Unbalanced snow loads on arched roof - Research for the national building code of Canada Conference

cited authors

  • Hochstenbach, FM; Baker, HA; Gamble, SL; Irwin, PA

fiu authors


  • According to the 1995 National Building Code of Canada (NBCC), unbalanced loading of arched roofs need only be considered for roofs with a rise (h) to span (b) ratio greater than 0.10. Recent building collapses have indicated that significant unbalanced loads can still occur for rise/span (h/b) values less than 0.10. The purpose of this research project was to investigate the lower bound of arched roof geometry for consideration of unbalanced snow loading recommended in the NBCC. Finite Area Element snow loading simulations were performed on roofs with five rise/span ratios using meteorological data from: Vancouver, B.C.; Edmonton, Alberta; Toronto, Ontario; Montreal, Quebec; and St. Johns, Newfoundland. The sample roofs were rotated azimuthally in 15 degree increments to find the orientation producing the greatest unbalanced loading for each city. Thirty-year return period design loads were obtained using a Fisher Typpett Type I extreme value fit. These loads were then compared to the NBCC unbalanced snow loads, as detailed in Figures H-2(a) and H-2(b), to assess the appropriateness of the 0.10 lower cutoff value for h/b. Revisions to the NBCC formula are proposed and a new lower cutoff of 0.05 is recommended. These recommendations were accepted as a special amendment to the National Building Code of Canada in April, 2002.

publication date

  • December 1, 2003

start page

  • 1680

end page

  • 1686


  • 2003