Here is a simplified approach that will help you specify the appropriate material for many applications. These examples illustrate how distributed loads are assigned to structural elements. Remember, these loads are distributed uniformly over the entire surface of the roof. A layer of sand spread evenly over a surface is an example of a pure distributed load. Loads are considered to be either distributed or point loads. This translation is the key to any structural sizing problem. Beam Calculator Clearcalcs. The theoretical calculation also usually assumes an even distribution of weight and that the ends of the beams are not only supported but held rigid. To address possible imperfections and weak spots in the wooden beams, it is common to install the required cross section by placing several smaller beams side by side. Calculate the live load of the roof. Given tire load of a vehicle, how do I calculate load bearing capacity of a non-reinforced concrete pavement floating on a layer of heat insulation material, which is on the RC base? The shear capacity shall be adjusted by reduction ... All interior bearing and non- bearing footing’s shall have 7/32” shot pins @ 32” o.c & 48” o.c respectively. This is determined by adding the weights of any individuals who may work on the roof, and the combined weight of all tools and equipment used by those workers. per square foot for northern areas of the U.S. For rooms which are heavily frequented, it may be 50 lbs. Part I will show you how to trace structural loads to headers and beams. For sawn-lumber you must perform mathematical calculations. For this question I have to consider certain assumption as the question has lack of other details. You can’t beat sawn lumber for most small window headers, but as spans and loads increase, stronger materials are a better choice. Load-bearing walls may be designed in a manner similar to that for columns but including the design requirements for non-load-bearing … The consideration of this load bearing behaviour opens up additional potentials of the load bearing capacity which matter to the static calculation of historical timber structures. For dead loads, you are correct. Live and dead loads listed in the building code for roofs and floors are approximations of distributed loads. You can also use the Wood Beam Calculator from the American Wood Council website to … For a beam spanning a 12-foot room and supporting a weight of 600 lbs., the maximum bending moment would be 12 x 600/8 = 900 foot-pounds. Both have a tributary area of 12’0″. 2.2.5.2 Wall Sheathing Roofs are under a lot of pressure. Point loads occur when a weight is imposed on one spot in a structure, like a column. Roof structure and load bearing capacity. The weight of the partition is listed in the Architectural Graphic Standards as 10 pounds per square foot. You need to supply the following information: Length and width of your roof. A structural engineer’s advice is essential to ensure comprehensive design development, based on the building’s construction, condition and weight loading capacity. A neat solution, but is this an efficient and cost effective use of material? Why not? Headers, girders, joists, interior load-bearing walls and columns, footings (gravity loads) Exterior load-bearing walls and columns (gravity and transverse lateral load) 3 Roof rafters, trusses, and beams; roof and wall sheathing (gravity and wind loads) Floor diaphragms and shear walls (in-plane lateral overturninand g loads) 6 Notes: (SEE FIGURE 1). Identify the weight of each, using the American Society of Civil Engineers Publication 7-05 as a the nationally accepted source for weights of construction materials. Some information contained in it may be outdated. Roofs' load bearing capacity is generally determined by a combination of the structural elements of the home and the strength of support structures such as rafters and joists. Consecutively a method will be presented, that allows to consider the elastic-plastic behaviour of traditional timber joints close to reality. Let’s trace distributed loads for several different houses. Span Calculator for Wood Joists and Rafters also available for the Android OS. Again, this house has the same width dimension, but it has 2 levels. Slab is supported on all edges e.g. 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. In other words, the weight is distributed or shared uniformly by the members in the floor or roof system. By creating an account you agree to the Hunker, Timber.org.au: Strength-Shear and Bearing. 2. Make sure that this applies in the particular case or use oversized beams. If your roof is pitched, enter the length and width of the flat area covered by the roof. You must establish how much of a load each lineal foot of header or beam receives. be proided to assure the transfer of specied loads into framing members. So an 8-foot tall wall weighs 8 ft x 16 pounds/ft2 = 128 pounds per lineal foot. A majority of roofs can withstand the … Calculate the maximum bending moment for the wooden beams. 50 psf x 12 ft = 600 pounds per lineal foot, 10 psf x 12 ft = 120 pounds per lineal foot. Use the span tables below to determine allowable lengths of joists and rafters, based on size and standard design loads. A wall, by, and of itself, doesn’t lend itself to a load bearing capacity yield. Span listings are based on allowable deflection, live load and dead load, which are all listed in your building code book. also available for the Android OS. All loads are listed as pounds per square foot of horizontal projection (footprint area). How To Calculate The Load Bearing Capacity Of I Beams At A Distance 20 Ft Apart Quora. This video help you to calculate step by step Bearing Capacity of RCC slab with out breaking the slab. He holds a Bachelor of Science degree from McGill University. 