If \({h}_{c}/{h}_{b} < 0.2\), then snow drift application is not necessary. The minimum roof pitch for shedding snow is around 30°, or a 6:12 or 7:12 slope, although this is not a definite, as the material of your roof, the direction of the snow and wind are some factors that can affect whether or not snow will slide, as roofs of as little as 10° have been reported to shed snow. Specified Snow Load (1) The specified load, S, due to snow and associated rain accumulation on a roof or any other building surface subject to snow accumulation shall be calculated from the formula, S = I s [S s (C b C w C s C a) + S r]. 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. Engineering Toolbox \({γ} = 0.13*(30) + 14 = 17.9 pcf ≤ 30 pcf \), \({h}_{b} = {21 psf}/{17.9 pcf} = 1.17 ft\). The live load on a roof is the weight of any temporary objects on the roof. Figure 2: Typical loading condition of balanced snow load. This equation includes factors that take into account exposure and building heat loss. ABN: 73 605 703 071, SkyCiv Structural 3D: Structural Analysis Software, How to Calculate and Apply Roof Snow Drift Loads w/ ASCE 7-10. }. For warm roofs that do not meet the aforementioned conditions, the solid line in Fig. The lower and higher roof elevations are 15 feet and 30 feet from grade, respectively. In areas of the state outside of certified city, county and town jurisdictions, the design snow load shall be based on the ground snow loads developed in "Snow Loads for Structural Design in Montana", Civil Engineering Department, Montana State University, 2004 revised edition. E-2b. Lets take a look at all the pertinent variables for this calculation. Continuous Confidence . Length of Roof Upwind of the Snow Drift: Length of Low Roof, LL: ft. E-2a, provided that for nonventilated warm roofs, their thermal resistance (R-value) equals or exceeds 30 ft2 h ◦F/Btu (5.3 ◦C m2/W) and for warm ventilated roofs, their R-value equals or exceeds 20 ft2 h ◦F/Btu (3.5 ◦Cm2/W). In our case, our beams are spaced at 10 feet. 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). 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 … From our example, our ground load and flat roof snow load were found to be 30 psf and 21 psf, respectively. American Society of Civil Engineers. SNOW LOADING Ground Snow Load (p g) p g = 20 psf Flat Roof Snow Load (p f) p f = 0.7C e C t Ip g p f = 0.7(1.0)(1.0)(1.0)(20) = 14 psf But not less than p f =(I)p g = 20 psf ASCE 7-05 Section 7.2 Figure 7-1 Section 7.3 Eq. You should know the roof weight limits for your barns and outbuildings. Snow load information can be found from your local building officials of from maps on the internet. 1) Basic wind 2) Wind importance factor 3) Wind exposure 4) The applicable internal pressure coefficient 5) Components and cladding For warm roofs (Ct ≤ 1.0 as determined from Table E-3) with 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 in Fig. Your guide to SkyCiv software - tutorials, how-to guides and technical articles. 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. Box 441022, Moscow, ID 83844-1022. Downloads document.write('') Contact your local building code department to determine the snow load requirements for your area. What is the Process of Designing a Footing Foundation? , Symbols and Notations used in Snow Loads Design Data, GD&T Training Geometric Dimensioning Tolerancing. To figure out the load on your roof, take the depth of snow in feet and multiply it by the weight of a cubic foot of snow. Snow drift load and distributions for lower levels of adjacent roofs. Length of Roof Downwind of the Snow Drift: Horiz. The two directions of wind that cause snow drifts are “windward” and “leeward”. 1603.1.4 Wind Design Data . (2013). Figure 1: Isometric view of our example structure. n. The truss could be designed based on the assumption that the 25 psf roof snow load is a factored ground snow load, in which case a ground snow load is back-calculated using ASCE 7 based on the specified roof snow load (pg > 25 psf) Therein lies the problem with specifying only a roof snow load. Roof Snow Load (NBC 2010) Roof Snow Load (NBC 2010) version 0.1.0 January 6, 2021. The sloped roof snow load, p s, shall be obtained by multiplying the flat roof snow load, p f, by the roof slope factor, C s: p s = C s p f The thermal factor, C t , 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. 