b'Figure 1: Vertical load results in drag load. Drag load is resisted by two bonds. Figure 2: Infrared and ultraviolet radiation from sunlight pass through theFigure 3: Calculation of vector force. This calculation should be done for snowbank, warming the roof surface and melting the temperature-sensitive bond.any snow retention system. System testing must prove that the strength of Snowbank insulates the process from subfreezing ambient temperatures. the system exceeds this calculated force. Note: psf = lb/ft 2 .Thesethreevariablesdeter- isdistributedtoeachpointofSnow Retention System mine the force that a system mustsystemattachmentthestand- Design and Application resistforanyslipperyroofsur- ingseams.Therefore,thetribu-face 2and should be included intary vector force to each seam isConsiderationsplans and specifications that alsofound by multiplying the vectorSystem Placementrequire an engineered system.force (in lb/ft. 2or kPa/m 2 ) by theSnowbankstypicallyaccumu-roof length (in feet or meters) bylate and densify in a cross-section-Vector Force the panel width (in feet or meters)al wedge pattern with the greatest Vectorforceisfoundbyre- (Figure 3). depth at the eave. All snow guards ducing the vertical load (lb/ft. 2orExample: rely on the snows own compres-kPa) by the sine of the roof angle.Design roof snow: 35 lb/ft. 2 sive strength to restrain its move-Theproductisthenmultipliedment.Gravitationalforcescom-by the tributary area (ft. 2or m 2 )Roof slope: 6:12 press the snowbank the most at tothesnowguardsystem.The(sin 26.565 = 0.447) its interface with the roof surface, loads for the entire length fromLength from eave to ridge: 40 ft. especially toward its lower (eave) eave to ridge are tributary to thePanel width (seam spacing): 18 in. end, so that is where compressive snowguardsystemrestraining2strength is greatest (Figure 5). Figure 4: While roof loads are usually less than ground loads, aerodynamic shade (drift it. For standing-seam metal roof35 lb/ft.0.44740 ft.1.5 ft.Theinterfaceofsnowreten- load, shadow load) can cause roof design loads on a lower roof to be several times greater (SSMR)profiles,tributaryforce= 938.7 lb/panel seam tiondevicesatthislocationisthan that of ground snow.ORN THE ONLY SOURCE FOR PROFESSIONAL ICI ROOFING CONTRACTORS IN ONTARIO ONTARIO ROOFING NEWSISSUE 3 202119'