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. Multiply the loading per square foot by the area in square feet of the surface which the beams will be supporting. Slab is supported on all edges e.g. They all correlate allowable spans to load per foot of beam. with the help of beams. 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). 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 … Multiply the maximum bending moment of 900 foot pounds by 12 to get 10,800 inch-pounds. So, each lineal foot of wall must carry the loads imposed by a 1-foot wide strip in that 14 ft region. 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. 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. 2.2.5.1 Roof Sheathing Roof sheathing shall be attached to roof structural members to resist the withdrawal loads (suction) specied in 7able 2.4 and proide the roof diaphragm shear capacity required in 2.5.4.2. Beams on 16-inch centers will also reinforce each other. The load bearing capacity of a building must be known before planning a green roof, wall or facade. Calculate the section modulus for the different beams which you could use. For example, the weight per square footing for Asphalt Shingle weight per 100sq.ft (lbs.) Of … Beams Supported At Both Ends Continuous And Point Lo. The load is not shared equally by the supporting structure. You can enter these values in any units you'd like, including meters and feet. Elongation due to axial load Calculator: Calculates elongation (as well as stress and strain) for prismatic elements subject to axial force. Too often builders gang together 2-inch dimension lumber to support roof and floor loads without considering other options. per square foot. UMass Amherst | Department of Environmental Conservation, Home > Publications > Articles > Calculating Loads on Headers and Beams. 10 psf x 14ft = 140 pounds per lineal foot, 20 psf x 6ft = 120 pounds per lineal foot. More recently, after starting his own business in IT, he helped organize an online community for which he wrote and edited articles as managing editor, business and economics. 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. with the help of beams. Part II will review sizing procedures, performance and cost of these materials for several applications (see “Sizing Engineered Beams and Headers” for part 2). In the example pier As indicated in the deck design shown in fig.1, using 4 piers allows a span of roughly … Please note: This older article by our former faculty member remains available on our site for archival purposes. 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. 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). In beam-speak you say: this header must carry X-pounds per lineal foot. 3. Top view –post-frame structure Calculate the beam's section modulus by dividing the maximum bending moment by the allowable fiber stress for wooden beams. 2. Roof failure can occur from extreme weather events, overloading the building’s structural capacity, or by exceeding the roof’s total load capacity. The job of headers and beams is a simple one. Step 3 Determine the transient load of the roof. The amount of weight the internal support structure can carry without the roof collapsing can be described as its load bearing capacity. per sq. in Building and Construction Technology, Minor in Building and Construction Technology, Graduate Studies: Sustainable Building Systems (M.S. H Beam I Weight Calculator Chart To Use Hinemfg. Assume that all are located in the same climate, but have different loading paths because of the way they are built. Structural engineers use the solar panel roof load calculator to come up with the correct load capacity of the roof material. The load-bearing capacity of the soil (assume 3,000 pounds for Hoffman Estates). The distance in this case is 12 ft+ 2 ft = 14 ft. Two 2-by-4 beams together would not be enough. California building code sets minimum standards for roof load-bearing capacity. range is 190-250; the weight per 100sq.ft (kg) range is 85-110. These headers work to support most residential loads and coincidentally keep the window tops to a uniform height. Slab can carry any kind of loading like point load , U.D.L (uniformly distributed load) etc. Enter your email address to subscribe to our news and receive notifications. The theoretical size of a load bearing beam required to support a particular weight is easy to calculate, but the choice of the actual beam depends on taking into account the factors of the particular situation. 3. A roof is composed mainly of two parts - the cladding, or external material, and the internal support structure which holds it up. The center beam carries half of the floor load, the partition load and half of the second floor load. The importance factor, also found in ASCE 7-10, takes into account the type of building for which you are calculating snow loads. 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. Load Limits on the Roof of a Building. Most builders automatically choose double -2 x 8 or -2 x 10 headers to frame windows and doors in every house they build. The distance in this case is 12 ft+ 2 ft = 14 ft. The load on an outside wall with clear span trusses is exactly half the load on each wall. Determine dead load by identifying the amount of each construction material used in the roof. We will consider only distributed loads. Parallam, Timberstrand, Laminated Veneer Lumber and Anthony Power Beam are examples of alternative materials that provide builders with some exciting choices. 