For example, a roof with 3 feet of light snow has an estimated roof load of 60 pounds per square foot (3 ft depth X 20 lb/ft2/ft depth density = 60 lb/ft2). SkyCiv Engineering. Make sure to read through Chapter 7 of ASCE 7-10 for more information about successive provisions for partial snow loading and unbalanced snow loading, as those conditions were not evaluated here. Snow Load Calculations. Snow load calculations for most residential structures are usually performed using the following method: Determine ground snow load based on location and elevation Calculate flat roof snow load p f using the following equation: p f = 0.7C e C t I s p g where: p f = Flat Roof Snow Load … If necessary, rebuild or fortify them to withstand worst-case scenario snow loads and meet local building standards. Length of Roof Upwind of the Snow Drift: Length of Low Roof, LL: ft. snow load = thickness * density. Disclaimer E-2c. Local building codes dictate the snow load required for residential roofs. Geometry of the roof and the direction of the wind are the two drivers that lead to snow drifts. document.write('') Figure 3: Typical loading condition service level snow design loads. n. Importance, occupancy, and use of the building . Roof snow load is defined as the weight of snow on the roof surface used in design of the building structure (IBC, 2012). Overestimation of snow loads can unnecessarily i… Project: Designer: Climatic Data. Leeward snow drifts occur when wind blows snow off of a higher elevation roof down onto an adjacent lower roof. E-2b shall be used to determine the roof slope factor Cs. Asphalt shingles, wood shingles, and shakes shall not be considered slippery. per square foot of roof surface is used for a simple structure with a sheet metal roof and siding and no sheathing, shingles, etc 2 Snow loads are measured in pounds per square foot (psf). The maximum drift height between the windward and leeward drift height will be used for design, therefore: The width of the snow drift load, \({w}\), depends on \({h}_{c}\) and \({h}_{d}\), If \({h}_{d} ≤ {h}_{c}\), then \({w} = 4{h}_{d}\), If \({h}_{d} > {h}_{c}\), then \({w} = 4{h}_{d}^2/{h}_{c}) and subsequently \({h}_{d} = {h}_{c}\). Snow loads are influenced by elevation, general weather and moisture patterns, slope direction, exposure, roof (or trail bridge) configuration, and wind direction and severity. Figure 2: Typical loading condition of balanced snow load. Our sample homes are in an area where the snow load is 50 pounds per square foot of roof area (treat snow as live load). The lower and higher roof elevations are 15 feet and 30 feet from grade, respectively. else Engineering Toolbox // --> E-2c shall be used to determine the roof slope factor Cs . Cold roofs are those with a Ct > 1.0 as determined from Table E-3. document.write(''); Note, all values are unfactored, service loads. Length of Roof Downwind of the Snow Drift: Horiz. Slippery surfaces shall include metal, slate, glass, and bituminous, rubber, and plastic membranes with a smooth surface. \({p}_{g}\) = ground snow load \({l}_{u}\) = length of upper roof \({l}_{l}\) = length of lower roof \({h}_{d}\) = height of snow drift \({w}\) = width of snow drift \({h}_{b}\) = height of balanced snow load \({h}_{c}\) = clear height from top of balanced snow load to closest point of adjacent roof \({h}_{r}\) = height difference between roofs Training Online Engineering Saturated snow weighs about 20 lbs./cubic foot. For cold roofs with Ct = 1.2 and an unobstructed slippery surface that will allow snow to slide off the eaves, the roof slope factor Cs shall be determined using the dashed line on Fig. This loading condition follows the entire length of the wall, in our course, the length of  the structure. Balanced loads shall be determined from the balanced load diagrams in Fig. E-2. Engineering Videos The distributed area for the beams in this plane is 10 ft because of the constant 10 ft beam spacing. The sloped roof snow load, ps, shall be obtained by multiplying the flat roof snow load, pf, by the roof slope factor, Cs: The thermal factor, Ct , from Table E-3 determines if a roof is “cold” or “warm.” “Slippery surface” values shall be used only where the roof’s surface is unobstructed and sufficient space is available below the eaves to accept all the sliding snow. For dead loads… GD&T Training Geometric Dimensioning Tolerancing }. A roof shall be considered unobstructed if no objects exist on it that prevent snow on it from sliding. In our case, \({h}_{c} = 13.8 ft\) and \({h}_{d} = 2.1 ft\), and therefore: Note, per ASCE 7-10 the snow drift width shall never exceed \(8{h}_{c}\). BOCA also allows you to reduce the snow load for roofs with slopes greater than 30 degrees, presumably because snow will slide or blow off steeply pitched roofs. The BOCA code recognizes this and allows you to use the horizontal projection of the roof when calculating snow loads. Estimate the weight of snow on your roof. In our case, our beams are spaced at 10 feet. \({γ} = 0.13*(30) + 14 = 17.9 pcf ≤ 30 pcf \), \({h}_{b} = {21 psf}/{17.9 pcf} = 1.17 ft\). Dead Load (psf) Span Calculator for Wood Joists and Rafters available for the iPhone. For all other cold roofs with Ct = 1.2, the solid line in Fig. Advertising Center | Contact. Leeward Snow Drifts - from adjacent higher roof Upper roof length lu = 100.0 ft 1608.1 Design snow loads shall be determined in accordance with Chapter 7 of ASCE 7, but the design roof load shall not be less than that determined by Section 1607. See Symbols and Notations used in Snow Loads Design Data for symbol data, Reference: American Society of Civil Engineering/Structural Engineering Institute Standards, © Copyright 2000 - 2021, by Engineers Edge, LLC All rights reserved From our example, our ground load and flat roof snow load were found to be 30 psf and 21 psf, respectively. Two types of warm roofs that drain water over their eaves shall be capable of sustaining a uniformly distributed load of 2pf on all overhanging portions: those that are unventilated and have an R-value less than 30 ft2 h ◦F/Btu (5.3 ◦C m2/W) and those that are ventilated and have an R-value less than 20 ft2 h ◦F/Btu (3.5 ◦Cm2/W). American Society of Civil Engineers. } Centroid Equations of Various Beam Sections, How to Test for Common Boomilever Failures, AS/NZS 1170.2 Wind Load Calculation Example →. Crane hook loads need not be combined with roof live load or with more than three-fourths of the snow load or one-half of the wind load. Roof Snow Load (NBC 2010) Roof Snow Load (NBC 2010) version 0.1.0 January 6, 2021. Roof designs usually present multitudes of roof elevations and rarely offer one single roof height. DFM DFA Training 1The load combinations and factors are intended to apply to nominal design loads defined as follows: D = estimated mean dead weight of the construction; H = design lateral pressure for soil condition/type; L = design floor live load; L r = maximum roof live load anticipated | Feedback | Advertising Dist. where, I s = importance factor for snow load as provided in Table, Online Books & Manuals g= 0.7(0.9)(1.2)(1.0)(33.3) = 25psf Note that the State of Montana requires a min- imum design snow load of 30psf. The result - snow load, or the pressure exerted by the snow - has the units of kN/m² or lbs/ft². document.write(''); The two directions of wind that cause snow drifts are “windward” and “leeward”. Roof Slope Factor for Multiple Folded Plate, Sawtooth, and Barrel Vault Roofs. Continuous Confidence . For ground snow loads greater than 20 pounds per square foot, the roof load is equal to 70% of the product of the exposure, thermal and importance factors, the ground snow load, and 20 (pounds). Snow load information can be found from your local building officials of from maps on the internet. n. Wind exposure of roof. Downloads