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Chapter 13

Chapter 13. Sill and Floor Construction. Chapter 13 Overview. Platform Framing / Balloon Framing Joists and Beams / Floor Trusses Subfloor Cantilevered Joists Engineered Wood Products Post and Beam Construction. (continued). Learning Objectives.

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Chapter 13

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  1. Chapter 13 Sill and Floor Construction 1

  2. Chapter 13 Overview • Platform Framing / Balloon Framing • Joists and Beams / Floor Trusses • Subfloor • Cantilevered Joists • Engineered Wood Products • Post and Beam Construction (continued) 2

  3. Learning Objectives • Explain the difference between platform and balloon framing. • Plan the appropriate floor support using joists or trusses for a structure. • Determine proper joist sizes using a typical span data chart. • Describe the components of a floor system. (continued) 3

  4. Learning Objectives • Explain the principles of post and beam construction. • Select the appropriate engineered wood products for specific applications in residential construction. 4

  5. Introduction • Framing methods vary from one section of the country to another. • Selection factors include, personal preference, climate, geography and local codes • Two basic types of floor framing are: • Platform framing. • Balloon framing. 5

  6. Introduction • Typical floor framing structural components include: • Plates. • Joists. • Studs. 6

  7. Platform Framing • In platform framing, floor joists form a platform on which the walls rest. • Another platform rests on top of the walls when there is a second story. • Platform framing is used more extensively than balloon framing. 7

  8. Platform Framing • Construction is safer because work is performed on a solid surface. • The sill is the starting point in constructing a floor. • Rests on the foundation and supports the floor joists or the studs. • Generally 2" x 6" lumber. • Box sill construction is generally used, which consists of a 2" x 6" plate called a mudsill or sill plate. 8

  9. Platform Framing • Box sill construction. 9

  10. Platform Framing • Detail of the first and second floor. • Using box sill construction. 10

  11. Sealing the Sill • A seal is required between the foundation and sill plate. • The seal prevents outside air from entering the house. 11

  12. Balloon Framing • Balloon framing has diminished in importance in recent years. • Distinguishing features include: • Wall studs rest directly on the sill plate. • Each floor “hangs” from the studs. • Two advantages of balloon framing are: • Small potential shrinkage. • Good vertical stability. 12

  13. Balloon Framing • Disadvantages of balloon framing are: • Less than desirable surface on which to work during construction. • The need to add fire-stops. • Two types of sill construction are used: • Solid (standard). • T-sill. 13

  14. Balloon Framing Sill Construction • Solid (standard) sill. • Studs are nailed directly to the sill and joists. • No header is used. 14

  15. Balloon Framing for Second Floor • Joists are supported by a ribbon and nailed to the studs on the second floor level. 15

  16. Joists and Beams • Joistsprovide support for the floor. • Usually made from a common softwood. • Southern yellow pine, fir, larch, hemlock, or spruce. • Engineered wood and metal joists are also available. • Floor joists range in size from 2" x 6" to 2" x 12". 16

  17. Joists and Beams • Standard lumber sizes. • See p.276 17 (National Forest Products Association)

  18. Joists and Beams(Joists) • Size of joist required depends on the span, load, species and grade of wood, and joist spacing. • When using metal joists, the gauge of metal should be considered instead of species and grade of lumber. • Floor joists may be spaced 12", 16", or 24" on center. 18

  19. Procedure for Using Span Data Chart • Select species of wood to be used. • Select appropriate live load. “30” • Determine lumber grade to be used. • Number 2 • Scan the span data chart. • Select the appropriate joist size. 16" OC spacing is typical. 19

  20. Floor Joist Span Data 20

  21. Span Data Example • Span is 14'-0" and number one dense southern pine is to be used. • Live load is 30 pounds per square foot. • Chart shows the following choices. • 2" x 8" joists 12" OC or 16" OC. • 2" x 10" joists 12" OC, 16" OC, or 24" OC. • 2" x 12" joists 12" OC, 16" OC, or 24" OC. • Best selection is 2" x 8" joists, 16" OC. This will span up to 14'-5". 21

  22. Steel Floor Joists • Steel floor joists are beginning to be accepted for residential construction. • Joist depths ranging from 6" to 12" with thicknesses from 0.034" to 0.101" are generally used. • Usual spacing is 24" OC, but other spacing is also used. 22

