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SOME Key Code Concepts about Framing Residential Structures: (the following is NOT a substitute for the building code- check you local code…)

                         Joists under bearing partitions.
Joists under parallel bearing partitions shall be of adequate size to support the load. Double joists, sized to adequately support the load, that are separated to permit the installation of piping or vents shall be full depth solid blocked with lumber not less than
2 inches (51 mm) in nominal thickness spaced not more than 4 feet (1219 mm) on center. Bearing partitions perpendicular to joists shall not be offset from supporting girders, walls or partitions more than the joist depth unless such joists are of sufficient size to carry the additional load.

                       Bearing.
The ends of each joist, beam or girder shall have not less than 1.5 inches (38 mm) of bearing on wood or metal and not less than 3 inches (76 mm) on masonry or concrete except where supported on a 1-inch-by-4-inch (25.4 mm by 102 mm) ribbon strip and nailed to the adjacent stud or by the use of approved joist hangers.

                    Joist framing.
Joists framing into the side of a wood girder shall be supported by approved framing anchors or on edger strips not less than nominal 2 inches by 2 inches .

                    Bridging.
Joists exceeding a nominal 2 inches by 12 inches (51mmby 305 mm) shall be supported laterally by solid blocking, diagonal bridging (wood or metal), or a continuous 1-inch-by-3-inch (25.4 mm by 76 mm) strip nailed across the bottom of joists perpendicular to joists at intervals not exceeding 8 feet (2438 mm).

                   Floor systems.
Joists framing from opposite sides over a bearing support shall lap a minimum of 3 inches (76 mm) and shall be nailed together with a minimum three 10d face nails. A wood or metal splice with strength equal to or greater than that provided by the nailed lap is permitted.

                   Sawn lumber.
Notches in solid lumber joists, rafters and beams shall not exceed one-sixth of the depth
of the member, shall not be longer than one-third of the depth of the member and shall not be located in the middle one-third of the span. Notches at the ends of the member shall not exceed one-fourth the depth of the member. The tension side of members 4 inches (102 mm) or greater in nominal thickness shall not be notched except at the ends of the members. The diameter of holes bored or cut into members shall not exceed one-third the depth of the member. Holes shall not be closer than 2 inches (51 mm) to the top or bottom of the member, or to any other hole located in the member. Where the member is also notched, the hole shall not be closer than 2 inches (51 mm) to the notch.

                  Engineered wood products.
Cuts, notches and holes bored in trusses, structural composite lumber, structural glue-laminated members or I-joists are prohibited except where permitted by the manufacturer’s recommendations or where the effects of such alterations are specifically considered in the design of the member by a registered design professional.

                 Framing of openings.
 Openings in floor framing shall be framed with a header and trimmer joists. When the header joist span does not exceed 4 feet (1219 mm), the header joist may be a single member the same size as the floor joist. Single trimmer joists may be used to carry a single header joist that is located within 3 feet (914 mm) of the trimmer joist bearing. When the header joist span exceeds 4 feet (1219 mm), the trimmer joists and the header joist shall be doubled and of sufficient cross section to support the floor joists framing into the header. Approved hangers shall be used for the header joist to trimmer joist connections when the header joist span exceeds 6 feet (1829 mm). Tail joists over 12 feet (3658 mm) long shall be supported at the header by framing anchors or on ledger strips not less than 2 inches by 2 inches (51 mm by 51 mm).

                  Alterations to engineered wood trusses.
Truss members and components shall not be cut, notched, spliced or otherwise altered in any way without the approval of a registered design professional. Alterations resulting in the addition of load (e.g., HVAC equipment, water heater, etc.), that exceed the design load for the truss, shall not be permitted without verification that the truss is capable of supporting the additional loading.

                   Top plate.
Wood stud walls shall be capped with a double top plate installed to provide overlapping at corners and intersections with bearing partitions. End joints in top plates shall be offset at least 24 inches (610 mm). Joints in plates need not occur over studs. Plates shall be not less than 2-inches (51 mm) nominal thickness and have a width at least equal to the width of the studs.

