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PublisherThe Goodheart-Willcox Co., Inc.Tinley Park, Illinois


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Chapter 13

Sill and Floor Construction


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Introduction

• Framing methods vary from one section of the country to another.

• Personal preference and experience are also factors.

• Two basic types of floor framing are:– Platform framing.– Balloon framing.


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Introduction

• Typical floor framing structural components include:– Plates.– Joists.– Studs.

• Post and beam construction is also used for walls and floors.


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Platform Framing

• In platform framing, floor joists form a platform on which the walls rest.

• Another platform rests on top of the walls when there is a second story.

• Platform framing is used more extensively than balloon framing.

• The platform automatically provides a fire-stop between floors.


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Platform Framing

• Construction is safe because work is performed on a solid surface.

• The sill is the starting point in constructing a floor.– Rests on the foundation and supports the

floor joists or the studs.– Generally 2" x 6" lumber.– Box sill construction is generally used,

which consists of a 2" x 6" plate called a mudsill.


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Platform Framing

• Box sill construction.


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Platform Framing

• Detail of the first and second floor.

• Using box sill construction.


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Sealing the Sill

• A seal is required between the foundation and sill plate.

• The seal prevents outside air from entering the house.


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Balloon Framing

• Balloon framing has diminished in importance in recent years.

• Distinguishing features include:– Wall studs rest directly on the sill plate.– Each floor “hangs” from the studs.

• Two advantages of balloon framing are:– Small potential shrinkage.– Good vertical stability.


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Balloon Framing

• Disadvantages of balloon framing are:– Less than desirable surface on which to

work during construction.– The need to add fire-stops.

• Two types of sill construction are used:– Solid (standard).– T-sill.


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Balloon Framing Sill Construction

• Solid (standard) sill.

• Studs are nailed directly to the sill and joists.

• No header is used.


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Balloon Framing Sill Construction• T-sill construction.

• Header rests on the sill and serves as a fire-stop.

• Studs rests on the sill and are nailed to the header as well as the 8" or 10" wide sill plate.


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Balloon Framing for Second Floor

• Joists are supported by a ribbon and nailed to the studs on the second floor level.


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Joists and Beams

• Joists provide support for the floor.

• Usually made from a common softwood.– Southern yellow pine, fir, larch, hemlock, or

spruce.

• Engineered wood and metal joists are also available.

• Floor joists range in size from 2" x 6" to 2" x 12".


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Joists and Beams

• Standard lumber sizes.

(National Forest Products Association)


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Joists and Beams(Joists)

• Size of joist required depends on the span, load, species and grade of wood, and joist spacing.

• When using metal joists, the gauge of metal should be considered instead of species and grade of lumber.

• Floor joists may be spaced 12", 16", or 24" on center.


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Procedure for Using Span Data Chart

• Select species of wood to be used.

• Select appropriate live load.

• Determine lumber grade to be used.

• Scan the lumber grade row and note the maximum spans.

• Select the joist size and spacing that will support the desired live load; 16" OC spacing is typical.


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Floor Joist Span Data


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Span Data Example

• Span is 14'-0" and number one dense southern pine is to be used.

• Live load is 30 pounds per square foot.

• Chart shows the following choices.– 2" x 8" joists 12" OC or 16" OC.– 2" x 10" joists 12" OC, 16" OC, or 24" OC.– 2" x 12" joists 12" OC, 16" OC, or 24" OC.

• Best selection is 2" x 8" joists, 16" OC. This will span up to 14'-5".


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Steel Floor Joists

• Steel floor joists are beginning to be accepted for residential construction.

• Joist depths ranging from 6" to 12" with thicknesses from 0.034" to 0.101" are generally used.

• Usual spacing is 24" OC, but other spacing is also used.


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Steel Framing Detail

• Typical steel framing where floor joists bear on the foundation.


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Joists and Beams(Beams)

• When the span is too great for unsupported joists, a beam or load-bearing wall is needed to reduce the span.

• A beam may be a solid timber, built-up beam, or a metal S- or W-beam.

• Load-bearing walls may be concrete block, cast concrete, or frame construction.


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Methods of Supporting Floor

Joists with Beams


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Supporting Partition Walls

• Partition walls that run parallel to the floor joists require added support.


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Openings in the Floor

• Openings in the floor for stairs and chimneys required double joist framing.


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Cross Bridging

• Cross bridging is used to stiffen the floor and spread the load over a broader area.

• Bridging boards or metal bridging are used.


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Metal Bridging


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Floor Trusses

• A truss is a rigid framework designed to support a load over a span.

• Floor trusses are often used in place of floor joists in residential construction.

