Introduction
- Snow loads are often established by the local building official as they can vary greatly over relatively small geographic areas.
- Appendix, Chapter 16 of the UBC covers snow loads in much more detail than '94 UBC 1605.4 or '97 UBC 1614 sections.
- This appendix, which is not addressed here, provides detailed information to calculate:
- Roof snow load as a function of ground snow load, building exposure, and importance.
- Unbalanced snow loads.
- Drift potential.
- This appendix, which is not addressed here, provides detailed information to calculate:
- Snow loads, full uniform or unbalanced, should be considered in place of roof live loads when their effect results in
larger members:
- Because various loads may act on the structure (in this case, the roof) simultaneously, you need to consider combinations of loads which are discussed in further detail in the Load Combinations sub-module.
- One of the five combinations of concern here, however, is:
- D + L + (Lr or S) ('94 UBC 1603.6 or '97 UBC 1612.3.1).
- For roofs with S > Lr, this load combination simply becomes D + S.
- Design snow load = f (roof slope):
- If basic roof snow load is greater than 20 psf and if roof slope ³ 20°, then Ra = S/40 - 1/2, where Ra = reduction in S in psf per degree > 20°.
- Flagstaff's basic S = 35 psf.
- Snow load is given along the horizontal plane.
- Other facts:
- 1" newly fallen snow » .5 psf.
- 1" packed snow » 1 psf.
