Ground snow load is used directly in the calculations for various drifting snow cases. The ground snow load values are provided by a map created by the National Weather Service. Ground snow loads do not discount that actual snow loads may exceed them, only that the risk of snow-load-induced failure is reduced to an acceptably low level. To find the ground snow load used to determine the design snow loads for buildings and other structures, refer to the online lookup tool or the online map published by the Structural Engineers Association of Oregon (SEAO). This equation includes factors that take into account exposure and building heat loss. This paper describes the development of a new snow load map for defining ground snow loads for building (roof) design in the state of Colorado. Snow Loads 40 psf. The roof or the entire structure can fail if the snow load exceeds the weight the building was designed to shoulder. B. Based on an expected ground snow load of 30 psf, the snow load on our theoretical 3:12 roof is 18.9 psf. If you need to gather ground snow load data programmatically, please consider our API Service. The National Building Code of Canada requires buildings to be designed to carry uniformly and nonuniformly distributed snow loads and the "Commentary on Snow Loads" in Supplement No. Use our Roof Snow Load Calculator to determine your design roof snow loads. For additional questions or concerns about specific ground snow loads please call us at 1-425-741-5555. 2005 Ground Snow Load Tables. Length of Roof Upwind of the Snow Drift: Length of Low Roof, LL: ft. Snow load is the downward force on a building’s roof by the weight of accumulated snow and ice. For the Cornell calculator, this includes the ground snow load for your area (from Step 1), terrain, exposure, roof type, pitch, and run (from Step 2), which is expressed as "W" in the calculator. “Modern buildings are designed with snow load in mind,” said Dr. Edwin Nagy at the University of Maine Department of Civil and Environmental Engineering. Any step snow conditions, valley conditions, over-ridge drift conditions, etc. The Ground Snow Load data along with the Building Geometry will generate factors that convert this Load into the applied Roof Snow, Snow Drift or Sliding Snow Loads. Manufacturers should revise their design based on these requirements as soon as possible. How snow load can damage your buildings. Or if the building was poorly designed or constructed. The ground snow load is pretty much what it sounds like: A predictable load situation that is derived from snowfall records over the years in a particular region (photo 2). The result becomes the required zone as it relates to structures built in the area. The ground snow load, P g, shall be indicated.In areas where the ground snow load, P g, exceeds 10 pounds per square foot (psf) (0.479 kN/m 2), the following additional information shall also be provided, regardless of whether snow loads govern the design of the roof: Flat-roof snow load, P f. Snow exposure factor, C e. Snow load importance factor, I. For example, consider a roof with a run of 12.2 metres (40 feet). The design roof snow load may not be less than 20 psf with rain-on-snow surcharge as applicable. Snow load is the downward force on a building’s roof caused by the weight of accumulated snow and ice. The basis for the snow load computation in ASCE 7-05 is the ground snow load. Please review our State Snow Loads page to investigate state specific snow load requirements. Measure the horizontal distance from eaves to the ridge -- the point where the roof is tallest -- and record the result labelled as "run." 2010 Ground Snow Load Table for Quebec. 2010 Ground Snow Load Table for Ontario. They inquire as to "how much snow can my roof support?" The equation for converting ground snow load, p g , to roof snow load, p f , is ASCE 7-05 equation 7-1. Once the ground snow load at the building site is determined, it must then be converted to roof snow loads according to ASCE 7, with appropriate treatment of exposure to wind, thermal properties of the roof, roof slope, unbalanced snow loads, drifting, and risk exposure. This tool allows a user to set the address of the project location or to click directly on the map. Spatial smoothing and altitude-dependent mapping procedures are described. Consequently, the roof design snow load is taken to be less than the ground snow load. 7.2-1 and Table 7.2-1 . One way to estimate snow load on a roof is to go to an area on the ground nearby the shed or barn. 2016 CBC section 1608.2 (and ASCE 7-10 chapter 7) requires an extreme value statistical analysis of data available in the vicinity of the site using a value with a 2-percent annual Posted at December 21, 2014, in Technical. Obtain the recorded snow load -- the maximum load expected to accumulate on the ground -- for your area. Ground snow load. It was released in 1986 by the Department of Civil Engineering at the