2. Flat Roof Snow Loads. 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 in psf C e = Exposure Factor, as determined by ASCE Table 7-2 below. ASCE705S is a spreadsheet program written in MS-Excel for the purpose of flat roof snow loading analysis for buildings and structures per the ASCE 7-05 Code. This program assumes only snow loading analysis for buildings with a flat roof, or low slope roof <= 5 degrees. р s = design snow load for a sloped roof. The standard guide in the U.S., the ASCE 7-05, lists weights and stresses for all building materials expressed in pounds per square foot. 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. Driven by recent changes to the ASCE 7 snow load provisions, this guide describes: While this may be more intuitive for flat or even gable/hip type roofs, the determination of snow loads is increasingly more difficult for arch roofs due to complex geometry. This program assumes only snow loading analysis for buildings with a flat roof, or low slope roof <= 5 degrees. 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. C t is Thermal factor. ASCE702S is a spreadsheet program written in MS-Excel for the purpose of flat roof snow loading analysis for buildings and structures per the ASCE 7-02 Code. I s is important factor. a) (ASCE 7, 7.2)Ground Snow Load, P g = 25 psf b) (ASCE 7, 7.3)Flat-roof snow load, P f = i) Exposure Factor, C e (ASCE 7, 7.3.1) = ii) Thermal Factor, C t (ASCE 7, 7.3.2) = iii) Importance Factor, I (ASCE 7, 7.3.3) = c) = Sloped Roof Snow Load, P s (ASCE 7, 7.4) i) Roof Slope Factor, C s (ASCE 7, 7.4.1) = 4. (Note: for reference, a 1:12 roof slope equates to 4.76 degrees, and the program allows a slope up to 1.05:12.) Input Data. The basis for ASCE 7-05 snow load computations is the ground snow load, p g. This value is modified to become a flat roof snow load, p f, by multiplying by a constant that accounts for roof snow loss that ground measurements don't see. р f = design flat roof snow load. ASCE 7-05 Code for Buildings with Flat or Low Slope Roofs (= 5 deg. Pg = ground snow load Pf = flat roof snow load = Pg*I*Ce*Ct Ps = sloped roof snow load = Pf*Cs The "minimum" Pf is defined in ASCE-7-98 as: I*Pg when Pg is less than or equal to 20psf I*20 when Pg is greater than 20psf +++++ The "minimum" that is specified is for cases when the Ce*Ct<1.00. I would agree with you if we use ASCE 7-05, which requires unbalanced snow on leeward side of the gable regardless of roof pitch. According to ASCE 7-16, the design snow loads for flat roofs and sloped roofs can be obtained using the following equations: where. Where flat roof snow loads exceed 30 psf (1.44 kN/m 2), 20 percent shall be combined with seismic loads. Question 3: Equation 16-21 (alternative basic load combination) also uses D+L+S+E/1.4. "ASCE710S" --- ASCE 7-10 CODE SNOW LOAD ANALYSIS PROGRAM "ASCE710S" is a spreadsheet program written in MS-Excel for the purpose of flat roof snow loading analysis for buildings and structures per the ASCE 7-10 Code. Snow load: (ASCE 7-05, 10, IBC 2006, 2009, 2012) ... Flat roof snow load: p f = 0.7 C e C t I s p g. C e is exposure factor. Step 4 - Determine the Flat Roof Snow Load Specifically, coefficients and related and required parameters Ground snow loads map (Figure 7-1 of ASCE 7-10 Code) Figure 7-1, pages 34-35 and Table 7-1, page 30 Table … (Note: for reference, a 1:12 roof slope equates to 4.76 degrees, and the program allows a slope up to 1.05:12.) About the Author Michael O'Rourke, Ph.D., P.E., is a professor in the Department of Civil and Environmental Engineering at Rensselaer Polytechnic Institute, where he teaches and pursues snow load research. Flat roof snow load — The flat roof snow load, p f, is calculated in pounds per square foot (psf) from Section 7.3 of ASCE 7 and is given by Equation 7-1: p f = 0.7C eC tI sp g 0.7 is the combined exposure reduction factor for ground-to-roof conversion for normal conditions. Specifically, coefficients and related and required parameters Ground snow loads map (Figure 7-1 of ASCE 7-05 Code) 1. Non-shaded (CS) areas require site-specific Case Studies to establish ground snow loads. Allows up to 10 different flat roof snow loads to be calculated by entering values for all of the parameters in accordance with ASCE 7. Snow Loading Analysis Calculator. Snow Load - Snow loading analysis for buildings with flat or low slope roofs Snow Map - Ground snow loads map (Figure 7-1 of ASCE 7-10 Code) Program Assumptions and Limitations: 1. If slope ≤ ½” in 12”, add rain-on-snow surcharge (Section 7.10 ASCE 7) 2 yes . 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. I have the same question as Q2 about the snow load used. The International Code specifies design snow loads are to be determined according to Section 7 of a document called ASCE 7. for Balanced Snow, Drift, and Rain-on-Snow Surcharge Loadings . 3. 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. (Section 7.11, ASCE 7) 2 Go to partial loading 1 If slope > 5°, calculate sloped roof snow load. = live roof load W = wind load S = snow load E = earthquake load R = rainwater load or ice water load T = effect of material & temperature H = hydraulic loads from soil F = hydraulic loads from fluids. ASCE 7 in fact clarifies that S may be the flat roof snow load or the sloped roof snow load, depending upon the slope of the roof. This one hour webinar presents design roof snow loads as per ASCE 7 for four increasing complex residential roofs. ASCE 7 Table 7-3 Calculate flat roof snow load pf 0.7CeCt Is pg no Is roof flat? The first is a simple, one story hip roof. This program specifically follows Section 7.0, Snow Loads, of the ASCE 7-10 Standard, "Minimum Design Loads for Buildings and Other Structures". р g = ground snow load. Use our ASCE Ground Snow Loads map to easily obtain the ground snow load (Figure 7-1 of ASCE 7-10) for any location in the contiguous United States. Load Calculations. 