A flat roof needs to be built right, and know how to handle rain and snow to survive our Canadian climate. All information is provided "AS IS." onto a lower flat roof) the code provisions are also not applicable. or vertical supports. All rights reserved. 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). 20 ft of the roof, multiply the drift load by the factor: 20 s 20 where s is the spacing in feet. In some of these cases special studies of the drift patterns are warranted. Warm roofs lose heat in such a way that it melts snow, while cold roofs lose heat that doesn’t contribute to melting. From our example, our ground load and flat roof snow load were found to be 30 psf and 21 psf, respectively. Too often builders gang together 2-inch dimension lumber to support roof and floor loads without considering other options. Snow type. Here at Pro Roofers, we specialize in flat roof installation and maintenance and over the years, we have gathered a wealth of expertise concerning flat roofs, so let’s set the record straight. 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. [left]I am building a single slope shed roof pole frame building. 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] 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. Leeward Snow Drifts - from adjacent higher roof Upper roof length lu = 100.0 ft Projection height h = 10.0 ft Building separation s = 0.0 ft Adjacent structure factor 1.00 Snow density γ = 19.2 pcf Balanced snow height hb = 1.40 ft hc = 8.60 ft hc/hb >0.2 = 6.1 Therefore, design for drift Drift height hd = 3.81 ft Drift width w = 15.23 ft Surcharge load: pd = g*hd =73.1 psf Parallam, Timberstrand, Laminated Veneer Lumber and Anthony Power Beam are examples of alternative materials that provide builders with some exciting choices. ground snow load is the snow expected to land on the ground. In this 2-part series we will review how sawn lumber and these engineered materials measure up as headers and beams. Since it is possible to use the attic for storage, the live load of the attic floor is set at 20 psf according to code. The Architectural Graphic Standards lists the weight of an exterior 2×6 wall as 16 pounds per ft2. In beam-speak you say: this header must carry X-pounds per lineal foot. In technical terms, the wall has a tributary width of 14 ft. From this we can readily see that each lineal foot of wall supports: 50 psf x 14ft = 700 pounds per lineal foot, 15 psf x 14ft = 210 pounds per lineal foot. You must determine the snow load for your region. The load of the snow on a roof tends to vary from the load of snow on the ground. The next step is to use the technical literature from any of the companies that make engineered wood components to determine span and beam size. Often changes of five or 10 pounds per square foot result in minimal differences in cost. These examples are typical of the types of calculations you will have to do to determine the uniform load that is distributed to a beam or header. Unfortunately, these roof types are not very common; most roofs have numerous obstructions. This will enable us to size beams for most common applications. shall be calculated in lb/ft2 (kN/m2) using the following formula: In regions with relatively low snow load values, the load from a single event may result in the peak loading. Flat Roof - Structure. home improvement and repair website. a new flat roof snow load (pf ) for this analysis only. When building a structure it is important to calculate wind load to ensure that the structure can withstand high winds, especially if the building is located in an area known for inclement weather. This data is dependent upon snowfall information collected over the decades. 1995-2018 MH Sub I, LLC dba Internet Brands. Certainly, the weight of snow can add up, but your home must support a variety of loads: wind, seismic, building weight, furniture, occupants etc. Understanding how loads are transferred through a structure and act on structural members is the first step to sizing headers and beams. To ensure our content is always up-to-date with current information, best practices, and professional advice, articles are routinely reviewed by industry experts with years of hands-on experience. This house is identical to our first example except it is stick-built. Under calm conditions, falling snow will cover the roof and ground with the same uniform layer, which will grow in depth with each successive fall provided the temperature of the air and the roof surface remain below the freezing point. See Section 7.4.5, ASCE 7. In addition, this option generates wind and snow loads according to the National Application Documents (NAD) of many European countries. 2010 Ground Snow Load Table for Quebec. Online Snow Load Calculator(for Buildings with Flat or Low Slope Roofs - for Balanced Snow, Drift, and Rain-on-Snow Surcharge Loadings) calculator (ASCE 7-05) for structural engineers, construction professionals and building planners. If you have any concerns as you are determining your flat roof snow load, consult with a structural engineer or roofing specialist. The span of the studied flat roof is 12.0 m, and the height is 3.0 m. I have a 200amp service panel outside for my main home. Increased Loads due to Limited Roof Drainage in Areas of High Rain-on-Snow Conditions– Low-slope roofs designed with only perimeter drainage can experience snow loads that exceed the loads indicated Case histories show that the snow load on a roof is typically less than that on the ground provided that drifting is absent. Questions of a Do It Yourself nature should be suggestions. H. Roof Drainage System: On the roof of a building, a system composed of storm- Span Calculator for Wood Joists and Rafters also available for the Android OS. Arena amid Friday and Sunday, that may acutely accent some roofs. Superpose the drift load on the base snow load. Increased Loads due to Limited Roof Drainage in Areas of High Rain-on-Snow Conditions– Low-slope roofs designed with only perimeter drainage can experience snow loads that exceed the loads indicated 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. Or if … So, each lineal foot of wall must carry the loads imposed by a 1-foot wide strip in that 14 ft region. Flat roof with no permanent access and altitude not exceeding 100m, 0.75 kN/m² UDL & 0.9 kN point load Most areas exceeding 100m but not exceeding 200m, (excluding parts of Scotland, Pennines, North East England, refer to BS 6399-3), 1 kN/m² UDL & 0.9 kN point load Most builders automatically choose double -2 x 8 or -2 x 10 headers to frame windows and doors in every house they build. The first step is the same for sawn- and engineered wood materials: add up all the loads acting on a header or beam and then translate this load into terms of how much load each lineal foot of header or beam will feel. Uniform roof snow load is based on flat, wide open roofs free from any obstructions. The same is true for beams like structural ridge beams and center girders. So consider a simple gable roof on a 24-foot wide ranch framed with 2x6 exterior walls and a 1 1/2 ridge: the span would be 11'5 3/4". Paolo Formichi, University of Pisa Italy. In such cases, the ponding load must be added to that of the snow or ice on the roof. Standard Loads of Materials. Point loads occur when a weight is imposed on one spot in a structure, like a column. onto a lower flat roof) the code provisions are also not applicable. Buy Now. (SEE FIGURE 1). 40 psf x 12 ft = 480 pounds per lineal foot, 30 psf x 12 ft =360 pounds per lineal foot, 10 psf x 12 ft =120 pounds per lineal foot. You can’t beat sawn lumber for most small window headers, but as spans and loads increase, stronger materials are a better choice. For roofs that are flat and with ground snow loads lower than 20 pounds per square foot, the roof snow load is equal to 70% of the product of the exposure, thermal and importance factors and the ground snow load. Roof snow load is defined as the weight of snow on the roof surface used in design of the building structure (IBC, 2012). e = 1.2 , flat roof load > p g 10 Outline Minimum Roof Snow Load Thermal Factor Unbalanced Load Drift Load on Adjacent Roof Parapet Wall & RTU drift Sliding Load on Adjacent Roof Ponding FAQ’s 11 Unbalanced Loads-Gable Roof Upper Limit Roof Slope - change Lower Limit Roof Slope - simplify Small Eave to Ridge Distance -change 12 See Section 7.9, ASCE 7. See Section 7.4.5, ASCE 7. 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 Check for loads due to snow sliding from an upper roof. Enter your email address to subscribe to our news and receive notifications. = 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 ARCH 331 Note Set 13.1 S2014abn 2 Determining Dead Load from Material Weights Ranging from “fully exposed” to “sheltered,” this factor helps to determine how much snow will be lost during the winter months due to exposure. 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