  23. Steel Framing Detail • Typical steel framing where floor joists bear on the foundation. 23

  24. Joists and Beams(Beams) • When the span is too great for unsupported joists, a beamis typically usedto reduce the span. • A beam may be a solid timber, built-up beam, or a metal S- or W-beam. 24

  25. Methods of Supporting Floor Joists with Beams 25

  26. Openings in the Floor • Openings in the floor for stairs and chimneys required double joist framing. 26

  27. Cross Bridging • Cross bridging is used to stiffen the floor and spread the load over a broader area. • Bridging boards or metal bridging are used. 27

  28. Metal Bridging 28

  29. Floor Trusses • A truss is a rigid framework designed to support a load over a span. • Floor trusses are often used in place of floor joists in residential construction. • Floor trusses consist of a top chord, bottom chord, and web. 29

  30. Floor Trusses • Trusses provide clear spans with a minimum depth in a lightweight assembly. 30 (Trus Joist)

  31. Engineered Floor Trusses • Usually fabricated from 2" x 4" or 2" x 6" lumber and generally spaced 24" OC. • Each truss has a built-in camber. • Webs may be metal or wood. • A floor truss will often eliminate the need for a beam. 31

  32. Typical Truss Webs 32 (TrusWal Systems, Inc.)

  33. Wood I-Beams or Joists 33 (Boise Cascade Corporation)

  34. Wood I-Beams or Joists • Wood I-beams or joists are generally made from 2" x 4" machined-stressed lumber or LVL. • Webs are usually made from 3/8" OSB. • They are available in flange widths of1-3/4" and 2-5/16" and depths from9-1/2" to 20" and lengths up to 66'. 34

  35. Wood I-Beams or I-Joists • Advantages of wood I-beams: • Speed of construction. • Have knockout holes for plumbing and electrical cable. • Dimensionally stable and very straight. • No cross bridging needed • Disadvantages of wood I-beams: • Require more effort to cut. • More expensive than lumber or trusses. 35

  36. Wood I-Beams or Joists • Installation of wood I-beams are similar to traditional floor joists or rafters. • Should not be mixed with solid lumber in the same assembly. • Use the size chart on p. 799 • “Trus Joist Recommended Spans” 36

  37. Wood I-Beams or Joists 37 (Boise Cascade Corporation)

  38. Cantilevered Joists • Cantilevered joists are required when a section of the floor projects beyond the foundation (or level below). • Generally, joists should extend inside the structure twice the distance they overhang 38

  39. Subfloor • The subflooris attached to the top of the floor joists and provides a work surface during construction. • Plywood, tongue-and-groove boards, common boards, and other panel products are used for subfloors. • Panel products reduce installation time. • 5/8" or 1/2" thick plywood is preferred. 39

  40. Typical Panel Products 40 (Georgia-Pacific Corporation)

  41. Installing Subfloor Panels • Joist spacing must be very accurate. • All panel edges must be supported. 41

  42. Installing Subfloor Panels • Plywood grain direction of the outer plies should be at right angles to joists. • To reduce squeking • Panels may be glued as well as nailed or screwed • Use tongue & groove panels. 42

  43. Engineered Wood Products • Engineered wood products (EWPs) combine wood veneers and fibers with adhesives to form beams, headers, joists, and panels. • They increase the supply of usable wood from smaller and inferior trees. 43

  44. Engineered Wood Products • The use of engineered wood products will continue to grow. • Advances in adhesive technology have made EWPs possible. 44

  45. Engineered Wood Products • Band boards are available in 9-1/4",11-1/4", 12", 14", and 16" depths. • Engineered headers are available in 1-1/4" depth and 3-1/2" width. 45 (Alpine Structures)

  46. Engineered Wood Products • Advantages of EWPs: • High quality and consistency. • No knots, checks, or warps. • Uniformly dried to 8% to 12% moisture content. • Provides superior design flexibility. • Disadvantage of EWPs: • Lack of industry standards. 46

  47. Engineered Wood Products • Application of EWPs. 47

  48. Oriented Strand Board • Oriented strand board (OSB) is made from long strands of wood and resin. • First introduced in 1978 as a low-quality particle board panel. • Outer layers are oriented to the long dimension, others are perpendicular. 48

  49. Oriented Strand Board 49 The Engineered Wood Association)

  50. Oriented Strand Board • Advantages of OSB: • Less expensive than plywood. • Unique appearance can be appealing as a design element. • Disadvantages of OSB: • Subject to swelling. • Not designed for exposure to the elements. 50

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