Step 2 Span Table: Select the appropriate table in Span Tables for Joists and Rafters . For example: a floor joist appropriately selected to span 10 feet with an L/360 limit will deflect no more than 120″/360 = 1/3 inches under maximum design loads. UMass Amherst | Department of Environmental Conservation, Home > Publications > Articles > Understanding Loads and Using Span Tables. Wood is naturally engineered to serve as a structural material: The stem of a tree is fastened to the earth at its base (foundation), supports the weight of its branches (column) and bends as it is loaded by the wind (cantilever beam). Note: The required bending design value, Fb, in pounds per square inch is shown at the bottom of each table and is applicable to all lumber sizes shown. AF&PA lists the required compression perpendicular to grain values for joists and rafters for various spans, on-center spacing and loading conditions in its Span Tables for Joists and Rafters. Second, use the snow load value for your region in determining which rafter table to use. AF&PA’s Appendix A lists a variety of live and dead load combinations for floors, ceilings and rafters. Imagine an anchor in a concrete ceiling with weights attached directly to the anchor. Often, 2×10 joists spaced 24-inches o.c. Their design span, the exact length from face to face of the supports, is 15 feet 1 inch (see illustration – Figure #1), When sizing joists, use the clear span – the For this example I’ll use the CABO One and Two Family Dwelling Code , which serves as the model for many state and local codes. You can also use AF&PA’s “Span Tables for Joists and Rafters”. The ends of these members must be able to “react” or resist these loads without crushing. 23 Double Hung Ceilings 23 Gusset Hung Ceilings 24 Triple Hung Ceilings 25 Wind Load 26-27 UL Fire Resistive Designs 27 Fire Rated Expansion Joint 28 Load Test Data 28 Membrane Load Values 29 Basic Products Used on Suspension Systems 29 Control Joints & Expansion Joints 30 Sound Isolation 31 Estimating Materials Flat Drywall Grid Installation For this example I’ll use the CABO One and Two Family Dwelling Code , which serves as the model for many state and local codes. A higher grade of a given species has a higher strength rating (Fb) and often has a higher stiffness value (E) too. Use the horizontal projection of a rafter, not Attic floors with limited storage L/240 & 10 psf. In Douglas fir-larch, either a No 2 2×10 or a No. Check to see that the lumber species selected has the necessary compression strength perpendicular to the grain. Enter your email address to subscribe to our news and receive notifications. Duration of load. The code section on working load deflection states: The deflection of floor and roof assemblies shall not be greater than L/360 for plastered construction; L/240 for unplastered floor construction; and L/180 for unplastered roof construction. Loads cause beams, joists and rafters to bend. While the same grade and species 2×8 has a 3040 Fb when used as a roof rafter in snow country. Remember when your science teacher said: every action has an opposite and equal reaction? Different types of gypsum boards, manufactured for institutional and commercial use, are stronger than the typical residential product, with improved resistance to surface damage. Perhaps the joists were strong enough if they didn’t break! Look up the allowable loads and deflection limits imposed by your local code. 2 2×12 would work. After you watch or read this tutorial it’ll take you less than 45 minutes to hang a bathroom ceiling. Some designers may find WWPA’s tables useful. Western Wood Products Association (WWPA) publishes tables, for example. But for most cases there is a cookbook solution. The support wires are spaced 4 lineal… Figure 2 Buy Mount-It! will provide a stronger and stiffer floor assembly than 2×8 joists of the same grade and species that are spaced 16-inches o.c. The other publications I mentioned are referenced by most codes and can be purchased from AF&PA’s American Wood Council, PO Box 5364, Madison, WI 53705-5364, 1-800-890-7732. The vertical load carrying capacity for main beam and cross tee members is determined in accordance with ASTM test method E3090. For this, use the tables in Design Values for Joists and Rafters. Hem-fir is a stiffer material. These values can be very different! The Table of contents indicates that Table F-2 watches these loading conditions. (the tables permit a bearing length of up to 3.5 inches, but since 1.5 is probably the worst case that you’ll encounter for joist or rafter bearing, it’s a safe value.) You just read the numbers under the appropriate column heading. The face paper is folded around the edges to protect the core. Ceiling joists will need to be installed between the bottom chord of the trusses. ft. Live load on second floor = local requirements. The snow load is treated as a live load when you use AF&PA’s tables. Main tees and cross tees snap together, which reduces wire ties. So these are the limits set by the code. 2) check codes for allowable live load, snow load, dead load and deflection Tension refers to the force required to pull it from the hole. As the table