b'Figure 7: Mechanical clamp attachment with round-point setscrews. The Metal Construction Association, Metal Building Manufacturers Association and U.S. Department of Defense advocate use of this type of attachment to mount snow guard systems on metal roofs.acomplextask:carefulsurfacearenotspecificallyengineered preparationandmanydaysoffor design loads. In the absence curing time at specific tempera- of snow guard police, we faceFigure 8: When tested and engineered correctly, a mechanical bracket attachment (for face-fastened tures are required.abuyer-bewarescenariowithroofs only) can be successfully used to mount a snow guard system. This attachment was not a success.Adhesivesystemsmayalsoregard to the appropriateness and initiallyseemlikealower-costproof of testing and engineeringufactureandproducthandoff.results.Eachlink(component)Testingofthesesystemcom-option, but the lower cost is of- performed by the vendor.Scrutiny of a vendors publishedin the chain must be proven byponentsshouldbeconducted tenonlyforparts.WhentotalHow do you discern prudentevidence can provide assurance totesting and/or engineering analy- by a third-party laboratory with projectcosts,includinglabourproductselectionfromsalesthe buyer that the vendors claimssis. The weakest link determinesISO 170255 accreditation. When and quantities required to do therhetoric?Inadditiontounder- are credible. A qualified vendorthestrengthofthechain.Thereviewing test findings, be aware job, are considered, this methodstanding the art and science be- shouldgladlyprovideproofofrequiredengineeringcannotbethatitisnotscientificallyac-may not be less expensive thanhind snow retention systems, youclaims and make them visible oncompletedwithoutreliable,ex- ceptabletoapplyatestresult the other techniques. Moreover,should vet the manufacturer andits website. tensive testing. fromonesetoftestspecimens thereplacementcostsovertheits product offerings. Anchorage of clamps or brack- to another similar-looking roof life of the roof can be quite highProof of Testing ets to the roof specimen shouldproductorassembly.Similarity for adhered snow guards becauseVet and Specify Toensurethatasnowreten- be repeatedly tested on the specif- is not proven by casual eyeball-the holding strength of the ad- Vendor transparency is a req- tion system can resist the forcesic substrate of the project. As seting. Ideally, all test results should hesives commonly used by snowuisitetoadequatelyvetasnowthat might be applied to it, theforth by the only recognized U.S.beavailableandpublishedon guard vendors diminishes whenguardsystem.Acompanythatsystemsfailurepointmustbestandard for this kind of testingthevendorswebsite.Whenin exposed to heat, cold, UV lightlauds the capabilities of its systemknown,aswellastheappropri- (for the County of Los Angeles,doubt, request third-party labora-and moisture. Replacement timebut fails to provide proof of thoseate factors of safety employed toCalif. 4 ), a minimum of three testtory reports from the vendor that is often within a few years afterclaimsmaybeblowingsmoke.determineallowablestructuralrepetitions should be conducted.provide anchorage values for the installation, depending on orien- Thedesignershouldscrutinizecapacity. (MCA says a minimumInthecaseofSSMRclampedappropriate testing used in engi-tation to the sun and other envi- vendor/manufacturerqualifica- safetyfactorof2.0.)Then,thesystems, the clamp testing shouldneering calculations and match to ronmental factors (Figure 9).tions and certifications to ensurepopulation and frequency of thebe specific to the roof materials,the actual project profile. Giventhediminishinghold- a safe, engineered application andsystem are determined so it can- gauge, brand or roof manufactur-ing strength over time, appropri- long-term service. 3This transpar- not fail. Because the system mayer, and seam profile of the projectProof of Engineering ate testing is not feasiblethatencyshouldextendfromrawcomprisemultiplecomponents,as holding capacities vary widelyProject-specificengineering is, there is no way to determinematerialsourcingthroughman- aloadpath(orloadchain)with these variables.should be provided by the ven-atwhatagethetestingshould bedone.Whenadheredsnow guardsfail,theycanalsorip awaypaintcoatings,leadingto corrosion(Figure10).Industry groups,suchastheMCA3and the Metal Building Manufactur-ers Association (MBMA), as well as the U.S. Army Corps of En-gineers,stronglyadviseagainst their use. How to Choose the Best Snow Retention System for Your ProjectVendorshaveintroducednu-meroussnowguardsystemsto themarket,eachclaimingthat their system is the best, ultimate,Commercial and Residential Roofingfirstorstrongestoption.ThereTrinity Roofing Ltd. specializes in a variety of roofing applications andare no industry standards or man- waterproofing for residential, commercial and institutional buildings.dates for design, manufacture, use ortestingofsnowguards.ThisPhone: 416-630-9213URL: www.trinitycanada.com marketspaceiscompletelyun- Fax: 416-630-1722 Email: info@trinitycanada.com regulated, and many applications ORN THE ONLY SOURCE FOR PROFESSIONAL ICI ROOFING CONTRACTORS IN ONTARIO ONTARIO ROOFING NEWSISSUE 3 202121'