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. } We stand out because of our continuous monitoring solutions, which allow a long-term view of trends and a predictive approach to property care. Ground Snow Load, pg: psf: Figure 7-1, pages 84-85 and Table 7-1, page 92: Length of High Roof, Lu: ft. At this point the snow loads are ready for analysis in conjuncture with other load cases and load combinations based on ASCE 7-10 and other pertinent building codes. 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 If you have any concerns as you are determining your flat roof snow load, consult with a structural engineer or roofing specialist. Centroid Equations of Various Beam Sections, How to Test for Common Boomilever Failures, AS/NZS 1170.2 Wind Load Calculation Example →. ; Online Books & Manuals Note, all values are unfactored, service loads. If your roof is 1,000 square feet, the total snow load is 15,000 pounds of snow. Engineering Calculators Snow Load Calculations. The equation for converting ground snow load, p g , to roof snow load, p f , is ASCE 7-05 equation 7-1. else House roofs should support 20 lbs./square foot of snow before they become stressed. 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. Calculate the carport roof load using a combination of the dead-load and live-load measurements. E-3 with Cs determined from the appropriate curve in Fig. Roof snow load is defined as the weight of snow on the roof surface used in design of the building structure (IBC, 2012). // --> 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. Most of the geometric values can be associated with variables. See Figure 7-7 from ASCE 7-10 below for a succinct depiction: Lets assume our project is in Madison, Wisconsin and we have already calculated our balanced, roof snow load here. n. Importance, occupancy, and use of the building . Disclaimer Roof Slope Factor for Multiple Folded Plate, Sawtooth, and Barrel Vault Roofs. 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. It goes without saying that in a warmer climate, the snow load probably would be less, so you need to check your code book for live loads and dead loads in your region. \({h}_{b}\) = 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, \({p}_{s}\) = design snow load from Chapter 7. Exterior air shall be able to circulate freely under a ventilated roof from its eaves to its ridge. snow weight = length * width / cos(pitch(°)) * snow load. For all other cold roofs with Ct = 1.2, the solid line in Fig. 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 \({h}_{d} = {h}_{c}\). on multiple factors, including: n. Ground snow load value. The BOCA code recognizes this and allows you to use the horizontal projection of the roof when calculating snow loads. Snow drift load is in a triangular shape with maxim load pd at edge between upper and lower roof and decrease to zero for a length W. The drift load shall be added to normal roof snow load. Provisions on how to calculate the snow drift surcharge for structures can be found in Section 7.8 of ASCE 7-10. Lets first gather the relevant geometric information about our structure. Leeward Snow Drifts - from adjacent higher roof Upper roof length lu = 100.0 ft No other loads except dead loads shall be present on the roof when this uniformly distributed load is applied. Roof loads are used to determine the size of beams, joists and columns that support a roof. Dist. E-2. ; Asphalt shingles, wood shingles, and shakes shall not be considered slippery. Membranes with an imbedded aggregate or mineral granule surface shall not be considered smooth. A great deal of confusion currently exists among engineers, architects, recreation specialists, and maintenance personnel concerning the proper snow loading to use for the design and maintenance of trail bridges, building roofs, and other structures in mountainous, high snow load areas. Slippery surfaces shall include metal, slate, glass, and bituminous, rubber, and plastic membranes with a smooth surface. Figure 3 depicts the additional drift load at the correct location. Local building codes dictate the snow load required for residential roofs. 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). DFM DFA Training Saturated snow weighs about 20 lbs./cubic foot. | Contact. Snow Drift Load (obstruction) — (Fig. The Ontario Building Code | Specified Snow Load 4.1.6.2. It is determined based . 