Floor Framing - Chapter 15 PDF

Floor Framing 15 Section 15.1 Floor Framing Basics Section 15.2 Framing with Joists & Girders Section 15.3 Subﬂoors Chapter Objectives After completing this chapter, you will be able to: Identify the basic ﬂoor- framing components and explain the purpose of each. Construct posts and girders. Explain sill plates and the layout of basic joist spacing. Recognize cases where special framing details may be required, such as beneath a bearing wall. Construct a panel subﬂoor. Recognize other types of framing systems and products, such as those using trusses and girders. Discuss the Photo Subﬂooring The layer of material that goes over a ﬂoor frame is called the subﬂoor. What might go over a subﬂoor? Writing Activity: Observe and Record Examine the ﬂoor system at your house or the house of a friend. Can you determine which trades might be affected by the work of the ﬂoor-framing carpenter? With a classmate, try to identify other parts of the house that could be affected by the quality of the ﬂoor framing. Summarize your thoughts in a bulleted list. 394 Chapter 15 Floor Framing apawood.org 15 Before You Read Preview Floor framing depends on a precise arrangement of joists, beams, and panel products in order to perform properly. Choose a content vocabulary or academic vocabulary word that is new to you. When you find it in the text, write down the definition. Content Vocabulary girder bridging tail joist box sill bearing wall cantilever subflooring header crown trimmer joist Academic Vocabulary You will find these words in your reading and on your tests. Use the academic vocabulary glossary to look up their definitions if necessary. criteria perpendicular offset Graphic Organizer As you read, use a chart like the one shown to organize information about content vocabulary and their definitions, adding rows as needed. Content Vocabulary Deﬁnition girder a large principal horizontal number used to support ﬂoor joists Go to glencoe.com for this book’s OLC for a downloadable version of this graphic organizer. Academic Standards Mathematics Science Number and Operations: Understand the meaning of Science and Technology: Abilities of technological operations and how they relate to one another (NCTM) design (NSES) Geometry: Use visualization, spatial reasoning, and Physical Science: Chemical reactions (NSES) geometric modeling to solve problems (NCTM) Industry Standards English Language Arts Floor Systems Use information resources to gather information and Floor Framing Layout create and communicate knowledge (NCTE 8) Floor Framing Construction Participate as members of literacy communities (NCTE 11) NCTE National Council of Teachers of English NSES National Science Education Standards NCTM National Council of Teachers of Mathematics Chapter 15 Reading Guide 395 Floor Framing Basics 15.1 Posts, Girders, & Trusses by the foundation walls. A post is a wood or steel vertical member that provides interme- What components go into floor diate support for a girder. Girders and posts framing? can be made out of solid lumber, engineered When building a single-level house on lumber, or steel. Posts are sometimes made a concrete slab, the slab itself serves as the from concrete or brick. floor system. However, houses that have a basement or crawl-space foundation have a Posts floor system that is assembled from various Posts are often used in basements beneath types of wood framing and panel products. the main girder. They may also be used in a Floor framing consists of posts, girders, garage to support ceiling girders. They are sill plates, joists or trusses, and subfloor- generally spaced 8" to 10" on center (OC). The ing. These framing members are fastened exact spacing depends on the size of the load. together to form a strong platform that A wood post must be solid and not less supports the house. In first-floor framing, than a 4⫻4. It is often a 6⫻6. Its ends must joists rest on the sill plate. They may also be flat and securely fastened. The loads it rest on girders or be attached to them. In carries are transferred to a fairly small area second-floor framing, they rest on a double of the foundation. Because of this, a portion top plate. Once covered with sheathing, floor of the concrete slab directly below a post joists distribute loads to the foundation walls is made thicker to provide greater bearing and provide a solid base on which to walk. capacity, as shown in Figure 15-1. This must Nominal 2" lumber or laminated-veneer be done when the slab is poured. In some lumber (LVL) I-joists are generally used cases, a wood post is supported by a heavy- for floor framing. Floor trusses can be used gauge metal bracket that lifts it clear of any either as girders or as floor joists. Engineered moisture that might cause rot. materials offer the advantages of light weight, consistent strength, and long spans (see Post Chapter 13, “Engineered Wood”). This chap- Galvanized ter describes floor framing using conventional Concrete steel column lumber. However, framing with LVL I-joists base calls for similar techniques. Where they differ, the differences will be noted. In the average house, the distance between opposite foundation walls is too great for a single floor joist to span. A floor joist is any light beam that supports a floor. Pairs of joists are often used to span the distance. The outer ends of the paired joists are supported by Figure 15-1 Thickened Slab the foundation walls, while the inner ends Extra Support A concrete slab ﬂoor must be made are supported by a girder. A girder is a large thicker to support the load from a post. The thickened principal horizontal member used to support portion is called a footing. floor joists. The ends of a girder are supported 396 Chapter 15 Floor Framing Floor joist I-beam girder Bolt Steel post Bolt Figure 15-2 Lally Column Flange Steel Post The plates welded onto each end of the post are used for fastening it to the girder and to the slab. Why are Lally columns preferred in residential Concrete construction? pedestal Steel posts, sometimes called Lally columns, parallel to them. They may be made of wood are often preferred in residential construction or steel. Steel does not shrink as solid wood (see Figure 15-2). They are strong, easy to does. However, wood girders are lighter and handle, and take less space than solid wood therefore easier to install. It is also easier to posts. They must be at least 3" in diameter connect floor joists to wood girders. and protected against rust, such as with rust- In one framing method, the floor joists rest resistant paint. Steel posts have steel bearing on top of the girder as shown in Figure 15-3. plates at each end. In some cases the top plate However, the top of the girder must be at the has metal straps that can be used to secure same level as the top of the sill plate. (The it to a steel girder. Some posts are adjustable sill plate is the horizontal framing member to various lengths. Steel posts are sometimes anchored to the foundation wall.) If more filled with concrete for extra strength. clearance is needed, the girder can be installed so that its top surface is level with the top of the Girders floor joists as shown in Figure 15-4 on page 398. Girders are generally placed halfway In this case, metal framing connectors attached between the longest foundation walls and to the girder support the ends of the joists. Floor joist Girder Sill