2. This program specifically follows Section 7.0, Snow Loads, of the ASCE 7-10 Standard, "Minimum Design Loads for Buildings and Other Structures". Specifically, coefficients and related and required parameters are selected or calculated in order to compute the net design snow loads, including snow drift due on lower roofs and rain-on-snow surcharge. You can click on the map below to determine the design ground snow load, latitude and longitude and elevation for that location. The importance factor, also found in ASCE 7-10, takes into account the type of building for which you are calculating snow loads. Snow Loads: A Guide to the Use and Understanding of the Snow Load provisions of ASCE 7-02 is the only book that provides a detailed, authoritative interpretation of the snow load provisions of Minimum Design Loads for Buildings and Other Structures, Standard ASCE 7-02. Sloped Roof Snow Loads. Specifically, coefficients and related and required parameters are selected or calculated in order to compute the net design snow loads, including snow drift due on lower roofs and rain-on-snow surcharge. Warm roofs lose heat in such a way that it melts snow, while cold roofs lose heat that doesn’t contribute to melting. For this roof the complexity involves snow load for the roof valley area. or 1 in./ft.) Step 3 - Determine the Importance Factor. 2. Section 7.4 of ASCE 7-16 explains how to convert flat roof snow loads into sloped roof snow loads using the roof slope factor, C s. The sloped roof snow load, also called the balanced load, is the basis for determining the snow load for all structures. For C t = 1.0 and I s = 1.0, Equation 7-1 produces ground-to-roof snow Allows up to 10 different sloped roof snow loads. The second example is a one-story L-shaped roof. Exposure factor, C e: Exposure factor, C e is based on wind exposure of structure. Like its predecessors that accompanied earlier versions of ASCE 7, this new edition of Snow Loads discusses flat roof loads, sloped roof loads, partial loads, and all types of conventional drift loading. The complexity arises from the variable upwind fetch for unbalance or across-the-ridge drift loads. Snow Loads for Structural Design in Montana (Revised 2004) Gregory P. Theisen Michael J. Keller Jerry E. Stephens Fred F. Videon James P. Schilke December 2004 "ASCE705S" --- ASCE 7-05 CODE SNOW LOAD ANALYSIS PROGRAM "ASCE705S" is a spreadsheet program written in MS-Excel for the purpose of flat roof snow loading analysis for buildings and structures per the ASCE 7-05 Code. This document provides for all roof snow loads to be calculated from ground snow loads, however not every Building Department follows this procedure. ARCH 331 Note Set 13.1 S2014abn 2 Determining Dead Load from Material Weights Material density is a measure of how much mass in a unit volume causes a force due to gravity. 3. Calculating the load on a flat roof is a challenging task for the layperson that involves knowledge of building materials, their weights and local building codes. The flat roof snow load in ASCE 7-10, P f, is a function of the ground snow load and three factors related to the building and its surroundings: P f = 0.7C e C t I s P g. Where: C e is the exposure factor, C t is the thermal factor, and I s is the importance factor. Most residential structures are situated in a B or C terrain category and are partially exposed with a C e =1.0 C t = Thermal Factor, as determined by ASCE Table 7-3 below. Building Classification : Table 1-1, page 3: Ground Snow Load, pg: psf: Figure 7-1, pages 84-85 and Table 7-1, page 92: Length of High Roof, Lu: ft. Where flat roof snow loads exceed 30 psf (1.44 kN/m 2), 20 percent shall be combined with seismic loads. in ASCE 7-10, unbalanced snow load is not required for roof with slope > 30.2deg (or 7:12) 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. However, I still have a hard time making sense of it when comparing the calculated drifting snow loads of building with very steep (say 12:12) roof and that with flat roof :) 2. See Table 2.9 for importance factor values, depending on the category of the building. This program specifically follows Section 7.0, Snow Loads, of the ASCE 7-05 Standard, "Minimum Design Loads for Buildings and Other Structures". 7-1 F-6 PROTECTING MaNufaCTuREd HOMEs fROM flOOds aNd OTHER HazaRds A Multi-Hazard Foundation and Installation Guide. Herein the exposure and importance factors are taken to be 1.0. If slope ≤ ¼” in 12”, design to prevent ponding. Heat flow from poorly insulated roofs melts some of the roof snowpack. The ASCE 7-16 standard requires both balanced and unbalanced snow load case scenarios for a structure's design consideration. EXAMPLE CALCULATIONS F Section 7.3.1 Table 7-2 Section 7.3.2 Table 7-3 Section 7.3.3 … I = importance factor. Snow Loads is an essential supplement to ASCE/SEI Standard 7 for all engineers, architects, and construction professionals who work on projects in regions subject to snow. Can be obtained using the following equations: where only snow loading analysis for buildings a. 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