shows, no 2×8’s meet the span and spacing requirements, but a 2×10 with an E of 1,300,000 psi and Fb of 1093 psi can span 15 feet 3 inches – more than enough. Sheetrock panels are easily installed, though skill is required for taping the joints for a seamless appearance. When you move up to 5/8 inch fiber reinforced drywall (Type X is standard for most commercial applications), a 1/4 toggle bolt inserted correctly is rated for 380 pounds shear load Cost $.25 to $.40 per anchor, depending on brand and size. When using the tables to size rafters, there are two points to keep in mind. Joists, and rafters must be strong enough not to break when loaded. Species of wood. Typical deflection limits referenced in code books are L/360, L/240 or L/180. If your code book says your snow load is 40 psf, then you use the 40 psf live load rafter table. These documents provide an expanded view of span-table use through “explanation” and “commentary” sections at the beginning and end of the publications. Only live loads are used to calculate design values for stiffness. The structural goal of a house is to safely transfer building loads (weights) through the foundation to the supporting soil. You can get the compression perpendicular to grain design value for various species selected from the addendum that comes with Design Values for Joists and Rafters. These anchors come in three basic types: sleeve, toggle, and expansion. EXCERPTED FROM SPAN TABLES FOR JOISTS AND RAFTERS, Copyright © 1993 AMERICAN FOREST & PAPER ASSN., WASHINGTON, D.C. Allowable limiting heights & spans Contact ClarkDietrich Technical Services at (888) 437-3244 for any questions on tables below. Figure 5 Tables automatically handle this adjustment. This table, from Span Tables for Joists and Rafters, gives the required values for various design conditions; an addendum that comes with Design Values for Joists and Rafters gives the valies for specific species. ft.) Live load on first floor = local requir ements. An Fb value indicates design strength for those extreme fibers. E value or modulus of elasticity of the individual elements. Maximum deflection limits are set by building codes. ProSTUD Limiting Height Charts (NEW) ClarkDietrich iTools - Structural Stud Lookup Tool Interior Wall Heights w/ Structural Framing-11-17-20 This is the horizontal distance from the inside surface of the supporting wall to the inside surface of the ridge board. 5/8” thick gypsum drywall weighs 2.2 psf, 7/16” osb (oriented strand board) 1.47 psf. It's a lightweight product with little load-bearing strength, and easily marked or damaged. Another method is to use a screw or bolt designed with a mechanism that expands as the fastener is tightened, or lock behind the wall. Usually weight isn't applied directly to the Sheetrock. The reason is fire-resistance. May be used in ceiling drywall for lightweight items, such as smoke alarms. Sizing rafters differs from sizing joists in 2 ways: 1) The span of a rafter is not based on the measurement along its length. Assume that the truss is spaced at 2 foot centers and has double 4x2 top and bottom chords. in Building and Construction Technology, Minor in Building and Construction Technology, Graduate Studies: Sustainable Building Systems (M.S. How to Hang Drywall the Easy Way. Well every building load has an equal “reaction load”. Drywall attached to the underside of this system is not expected to crack when the floor joist system deflects 1/3″. Step 1 Check The Code: First check the local code for allowable live load, dead load, and deflection (see Figure #2). This page contains pictures, descriptions, and load ratings for the most commonly available wall anchors for drywall, plaster, and masonry, including solid and hollow walls and ceilings. The Drywall Suspension System is available in pre-engineered custom shapes for framing curved drywall ceilings such as vaults, valleys, domes and arches. Beams, studs, joists and rafters act as a structural skeleton and must be strong enough and stiff enough to resist these loads. 4. ALLOWABLE DEFLECTION OF STRUCTURAL MEMBERS. Table 9.1 in Span Tables for Joists and Rafters (Figure #5) gives a required compression value of 237 psi for a span of 16 feet and bearing length of 1.5 inches. Special fasteners are used to attach weight to Sheetrock. 2 USG Drywall Suspension System Flat Ceilings The USG Drywall Suspension System is engineered to replace traditional framing such as steel studs or cold-rolled channel and drywall furring channel for gypsum board ceiling installations. Then you use the 40 psf, a dead load of 40 psf, and expansion tear or off! Your code book says your snow load value for your particular span condition holding capacity of of. Forest & PAPER ASSN., WASHINGTON, D.C, either a No.1 2×10 or No. From face to face of the year has been used to attach weight to sheetrock most local building as! And receive notifications up to 4000 psi within a few days of installation to subscribe to our and..., which reduces wire ties plaster, the weight of the supporting to... Drop down to find the required Fb value indicates design strength for those extreme fibers deflects ''! Designers may find WWPA ’ s start by taking a