plate Foundation wall Post Figure 15-3 Joists on Top Method 1 Floor joists often rest on top of a girder. This method tends to reduce headroom in a basement. Section 15.1 Floor Framing Basics 397 Joist hanger LVL girder Face-nailing and Toenailing Through- out this book, many references will be made to face-nailing and toenailing. These terms refer to the two basic types of nailed connections. In face-nailing, a nail is driven straight through the thick- ness of the lumber and into another Joist piece. In toenailing, a nail is driven at an angle from the face through the edge Metal post of the lumber and into another piece. In general, toenailing calls for smaller nails than face-nailing. This reduces the risk of Figure 15-4 Joists Flush splitting the wood. Both types of connec- Method 2 Joists can also be supported by joist hangers tions can be made by hand-nailing or by nailed to the side of the girder. using a pneumatic nailer. Wood Girders Wood girders are available in Face-Nailing several forms. Solid wood girders were once common, but solid wood of suitable size Nail through and quality is no longer readily available. face at 90 Another approach is to use built-up wood girders. These are built on-site and consist of three or four pieces of solid lumber nailed face to face, as shown in Figure 15-5. To determine material requirements, refer to Nail Table 15-1. To make a built-up girder, face-nail each layer with 10d nails as follows: Stagger the nails 32" OC at top and bottom. Nail two or three times at the end thickness of the beam’s steel determine of every board (depending on size), how strong the beam is, not the size of the including splices. flanges. Steel girders come in two basic shapes. An I-beam looks like a capital I, Stagger the joints. with the web wider than the flanges. A Glue-laminated beams and laminated- W-beam, sometimes called a wide-flange veneer lumber can also be used as girders. beam, is squatter in appearance because the They offer the dimensional stability of steel web and flanges are the same width. and the easy installation of wood. Steel beams are ordered based on two Steel Girders A steel beam has great strength criteria: height and weight. Height is and is often used in floor systems as a measured from flange to flange. Weight girder. Like a wood I-joist (see Section is based on the weight of a one-foot length 13.2), a steel beam consists of horizontal of beam. For example, a steel beam might flanges separated by a vertical element be specified this way: W12 ⫻ 45#. This called a web. The depth of the web and the would refer to a wide flange beam (W) 398 Chapter 15 Floor Framing Sill plate Foundation wall 1/2" clearance Built-up girder Stagger joints 4" minimum bearing Toenail to post Post Figure 15-5 Built-Up Girder Layers of Lumber A built-up girder consists of layers of solid wood. This girder ﬁts into a notch in the foundation wall called a beam pocket. Table 15-1: Estimating for Built-Up Girders(a) with flanges that are 12" wide. The beam would weigh 45 lbs. per foot. An I-beam Size of Board Feet per Nails per 1,000 would be designated with an S instead of Girder Lineal Foot Board Feet a W. If it is to be used as a girder, a wood 4ⴛ6 2.15 53 bearing plate must be attached to the top 4ⴛ8 2.85 40 of the beam. The plate will enable you to toenail floor joists to the beam, as shown in 4ⴛ10 3.58 32 Figure 15-6 on page 400. 4ⴛ12 4.28 26 Wood bearing plates can be fastened to 6ⴛ6 3.21 43 steel with steel pins. The pins are driven with a powder-actuated fastening tool. 6ⴛ8 4.28 32 An explosive gunpowder charge, called 6ⴛ10 5.35 26 a load, drives the hardened steel pins into 6ⴛ12 6.42 22 steel or concrete. Attaching the plate to a girder with pins may be easier to do before 8ⴛ8 5.71 30 the girder is lifted into place. As an alterna- 8ⴛ10 7.13 24 tive, the steel fabricator can weld short lengths of threaded steel rod to the top 8ⴛ12 8.56 20 of the girder. The wood plate can then be (a) A 4⫻6 girder 20" long contains 4" board feet of lumber drilled to match and be secured with nuts (20 ⫻ 2.15 ⫽ 43). and washers. Section 15.1 Floor Framing Basics 399 plates. The open webs allow heating ducts, water lines, drain lines, and other items to be passed through with ease. The most common type of floor truss in residential construction is the parallel-chord floor truss. The top and Steel pin bottom chords are parallel to each other over Bearing Joist plate the length of the truss. It is important to brace floor trusses as Steel they are being installed. This increases the I-beam safety of workers installing the subfloor. It also prevents the trusses from being dam- aged by sideways movement before the subfloor is laid. The truss fabricator can provide detailed bracing instructions. Figure 15-6 Bearing Plate Installing Posts and Girders Attachment Aid Fasten a wood bearing plate to a Posts and girders are installed after the steel girder so that joists can be nailed to the plate. This girder is an I-beam. foundation walls are complete and the forms have been stripped. In houses that will have a basement, the basement floor slab may also be Floor Trusses in place. Posts should be located only where A floor truss is another structural product the slab has been made thicker to distribute the that can be used as a girder. These trusses are expected loads. To locate these points, metal made in a factory to the specifications of the anchors are sometimes placed when the slab job. Floor trusses can also be used in place of is poured. The posts can then be plumbed, lumber joists where long spans are required, braced temporarily, and bolted to the anchors. as shown in Figure 15-7. A floor truss has only If there are no anchors to indicate the location three basic parts: chords, webs, and connector of posts, consult the plans for the location. Temporary brace Top chord Connector plate Bottom chord Web Figure 15-7 Parallel-Chord Trusses Engineered Support Floor trusses should be braced temporarily with 2⫻4 stock until they are sheathed. 400 Chapter 15 Floor Framing After the posts are in place, install the be attached to the post, such as bearing plates. girder and brace it if necessary. Steel and For a prefabricated steel post, the height from glulam girders are placed by a small crane the floor to the bottom of the girder is all that or a special forklift. Solid wood and built-up is needed. The post should be centered on the girders can sometimes be lifted into position girder’s width. by hand. The ends of wood girders should bear at least 4" on masonry walls. This will reduce the risk of crushing the wood fibers. A 1⁄2" clearance should be provided at each end and at each side of a wood girder Powder-Actuated Tools Because a powder- framed into the masonry (see Figure 15-5 on actuated fastening tool can be dangerous if page 399). This will prevent the wood from used improperly, special training is required. absorbing moisture from the masonry. The Only qualiﬁed users should operate this tool. bearing details for a steel girder are specified It is also essential that users wear hearing and on the plans. eye protection. Others in the area should To determine the height of a post, stretch be warned when the tool is to be used. See a string line tightly across the foundation. Chapter 3 for more on safety requirements for Measure from the floor to the line. Then calcu- powder-actuated tools. late the length of the post based on deducting Go to glencoe.com for this book’s OLC for more on the depth of the girder. Be sure to account for job safety. the thickness of any other elements that will 15.1 After You Read: Self-Check 1. What is a girder, and what supports it? 2. What is a Lally column, and why are Lally columns often preferred in residential construction? 