University of Idaho. (3) The ground snow load should be 40 psf. County Roof Snow Loads) loads established are the minimum roof snow load up to the maximum elevation listed. Dlubal Software has integrated the ground snow load maps found directly in the ASCE 7-16 with Google Maps Technology to create the Geo Zone Tool available on the Dlubal website. For areas not listed within Table 1-C the following shall be used when calculating the site specific snow load: 1) Ground Snow Load. While there is one roof snow calculated (or specified by code) it covers the uniform application only. Ground Snow Load Values for Ontario and Quebec. The ground snow load shall be determined in accordance with the following criteria: (1) For general County code information, see CB13-2019 (2) The roof design live load should be 40 psf; but 30 psf could be used for flat roof up to 2%. Maps of ground snow loads in IBC and in ASCE 7 indicate a 2 percent probability of the indicated load being equaled or exceeded in any given year. counties list ground snow load, some list roof snow load and some don’t specify what their snow load is. Ground snow loads are converted to top chord live loads when ordering trusses. Roof snow load calculation. This Load is measured in Pounds per Square Foot (English). These numbers represent the peak snow load that has a 50 yearly mean re-occurrence interval of a 2% probability of being exceeded in any given year. Ground and Roof Snow Loads for Idaho - 1986 This report was compiled by Ron Sack and A. Sheikh-Taheri through years of research. 1995 Ground Snow Load Table. These figures are established by the local jurisdiction, in my case the state of Massachusetts, which lists ground snow loads for each town in the state. The amount of packed snow for the area, over a period of time, will determine a Snow Zone. Pf is FLAT ROOF SNOW LOAD – If, as a consumer, your concern is snowfall and you want to upgrade the ability of your building to carry it, THIS is the value to increase. Estimating the weight of snow and ice on a roof is difficult because snow density can range from 3 pounds per cubic foot (pcf) for light, fluffy snow to 21 pcf for wet, heavy snow. Economical structural design in these areas requires an accurate prediction of the ground snow, plus an understanding of how the snow is distributed on the roofs. Design loads: Expressed in psf (pounds per square foot). 4 to the National Building Code of Canada gives detailed design information. Ground Snow Load, pg: psf: Figure 7-1, pages 84-85 and Table 7-1, page 92: Length of High Roof, Lu: ft. use the original ground snow load value in … Ground Snow Load (Pg) This edit box is used to define the Ground Snow Load for the Building or Shape. The Ground Snow Load ranges from 45 lbs to 65 lbs per horizontal square foot depending on each community and the zone in which it is located. The newly proposed Colorado maps aim to ensure that structures designed across the state achieve the target safety index of 3 defined in ASCE 7. (2) The basic roof snow load factor, C b, shall be 0.8, except that for large roofs it shall be, (a) 1.0 – (30/l c) 2, for roofs with C w = 1.0 and l c greater than or equal to 70 m, or (b) 1.3 – (140/l c) 2, for roofs with C w = 0.75 or 0.5 and l c greater than or equal to 200 m, where, l c = characteristic length of the upper or lower roof, defined as 2w-w²/l, in metres, Likewise, unbalanced snow loads — whether the result of wind drifts, uneven melting effects from the sun, or uneven snowfall based on variable protection (usually from trees) — aren't necessarily more likely to cause a roof collapse, but they do stress a roof and its connections in places that balanced loads do not. 780 CMR Commercial Mass State Building Code Table 1604.11 provides snow load for roofs. You can click on the map below to find the design ground snow load for that location. Dist. GROUND AND ROOF SNOW LOADS FOR IDAHO By R. L. Sack and A. Sheikh-Taheri Snow loading is the most severe test of roof structures in many parts of the State of Idaho. Background and Applications Section 4 - Snow load on the ground The snow load on the roof is derived from the snow load on the ground, multiplying by appropriate conversion factors (shape, thermal and exposure coefficients). Table R301.2(1) Climatic and Geographic Design Criteria Ground Snow Load: From our example, our ground load and flat roof snow load were found to be 30 psf and 21 psf, respectively. The value used for the ground snow load should represent the snow load that has a 50 year mean recurrence interval, or, in other words, a 2% probability of being exceeded in any given year. Provisions on how to calculate the snow drift surcharge for structures can be found in Section 7.8 of ASCE 7-10. An equivalent ground snow load of 73 psf may be used to calculate roof loads with no reductions. Length of Roof Downwind of the Snow Drift: Horiz. 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