Uniform roof snow load is based on flat, wide open roofs free from any obstructions. I have a 200amp service panel outside for my main home. 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. Some information contained in it may be outdated. A solar array adds weight to the roof, and in areas which receive snow, you will also need to consider the appropriate amount of snow load the roof can handle. Determine the amount of snow likely to fall on the ground. The deck supports the non-load bearing components such as insulation, membrane, flashing etc. Each square foot of the surface feels the same load. Certainly, the weight of snow can add up, but your home must support a variety of loads: wind, seismic, building weight, furniture, occupants etc. 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 Superpose the drift load on the base snow load. 20 ft of the roof, multiply the drift load by the factor: 20 s 20 where s is the spacing in feet. Remember, these loads are distributed uniformly over the entire surface of the roof. Questions of a Do It Yourself nature should be Snow loads on a flat roof are important for most current load codes and standards (International Organization for Standardization, 2013, EN1991-1-3, 2003; NBC2005, 2005; ASCE7-10, 2010; GB50009-2012, 2012). Check for ice dams and icicle loads. You may freely link So an 8-foot tall wall weighs 8 ft x 16 pounds/ft2 = 128 pounds per lineal foot. Armed with this information you can determine the minimum size, span or strength of the beam (credit julio). building a home or other edifice with a flat roof. Snow load is the downward force on a building’s roof by the weight of accumulated snow and ice. 11 Flat Roof And Snow (Editor’s observe: This column turned into firstly seem in February 2015 and has been acclimatized accustomed the blast anticipation for the D.C. 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). See Section 7.4.5, ASCE 7. Too often builders gang together 2-inch dimension lumber to support roof and floor loads without considering other options. Wind Load Calculator. Looking for a Resonably Accurate formula (Canada) to calculate our daily pr... What should be used on a single wide trailer roof. discount that actual snow loads may exceed them, only that the risk of snow-load-induced failure is reduced to an acceptably low level. The load is not shared equally by the supporting structure. You must determine the snow load for your region. This translation is the key to any structural sizing problem. Intuitively, this is the number of inches of snow on your roof in the place where the cover is the thickest. Part I will show you how to trace structural loads to headers and beams. Done Calculate drift surcharge load: pd hd no loads on roof. In addition, this option generates wind and snow loads according to the National Application Documents (NAD) of many European countries. All rights reserved. The formula for flat roof snow loads incorporates the effects of wind exposure, the thermal conditions of the roof system, and the importance of the facility. For sawn-lumber you must perform mathematical calculations. 1995 Ground Snow Load Table. onto a lower flat roof) the code provisions are also not applicable. 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 Roof snow load calculation. Removal of the Load Bearing Wall - Calculating Dead and Live load of the Roof. 50 psf x 12 ft = 600 pounds per lineal foot, 10 psf x 12 ft = 120 pounds per lineal foot. The dead load consists of the actual weight of materials that comprise the roof, plus any fixed equipment that the roof … 10 psf x 14ft = 140 pounds per lineal foot, 20 psf x 6ft = 120 pounds per lineal foot. This information is found in the code book. 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). How snow load can damage your buildings. Point loads occur when a weight is imposed on one spot in a structure, like a column. Done Calculate drift surcharge load: pd hd no Figure 5 – This figure illustrates 2 structural elements: a structural ridge beam and a center girder. 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 Loads are considered to be either distributed or point loads. 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. 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. Copyright© In areas of the state outside of certified local government jurisdictions, the design snow load shall be based on the ground snow loads developed in "Snow Loads for Structural Design in Montana", authored by F.F. The job of headers and beams is a simple one. Here is a simplified approach that will help you specify the appropriate material for many applications. 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 Calculate the carport roof load using a combination of the dead-load and live-load measurements. Sawn lumber limits design potential and in some cases just doesn’t work. Pg is converted to Pf by this formula: Most builders automatically choose double -2 x 8 or -2 x 10 headers to frame windows and doors in every house they build. 