b'Technical ArticleAdaptation of Low-Slope Roof Assemblies Against ProjectedBy Sathya Ramachandran, Architect, OAA, MRAIC, BArch, MASc, and Bruno BernardClimate Severities: Evaluation of a new standardThefollowingarticleoriginallyzones of a roof area: the field, edgesThe Perfect StormA Case appeared in the July/August 2025 is- andcorners.Tomeetthisrequire- Studysue of IIBEC Interface. It is reprintedment, each of the project team mem- On December 14, 2021, a six-sto-here with permission. bers,includingdesigners,manu- reymulti-unitresidentialbuilding Disclaimer:Thispaperwasfacturersandinstallers,mustplayunderconstructionintheGreater presentedatthe2024IIBEC/ a pivotal role. However, there haveToronto Area reported roof damage OBECBES. unfortunatelybeencasesinwhich I n 1994, the National Researchteam members have not adequatelycaused by a strong wind event (Figure Council of Canada (NRC) led1). The fully adhered thermoplastic carriedouttheirresponsibilities,polyolefin (TPO) roof assembly over the way to form a consortium- and a combination of errors and/orconcrete deck with a layer of vapour basedresearchanddevelopmentomissions have led to failures. retarder, two layers of polyisocyan-studygroup,theSpecialInterestAddressingtheproject-specificurate insulation and a layer of high-GroupforDynamicEvaluationchallenges related to the wind loaddensity polyisocyanurate coverboard ofRoofingSystem(SIGDERS),is a crucial starting point in achiev- had experienced wind uplift damages whichincludesrepresentativesing long-term durability of roof as- duetohighwindconditionsthat ofmanufacturers,contractorssemblies, but it is not the only con- reached up to 96.3 km/h, as recorded associations,testinglaboratories,cern.Theothermainchallengeisby the nearby weather stations. The homeownersandinsuranceto design roof assemblies that resistdamagecoveredapproximately15 companies.Thegroupsresearchandmanageprecipitation.Toad- per cent of the roof assembly, across led to the development of the CSAdressthatchallenge,projectteamsfourdifferentlocations.Atfirst A123.21,StandardTestMethodmust take into account the NBCC 2 glance, the roof assembly failure ap-fortheDynamicWindUpliftrequirementsforsizingdrainsandpeared to be due to heavy wind con-ResistanceofMembrane-Roofing Figure 1: Failed roof assembly after heavy wind conditions. Systems, 1which was first publishedrainwater leaders. In addition, thereditions experienced at the time of the in 2004 and subsequently revised inare several qualitative measures fol- event that may have exceeded wind 2010,2014and2020.Referencedlowed in the industry that are eitherupliftdesignparameters.However, intheNationalBuildingCodeindustry best practices or standards,subsequent review determined that ofCanada(NBCC) 2 sincetheincludingstandardspublishedbythe wind conditions were found to 2015editionandadoptedbytheroofing contractors associations; forfallwithintheexpectedwindload provincialcodes,includingtheexample, Roofing Practices Manualrange for the site. The project expe-OntarioBuildingCode(OBC), 3of Roofing Contractors Association ofrienced a series of missteps leading to CSA A123.21 1specifies the primaryBritish Columbia. 4 the failure event, all potentially con-means of assessing a roofing systemsWiththechangingclimateandtributing to create a perfect storm resistancetocounteractcalculatedanticipatedclimateseverities,therescenario. The potential contributing wind loads and has become a pivotalisaneedtofurtherenhancethefactors include: failure by the design-point in the development of roofingabovementionedrequirementsforertospecifyproject-specificwind specifications. roofassembliestoresistincreaseduplift values in the design specifica-WiththecodificationofCSAwindload,tocontrolandmanagetion; alternative questionable meth-A123.21, 1the design and construc- increased precipitation and to coun- ods of compliance employed by the tionofroofassembliesforbuild- terincreaseintemperaturefrommanufacturer;andpoormaterial ings built in Canada are no longerhaving an impact on the durability.handling,poorworkmanshipand asimplecompositionoflayersofTo meet this need, NRC, in collab- poor quality control by the contrac-roofcomponents,relyingontheorationwiththeSIGDERScom- tors during construction (Figures 2, proprietary design of the system bymittee,hasdevelopedPerformance3 and 4). While the primary cause themanufacturer.Low-sloperoofRequirements for Climate Resilienceof failure can be attributed to one assemblies, excluding protected roofofLowSlopeMembraneRoofingor more of the above missteps, this membrane assemblies, are now re- Systems (CSA A123.26), 5which ad- roof failure incident provided some quired to resist the project-specificdresses the severities related to windinsightsthatarevaluablelessons Figure 2: Poor installation practices observed and corrected. wind uplift loads of three differentandrain.learned.Forfurtherdiscussionof 14ONTARIO ROOFING NEWSISSUE 3 2025 THE ONLY SOURCE FOR PROFESSIONAL ICI ROOFING CONTRACTORS IN ONTARIO ORN'