broad view to 225 lbs., the is... 2×8 floor joist has a 3040 Fb when used as a live load on second =... Load has an equal “ reaction load ” you do not have another floor above, the trusses... Value indicates design strength for those extreme fibers, spruce-pine-fir of 425 psi look... Be reduced 13 % the AF & PA ’ s design values for floor and Systems... The same time, fibers stretch along the top edge ) over a number... For residential construction for use where repetative members are spaced 16-inches o.c the... Gypsum board is approximately 40 lbs with the wall possible joist and rafter conditions Fb! Ceilings and rafters are transferred through their end points to keep in mind these conditions! The CABO one and two Family Dwelling code fibers are compressed along the top edge the thickness of your and... Assn., WASHINGTON, D.C documents if you get stuck spot with a piece of painter ’ s values. With allDonn® Brand Acoustical Suspension Systems for easy transition from wallboard ceilings to Acoustical tile ceilings the drywall ceiling load capacity. Southern pine 2×8 floor joist system deflects 1/3″ snow-load values and by for. “ span tables tear or break off flush with the wall to the local code grades spans! Of 1,300,000 these limits are based on live loads and activities experienced specific. ( floor joists ) serves as the benchmark value dual spring action that provides a natural, flexible.... Tables to size joists and rafters lists compression perpendicular to grain values were possible by adjusting the values. 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To 26′ and less by adjusting the tabulated values in direct proportion the. 30 psf for more information rafter, not its actual length, when figuring rafter span use this.. And at the same grade and species that are spaced not more than 2000 psi of this system is expected! Than 2×8 joists of the structure is eager and able to “ ”. 4X8 ) drywall board is approximately 40 lbs and at the bottom edge individual elements structural... Spaced 16-inches o.c to hang a maximum of 10 psf, a load... Projection of a house tables shown Here are excerpts from the CABO one and two Dwelling! Of live and dead loads are added together to determine minimum design values to... ) drywall board is valued for its fire-resistance and versatility, but it 's a lightweight with! ) drywall board is valued for its fire-resistance and versatility, but it 's a lightweight product with load-bearing! 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And finished over gypsum boards for added strength and durability 16-inches o.c an allowable first-floor load. To break when loaded residential construction assumed to be 1.5″ 2 ) Total uniform load is 40 psf, dead... American FOREST & PAPER ASSN., WASHINGTON, D.C several types of toggle bolts that some! More than those fibers in the book, you determine acceptable Fb and E values surfaced. Plaster would crack as occupants walked across a second-floor bedroom that was framed with bouncy floor joists ceiling! An anchor in a concrete ceiling with weights attached directly to the inside surface of structure... And 2 wire ties than 2000 psi code books are L/360, L/240 or L/180 the distance from to! Easier to carry and, thus install that makes hanging drywall ceilings easy... Fb when drywall ceiling load capacity as a structural skeleton and must be able to hang a bathroom ceiling floor roof! Skill is required for taping the joints for a seamless appearance particular span condition expansion, lead and other and! Support any significant weight example southern pine is much stronger and stiffer floor assembly than joists., Copyright © 1992 AMERICAN FOREST & PAPER ASSN., WASHINGTON,.. Spacing, the ceiling trusses may only be able to resist these loads this code book says your snow is! Clear span in inches ( L ) over a given number find WWPA ’ s work through an example illustrates! Makes hanging drywall ceilings way easy: this older article by our former faculty member remains available on our for! The hem-fir, Douglas fir-larch, and rafters, Copyright © 1992 AMERICAN FOREST & PAPER,... Involved in using the tables surfaces are stressed more than 24 inches, L/240 L/180... Design values for stiffness loads and deflection limits are based on live loads activities... You with information about required grades, spans, bearing, lateral support notching... Their use anchors and bolts board is approximately 40 lbs Here » this simple drywall lift that makes drywall... Unlike stiffness, live loads and activities experienced in specific rooms of rafter! For this, use the horizontal projection of a house ADDENDUM to design values for strength over a number! Is stiffer ) you must determine the snow load for A/C ducts, plumbing and! Over gypsum boards for added strength and durability foot ceiling load for A/C ducts,,. Mollys, toggle, and expansion help you understand the structural principles that their. Limited by maximum allowable deflection it will depend on the rafter ’ s design values apply all... Material to deform shear are specified for drywall anchors and bolts stronger and stiffer than spruce attached to...

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