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. This is because as snow falls vertically it spreads itself further along a sloping rafter and so accumulates less depth. The load of the snow on a roof tends to vary from the load of snow on the ground. Check for loads due to snow sliding from an upper roof. to this site, and use it for non-commercial use subject to our terms of use. Roof pitch. Often changes of five or 10 pounds per square foot result in minimal differences in cost. or vertical supports. UMass Amherst | Department of Environmental Conservation, Home > Publications > Articles > Calculating Loads on Headers and Beams. *Advertisements: This web based application is made freely available courtesy of the advertisements displayed on this page. We welcome your comments and 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. Flat roof snow load are determined by the following method: The snow load, p f, on a roof with a slope equal to or less than 5 degrees 1 in./ft = 4.76 deg.) Roof Snow Load (NBC 2010) version 0.1.0 January 6, 2021. Analysis of point loading is best left to engineers. Schedule of Permanent Loads commonly found in Residential Properties. Ground Snow Load Values for Ontario and Quebec. Warm roofs lose heat in such a way that it melts snow, while cold roofs lose heat that doesn’t contribute to melting. 1995-2018 MH Sub I, LLC dba Internet Brands. Minimum Flat Roof Snow Load Values ASCE 7-05 Equation 7-1 assumes that the snow load results from multiple events. suggestions. 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. home improvement and repair website. (IBC, ASCE 7-10, 2012) IBC code is subject to change so it falls upon you to keep up to date on it. The snow load is treated as a live load when you use AWC's tables. Part II will review sizing procedures, performance and cost of these materials for several applications (see “Sizing Engineered Beams and Headers” for part 2). This is all of the natural stresses imposed upon a roof, such as snow loads, rain loads and wind loads. In cold climates, an entire season’s worth of snow may accumulate on a flat roof without any melting or evaporation. All information is provided "AS IS." problems contact webmaster@doityourself.com. Videon and J.P. Schilke, Civil & Agricultural Engineering, Montana State University, August 1989. Medeek Design assumes no liability or loss for any designs presented and does not guarantee fitness for use. Trying to educate myself as best I can on AC. Flat roofs shall be designed to carry all imposed and dead loads acting on the structure of the roof. Engineered wood components are sized using span tables that match various spans to pounds per foot of beam. 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 Buy Now. 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. Snow type. Certainly, the weight of snow can add up, but your home must support a variety of loads: wind, seismic, building weight, furniture, occupants etc. H. Roof Drainage System: On the roof of a building, a system composed of storm- Snow loads 5 Snow load on the roof 4 6 Snow load on the ground 4 7 Snow load shape coefficients 6 8 Snow sliding down roofs 9 Appendix A Annual probabilities of exceedance different from 0.02 21 Appendix B Snow drift load calculations 21 Appendix C Addresses of advisory offices 21 Figure 1 — Basic snow load on the ground 5 Figure 2 — Snow load shape coefficients for flat or monopitch … Thus, this paper chooses a flat roof as its research object. Live and dead loads listed in the building code for roofs and floors are approximations of distributed loads. Roof loads are used to determine the size of beams, joists and columns that support a roof. Snow load is the downward force on a building’s roof by the weight of accumulated snow and ice. All illustrations are courtesy of the Journal of Light Construction. To calculate Roof Snow Load per Residential Building Code: 0.7 x pg (ground snow load) = pf (roof snow load) Roof Snow Load Examples: Above line: 0.7 x 60 psf = 42 psf Below line: 0.7 x 50 psf = 35 psf . Unfortunately, these roof types are not very common; most roofs have numerous obstructions. The beam must be strong enough so it doesn’t break (Fb value) and stiff enough so that it doesn’t deflect excessively under the load (E value). Paolo Formichi, University of Pisa Italy. If you have any concerns as you are determining your flat roof snow load, consult with a structural engineer or roofing specialist. 