3. How is a built-up wood girder constructed? 4. What must be done to a steel beam before it is ready to use as a girder? Academic Integration: Mathematics 5. Word Problems A 56' long girder will be supported at each end by foundation walls. It will be supported along its length by posts spaced 8' OC. How many posts are needed to support the girder? Many word problems can be solved using the four basic operations: addition, subtraction, multiplication, and division. Identify what information is required and choose the operations that you need to solve the problem. Starting Hint Divide the length of the girder in feet by the OC spacing of the posts in feet. Go to glencoe.com for this book’s OLC to check your answers. Section 15.1 Floor Framing Basics 401 Framing with Joists & 15.2 Girders Framing with Joists 2⫻6 preservative-treated lumber. Preservatives What is the lowest member of a wood protect the wood against moisture damage frame? and insect attack. Joists are typically toenailed to the plate but may be secured with metal Solid lumber was once the only material framing anchors where required by code. used for floor joists but modern builders Sill plates establish the quality of all the now use laminated-veneer lumber (LVL) as framing that will follow. If they are not level, well. The most common LVL product is the the entire floor system will not be level. If I-joist, shown in Figure 15-8. The informa- they are poorly secured to the foundation, tion that follows relates to solid lumber as the house may not survive very severe well as to LVL floor framing. Any differences weather or an earthquake. Follow local between the two will be noted. building codes carefully. Box sill construction is used for platform- Anchor bolts or straps for the sill plates framed floors. A box sill consists of a sill are installed when the foundation is placed. plate (also called a mudsill, or just the sill) However, always verify that the bolts have and a rim (or band) joist. The sill plate is been placed correctly. Sill plates should be anchored to the foundation wall and the rim anchored to the foundation with at least joist is toenailed to the sill plate. Floor joists two 1⁄2" bolts in each plate. According to the and subflooring complete the floor system. building codes, the bolts must be spaced no Subflooring consists of engineered wood more than 6' OC and there must be a bolt sheets such as plywood or oriented-strand within 12" of each end of every plate. board (OSB). The elements of box sill con- To prevent cold air from leaking into the struction are shown in Figure 15-9. house, the plate should be set on top of a foam Installing the Sill Plate or fiberglass sill sealer. This product comes in The sill plate is the lowest member of the wood frame and provides a smooth bearing Wall framing surface for the floor joists. It is made of 2⫻4 or Subflooring Rim joist Sill plate (sill sealer beneath) Foundation wall Figure 15-8 I-Joist Figure 15-9 Box Sill Construction Floor Framing Option This I-joist is typical of those Key Elements First-ﬂoor framing at the exterior wall used for ﬂoor framing. using box-sill construction. 402 Chapter 15 Floor Framing David R. Frazier Photolibrary, Inc. a roll approximately 6" wide. It fills any gaps between the irregular surface of the concrete and the smooth surface of the sill plate. Steps for installing sill plates are given on Termite Shields Where termites are a signiﬁcant page 404. problem, a metal termite shield should be installed beneath the sill plate. This shield makes it difﬁcult Installing Lumber Joists for termites to reach wood members directly from Joists are usually placed perpendicular to the foundation walls without being noticed. girders on 16" or 24" centers. However, check Go to glencoe.com for this book’s OLC for the house plans for the exact size, spacing, more information about regional concerns. and direction of the joists. If the sizes for joists are not specified, refer to Table 15-2. Plans will also specify a lumber grade. Nonstress-Graded Lumber provides informa- The Ready Reference Appendix table tion about grades. Table 15-2: Floor Joist Spans for Common Lumber Species Dead Load = 10 psf Dead Load = 20 psf 2×6 2×8 2×10 2×12 2×6 2×8 2×10 2×12 Maximum ﬂoor joist spans Joist Spacing Species and Grade ft.-in. ft.-in. ft.-in. ft.-in. ft.-in. ft.-in. ft.-in. ft.-in. (inches) Douglas ﬁr-larch SS 11-4 15-0 19-1 23-3 11-4 15-0 19-1 23-0 Douglas ﬁr-larch #1 10-11 14-5 18-5 21-4 10-8 13-6 16-5 19-1 Douglas ﬁr-larch #2 10-9 14-1 17-2 19-11 9-11 12-7 15-5 17-10 Douglas ﬁr-larch #3 8-5 10-8 13-0 15-1 7-6 9-6 11-8 13-6 Hemlock-ﬁr SS 10-9 14-2 18-0 21-11 10-9 14-2 18-0 21-11 Hemlock-ﬁr #1 10-6 13-10 17-8 20-9 10-4 13-1 16-0 18-7 Hemlock-ﬁr #2 10-0 13-2 16-10 19-8 9-10 12-5 15-2 17-7 Hemlock-ﬁr #3 8-5 10-8 13-0 15-1 7-6 9-6 11-8 13-6 16 Southern pine SS 11-2 14-8 18-9 22-10 11-2 14-8 18-9 22-10 Southern pine #1 10-11 14-5 18-5 22-5 10-11 14-5 17-11 21-4 Southern pine #2 10-9 14-2 18-0 21-1 10-5 13-6 16-1 18-10 Southern pine #3 9-0 11-6 13-7 16-2 8-1 10-3 12-2 14-6 Spruce-pine-ﬁr SS 10-6 13-10 17-8 21-6 10-6 13-10 17-8 21-4 Spruce-pine-ﬁr #1 10-3 13-6 17-2 19-11 9-11 12-7 15-5 17-10 Spruce-pine-ﬁr #2 10-3 13-6 17-2 19-11 9-11 12-7 15-5 17-10 Spruce-pine-ﬁr #3 8-5 10-8 13-0 15-1 7-6 9-6 11-8 13-6 Douglas ﬁr-larch SS 9-11 13-1 16-8 20-3 9-11 13-1 16-2 18-9 Douglas ﬁr-larch #1 9-7 12-4 15-0 17-5 8-8 11-0 13-5 15-7 Douglas ﬁr-larch #2 9-1 11-6 14-1 16-3 8-1 10-3 12-7 14-7 Douglas ﬁr-larch #3 6-10 8-8 10-7 12-4 6-2 7-9 9-6 11-0 Hemlock-ﬁr SS 9-4 12-4 15-9 19-2 9-4 12-4 15-9 18-5 Hemlock-ﬁr #1 9-2 12-0 14-8 17-0 8-6 10-9 13-1 15-2 Hemlock-ﬁr #2 8-9 11-4 13-10 16-1 8-0 10-2 12-5 14-4 Hemlock-ﬁr #3 6-10 8-8 10-7 12-4 6-2 7-9 9-6 11-0 24 Southern pine SS 9-9 12-10 16-5 19-11 9-9 12-10 16-5 19-11 Southern pine #1 9-7 12-7 16-1 19-6 9-7 12-4 14-7 17-5 Southern pine #2 9-4 12-4 14-8 17-2 8-6 11-0 13-1 15-5 Southern pine #3 7-4 9-5 11-1 13-2 6-7 8-5 9-11 11-10 Spruce-pine-ﬁr SS 9-2 12-1 15-5 18-9 9-2 12-1 15-0 17-5 Spruce-pine-ﬁr #1 8-11 11-6 14-1 16-3 8-1 10-3 12-7 14-7 Spruce-pine-ﬁr #2 8-11 11-6 14-1 16-3 8-1 10-3 12-7 14-7 Spruce-pine-ﬁr #3 6-10 8-8 10-7 12-4 6-2 7-9 9-6 11-0 Source: 2006, International Code Council, Inc., Falls Church, Virginia. 