecificfasteneroradhe-from Article 5.2.2.2. is the reference totestmethodCSA-A123.21Dynamicsivepatterns.Toextrapolatethetest loadcalculations:windloadsmustbeWindUpliftResistanceofMembranedatatonon-testedconfigurations, determined in accordance with ArticleRoofing Systems. The nature and appli- refertoANSI/SPRIWD-1,Wind 4.1.7.1. With this seemingly innocuouscation of a Tested Assembly is devel- Design Standard Practice for Roofing statement,Article5.2.2.2.bridgestwooped in the Notes to Part 5. Assemblies, for a rational calculation seemingly disparate Parts of the CodeTheNotestoPart5arecritical.procedure.However,inusingthis Part5(whichdealswiththefunc- FormerlycollectedinAppendicesAextrapolationprocedure,windloads tional nature of the enclosure), and Partand B and now offered at the end ofshouldbecalculatedinaccordance 4 (which is exclusively about structuraleach Part, the Notes to Part 5 provide awith the BCBC. NRCs guide for wind loads). Even the use of the term spec- fuller explanation of the requirements indesignreferencedaboveprovides ified wind load in Article 5.2.2.2. is aArticle 5.2.2.2. Sentence (4) is supportedfurther guidance and examples of wind structural term used in Division B, Partby Note A-5.2.2.2.(4). The entire Note isload calculations.4. What does this all mean? replicated below. Noticeseveralthings.First,notice It means this: a roof system isnt justA-5.2.2.2.(4) Membrane Roofingthat the entire note is new (blue text). somethingthatseparatestheinsideSystems. Wind loads for membraneSecond,notethatthemembraneroof from the outside. The roof is a struc- roofingsystemsmustbecalculatedsystemmustbedesignedasastruc-tural component of the building. It func- inaccordancewithPart4.Theturalelement(windloadsaredeter-tions as a diaphragm to support the wallstested uplift resistance and factoredmined using the means and methods in and the rest of the structure from collapseDivision B, Part 4). Lastly, notice that the under gravitational loads, and it resists the13 Both the 2012 and 2006 British Columbia BuildingCSA test method is limited in its scopeupward lifting loads generated by windCodes are available online, free of charge through BCtomembraneroofsthatareadhered Publications. In 2006, Article 5.2.2.2. was titled Wind which, if left unchecked, can jeopardizeLoad and Other Air Pressure Loads. The current Articleormechanicallyfastened,andthatthe the function of the roof system. name was adopted in the 2012 iteration of the Code. method does not apply to ballasted roofs 18lROOFINGBC l SUMMER 2021'