Chapter 10 Floor Framing Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly...

Chapter10Floor Framing

Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly accessible website.

• 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


• 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.

Objectives (Cont.)


• 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

Types of Framing


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


• 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

Pro Tip


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


• 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

Code Note


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


• 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

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


• 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

Safety Note


• 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

Thinking Green


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


• 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

Cutting Holes in I-Joists


• 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

Open-Web Floor Trusses


• 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

Subfloors


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


• 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

Plywood Subflooring


• 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

Estimating Materials

Chapter 10 Floor Framing Copyright Goodheart-Willcox Co., Inc. May not be posted to a publicly...

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