2006 International Residential Code. Reprinted with permission of the author. All rights reserved. Section 15.2 Framing with Joists & Girders 403 Installing Sill Plates Sill plates on opposite walls should be installed so that they are parallel to each other. Step 1 Check to see that foundation is level and distance on the plate, starting from the edge that is square. To check a simple rectangular foundation, resting against the bolt. Mark the bolt centerline at measure diagonally from corner to corner. To check this point. a more complex foundation, use the 3-4-5 method for squaring walls (see Chapter 16, Wall Framing & Step 5 Using a 5⁄8" spade bit, bore holes through the Sheathing). Adjust the plates as needed so they will plate at each marked point. (If termite shields will be be square. used, bore holes at the same locations in them, using a suitable drill bit.) Step 2 Establish the location of the sill plate. From the outside edge of the foundation wall, measure back a Step 6 Roll out sill sealer over the top of the founda- distance equal to the width of the sill plate. If the out- tion walls and press it into place. (See Figure 15-11.) side of the wall sheathing will be ﬂush with the outside The weight of the building presses the sill sealer edge of the foundation wall, measure back the width of against the foundation wall to stop drafts. the sill plate plus the thickness of the sheathing. Step 7 Slip the sill plate over the anchor bolts. Start Step 3 Place sill plate stock around the foundation. at the high point of the foundation wall and check to Use only straight, ﬂat lumber that has been preservative- see that the sill plate is level, using a builder’s level. treated. Any wood placed against concrete should be An even more accurate technique would be to check preservative-treated to resist rot. Place the edge of the plate with a laser level set up in a location that each piece against the foundation anchor bolts and would allow you to check the entire foundation. mark the centerline of the bolts on the plate. Using a Shim beneath the sill plate with cement grout or with square, extend these marks across the width of the sill preservative-treated wood shims, as needed, to make plate. (See Figure 15-10.) it level. Step 4 Measure from the center of each bolt to Step 8 Place a ﬂat washer and a nut on each founda- the chalk line on the foundation. Measure the same tion bolt. Use a wrench to tighten each nut securely. X minus sheathing thickness Sill plate X Figure 15-10 Sill Plate Layout Figure 15-11 Installing Sill Sealer Go to glencoe.com for this book’s OLC for additional step-by-step procedures, applications, and certiﬁcation practice. 404 Chapter 15 Floor Framing Joist Layout Joists are spaced evenly from one end of the house to the other. However, certain factors may interrupt this spacing, such as the need to provide a stairwell opening or extra room for plumbing drain lines. Always consult the plans to identify these issues before you begin the joist layout. Use a tape measure to lay out the desired joist spacing on the sill or wall plate. Begin the layout by measuring from the corner of the sill plate. Make a mark 151⁄4" from the outside edge of the sill plate. This will be the location to the edge of the first joist. Mark an X on the side of the line where the joist will be, as shown in Figure 15-13. That will ensure that the joist will not be placed on the wrong side of the layout line. From that point on, mark every 16" to indicate the posi- tions of all the joists on that plate, as shown in Figure 15-14. Figure 15-12 Installing a Joist Hanger When you have marked the position of all Secure Connection Joist hangers strengthen the the joists, double-check to be sure that a joist connection between ﬂoor joists and the rim joist. is centered every 4'. When joists are laid out in this way, the edges of the floor sheathing Joists are often nailed into place. How- panels will always fall along the centerline of ever, metal connectors can be used to a joist. replace many of the nailed connections If the joists span the distance from one described in this chapter. The most com- foundation wall to the opposite wall, as mon metal connector used in floor framing I-joists often do, the layout on both sill plates is the joist hanger, shown being installed in Figure 15-12. Rim joist 16" OC First joist 16" OC 16" OC Spacing of joists Plate Figure 15-13 Locating the First Joist Figure 15-14 Layout of Remaining Joists Initial Layout The X next to each layout mark indicates Important Location Notice that the edge of the ﬁrst which side of the line the joist will be on. joist will be 15¼" from the outside edge of the sill plate. Section 15.2 Framing with Joists & Girders 405 Arnold & Brown will be identical. However, when joists will are on its compression (top) side. They are be overlapped at a girder, the layouts will less likely to cause failure in this location. A differ as shown in Figure 15-15. In this case, large knot on the tension side of a joist can be first mark the layout on one sill plate. Mark pulled apart, weakening the joist as shown the same layout on the girder. On the oppo- in Figure 15-16. site wall, offset the position of joists by 11⁄2" Alternate Layout Method Some carpenters lay (the thickness of a joist) to ensure that the out the spacing of the floor joists by marking joists overlap at least 3". In this case, the floor the sill plates. Others prefer to mark their sheathing panels will slightly overhang the layout on the top edge of the rim joists. This offset joists. is done after the rim joist has been toenailed Select floor joist lumber carefully so the to the plate. floor will be flat and strong. Any joists having a slight edgewise bow should always Installing I-Joists be placed with the crown on top. The crown The specific installation details for I-joists is the outermost curve of the bow. Mark the vary according to the product’s manufac- joist with an arrow pointing to the crown. turer. Always read the instructions for the A crowned joist will tend to straighten out specific I-joist you plan to use. You must when subfloor and normal floor loads are placed on it. Be sure that knots in the joist LOADS Rim joist Sill plate Saw cut at bottom of board opens up A Girder LOADS Lapped joists Saw cut at top of board will compress Top of B foundation wall Figure 15-16 The Effect of Lumber Defects Choose Joists Carefully A knot or other defect in a Figure 15-15 Layout of Lapped Joists joist will have the same results as a saw cut. A. With a Layout Offset Lapped joists call for a different layout saw cut at the bottom, the joist opens up and breaks. on opposite plates to compensate for the thickness of B. A saw cut at the top closes up (compresses), so the the joists. joist retains more strength. 406 Chapter 15 Floor Framing Measurement also check the span tables for that product, not the span tables for lumber joists. Do Squaring Floors Floors need to be not assume that the span listed for one line “squared up” as they are being constructed. of engineered lumber products will be the All four angles of a rectangular wall or ﬂoor same as the span for another line. In general, must be right angles. The diagonals run- however, an I-joist floor system will have ning from opposite corners of a rectangular wall must also be equal. It is important to details such as those shown in Figure 15-17. know the length of each of these diagonals. Layout of I-joists on the plates is largely the Calculate the length of the diagonals of a same as layout for lumber joists. The differ- ﬂoor that measures 24' ⫻ 32'. ence is that I-joists are not generally lapped Starting Hint The Pythagorean Theorem over a girder because they are available in states that the square of the hypotenuse of long lengths. a right triangle is equal to the sum of the The following details are generally used squares of the other two sides. when installing I-joists. a² ⫹ b² ⫽ c² Backing and Blocking I-joists are nearly always a = altitude; b ⫽ base; c ⫽ hypotenuse supported by metal joist hangers. The width of the hanger should match the width of Backer Temporary braces block (14 minimum) at 6' OC Web stiffeners Fasten at each joist with 2-8d (21/2") nails minimum Subflooring Rim board