Floor Framing & Connections — Raised Floor Living

Floor Framing & Connections - Raised Floor Living

Floor Framing & Connections

Floor framing consists of a system of sills, beams, girders, joists, and subflooring, all properly sized and connected together. Floor framing provides support for floor loads, and gives lateral support to exterior walls.

Fasteners and Connections

Proper design, specification, and installation of fasteners and connections is crucial to the long-term performance and structural integrity of any structure. Nails, used alone or in combination with metal framing anchors and construction adhesives, are the most common method of fastening framing lumber and sheathing panels. Nail joints provide best performance when loads are applied at right angles to the nails. Nailed joints with the load applied parallel to the nail (in withdrawal) should be avoided. Metal products in contact with pressure-treated wood must be corrosion resistant.

Sill Plates on Foundation Walls

Sill plates resting on continuous foundation walls (stem walls) are generally of nominal 24 or 26 pressure-treated lumber. They are anchored to concrete, masonry, or wood walls with steel anchor bolts or proprietary metal anchor straps. The required size and spacing of the bolts or straps is dependent upon the forces acting on the building.

Typically, 1/2-diameter anchor bolts are placed within 12 from each end of the sill plate and then spaced a maximum of 6 on center. These bolts are usually embedded at least 7 in concrete or masonry (15 in masonry for uplift loads). Proprietary metal anchor straps providing equivalent anchorage may also be used in lieu of anchor bolts. Closer anchor bolt spacing and/or a larger bolt diameter may be required in seismic design categories D1 and D2 and where the design wind speed exceeds 110 mph. Consult the ANSI/AF&PA Wood Frame Construction Manual  from the American Wood Council or your local building code official for specific anchorage requirements.

Sill Beams on Piers or Piles

Sill beams supported by freestanding piers or piles must be of adequate size to support imposed loads between piers. They must also be adequately attached to the supporting piers. In addition, sill beams must be preservative treated if bearing on concrete or masonry, or if closer than 12 to exposed soil.

Sill beams are generally of solid-sawn lumber (typically 46) or timbers (typically 66 or 68), or glued-laminated timber.

Beams and Girders

Beams and girders are generally of solid-sawn lumber or timbers, glued-laminated timber, or structural composite lumber. They can also be built-up (nail-laminated) with multiple pieces of nominal 2 lumber nailed together with the wide faces vertical. These multiple pieces should be nailed together with two rows of 20d nails — one row near the top edge, and the other near the bottom edge. Nails in each row are spaced 32 apart. End joints of the nailed lumber should occur over the supporting column or pier.

Floor Framing & Connections - Raised Floor Living

Beams and girders must be adequately attached to supports, and should be tied together across supports if they are not continuous members. Beams and girders must be preservative treated if entering exterior masonry or concrete walls without a minimum 1/2 air space on top, sides and end, or if closer than 12 to exposed soil.

SFPAs allowable load tables provide maximum pounds per lineal foot (plf) and required bearing lengths for the following Southern Pine beam and girder options:

  • Solid-sawn, heavy dimension lumber or timbers (Table 12)
  • Glued-laminated timber (Table 13)

For additional information, refer to the SFPA publication, Southern Pine Headers & Beams .

Floor Joists

Floors are commonly framed with solid-sawn lumber, floor trusses, or wood I-joists. Joist end-bearing should not be less than 1-1/2 on wood or metal, or 3 on masonry. Joists are usually attached to sills by toe-nails or by metal framing anchors. Table 10  provides the typical nailing schedule for floor framing, while Figure 17  illustrates floor framing connections. Floor joists must be preservative treated if closer than 18 to exposed soil.

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