                Drilling and notching of top plate.
 When piping or ductwork is placed in or partly in an exterior wall or interior load-bearing wall, necessitating cutting, drilling or notching of the top plate by more than 50 percent of its width, a galvanized metal tie of not less than 0.054 inch thick (1.37 mm)(16 ga) and 1 1/2 inches (38 mm) wide shall be fastened across and to the plate at each side of the opening with not less than eight 16d nails at each side or equivalent.

Exception: When the entire side of the wall with the notch or cut is covered by wood structural panel sheathing.

              Drilling and notching of wood wall framing–studs.
Drilling and notching of studs shall be in accordance with the following:

1. Notching. Any stud in an exterior wall or bearing partition may be cut or notched to a depth not exceeding 25 percent of its width. Studs in nonbearing partitions may be notched to a depth not to exceed 40 percent of a single stud width.

2. Drilling. Any stud may be bored or drilled, provided that the diameter of the resulting hole is no more than 60 percent of the stud width, the edge of the hole is no more than 5/8 inch (16 mm) to the edge of the stud, and the hole is not located in the same section as a cut or notch. Studs located in exterior walls or bearing partitions drilled over 40 percent and up to 60 percent shall also be doubled with no more than two successive doubled studs bored.

Exception: Use of approved stud shoes is permitted when they are installed in accordance with the manufacturer’s recommendations.

                Roof Framing :  Framing details.
 Rafters shall be framed to ridge board or to each other with a gusset plate as a tie. Ridge board shall be at least 1-inch (25 mm) nominal thickness and not less in depth than the cut end of the rafter .At all valleys and hips there shall be a valley or hip rafter not less than 2-inch (51 mm) nominal thickness and not less in depth than the cut end of the rafter. Hip and valley rafters shall be supported at the ridge by a brace to a bearing partition or be designed to carry and distribute the specific load at that point. Where the roof pitch is less than three units vertical in 12 units horizontal (25-percent slope), structural members that support rafters and ceiling joists, such as ridge beams, hips and valleys, shall be designed as beams.

               Ceiling joist and rafter connections.

Ceiling joists and rafters shall be nailed to each other in accordance with the  code. . Ceiling joists shall be continuous or securely joined in accordance with  where they meet over interior partitions and are nailed to adjacent rafters to provide a continuous tie across the building when such joists are parallel to the rafters.

             Ceiling joists lapped.
Ends of ceiling joists shall be lapped a minimum of 3 inches (76 mm) or butted over bearing partitions or beams and toe-nailed to the bearing member. When ceiling joists are used to provide resistance to rafter thrust, lapped joists shall be nailed together in accordance with the adopted code and butted joists shall be tied together in a manner to resist such thrust.

             Purlins.
Installation of purlins to reduce the span of rafters is permitted as directed by the building code. Purlins shall be sized no less than the required size of the rafters that they support. Purlins shall be continuous and shall be supported by 2-inch by 4-inch (51 mm by 102 mm) braces installed to bearing walls at a slope not less than 45 degrees from the horizontal. The braces shall be spaced not more than 4 feet (1219 mm) on center and the unbraced length of braces shall not exceed 8 feet.

            Bearing.
The ends of each rafter or ceiling joist shall have not less than 11/2 inches (38 mm) of bearing on wood or metal and not less than 3 inches (76 mm) on masonry or concrete.

           Bridging.
 Rafters and ceiling joists having a depth-to- thickness ratio exceeding 6 to 1 based on nominal dimensions shall be supported laterally by solid blocking, diagonal bridging (wood or metal) or a continuous 1-inch by 3-inch  wood strip nailed across the rafters or ceiling joists at intervals not exceeding 8 feet (2438 mm).

         Lateral support.
Rafters and ceiling joists having a depth-to-thickness ratio exceeding 5 to 1 based on nominal dimensions shall be provided with lateral support at points of bearing to prevent rotation.

        Engineered wood products. Cuts, notches and holes bored in trusses, structural composite lumber, structural glue-laminated members or I-joists are prohibited except where permitted by the manufacturer’s recommendations or where the effects of such alterations are specifically considered in the design of the member by a registered design professional.
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Frame Construction Basics :

The most common materials used for residential construction are wood and concrete. Most  homes have a combination of both. In this section, we will look at some of the details of wood  frame construction. Concrete will be dealt with in the following section.