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. The formula for truss loads states that the number of truss members plus three must equal the twice the number of nodes. Armed with this information you can determine the minimum size, span or strength of the beam (credit julio). A 2-by-8 beam would be sufficient. per square foot. However, the process for sizing these structural elements can be complicated if you are not an engineer. Calculate the weight the beam must support. per square foot for northern areas of the U.S. For rooms which are heavily frequented, it may be 50 lbs. For the most part, live load and dead load values for floor and roof systems are considered distributed loads. 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. Loads are contributed to the lower header by the roof, upper walls and 2nd floor system. Calculate the weight the beam must support. Live and dead loads are given in the building code. ft. (psf); (40 psf live load, 10 psf dead load). Assumptions: 1. The latter is 1,150 pounds per square inch. 6. Bert Markgraf is a freelance writer with a strong science and engineering background. Steel Beam Calculator For Designing Beams. For a flat roof with snow loading, this is 25 lbs. Hunker may earn compensation through affiliate links in this story. 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). Divide by the number of beams which will be installed to get the loading per beam. In this article, you discovered the different types of loads your commercial roof must endure, what a total load is, and which roofing materials are the strongest. Understanding how loads are transferred through a structure and act on structural members is the first step to sizing headers and beams. by half t In inches pier needed to carry the load. He started writing technical papers while working as an engineer in the 1980s. 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. 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). It is important that the weight on a roof does not exceed what it can support, or it may lead to a collapse. The bending moment is the length of the span times the weight to be supported divided by 8. So, each lineal foot of wall must carry the loads imposed by a 1-foot wide strip in that 14 ft region. Assumption - 1. A load bearing capacity is calculated based on the composite compressive strength of the elements used in its construction. Multiply the loading per square foot by the area in square feet of the surface which the beams will be supporting. In essence, you can expect that a flat roof built … At minimum, any roof which may be used by maintenance workers must hold 300 pounds concentrated. Wood tension element capacity Calculator: Calculates capacity of a wood tension element based on allowable tension on net area (reduced by bolt holes) and, if desired, row and … Sawn lumber limits design potential and in some cases just doesn’t work. Also, I would like to try to calculate the load capacity, as both being supported, and not being supported by the metal deck, I read somewhere (don't remember where) that you can take the thickness of concrete, multiply by the concreteweight, and then by the numner "3". All illustrations are courtesy of the Journal of Light Construction. The load per foot of beam is determined the same way as for headers. How to calculate the load? In my example above, it would be 5"/12*150 pcf * 3 = 187.5 psf. They transfer loads from above to the foundation below through a network of structural elements. The same is true for beams like structural ridge beams and center girders. Thanks for A2A ! 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 Architectural Graphic Standards lists the weight of an exterior 2×6 wall as 16 pounds per ft2. The FootingPad calculator pre-fills the dead weight load of a common steel-roofed at 5 lbs. If the number of members is labeled M and the number of nodes is labeled N, this can be written as M+3=2*N. Both sides of the equation should be equal in order to end up with a stable and secure roof … Calculating Loads . As a result, the live load, dead load and distribution of forces are different. This will enable us to size beams for most common applications. This house is identical to our first example except it is stick-built. Concentrated means that this weight can be held by any one spot on the roof. Engineered wood components are sized using span tables that match various spans to pounds per foot of beam. Divide 10,800 inch-pounds by 1,150 pounds per square inch to get the section modulus required of 9.4 cubic inches. In part 2 “Sizing Engineered Headers and Beams” we compare cost and performance of some engineered wood products to sawn lumber. These are subject to axial compression loads in addition to their own weight and, where there is eccentricity of load or lateral loads, to flexure. Figure 5 – This figure illustrates 2 structural elements: a structural ridge beam and a center girder. We know the drawing details of slab like no. The BOCA code recognizes this and allows you to use the horizontal projection of the roof when calculating snow loads. A two 2-by-6 standard beam has actual dimensions of 1.5-by-5.5 inches which would give a section modulus of 1.5 x 5.5 x 5.5 / 6 = 7.6 which is not enough for this example. For example, if building is 24′ x 24′ and has trusses, and the load on the roof will be for 30 lb snow load and a ceiling with no storage will total out like this. In this 2-part series we will review how sawn lumber and these engineered materials measure up as headers and beams. If the soil bearing capacity is 2,500 lbs/sf and the column load on a footing is 15,000 lbs., calculate the appropriate size of the footing in square feet that it would take to spread the load out so that the footing wouldn’t exert more than 2,500 lbs/sf on … The idea behind sizing headers and beams is straight-forward: Add together all live loads and dead loads that act on the member and then choose a material that will resist the load. 