APB » Roof Trusses » Snow Load Tutorial

Ground Snow Load

                  Ground snow loads are converted to top chord live loads when ordering trusses.

                  Design loads: Expressed in psf (pounds per square foot). The amount of packed snow for the area, over a period of time, will determine a Snow Zone. The result becomes the required zone as it relates to structures built in the area. Different states have varying ideas regarding how to handle these design factors.

                  Snow Zones are expressed in psf (40 psf or 25 psf as examples) Snow load calculations change based upon building class, design & geographical location. The permitting office is the final determining factor on what snow load your structure requires.

                  General Class of Buildings:
                   Class A -- 100 years - Permanent buildings with a high degree of hazard to life and assets in case of failure.
                   Class B -- (50 years) Human occupancy type buildings that are permanent.
                   Class C -- Buildings not housing humans.

                  Snow Loads: Snow loads can be presented in two different ways:
                   Ground Snow Load or Roof Snow Load

                       Snow Load:    70    60    50    40    35    30    25
                                   x0.7  x0.7  x0.7  x0.7  x0.7  x0.7  x0.7
                  Roof Snow Load:   49*    42*   35*  28*  24.5*   21* 17.5*

                  *Assumed Value
                     Thermal factor Ct : 1.0
                    Exposure factor Ce : 1.0
                   Importance factor I : 1.0

                  Dead Loads: Weight of permanent materials like trusses, sheathing, and roofing material. Dead load is calculated from the weight of the building materials supported by structural members.

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