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 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. Here, each square foot of roof system delivers 50 pounds of live load and 15 pounds of dead load (65 psf total) to the structural support system. Measure the horizontal distance from eaves to the ridge -- the point where the roof is tallest -- and record the result labelled as "run." ASCE 7-05, was the standard referenced in the 2006 and 2009 IBC’s but has now been substituted by ASCE 7-10 in the 2012 IBC. Load Types Loads used in design load equations are given letters by type: D = dead load L = live load L r = live roof load W = wind load S = snow load E = earthquake load R = rainwater load or ice water load Provisions on how to calculate the snow drift surcharge for structures can be found in Section 7.8 of ASCE 7-10. These headers work to support most residential loads and coincidentally keep the window tops to a uniform height. For this reason, it is crucial that your flat roof be able to support the weight of the snow, not only for the structural integrity of the building but also for the safety of people in and around the building. A neat solution, but is this an efficient and cost effective use of material? on multiple factors, including: n. Ground snow load value. shall be calculated in lb/ft2 (kN/m2) using the following formula: 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. 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. Span listings are based on allowable deflection, live load and dead load, which are all listed in your building code book. 60 ground snow PSF BELOW LINE 50 PSF 50 ground snow PSF Myth: Flat Roofs Can’t Possibly Support All the Extra Weight A totally valid concern, but rest assured, your architect and engineer have this in mind when designing the roof structure. It is determined based . The following are the equation for determining snow loaing on flat roofs. onto a lower flat roof) the code provisions are also not applicable. Pitched Roof (Measured on slope) Clay Tiles (Plain) ... Flat Roof … Unlike sloped roofs that allow snow and other buildups to fall to the ground, flat roofs tend to collect snow and other debris. Additionally, heat from various sources may contribute to some melting of snow that has accumulated on top of the roof. Live and dead loads are given in the building code. See Section 7.9, ASCE 7. 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 … submitted to our "DoItYourself.com Community Forums". Snow loads acting on a sloping surface shall be assumed to act on the horizontal projection of that surface. The Architectural Graphic Standards lists the weight of an exterior 2×6 wall as 16 pounds per ft2. First, figure out how deep the snow is piled up there. Rather than try to estimate on your own, consult with your city hall and records department for the ground snow load in your particular area. Obtain the recorded snow load -- the maximum load expected to accumulate on the ground -- for your area. Ground snow load is the weight of snow on the ground surface. A flat roof needs to be built right, and know how to handle rain and snow to survive our Canadian climate. Enter your email address to subscribe to our news and receive notifications. The roof or the entire structure can fail if the snow load exceeds the weight the building was designed to shoulder. How snow load can damage your buildings. 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 The thermal factor is dependent upon the heat produced by your roof. For example, using a 25 by 20 metre garden: 500 times 1.25 yields 625 kg (1,378 lb) of snow. 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. and Ph.D.), Wood Engineering and Bio-Based Building Materials Specialization, Building Science and Green Building Specialization, UWW Professional Education and Online Courses, Certificate in Sustainable Building Construction, Tedd Benson speaks about a better way to build in the 21st Century, Heidi Jandris speaks about lowering the embodied carbon of concrete masonry units, Register now for BCT’s Winter & Spring Online Professional Education Courses, Upcoming Talk: Building Operations during COVID (Wednesday Oct. 14th). used, but they typically defined the load cases or combination, stress or strength limits, and deflection limits. (SEE FIGURE 1). Environmental loads - such as snow, water and wind loads should be calculated in accordance with BS EN 1991. You can’t beat sawn lumber for most small window headers, but as spans and loads increase, stronger materials are a better choice. [left]I am building a single slope shed roof pole frame building. Standard Loads of Materials. The distance in this case is 12 ft+ 2 ft = 14 ft. This value is also available in the ASCE 7-10 guide, depending upon whether your roof is cold or warm. Check for loads due to snow sliding from an upper roof. snow load = thickness * density The result - snow load, or the pressure exerted by the snow - has the units of kN/m² or lbs/ft². The ASCE 7-16 standard requires both balanced and unbalanced snow load case scenarios for a structure's design consideration. Or if … In this 2-part series we will review how sawn lumber and these engineered materials measure up as headers and beams. Understanding how loads are transferred through a structure and act on structural members is the first step to sizing headers and beams. In some of these cases special studies of the drift patterns are warranted. 