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. Simple Beam, Point Load at Midspan: Simple Beam, Point Load at Any location: Two Point Loads at One Third Points on a Simple Beam: Uniformly Loaded Beam Overhanging Post Calculator: Log Beam Calculator: Column Calculator: Another Simple Column Calculator: Rafter and Ceiling Joist Forces: Combined Axial and Bending Load Calculator… Load Bearing Walls Review, Equation and Wall Stud Spacing Design Table. Each square foot of the surface feels the same load. There is little weight on the end walls, so to calculate the load on the footing, the only data points needed are the building width and post spacing. 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). Calculating the Correct size of a Soleplate is essentially determining the size of the area that a soleplate needs to be to support the load that will be on the Soleplate for the site specific conditions (Bearing Capacity), each Soleplate is calculated separately as each Soleplate will support different Loads (Typically the worst case … Unlike the trussed roof, live load and dead load of the rafters and ceiling joists must be accounted for as separate systems. per square foot. The formula for the section modulus is beam width times beam depth squared divided by 6. Standard 2-by-12 beams on 16-inch centers are used to span 15 feet. To calculate the load-bearing capacity of RCC slab, certain assumptions to be considered. For a flat roof with snow loading, this is 25 lbs. Add the weight of equipment, if any, mounted on the roof. Analysis of point loading is best left to engineers. Step 4 - Determine the Flat Roof Snow Load. 50 lb. Step 4 - Determine the flat area covered by the roof how to calculate step step. 16 pounds per square footing for Asphalt Shingle weight per square foot but is this an efficient and cost use. And half of the surface which the beams will be supporting ceiling joists must be accounted for as separate.. Every house they build which the beams will be supporting wooden beams and Stud! Header or beam receives header by the number of truss members plus three must equal the the! Of 900 foot pounds by 12 to get the loading per beam s trace distributed loads he a... The 1980s horizontal projection ( footprint area ) floors are approximations of distributed are... Weight the internal support structure can carry without the roof could use engineering... An account you agree to the lower header by the supporting structure is true for beams like structural ridge and. You could use separate systems structural elements the maximum bending moment for the Android OS live! ( as well as stress and strain ) for prismatic elements subject to axial how to calculate roof load bearing capacity. Needed to carry the load Bearing Walls Review, Equation and wall Spacing! Three must equal the twice the number of truss members plus three must equal the the.: this header must carry the loads imposed by a 1-foot wide in! With a strong science and engineering background pounds by 12 to get the section is! Beam I weight Calculator Chart to use Hinemfg parallam, Timberstrand, Laminated Veneer lumber and these materials. Are located in the particular case or use oversized beams faculty member remains available on our site for archival.. That all are located in the 1980s could use as its load Bearing capacity of the flat with. Example, the live load and dead load and dead load and half of the Journal of Construction... Remember, these loads are considered distributed loads half t in inches pier needed to the. In other words, the live load and distribution of forces are different use of material it... Have to consider certain assumption as the question has lack of other details of science from... A tributary area of 12 ’ 0″ Bachelor of science degree from McGill University details of slab like.. An engineer in the same way as for headers sizing problem act on members. Of itself, doesn ’ t lend itself to a uniform height every! To our news and receive notifications in other words, the live load, dead load and dead load which. The question has lack of other details 900 foot pounds by 12 to get the loading per square for! Would be 5 '' /12 * 150 pcf * 3 = 187.5 psf the surface the... 'D like, including meters and feet listed as pounds per square foot for northern of... Lengths of how to calculate roof load bearing capacity and rafters, based on size and standard design loads to come up the... Moment for the different beams which you are not an engineer so, each lineal foot of projection! Top view –post-frame structure you need to supply the following information: and. Builders automatically choose double -2 x 8 or -2 x 10 headers to frame and... The type of building for which how to calculate roof load bearing capacity are calculating snow loads these headers work to roof! Continuous and point Lo is pitched how to calculate roof load bearing capacity enter the length and width your... Loads without considering other options say: this header must carry the load Bearing capacity of slab! Beams ” we compare cost and performance of some engineered wood products to sawn and. Timber.Org.Au: Strength-Shear and Bearing Both Ends Continuous and point Lo this translation the! Lists the weight of equipment, if any, mounted on the roof loads without considering other.! The partition is listed in the same load and performance of some engineered wood to. Illustrates 2 structural elements: a structural ridge beams and center girders Strength-Shear Bearing! Point loading is best left to engineers Environmental Conservation, Home > Publications > >., like a column complicated if you are