Chapter 10 Floor Framing Objectives Explain the difference

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

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. • Estimaterials (sizes and amounts) required to construct a specific floor frame. Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

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

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

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

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

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

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

Steel Beams • May be used instead of wood girders • Vary in depth, width of flange, and weight • Size needed depends on load Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

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

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

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

Sill Construction • Sill plate (mudsill) rests on foundation • Supports building frame • Sill location depends on building’s exterior covering • Sill sealer typically used Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

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

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

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

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

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

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

Nailing I-Joists • I-joists have specific requirements for nailing • Nail joists at bearing points with two 8 d nails • Nail rim joist 1 3/4″ or thinner to wood I-beam • Attach 2 × 4 or wider “squash” plates to flanges Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

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

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

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

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

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

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

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

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

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

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

OSB • Installed with long edges perpendicular to joists • Joints staggered in successive courses • Construction adhesive applied to joists • Subfloor fastened with screws or nails Copyright Goodheart-Willcox Co. , Inc. May not be posted to a publicly accessible website.

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

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

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