Structural Components

There are many framing styles used for residential homes, but the names for many of the  various structural components are essentially the same. Below are diagrams of two
standard framing styles with the components labeled. Below the diagram, the structural
components are listed with descriptions and comments. We will spend time in class
discussing the primary types of stress to which these components are subjected.

If you know of a house that is in the framing stage of construction, try to visit the site and
see how many of the structural components you can identify. Of course, be sure to
 obtain permission from the owners/builders. 
 

• Roofers and Planks
  These terms are often used interchangeably, but plank is a common term for a
• generally wider (and perhaps thicker) board. Floor boards are usually called planks.
•  A wider and thicker plank can safely span greater distances between rafters.
• (But thinner boards can span larger distances if the boards are interlinked with
• a "tongue and groove" type design.) It is also common to use plywood for the
• roofing material. Plywood is constructed of many wood plies, in which the direction
• of the grain is alternated, creating a strong and stable material.

• Rafters, Beams and Joists
  Rafters support the roofing material. Large rafters, which can be spaced
• further apart, are often called beams. Roof beams are typically used for
• aesthetic purposes when the interior of the roof is to be exposed. A beam
• also refers to any large structural element that spans long distances
• and supports significant loads. The beams that support the floors are
• referred to as joists. But the horizontal members that connect to the
• rafters at the wall, labeled "ties" in the first diagram, are called joists as well.

• Studs, Posts and Plates
  Studs comprise the skeleton of a wall. They are typically 2 x 4's and the industry
• standard is to space them 16 inches center to center for 8 to 10 ft high walls. Posts
• are larger studs (often two 2 x 4's nailed together) used on either side of doorways
• and large windows. Posts are often centered above major floor beams, as shown
• in the second diagram, to help carry the weight of the roof or upper floors.

        The post and beam style of construction uses large vertical posts and horizontal beams  to provide the main skeletal structure of the house. The posts and beams are usually tied  together with bolts or metal plates. Floors, walls, and the roof are essentially added to the  skeletal structure.

• Lintels, Plates and Sills
  Lintels (also called headers) are horizontal structures found above doorways and
• large windows and function to carry the load of the upper studs (These shorter studs
• are called cripple studs.) which rest upon them. The larger the distance spanned,
• the wider the lintel must be.

  Plates are used to cap the studs (and are often called caps) at the top and bottom of

• the wall. If the plate also rests on the foundation, it is called a sill.

• Often a "header", a 2 x 8 or 2 x 10, is placed on edge between the foundation sill

• and the floor plate. In this case, the floor joists are connected to the header, rather

•  than resting on the sill.

  Roof Types

  A simply survey of houses indicates a large variety of roof shapes. Indeed, you can construct a roof of nearly any shape. A few common designs are shown below. The gambrel is often used for storage buildings where vertically space is needed. It is also found in homes in which the area under the roof is used as a living space. The lean-to or shed design is the simplist to construct, but provides little or no natural ventilation space. It isa used primarily for storage buildings.  Although similar to the gable, the hip roof can be more strongly anchored into the walls and offers a more aerodynamic profile to wind, an important consideration in hurricane proned areas.

  Trussing

  If a roof is constructed with 2x4 rafters, rather than heavier beams, trusses are usually installed for additional structural support. Trusses are elements that connect the rafters to joists and/or other rafters. The diagram below shows a variety of truss designs for different roof shapes. You may occassionally find trusses in open ceiling designs, but usually it is used when there is an attic and the structure is hidden by a ceiling attached to the roof joists.

  An important characteristic that all the designs have in common, is the use of the triangle. As you may have learned as early as grade school, triangular structures are rigid because the shape of a triangle cannot change without changing the length of its sides. Consider the two frames shown below. For simplicity, assume the structural components (struts) are connected at each vertex with a single nail. When external forces are applied in any direction to the triangular structure, the forces generated at the vertices will be shear forces. Provided the members themselves are sufficiently strong, the nails would have to be sheared for the structure to fail.