joint between joists I-joist PSL rim joist Cantilever Blocking panel Protect wood from direct contact with concrete Bearing plate to be flush with inside face of wall or beam See manufacturer's literature for Intermediate bearings: allowable holes Load-bearing wall must stack over wall below. Blocking panels may be required at shear walls above or below. Figure 15-17 An I-Joist Floor System Typical Details The overall arrangement of I-joists is similar to a solid lumber ﬂoor system but many details differ. Section 15.2 Framing with Joists & Girders 407 the I-joist. A backing block can be nailed to Plate Joist hanger both sides of the I-joist to improve the fit as shown in Figure 15-18. Where an I-joist runs continuously over a support (a girder, for example), web stiffen- ers should be nailed to both sides of the web. They will improve load-bearing ability of the I-joist. The stiffeners can also provide addi- tional bearing surface for lumber or I-joist blocking. Depending on the dimension of the I-joist, web stiffeners may be made of 1⁄2", 5⁄8", or 1" thick plywood or OSB-rated sheath- ing. I-joists with unusually wide flanges may even require a web stiffener made from nom- inal 2" lumber. Stiffeners are 1⁄8" shorter than Backing block the exposed portion of the web so that they Figure 15-18 Backing Blocks do not force the upper flange out of position. Improves Fit A backing block prevents an I-joist from One method of installing a stiffener is shown moving in the joist hanger. in Figure 15-19. A method recommended by Installing Lumber Joists Inspect each piece for usability before carrying it to the foundation. Set aside unusable lumber to cut up later for blocking. Step 1 Toenail the rim joists to the sill Joist Rim joist plates, using 16d nails every 16" OC. Be sure that the outside face of the joist is in Sill plate the same plane as the outside edge of the sill plate. Step 2 Place the joists over the layout marks, laying them ﬂat for now. Add extra joists or leave out joists where large openings will be located. Face-nail Step 3 Tip the outermost joist up on Toenail edge and align one end with the end of a rim joist. Nail through the rim joist and into this joist with two 16d nails as shown in the ﬁgure below. Toenail this joist to the plate with 16d nails spaced 16" OC. Step 4 Proceeding from one end of the house to the other, tip each joist on edge, crown up, and align it with the layout marks. This process is sometimes called rolling the joists. Nail through the rim joist and into each ﬂoor joist with two 16d nails. Toenail each joist to the sill plate with three 8d nails. Step 5 Toenail each joist to the girder with 8d nails. Step 6 Face-nail overlapping joists to each other with at least three 10d nails. Go to glencoe.com for this book’s OLC for additional step-by-step procedures, applications, and certiﬁcation practice. 408 Chapter 15 Floor Framing Web stiffener I-joist I-joist Small gap (1/4" ) 2" Girder 2" Steel column Tight fit A Web B Figure 15-19 Web Stiffeners Installing Stiffeners Web stiffeners should be installed on both sides of an I-joist where it crosses a support, as shown in A. One method of installing stiffeners is shown in B. In this case, spiral-shank nails were used. another manufacturer calls for installing the common or box nail penetrates the center of stiffeners using 10d clinched nails. A clinched each flange. nail is a nail of any size or type whose point has been bent over with a hammer where it Cutting and Notching Floor Joists exits the wood. This prevents the nail from During installation of ducts, plumbing pulling out. Always follow manufacturer’s pipes, or wiring, solid-wood floor joists must nailing details when installing stiffeners. sometimes be notched or drilled. A notch is a Where solid-wood blocking would be saw cut made in the end or edge of lumber. required on a solid-wood joist system, similar blocking may be required for an Wall framing I-joist floor. Short lengths of I-joist stock may be used instead of solid lumber. Where I-joist blocks intersect I-joists, a backing block or web stiffener may be required. Rim board Rim Boards A solid-wood rim joist is not suit- able for use with an I-joist floor. Instead, an engineered product such as LVL is used. This piece, shown in Figure 15-20, is called a rim board. A rim board ties the ends of the I-joists together. It does not shrink as much as solid lumber and comes in lengths of up to 24'. It may be up to 11⁄8" thick and must be the same depth as the I-joists. To install a rim board, toenail it to the I-joist sill plate with 8d common or box nails Figure 15-20 Rim Board spaced 6" OC, or as recommended by the End Tie A rim board ties the ends of I-joists together. manufacturer. When nailing through the rim Here it is shown on second-story in-line ﬂoor framing. board and into an I-joist, make sure one 8d Section 15.2 Framing with Joists & Girders 409 1/3 of span 2" min. Joist D/4 max. D/6 max. D/3 max. Depth "D" D/6 max. D/4 max. 2" max. Notches may not be Lumber located in middle third floor joist of joist span Figure 15-21 Notching Lumber Joists Code Restrictions The location and size of notches permitted in a solid-wood ﬂoor joist are based partly on the depth (D) of the ﬂoor joist. In some cases a notch might also be made hole is visible in Figure 15-8 on p. 402. If when the joists are being installed. Careless holes of any other size are needed, consult notching or drilling will reduce the strength the manufacturer’s literature. of a joist. For this reason, building codes Bridging Long joists should be stiffened with restrict notching, as shown in Figure 15-21. bridging. Bridging is a method of bracing For example, joists must never be notched in between joists. It is done to distribute loads, the middle one-third of their span or on the prevent the joists from twisting, and add bottom edge. Codes also restrict the size and stability and stiffness. position of holes. For example, holes must be There are two types of bridging. Solid at least 2" away from the top and bottom of bridging is made of solid lumber that is the a joist. same dimension as the joists, as shown in The situation with I-joists is more straight- Figure 15-22A. Cross bridging (also called forward. Except when cutting an I-joist to diagonal bridging) is more common because length, the flanges must never be cut, drilled, it is very effective and requires less material. or notched. The existing knockouts in the Precut 1⫻3 or 2⫻2 lumber is sometimes used web of the I-joist are used for utility access. for cross bridging, as in Figure 15-22B. Metal- These pre-scored holes can be punched out strap cross bridging with nailing flanges may by striking them with a hammer. One such also be used, as in Figure 15-22C. Using a Pneumatic Nailer Many carpen- ters use a pneumatic nailer to install ﬂoor joists. When nailing through the rim joist or rim board and into the ends of a joist, always Installing Bridging Before installing place the bottom nail ﬁrst. This holds the bridging, snap a chalk line across the tops two pieces together so you can move your of the joists as a guide. When installing hand out of harm’s way as you ﬁre the upper solid-wood cross bridging, leave the bottom nail into place. Do not forget to wear eye ends loose until the subﬂoor has been laid. protection. This permits the joists to adjust themselves Go to glencoe.com for this book’s OLC for more on to their ﬁnal positions. Then, complete the job safety. nailing later. 