• Floor trusses consist of a top chord, bottom chord, and web.

• Chords are the horizontal flanges on the top and bottom of the truss.

• The web is the truss framework.


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Floor Trusses

• Trusses provide clear spans with a minimum depth in a lightweight assembly.

(Trus Joist)


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Engineered Floor Trusses

• Engineered floor trusses are designed with the aid of computers.

• Usually fabricated from 2" x 4" or 2" x 6" lumber and generally spaced 24" OC.

• Each truss has a built-in camber.

• Stress-graded lumber is used in their construction to reduce material.

• Webs may be metal or wood.


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Typical Truss Webs

(TrusWal Systems, Inc.)


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Subfloor

• The subfloor is attached to the top of the floor joists and provides a work surface during construction.

• Plywood, tongue-and-groove boards, common boards, and other panel products are used for subfloors.– Panel products reduce installation time.– 5/8" or 1/2" thick plywood is preferred.


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Typical Panel Products

(Georgia-Pacific Corporation)


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Installing Subfloor Panels

• Joist spacing must be very accurate.

• All panel edges must be supported.


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Installing Subfloor Panels

• Plywood grain direction of the outer plies should be at right angles to joists.

• Panel products should be staggered so that end joints of adjacent panels are on different joists.

• Panels may be glued as well as nailed to the joists to increase strength and reduce squeaking and nail pops.


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Cantilevered Joists

• Cantilevered joists are required when a section of the floor projects beyond a lower level.

• When floor joists run perpendicular to the cantilevered section, longer joists form the cantilever.

• When joists are parallel to the overhanging area, cantilevered joists are required.


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Cantilevered Joists

• Generally, joists should extend inside the structure twice the distance they overhang.


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Framing Under Slate or Tile

• Flooring materials such as ceramic tile, slate, or stone floors require a substantial base.

• If a concrete base is provided, the floor framing must be lowered to provide for the concrete.

• Dead weight may be as much as 50 pounds per square foot.


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Framing Under Slate or Tile

• A smaller size joist may be used and the space between joists reduced to provide adequate support.

• Cement mortar mix is generally used for the base.


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Engineered Wood Products

• Engineered wood products (EWPs) combine wood veneers and fibers with adhesives to form beams, headers, joists, and panels.

• EWPs have uniformly high quality and strength.

• They increase the supply of usable wood from smaller and inferior trees.


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• The use of engineered wood products will continue to grow.

• Advances in adhesive technology have made EWPs possible.– Phenol-formaldehyde and urea-

formaldehyde are the most common types.– Phenolics are more expensive than urea

resins.


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• Band boards are available in 9-1/4",11-1/4", 12", 14", and 16" depths.

• Engineered headers are available in 1-1/4" depth and 3-1/2" width.

(Alpine Structures)


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• Advantages of EWPs:– High quality and consistency.– No knots, checks, or warps.– Uniformly dried to 8% to 12% moisture

content.– Provides superior design flexibility.

• Disadvantage of EWPs:– Lack of industry standards.


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• Application of EWPs.


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Oriented Strand Board

• Oriented strand board (OSB) is made from long strands of wood and resin.

• First introduced in 1978 as a low-quality particle board panel.

• Aspen is the preferred wood for making OSB.

• Outer layers are oriented to the long dimension, others are perpendicular.


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The Engineered Wood Association)


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• Advantages of OSB:– Less expensive than plywood.– Unique appearance can be appealing as a

design element.

• Disadvantages of OSB:– Subject to swelling.– Not designed for exposure to the elements.


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• OSB is made in panel sizes similar to plywood, typically 4' x 8'.

• Available in sizes up to 8' x 24'.

• Allow 1/8" space along edges to prevent buckling problems.

• Use the same nailing schedules that apply to plywood.


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Parallel Strand Lumber• Parallel strand lumber (PSL) is made

from thin strands of wood.

• Fairly new category of EWP.

• Used for beams, columns, and headers.

• High strength and span capacity.

• Low-moisture content eliminates shrinking and checking.

• Large billets 12" wide by 17" deep are formed and then sawn to specific sizes.


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Parallel Strand Lumber

(Alpine Structures)


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Parallel Strand Lumber

• Advantages of PSL:– Very strong.– Allows long spans and more design

flexibility.

• Disadvantages of PSL:– Engineered connections are required for

side-loading joists on one side.– Should not be drilled or notched.– Storage conditions should prevent swelling.


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Parallel Strand Lumber• Widths available from

1-3/4" to 7".

• Two plies of 2-11/16" members will match a typical 5-1/2" wall.

• Lengths up to 66' available.

• Eliminates the need for built-up beams.