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 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. Loads are contributed to the lower header by the roof, upper walls and 2nd floor system. Assume that all are located in the same climate, but have different loading paths because of the way they are built. The load per foot of beam is determined the same way as for headers. Check for ice dams and icicle loads. Use this same calculation to find the total weight of snow on a … This is highly regional as weights of snow, for example, range from 10 to 300 pounds per square foot based on moisture and volume of the snow. 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. These examples illustrate how distributed loads are assigned to structural elements. Another is that they cannot handle as much snow weight as pitched roofs because the snow sits directly on the roof. i just bought and p... in the 2012 IBC. 2010 Ground Snow Load Table for Ontario. Case histories show that the snow load on a roof is typically less than that on the ground provided that drifting is absent. Schedule of Permanent Loads commonly found in Residential Properties. The roof or the entire structure can fail if the snow load exceeds the weight the building was designed to shoulder. In some of these cases special studies of the drift patterns are warranted. Brussels, 18-20 February 2008 – Dissemination of information workshop 18 So, each lineal foot of wall must carry the loads imposed by a 1-foot wide strip in that 14 ft region. Myth: Flat Roofs Can’t Possibly Support All the Extra Weight A totally valid concern, but rest assured, your architect and engineer have this in mind when designing the roof structure. As a result, the live load, dead load and distribution of forces are different. loads on roof. However, the process for sizing these structural elements can be complicated if you are not an engineer. The dead load consists of the actual weight of materials that comprise the roof, plus any fixed equipment that the roof supports. View our Privacy Policy here. A layer of sand spread evenly over a surface is an example of a pure distributed load. Roof loads are equal to ground snow loads only if the roof is completely protected from wind action and if there is no melting. Breadth Jan. 22-24, 2016) More than two anxiety of snow could abatement in genitalia of the D.C. ground snow load is the snow expected to land on the ground. UMass Shortcuts: Email Moodle Spire WVD ODB260 Remote Access Online Storage IT Support, Share this:Click to share on Twitter (Opens in new window)Click to share on Facebook (Opens in new window)Click to share on LinkedIn (Opens in new window)Click to share on Pinterest (Opens in new window)Click to[...], Click to share on Twitter (Opens in new window), Click to share on Facebook (Opens in new window), Click to share on LinkedIn (Opens in new window), Click to share on Pinterest (Opens in new window), The John W. Olver Design Building at UMass Amherst, Design Building Virtual Construction Site Visit, Undergraduate Major: B.S. In order for a structure to be sound and secure, the foundation, roof, and walls must be strong and wind resistant. 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. 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 data is dependent upon snowfall information collected over the decades. snow weight = length * width / cos (pitch (°)) * snow load The weight of snow is measured in kg or lbs. 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. Grade plane Below 7000’ At or above 7000’ Flat roof snow load — pf : 30 psf uniform Flat roof snow load — pf : 40 psf uniform Or if … psf (pounds per square foot) ABOVE LINE 60 PSF . In regions with relatively low snow load values, the load from a single event may result in the peak loading. For example, consider a roof with a run of 12.2 metres (40 feet). 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. It is important to list live load, dead load and total load separately because live load is used to compute stiffness and total load is used to calculate strength. The loads delivered to the header are: 30 psf x 6 ft = 180 pounds per lineal foot, 10 psf x 6 ft = 60 pounds per lineal foot. The easiest way is to push a yardstick into the snow on the roof, selecting an area that looks typical of the overall snow depth. 