410 Chapter 15 Floor Framing Joist A B C Figure 15-22 Joist Bridging Three Types Bridging comes in various forms. A. Solid bridging. Offsetting the blocks allows them to be end nailed. B. Wood cross bridging. C. Metal-strap cross bridging. Bridging is not generally required by code Framing Under Bearing Walls Joists should be unless joists exceed 2⫻12 in depth. However, doubled under each load-bearing wall that is bridging is a cost-effective and efficient way parallel to the joists. If needed, a double joist to stiffen a floor. Many builders add it even hanger or two joist hangers could be used as in though it is not required. If the joists are Figure 15-23. A bearing wall is a wall that sup- over 8' long, install one row of bridging at ports loads in addition to its own weight. If the the center of the joist span. For joists 16' and wall will contain plumbing pipes or heating longer, install two rows of bridging equally ducts, the joists can be separated by blocking. spaced on the joist span. The blocking must be cut from the same size Special Floor Framing Conditions stock as the floor joists. Blocking should be spaced not more than 4' OC. Often a carpenter must adjust the layout of a floor system to accommodate special Framing Large Openings It is often necessary conditions. These conditions should be to create large openings in the floor system, identified before the joist layout begins. such as for framing around stairwells and Bearing wall LVL Floor girder sheathing Blocking 4' OC A Doubled joists B Doubled joists beneath bearing wall Figure 15-23 Joists Under Bearing Walls Added Support Floor joists should be doubled under bearing walls, as in A. If clearance space is needed for plumbing drains, the joists can be installed as in B. Section 15.2 Framing with Joists & Girders 411 chimneys. In these cases, the joists framing least 37" wide. If 1⁄2" drywall will be used the opening should be doubled, and the inter- to cover the walls of the stairwell, this will rupted joists must be supported by headers leave a finished opening of 36", as required as in Figure 15-24. A header is a horizontal by code. The length of a stairwell opening member that carries loads from other mem- is specified on the plans. (For further infor- bers and directs them around an opening. In a mation about stairwells, see Chapter 25, floor system, a header is supported by trim- “Stairways.”) Steps in framing an opening mer joists. A trimmer joist is used to form the are given on page 415. sides of a large opening. A tail joist is a floor Cantilevered Floor Framing The framing for a bay joist interrupted by a header. window or similar projection is often arranged The exact layout of headers is based on the so that the floor joists extend beyond the flooring loads, as well as the size and shape foundation wall. A cantilever is a supporting of the opening. However, doubled lengths member that projects into space and is itself of joist stock are generally used when the supported at only one end. The joists carry header must span more than 4'. In the case of the necessary loads, and there is no need for an I-joist floor, an LVL header is often used. separate foundation walls. This cantilevered Consult the plans for framing details as well extension should normally not exceed 2'. as for rough opening sizes. The joists forming each side of the bay, The difficulty of framing a stairwell as well as the header, should be doubled. depends on whether the opening runs How this is done depends on whether the parallel to the floor joists, as in Figure 15-25, floor joists run parallel to the cantilevered or perpendicular to them, as in Figure 15-26. section, as in Figure 15-27 on page 414, or A parallel opening is easier to frame. In perpendicular to them, as in Figure 15-28 either case, the rough opening must be at on page 414. Nailing, in general, should Subflooring Tail joists Hearth Double header 2" min. Trimmer joists Figure 15-24 Joist Headers Transferring Loads A header is often found in the ﬂoor framing near a ﬁreplace. 412 Chapter 15 Floor Framing Stairway rough opening Double header W idt h Tail joist gth Len Double trimmer joists Joist Figure 15-25 Stairwell Parallel to Joists Parallel The framing for this type of stairwell is relatively simple. Exterior wall conform to that for floor openings. The Bathroom Floor Framing The weight and subflooring is extended to the outer fram- drainage requirements of plumbing fixtures ing member and sawed flush with that involve special framing. Bathroom floor member. Check local building codes for joists that support a tub or shower should other rules related to cantilevered framing. be arranged so that no cutting is necessary For example, preservative-treated lumber when connecting the drainpipe, as in may be required. Figure 15-29 on page 414. This may require Double trimmer Joist Stair Joist hanger Girder or wall th l e ng ) r m a de bea he as a x. ed m ign Double header 0 '0" des 1 en h (W Figure 15-26 Stairwell Double trimmer Perpendicular to Joists Tail joist Perpendicular The framing for this type of stairwell may require additional Post support for structural support. header and trimmer Section 15.2 Framing with Joists & Girders 413 Joist Figure 15-27 Cantilever Framing Double Joist direction In Line In this case, the regular ﬂoor joist joists can be extended to provide support for a bay window. 16d nail Girder Doubled joist Lookout joist Figure 15-28 Another Type of Subflooring Cantilever Framing Double plate Perpendicular In this second story framing, lookouts have to be installed and must be attached to a doubled ﬂoor joist. Blocking Subfloor Double joists Figure 15-29 Framing Under a Bathtub Spacing Adjustment The joists under the bathtub are placed 12" OC. For a cast-iron bathtub, a double Space as needed to clear drain joist may be needed. 414 Chapter 15 Floor Framing Framing an Opening The opening frame can be assembled entirely with nails. However, it is easier to use metal framing connectors, as described here. Step 1 Make sure the trimmer joists have been doubled. Double-check the width of the opening Header against the plans. Step 2 Use a square to lay out the position of both headers. The dimensions of the rough opening will be noted on the plans. Step 3 Attach framing connectors to the sides Joist of the trimmer joists (see Figure 15-12 on page hanger 405). Framing connectors are required by code Tail if the header spans more than 6'. Nail with 16d joist common nails or as speciﬁed by the connector’s manufacturer. Step 4 Cut header stock to ﬁt snugly between the trimmers. Insert the stock into the connectors. Nail into the header with 10d common nails or with joist-hanger nails. Step 5 Install the tail joists. Support the tail joists on joist hangers nailed as in Step 4. According to the building code, tail joists over 12' long must be supported by framing connectors or on 2" square (or larger) ledger strips. Go to glencoe.com for this book’s OLC for additional step-by-step procedures, applications, and certiﬁcation practice. only a small adjustment in spacing the joists. where a wall runs perpendicular to the floor When joists are parallel to the length of a joists. If 2⫻6 blocks are centered over a 2⫻4 tub, they are usually doubled under its outer partition wall, they will provide a nailing edge. Unusually large tubs and whirlpool surface of approximately 1" on each side of tubs may require additional support. the wall. Blocks should be firmly secured Second-Story Framing The layout and instal- with 16d common nails so that they will lation of second-story floor joists is basically not be hammered out of position when the the same as for the first story. However, drywall is installed. instead of resting on a sill plate, the joists rest on the double top plate of the first-story walls. It is also important to remember that finish ceiling materials will be nailed to the Recall What is a cantilever? underside of the second-story floor joists. This calls for some special framing details. At the junction of a wall and ceiling, Framing with Girders doubled joists provide a nailing surface What is the difference between a girder for the ceiling and interior wall finish, as floor and a joist floor? shown in Figure 15-30 on page 416. Another The floor of most houses is built using method of providing nailing at the ceiling some type of floor joist. However, there line is to install solid blocking as in Figure are other ways to build floor systems. 