(Alpine Structures)


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Laminated Veneer Lumber

• Laminated veneer lumber (LVL) is made from veneers stacked parallel to each other.

• LVL is used for headers, beams, joists, columns, and flanges for wood I-beams.

• Similar to plywood, but all plies are parallel to provide maximum strength.

• Southern yellow pine and Douglas fir are generally the woods of choice.


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• LVL is produced in a continuous billet up to 1-3/4" thick and 4' wide and two or more billets can be glued together to form thicker pieces.

(Trus Joist)


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• Advantages of LVL:– High strength allows long spans.– Can be built-up on site to form larger

members.

• Disadvantages of LVL:– More expensive than solid lumber.– Lower moisture content than solid lumber.– Must be sized for specific load conditions.


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• The 1-3/4" thick billet is most common.

• Can be used individually for joists or combined to form headers or beams.

• Available in depths from 5-1/2" to 14" and lengths up to 66'.

• LVL generally should not be mixed with solid lumber in the same floor assembly.

• LVL beams should not be drilled .


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Glue-Laminated Lumber• Glue-laminated members (glulam

beams) consist of 1x or 2x lumber glued into desired shapes.

• Glue-laminated beams, columns, and arches were the first engineered wood products.

• Virtually any length or depth can be produced.


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Glue-Laminated Lumber

• This construction makes extensive use of glue-laminated beams.


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• Glue-laminated beams are accepted by all three US model building codes.

• Three appearance grades are available.– Industrial grade: The least attractive

containing visible glue stains, press marks, and knot holes.

– Architectural grade: Sanded on four sides with knot holes filled with putty.

– Premium grade: All checks and holes filled.


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• Advantages of glulams:– High strength.– Available either straight or cambered.– Dimensionally stable and attractive.

• Disadvantages of glulams:– Cost is high.– Requires special handling and storage.– Requires special equipment to handle.


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• Installation– Technical support is generally required.– Producers provide span charts, installation

details, technical assistance.– Special connectors are required for these

large members and heavy loads.– Special handling is required to reduce

checking and preserve the finish.


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Wood I-Beams or Joists

• Wood I-beams or joists are generally made from 2" x 4" machined-stressed lumber or LVL.

• Webs are usually made from 3/8" OSB.

• They are available in flange widths of1-3/4" and 2-5/16" and depths from9-1/2" to 20" and lengths up to 66'.

• Presently, each manufacturer uses their own proprietary process.


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(Boise Cascade Corporation)


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• Advantages of wood I-beams:– Speed of construction.– Have knockout holes for plumbing and

electrical cable.– Dimensionally stable and very straight.

• Disadvantages of wood I-beams:– Require more effort to cut.– Not universally accepted.– More expensive than lumber or trusses.


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• Installation of wood I-beams are similar to traditional floor joists or rafters.– Typical nails, tools, and metal connectors

can be used.– Should not be mixed with solid lumber in

the same assembly.– Web stiffeners or blocks are normally used

at bearing points.


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• Several types of engineered lumber are used in this dwelling.

(Boise Cascade Corporation)


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Post and Beam Construction

• Post and beam construction provides greater freedom of design.

• The system uses larger structural sizes, framing connectors, and unique joining methods.

• Posts carry most of the weight

• The walls are usually curtain walls.

• Curtain walls provide for wide expanses of glass without the need for headers.


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(The Engineered Wood Association)


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• Curtain wall example.(Pozzi Wood Windows)


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• Foundation for a post and beam structure may be continuous or isolated footings on which each post is located.

• Posts should be at least 4" x 4" or 6" x 6" if they support the floor.

• Beams should be solid, laminated, reinforced with steel, or plywood box beams.


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• A variety of beams used in post and beam construction.


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• The spacing and span of the beams will be determined by the size and type of materials and the load to be supported.

• Generally, a span of 7'-0" may be used when 2" thick tongue-and-groove decking is applied.

• Thicker beams should be used if the span exceeds 7'-0".

• Span tables are provided in the text.


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• There are two systems of roof beam placement:– Longitudinal method: Beams are placed at

right angles to the roof slope; roof decking is laid from the ridge to the eaves.

– Transverse method: Beams follow the roof slope; decking runs parallel to the roof ridge.


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• The longitudinal method.


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• The transverse method.


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• Metal connectors.


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• Installation– Nailing does not provide a satisfactory

connection in post and beam construction; lag bolts are used.

– Metal plates or connectors are used to attach post and beam segments.

– Decking planks range in thickness from 2" to 4" and are usually tongue-and-grooved along the long edges.


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• Several plank designs used in post and beam construction.

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