10 Chapter Floor Framing

Objectives Explain the difference between platform, balloon, and post-and-beam framing. Identify the main parts of a platform frame. Calculate the load on girders and beams used in residential construction. Lay out and install sills on a foundation wall.

Objectives (Cont.) Describe how layouts are made on a header joist. Explain the correct procedure to follow when correcting problems with floor frames. Identify the parts of a floor truss. Describe materials used for subflooring. Estimate materials (sizes and amounts) required to construct a specific floor frame.

Types of Framing Three types used in residential construction Platform framing, or western framing, is popular Balloon framing is no longer used in new construction Post-and-beam framing, also called plank-and-beam framing, uses heavy structural members

Framing Example

Platform Framing First floor built on top of foundation wall as platform Wall sections are one story high First-floor platform rests on sill or underpinning

Architectural Detail Drawings

Balloon Framing Studs are continuous from sill to rafter plate Second floor joists rest on ribbon set into studs Shrinkage is reduced because amount of cross-sectional lumber is low

Girders and Beams Joists are horizontal members of floor frame Girders, also called beams, support joists at midpoint Built-up girders can be made of pieces of 2″ lumber nailed together

Steel Beams May be used instead of wood girders Vary in depth, width of flange, and weight Size needed depends on load

Posts and Columns Steel posts are popular for girder and beam support Adequate footings must be provided for girder posts and columns Post anchors used to securely hold wood posts

Pro Tip Be sure tops of posts and columns and pockets in foundation walls are flat This ensures girder or beam is well supported with its sides plumb

Framing over Girders and Beams Joists are supported on top of steel beam Top of beam is set flush with top of wall Ledgers and hangers or stirrups may be used

Sill Construction Sill plate (mudsill) rests on foundation Supports building frame Sill location depends on building’s exterior covering Sill sealer typically used

Code Note IRC requires anchor bolts be Embedded at least 7″ into concrete foundation Minimum diameter of 1/2″ Spaced no further than 6′ O.C. Anchor bolt required within 12″ of end of sill Each board in sill must contain at least two anchor bolts

Termite Shields Wood sill should be at least 8″ above ground Protective metal shield should extend out over foundation wall Chemically-treated lumber may be used for framing Soil around and under structure can be treated

Installing Sills Two sill anchor types Anchor straps Anchor bolts Each section is laid out and holes bored Sills are positioned over bolts to check for accuracy

Joists Carry weight of floor between sills and girders I-joists Nominal 2″ lumber placed on edge Open-web truss joists Steel bar joists and reinforced concrete joists Building codes usually specify allowed deflection of joists

Laying Out Joists Floor joists can be laid out on sill or band joists Sills and band joists may need to be set back from edge Joists are doubled where extra loads must be supported and around openings

I-Joists Engineered joists with flanges made from Douglas fir in solid lumber or LVL Have web glued into grooves cut in flanges Often attached to joist headers and girders with steel hangers Weyerhaeuser

Nailing I-Joists I-joists have specific requirements for nailing Nail joists at bearing points with two 8d nails Nail rim joist 1 3/4″ or thinner to wood I-beam Attach 2 × 4 or wider “squash” plates to flanges

Rim Boards Framing members between sill and bottom of wall framing Engineered rim boards designed for use with I-joists May be made with LVL, LSL, or OSB

Safety Note Never allow workers to walk on joists until braced Do not stack building materials on unsheathed joists Install and nail all blocking, hangers, and rim boards at ends of joists Keep flanges straight with tolerance of no more than 1/2″ of true alignment

Thinking Green I-joists use 50% less wood than sawn 2 × joists LVL, used for girders and rim boards, also conserves wood LSL can be made from small-diameter trees, conserving resources Engineered wood products come in any length This reduces waste at construction sites

Framing Openings Trimmers are full-length joists or studs that reinforce rough openings Length of headers can be found from layout on band joist Metal joist hangers are used to assemble headers, trimmers, and tail joists

Bridging Keeps joists in vertical position and transfers load to next joist Herringbone, or cross Solid, or blocking After bridging installed, frame is ready to receive subflooring Timber Engineering Co.

Special Framing Problems Buildings may include section of floor that overhangs lower floor If joists are parallel to supporting wall, use cantilevered joists Smaller, doubled joists are used when concrete base is needed

Cutting Openings in Wood Floor Joists Cut holes at or close to vertical middle of joist Hole limited to 1/3 of total joist width has little effect on joist’s strength Hole is more likely to reduce strength of joist if near center of span

Cutting Holes in I-Joists Most I-joists have perforated knockouts Special rules apply for cutting through I-joists Leave 1/8″ of web on top and bottom of hole Do not cut flanges Cut holes through cantilever no more than 1 1/2″ in diameter Provide at least 1 1/2″ between hole and bearing surface

Open-Web Floor Trusses Made of lumber chords and galvanized steel webbing Factory-built to specs for their intended use Provide wide nailing surface because chord is laid flat

Subfloors Final step in completing floor frame Serve three purposes Add rigidity to structure Provide base for finish flooring Furnish work surface for additional framing Made from panel materials: OSB and plywood

OSB Installed with long edges perpendicular to joists Joints staggered in successive courses Construction adhesive applied to joists Subfloor fastened with screws or nails

Installed OSB Subfloor

Plywood Subflooring Applied much like OSB May have tongue-and-groove edges Available in panels for joist spacing of 16″, 20″, 24″, or 48″ Has maximum support spacing stamped on each panel

Estimating Materials Check plans and determine lengths of floor joists needed Allow sufficient length for full bearing on girders and partitions Numbers of joist headers will be lengths of foundation sections For subflooring, multiply length by width and subtract major areas not to be covered