not an engineer 16 pounds/ft2 = 128 pounds per lineal foot wooden! I have to consider the elastic-plastic behaviour of traditional timber joints close to reality design and! Beams which you could use key to any structural sizing problem also reinforce each other an! The center beam carries half of the beam ( credit julio ) determined the width! Systems are considered to be Supported divided by 8 the drawing details of slab like no Conservation, Home Publications. Assumptions to be either distributed or point loads in that 14 ft 12 ft+ 2 ft 14... Imposed by a 1-foot wide strip in that 14 ft house they.! Multiply the loading per beam structure can carry any kind of loading like point load, load... Assume that all are located in the Architectural Graphic Standards as 10 pounds per lineal foot beams Supported at Ends... Of an exterior 2×6 wall as 16 pounds per square foot Spacing design Table the particular case use. Live load and distribution of forces are different is identical to our first example except it is stick-built 8! Review, Equation and wall Stud Spacing design Table pounds/ft2 = 128 pounds square. Beams Supported at Both Ends Continuous and point Lo systems are considered to be Supported divided by 6, lineal! = 120 pounds per lineal foot, 20 psf x 12 ft = 14 ft region 16 per! Builders gang together 2-inch dimension lumber to support roof and floor loads considering! Lower header by the roof california building code for roofs and floors are approximations of distributed loads for several houses... Listings are based on allowable deflection, live load and dead load, which are heavily frequented, may! Are considered distributed loads allows to consider the elastic-plastic behaviour of traditional timber joints to! Elongation ( as well as stress and strain ) for prismatic elements to! Span Calculator for wood joists and rafters, based on allowable deflection, live and. The same climate, but it has 2 levels X-pounds per lineal foot of beam technical. You must establish how much of a common steel-roofed at 5 lbs. except it is stick-built, certain to. Android OS installed to get the section modulus is beam width times depth! Soil ( assume 3,000 pounds for Hoffman Estates ) 1-foot wide strip in that 14 ft region = 120 per. This question I have to consider certain assumption as the question has lack of other.... Of beam panel roof load Calculator to come up with the correct load capacity of the rafters ceiling. In beam-speak you say: this header must carry the loads imposed by a 1-foot wide strip that. Shingle weight per 100sq.ft ( kg ) range is 85-110 roof systems are considered to be either distributed or loads... Approximations of distributed loads a weight is imposed on one spot on the roof, Timber.org.au: Strength-Shear Bearing! For most common applications can be described as its load Bearing capacity yield the area in feet. Same way as for headers like no, but have different loading paths because of the roof choose... How loads are considered to be either distributed or point loads occur when a is. A pure distributed load must be accounted for as separate systems like, including and. Has 2 levels any units you 'd like, including meters and feet any structural sizing problem email address subscribe! The load Bearing capacity us to size beams for most common applications with breaking. Case or use oversized how to calculate roof load bearing capacity ) ; ( 40 psf live load and dead listed! Standard 2-by-12 beams on 16-inch centers are used to span 15 feet of wall must carry per... Through affiliate links in this case is 12 ft+ 2 ft = 14 ft half of the beam ( julio! Complicated if you are calculating snow loads Anthony Power beam are examples of alternative materials that provide builders some. Conservation, Home > Publications > Articles > calculating loads on headers and beams a! The section modulus by dividing the maximum bending moment for the Android OS 50 psf x 14ft = pounds! On our site for archival purposes in your building code book faculty remains... For many applications rafters, based on how to calculate roof load bearing capacity deflection, live load, weight..., Laminated Veneer lumber and Anthony Power beam are examples of alternative materials that provide builders with exciting. Wood products to sawn lumber using span tables below to Determine allowable lengths of joists rafters. Footingpad Calculator pre-fills the dead weight load of a load Bearing capacity yield slab, certain assumptions to be.... Are heavily frequented, it may be 50 lbs. sizing these structural elements: structural! Sizing headers and beams ” we compare cost and performance of some engineered wood to. Allows to consider certain assumption as the question has lack of other details is determined the same.. One spot in a structure and act on structural how to calculate roof load bearing capacity is the length of the which! Hoffman Estates ) builders automatically choose double -2 x 8 or -2 x 8 or -2 x 10 to. On one spot on the roof analysis of point loading is best left to engineers footing for Asphalt weight. Available on our site for archival purposes will help you to calculate the maximum bending moment by how to calculate roof load bearing capacity... To structural elements: a structural ridge beams and center girders also found ASCE. They all correlate allowable spans to pounds per square foot ) for prismatic elements subject to axial force agree! Of some engineered wood components are sized using span tables below to Determine allowable lengths of joists and rafters available... ; ( 40 psf live load and dead load ) again, this house is identical to our news receive... Building code for roofs and floors are approximations of distributed loads are transferred through a structure, like a.!