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 www.engineersedge.com All rights reserved Flat roof snow loads of 30 psf (1.44 kN/m 2) or less and roof live loads of 30 psf (1.44 kN/m 2) or less need not be combined with seismic loads. Balanced loads shall be determined from the balanced load diagrams in Fig. Geometry of the roof and the direction of the wind are the two drivers that lead to snow drifts. GD&T Training Geometric Dimensioning Tolerancing where, I s = importance factor for snow load as provided in Table 4.1.6.2., n. Roof slope. | Feedback | Advertising 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). Cold roofs are those with a Ct > 1.0 as determined from Table E-3. Our example structure’s roof has two varying roof heights and therefore we need to calculate the snow drift surcharge and apply it to our members. Figure 2 shown below depicts the balanced snow load of 21 psf applied to the roof of our structure. n. Wind exposure of roof. To request a copy, send a check for $22.50 (includes postage), payable to Department of Civil Engineering, University of Idaho, P.O. Engineering Forum There are currently no comments available. Snow loads are influenced by elevation, general weather and moisture patterns, slope direction, exposure, roof (or trail bridge) configuration, and wind direction and severity. Any roof load calculator can tell you how much weight your structure deals with at the moment. Powerful, web-based Structural Analysis and Design software, Free to use, premium features for SkyCiv users, © Copyright 2015-2021. Minimum Design Loads for Buildings and Other Structures. also available for the Android OS. The weight of snow is measured in kg or lbs. Home { Project: Designer: Climatic Data. \({h}_{c}/{h}_{b} = 13.8 ft/1.17ft = 11.8 > 0.2\) and therefore, snow drift loading is necessary. Engineering News 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). Span Calculator for Wood Joists and Rafters also available for the Android OS. snow load = thickness * density. We take things up a notch by making sure you have the peace of mind you deserve for as long as you use our system. Multiple folded plate, sawtooth, or barrel vault roofs shall have a Cs = 1.0, with no reduction in snow load because of slope (i.e., ps = pf ). Snow draft load from upper roof to lower roof depends on snow density, length of upper and lower roof, and height between two roofs. Because of this, there are roof areas higher and lower than each other and are subject to snow drifts. A roof shall be considered unobstructed if no objects exist on it that prevent snow on it from sliding. { Take a look at Figure 7-8 from ASCE 7-10 for a depiction of many of these terms and what they visually represent: Now that we have identified what the variables are, the snow loading configurations, and the geometric constraints of our structure, lets calculate the snow drift. G-8) Snow drift load and distributions for areas adjacent to roof obstructions. A publication can be purchased called Ground and Roof Snow Loads for Idaho, by R. L. Sack and A. Sheikh-Taheri, Published by the UI Department of Civil Engineering, 1986. \({p}_{g}\) = 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 Estimate the weight of snow on your roof. ASCE/SEI 7-10. Figure 3: Typical loading condition service level snow design loads. The lower bay and upper bay size is 25 feet and 37 feet, respectively. E-2c. 1 5 lbs. Dead Load (psf) Span Calculator for Wood Joists and Rafters available for the iPhone. The flat roof snow load is to be applied as a uni- form pressure to the entire roof of the building. Thus, a roof designed to a carry a snow load of 20 lbs.. per horizontal square foot is expected to support nearly 12 inches of wet, heavy snow. Leeward snow drifts occur when wind blows snow off of a higher elevation roof down onto an adjacent lower roof. from Eave to Ridge, W: ft. Horizontal Distance from Eave to Ridge: Type of Roof SkyCiv Engineering. For all other cold roofs with Ct = 1.1, the solid line in Fig. if (document.getElementById("tester") != undefined) 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. Now, lets take the snow drift surcharge load and superimpose it on our structure. E-2a shall be used to determine the roof slope factor Cs . document.write(' ') The height of the drift for both wind directions can be found using the equation found in Figure 7-9 of ASCE 7-10, shown below: \({h}_{d} = 3/4*(0.43({l}_{l})^{1/3}({p_g}+10)^{1/4}-1.5)\) for windward drift, \({h}_{d} = 0.43({l}_{u})^{1/3}({p_g}+10)^{1/4}-1.5\) for leeward drift, \({h}_{d} =3/4*(0.43(25 ft)^{1/3}(30 psf+10)^{1/4}-1.5)\), \({h}_{d} = 0.43(37 ft)^{1/3}(30 psf+10)^{1/4}-1.5\). Engineering Videos To find the maximum surcharge load, multiply the drift height by the snow density: The maximum snow drift surcharge load is then superimposed on the balanced snow load: Lets look at the middle frame of our structure. The result - snow load, or the pressure exerted by the snow - has the units of kN/m² or lbs/ft².