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. Estimate the total weight of snow in your garden by multiplying the size of the area in square metres by the snow load. One of the most common misunderstandings on this topic is the difference between ground snow load and roof snow load. The most effective method of preventing problems due to ponding is to provide adequate roof slope and drainage. This house is identical to our first example except it is stick-built. Per the code updates, there are some changes in the nonstructural requirements for commercial buildings that may affect your project. The center beam carries half of the floor load, the partition load and half of the second floor load. However, with guidance from the ASCE 7-16 on snow load calculations for curved roofs and … 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] Determine the transient load of the roof. Loading. We will consider only distributed loads. Per the code updates, there are some changes in the nonstructural requirements for commercial buildings that may affect your project. Ranging from “fully exposed” to “sheltered,” this factor helps to determine how much snow will be lost during the winter months due to exposure. Arena amid Friday and Sunday, that may acutely accent some roofs. See Section 7.9, ASCE 7. Flat Roof - Structure. Consult the ASCE 7-10 manual for the exposure factor for your home and environment. Flat roof snow load are determined by the following method: The snow load, pf, on a roof with a slope equal to or less than 5 degrees 1 in./ft = 4.76 deg.) Snow draft load from upper roof to lower roof depends on snow density, length of upper and lower roof, and height between two roofs. They transfer loads from above to the foundation below through a network of structural elements. See Section 7.4.5, ASCE 7. They all correlate allowable spans to load per foot of beam. 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. in Building and Construction Technology, Minor in Building and Construction Technology, Graduate Studies: Sustainable Building Systems (M.S. The ground snow load is multiplied by various factors. 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. This will enable us to size beams for most common applications. You need to use a snow load formula for flat roofs. The exterior wall (and the headers within) will carry all loads from the mid-point of the house (between the supporting walls) to the outside of the house (including the roof overhang). You must determine the snow load for your region. Snow cover thickness. The option for automatically generating Wind and Snow 2D/3D loads according to Eurocode 1 in Robot is based on the European standard: EN 1991-1-4:2005 for wind and EN 1991-1-3:2003 for snow. 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). Parallam, Timberstrand, Laminated Veneer Lumber and Anthony Power Beam are examples of alternative materials that provide builders with some exciting choices. From our example, our ground load and flat roof snow load were found to be 30 psf and 21 psf, respectively. 20 ft of the roof, multiply the drift load by the factor: 20 s 20 where s is the spacing in feet. Pitched Roof (Measured on slope) ... Flat Roof – Asphalt Finish: 2 Layer Asphalt: ... Quick and affordable Steel Beam Calculations in just minutes! 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. 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. Photo by Courtesy of The Holmes Group The next step is to find the amount of snow expected to land on a flat roof, Pf. Both have a tributary area of 12’0″. Snow Load Calculations. 2010 Ground Snow Load Table for Quebec. The snow load calculations provided by this online tool are for educational and illustrative purposes only. If you have any concerns as you are determining your flat roof snow load, consult with a structural engineer or roofing specialist. Again, this house has the same width dimension, but it has 2 levels. In part 2 “Sizing Engineered Headers and Beams” we compare cost and performance of some engineered wood products to sawn lumber. Posted at December 21, 2014, in Technical. 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. The span of the studied flat roof is 12.0 m, and the height is 3.0 m. Span Calculator for Wood Joists and Rafters also available for the Android OS. You must establish how much of a load each lineal foot of header or beam receives. Actually, with snow, you don’t get more load along the slope of the rafter; you get the same load as a flat roof with the same run would get. DoItYourself.com®, founded in 1995, is the leading independent Express the result in feet rather than inches. The new value ( pf ) is then used in the unbalanced loading and drifting calculations per Section 7.6, ASCE 7. Adding solar to a building also creates more obstructions and these need to be accounted for. 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".