15-31 on page 416. This may be required For example, girder floor framing is Section 15.2 Framing with Joists & Girders 415 Joist Joist Stud 26 block Stud Figure 15-30 Providing a Nailing Surface Extra Joist Joists can be added or spaced differently Figure 15-31 Ceiling Finish Blocking to provide a nailing surface for interior wall ﬁnish or Extra Stock Horizontal blocks can be installed as ceilings. needed to support the edges of ceiling ﬁnishes. common in mild climates. It is a form reasonably straight line. Their height is not of post-and-beam framing. A girder in critical because the posts will be cut to length this system serves a similar role to the as needed. The sill is then cut to size and girders noted in Section 15.1. However, in bolted in place. a girder floor system the girders are used The bearing posts must be cut to length like joists because they directly support a accurately to provide a level floor. A string subfloor. is pulled tight from opposite sill plates over the piers. Then the distance is measured from Components of the Floor the line to the top of each pier and recorded. The girder method of floor framing is This process is repeated for each line of piers sometimes used where homes are built until the height of each bearing post has been over a crawl space instead of a basement. determined and recorded. Posts can be cut to A system of posts and girders, instead of length with a circular saw or radial-arm saw. joists, supports the subfloor. Frequently, Each post is attached to a pier. Then the 4⫻6 girders are used and spaced 4' OC. girders are cut to length and toenailed to They are supported by 4⫻6 posts spaced the posts. If a low house profile is desired no more than 5' OC. Sometimes girders are or if the finished floor is to have a step- combined with box-sill framing, as shown down area, the tops of the girders in the in Figure 15-32. In other cases, the box sill is step-down area are set flush with the top replaced by a plate. Asphalt roofing mate- of the sill. A special metal hanger is used to rial or metal post anchors keep the wood support the girder. from contacting the pier. If square-edge Working space under the girders is subflooring panels are used instead of T&G limited, so plumbing and heating lines are (tongue-and-groove) panels, blocking is roughed in before the subfloor is laid. The required at unsupported edges. subfloor is then cut and nailed in place. Installation Details After the foundation walls Laying the Subﬂoor The subfloor is usually of are in place, locations for concrete piers 11⁄8" or thicker tongue-and-groove plywood. are laid out and holes can be dug for the Some local building codes permit the use of pier footings. The piers should be set in a 2⫻6 tongue-and-groove plank subflooring 416 Chapter 15 Floor Framing T&G sheathing Stagger end joints Girder Post Asphalt roofing Rim joist Sill plate Figure 15-32 Girder Floor Framing Posts and Girders Girder construction with box-sill framing. over girder floor framing. The subflooring is the tongue and to face-nail at a joint on all cut even with the outside of the framing and girders. After the subfloor has been cut and nailed to the top of the girders, as shown in nailed in place, the surface is ready for the Figure 15-33. 16d nails are used to toenail at layout and erection of the walls. Figure 15-33 Plank Subﬂooring Lots of Lumber Wall framing on top of girder construction using 2⫻6 T&G plank subﬂooring. Section 15.2 Framing with Joists & Girders 417 Arnold & Brown Table 15-3: Board Feet in Standard Lumber Length (feet) Width and Depth (inches) 10 12 14 16 18 20 22 24 1ⴛ2 12⁄3 2 21⁄3 22⁄3 3 31⁄3 32⁄3 4 1ⴛ3 21⁄2 3 3 4 4 5 5 6 1ⴛ4 31⁄3 4 42⁄3 51⁄3 6 62⁄3 71⁄3 8 1ⴛ5 41⁄6 5 55⁄6 62⁄3 71⁄2 81⁄3 91⁄6 10 1ⴛ6 5 6 7 8 9 10 11 12 1ⴛ8 62⁄3 8 9 102⁄3 12 13 142⁄3 16 1ⴛ10 81⁄3 10 112⁄3 131⁄3 15 162⁄3 181⁄3 20 1ⴛ12 10 12 14 16 18 20 22 24 11⁄4 ⴛ4 41⁄6 5 55⁄6 62⁄3 7 81⁄3 91⁄6 10 11⁄4ⴛ6 61⁄4 71⁄2 83⁄4 10 111⁄4 121⁄2 13 15 11⁄4ⴛ8 8 10 112⁄3 131⁄3 15 162⁄3 181⁄3 20 11⁄4ⴛ10 10 12 141⁄2 162⁄3 182⁄3 205⁄6 225⁄6 25 11⁄4ⴛ12 121⁄2 15 171⁄2 20 221⁄2 25 27 30 11⁄2ⴛ4 5 6 7 8 9 10 11 12 11⁄2ⴛ6 71⁄2 9 101⁄2 12 131⁄2 15 16 18 11⁄2ⴛ8 10 12 14 16 18 20 22 24 11⁄2ⴛ10 12 15 17 20 22 25 27 30 11⁄2ⴛ12 15 18 21 24 27 30 33 36 2ⴛ4 62⁄3 8 91⁄3 102⁄3 12 131⁄3 142⁄3 16 2ⴛ6 10 12 14 16 18 20 22 24 2ⴛ8 131⁄3 16 182⁄3 211⁄3 24 262⁄3 291⁄3 32 2ⴛ10 162⁄3 20 231⁄3 262⁄3 30 331⁄3 362⁄3 40 2ⴛ12 20 24 28 32 36 40 44 48 2ⴛ14 231⁄3 28 322⁄3 371⁄3 42 462⁄3 511⁄3 56 4ⴛ4 131⁄3 16 182⁄3 21 24 262⁄3 291⁄3 32 4ⴛ6 20 24 28 32 36 40 44 48 4ⴛ8 262⁄3 32 171⁄3 422⁄3 48 531⁄3 582⁄3 64 4ⴛ10 331⁄3 40 462⁄3 531⁄3 60 662⁄3 731⁄3 80 4ⴛ12 40 48 56 64 72 80 88 96 418 Chapter 15 Floor Framing This estimating and planning exercise will prepare you for national competitive events with organizations such as SkillsUSA and the Home Floor Framing Builder’s Institute. Number of Joists joists placed 16" OC, 102 board feet of lumber Estimating methods are similar for both are needed for each 100 sq. ft. of floor surface solid-lumber joists and I-joists. area. Step 1 To find the number of joists needed Step 3 Divide the total floor area by 100, and for a house, first divide the length of the multiply by the number of board feet that floor (in feet) by the joist spacing (in feet). you obtained from the table. The answer Conventional joist spacing is 16" (1.33') to the example problem is 816 board feet: on center. Dividing by 1.33 is the same as 800 ⫼ 100 ⫽ 8, and 8 ⫻ 102 ⫽ 816 multiplying by 0.75. Therefore, for joists 16" Step 4 By multiplying the cost per board on center, simply take three-fourths of the foot of lumber by the number of board length of the building. For example, for a feet required, you can obtain a rough cost building that is 40' long, multiply 0.75 by 40. estimate. The answer is 30. Step 5 Table 15-4 also helps determine the Step 2 Add 1 for the end joist, which gives a number of nails needed. For 2⫻6 joists, 10 lbs. total of 31 joists. of nails are needed for each 1,000 board feet. Step 3 I-joists may extend from wall to wall, Since our floor has only 800 board feet, it will but solid lumber joists usually do not. More are require about 8 lbs. of nails. needed. Suppose that the building in Step 1 is Step 6 Multiply the number of pounds 20' wide and that you are using 10' joists. The needed by the cost per pound to find the total joists will extend only from one wall to a center cost of the nails. girder. Another 31 joists will be needed to cover the span from the girder to the opposite wall, for a total of 62 joists. Labor Costs To determine the labor cost for framing a Step 4 Add one extra joist for each wall for floor, you must know the joist size. which double joists are specified. Step 1 In our example, the joists are 2" ⫻ 6" Material Costs ⫻ 10'. Refer to Table 15-3, which shows that An accurate cost estimate of materials is 2" ⫻ 6" ⫻ 10' boards contain 10 board feet. For made by multiplying the number of joists a building with 62 joists, as in our example, required by the cost per joist. However, a rough there would be a total of 620 board feet of estimate can be made without knowing the joists: exact number of pieces needed. 10 ⫻ 62 ⫽ 620 Step 1 Find the area of the floor by Step 2 Refer to Table 15-14 on page 420 to find multiplying the length times the width for the labor rate. One worker in one hour can each level. For example, a one-story building frame 65 board feet of 2⫻6 joist material. 20' wide and 40' long has a floor area of Step 3 To find the total hours needed, divide 800 sq. ft.: the total board feet by the number of board 20 ⫻ 40 ⫽ 800 feet framed in one hour. The answer is Step 2 The number of board feet required for 9.5 hours (620 ⫼ 65 ⫽ 9.5). joists can be found by referring to Table 15-4 Step 4 Multiply the number of hours by the on page 420. According to the table, using 2⫻6 hourly rate. Section 15.2 Framing with Joists & Girders 419 Table 15-4: Estimating Board Feet, Nails, and Labor Joists Nails Labor Per 1,000 Bd. Bd. Ft. Board Feet Required for 100 Sq. Ft. of Surface Area Ft. (pounds) (per Hour) Size of Joist 12" OC 16" OC 20" OC 24" OC 2ⴛ6 128 102 88 78 10 65 2ⴛ8 171 136 117 103 8 65 2ⴛ10 214 171 148 130 6 70 2ⴛ12 256 205 177 156 5 70 15.2 After You Read: Self-Check 1. What is a sill plate, and what is its purpose? 2. What size and type of bit should be used when boring holes in the sill plate for foundation anchor bolts that are ½" in diameter? 3. What does the term crown refer to, and why is it important? 4. What is the purpose of a web stiffener? Academic Integration: Mathematics 5. Estimate Floor Joists Normally floor joists are placed 16" or 24" OC. Estimate the number of 2' ⫻ 8' ⫻ 22" joists laid 16" OC needed for a 42' ⫻ 66'-6" structure. A girder supported by posts runs the entire length of the building. When estimating, be sure that all your calculations are in the correct units (such as feet, meters, or inches). Step 1: Divide 12" by the OC spacing in inches (16") to convert to a decimal factor. Step 2: Convert the length of the structure (66'-6") to decimal feet. Step 3: Multiply the length of the structure (66.5') times the decimal factor (0.75), and round up. Step 4: Add 1 starter joist. Step 5: Multiply the joists by 2 to account for both sides of the floor system. (Joists are 22' long and the building width is 42'. The joists overlap over the girder.) Step 6: To determine the extra stock needed for rim joists, multiply the length (66.5') by 2, and divide by 22'. Add the quotient to the number of joists. Go to glencoe.com for this book’s OLC to check your answers. 420 Chapter 15 Floor Framing Subﬂoors 15.3 Installing Subﬂooring safe working surface for building the house. Many years ago, floor sheathing was Are there any disadvantages to both made of solid 1⫻ boards, which were nailed gluing and nailing a subfloor? diagonally across the floor joists. Today, The layer of material directly over the floor solid lumber sheathing has been replaced joists is called floor sheathing. It forms what is by 4' ⫻ 8' engineered panel products such as called the subfloor. Sheathing serves several plywood and OSB. These panels are easier to important purposes. It lends bracing strength install and create a stiffer subfloor that is less to the building. It provides a solid base for the likely to squeak. finish floor. By acting as a barrier to cold and A typical subfloor consists of sheathing dampness, it helps keep the building warmer panels fastened directly to joists or girders, and drier in winter. In addition, it provides a as shown in Figure 15-34. Resilient tile, carpet, linoleum, or other non-structural flooring Combined subfloor-underlayment Blocking for square-edge panels nsion ime gd Lon 1/8" spacing recommended at all panel edge and end joints Full panel Half panel Joists Tongue-and-groove edges (or provide edge blocking) Figure 15-34 Subﬂooring Single Layer Subﬂooring can be laid over supports spaced up to 48" apart, depending on the design of the ﬂoor system and the thickness of the panel. Section 15.3 Subﬂoors 421 Table 15-5: Fastening Schedule for Subﬂoors(a) Span Rating Fastening: Glue-Nailed(c) Fastening: Nailed Only (Maximum Panel Spacing (inches) Spacing (inches) Joist Thickness Nail Size Nail Size Spacing) (inches)(b) and Type Supported Intermediate and Type Supported Intermediate (inches) Panel Edges Supports Panel Edges Supports 16 6d ring- 12 12 6d ring- 6 12 20 3⁄4" or less or screw- 12 12 or screw- 6 12 24 shank(d) 12 12 shank 6 12 24 8d ring- 6 12 8d ring- 6 12 7⁄8", 1" 32 or screw- 6 12 or screw- 6 12 48 11⁄8" shank(e) 6 (e) shank 6 (e) (a) APA Rated Sturd-I-Floor. Special conditions may impose heavy trafﬁc and concentrated loads that require construction in excess of the minimums shown. (b) Panels in a given thickness may be manufactured in more than one span rating. Panels with a span rating greater than the actual joist spacing may be substituted for panels of the same thickness with a span rating matching the actual joist spacing. (c) Use only adhesives conforming to APA Speciﬁcation AFG-01, applied in accordance with the manufacturer’s recommendations. If non-veneered panels with sealed surfaces and edges are to be used, use only solvent-backed glues; check with panel manufacturer. (d) 8d common nails may be substituted for ring- or screw-shank nails if ring- or screw-shank nails are not available and 10d common nails may be substituted with 11⁄8" panels if supports are well seasoned. (e) Space nails 6" for 48" spans and 12" for 32" spans. If the sheathing has a smooth surface, fin- has been applied in a small area. If the adhe- ish flooring such as carpeting, resilient tile, sive is applied too long in advance, it will and sheet flooring can be applied directly to dry out or harden and will not hold. Hand it. Sheathing rated for this purpose is identi- nailing a subfloor is time consuming and fied by a grade mark stamped on the back of physically difficult. Using pneumatic nailers the panel. is much more efficient. This has become the standard method. For builders who prefer to screw the sheathing to the joists, special attachments Contrast Why are 4⫻8 engineered panel enable electric drills to drive a great number products used in place of solid lumber for ﬂoor of screws quickly. These attachments use sheathing? coils of screws, automatically feeding each one to the tip of a drill such as the one in Fastening Details Figure 15-35. Some models are fitted with a For fastening details, refer to Table 15-5. long extension so that the carpenter does not Common nails are often used to install have to lean over during installation. floor sheathing. When panels are glued and nailed, fewer nails are required, as

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