2 Sill and Floor Construction Chapter18Sill and Floor Construction
3 Objectives Describe the components of a floor system. Explain the difference between platform and balloon framing.Determine proper joist sizes using a typical span data chart.Plan the appropriate floor support using joists or trusses for a structure.
4 ObjectivesSelect the appropriate engineered wood products for specific applications in residential construction.Explain the principles of post and beam construction.
5 IntroductionFraming methods vary from one section of the country to anotherTwo basic types of floor framing are platform framing and balloon framingUse plates, joists, and studsPost and beam construction is used for walls and floors
6 Platform Framing Floor joists form a platform on which walls rest Another platform rests on top of walls when there is a second storyAdvantages include:easy and fast to constructshrinkage is uniformplatform provides a fire-stop between floors
7 Platform Framing The sill is starting point in constructing a floor Lowest member of structure’s frameRests on foundation andSupports floor joists or studsGenerally 2 x 6 lumberBox sill construction generally used in platform framing
9 Platform Framing Box sill construction Detail of first and second floor
10 Balloon Framing Wall studs rest directly on the sill plate Each floor “hangs” from the studsAdvantages: small potential shrinkage, good vertical stabilityDisadvantages: less safe work surface, need to add fire-stopsTwo types of sill construction used: solid (standard) or T-sill
11 Balloon Framing Solid (standard) sill construction Studs nailed directly to sill and joistsNo header used
12 Balloon Framing T-sill construction Header rests on sill Serves as firestopStuds rest on sillNailed to header and to sill plate
13 Balloon Framing First and second floor construction Joists supported by a ribbon and nailed to studs on second floor level
14 Joists and Beams Joists provide support for floor Usually made from Southern yellow pine, fir, larch, hemlock, or spruceEngineered wood and metal joists are also availableFloor joists range in size from 2 x 6 to 2 x 12
15 JoistsSize based on span, load, species and grade of wood, and joist spacingWhen using metal joists, consider gauge of metal instead of species and grade of lumberSpaced 12", 16", or 24" on center
16 Using a Span Data Table Select species of wood to be used Select appropriate live loadDetermine lumber grade to be usedScan the lumber grade row and note maximum spansSelect joist size and spacing that will support desired live load; 16" OC spacing is typical
17 Span Data Example Span is 14'-0" Using number one dense southern pine Live load is 30 pounds per square footChart shows following choices:2 x 8 joists 12" OC or 16" OC2 x 10 joists 12" OC, 16" OC, or 24" OC2 x 12 joists 12" OC, 16" OC, or 24" OCBest selection: 2 x 8 joists, 16" OC, will span up to 14'-5"
18 Steel Floor Joists Depths typically 6" to 12" Thicknesses from 0.034" to 0.101"Common spacing 24" OC, but other spacing also used
19 BeamsWhen span is too great for unsupported joists, a beam or load-bearing wall is needed to reduce spanBeam can be solid timber, built-up, or metal S- or W-beamLoad-bearing walls may be concrete block, cast concrete, or frame construction
21 Supporting Partition Walls Partition walls that run parallel to floor joists require added support.
22 Openings in FloorOpenings in the floor for stairs and chimneys required double joist framing.
23 Cross BridgingCross bridging stiffens floor and spreads load over broader areaBridging boards or metal bridging are used
24 Green Architecture Engineered floor joists Sustainable alternative to solid wood joistsCan be made from wood chips and other wood products formerly considered wasteStronger and can span longer distances than solid wood joistsFewer joists needed to meet building codes
25 Floor TrussesFloor trusses have rigid framework designed to support a load over a spanOften used in place of floor joists in residential constructionConsist of top chord, bottom chord, and webChords are horizontal flanges on top and bottom of trussWeb is truss framework
26 Engineered Floor Trusses Designed using computersUsually fabricated from 2 x 4 or 2 x 6 lumber and spaced 24" OCHas built-in camberStress-graded lumber used in construction to reduce materialWebs may be metal or wood
27 Subfloor Subfloor affixed to top of floor joists Glued or nailed to joistsProvides surface for underlaymentMade from plywood, tongue-and-groove boards, common boards, and other panel products
28 Installing Subfloor Panels Joist spacing must be accurateAll panel edges must be supported
29 Cantilevered (Overhanging ) Joists Section of floor that projects beyond a lower level called cantilever or overhangWhen floor joists run perpendicular to cantilevered section, longer joists form cantileverWhen joists are parallel to overhanging area, cantilevered joists are required
30 Cantilevered JoistsGenerally, joists should extend inside the structure twice the distance they overhang.
31 Framing Under Slate or Tile Requires substantial baseConcrete base needs lowered floor framingUse smaller size joists, reduce space between joistsUse beams under section to support added weightUse cement mortar mix
32 Employability Respecting diversity Characteristics that vary from person to person is known as diversityBeing able to work with a diverse group is an important job skillGetting to know those who differ from us makes us less likely to subject others to generalizations or preconceived biases we may have
33 Engineered Wood Products Engineered wood products (EWPs) combine wood veneers and fibers with adhesives to form beams, headers, joists, and panelsInclude:oriented strand board (OSB)parallel strand lumber (PSL)laminated veneer lumber (LVL)glue-laminated lumberwood I-joists
34 Engineered Wood Products Advantages:high quality and consistencyno knots, checks, warpsuniformly dried to 8% to 12% moisture contentprovides superior design flexibilityDisadvantage:lack of industry standards
35 Oriented Strand Board (OSB) Made from long strands of wood and resinAspen is preferred woodAdvantages:Less expensive than plywoodUnique appearanceDisadvantages:Subject to swellingNot designed for exposure to elements
36 Oriented Strand Board (OSB) Made in panel sizes, typically 4' x 8'Available in sizes up to 8' x 24‘1/8" space along edges prevents bucklingUse same nailing schedules used on plywood
37 Parallel Strand Lumber (PSL) Made from thin strands of woodUsed for beams, columns, headersHigh strength and span capacityLow-moisture content eliminates shrinking and checkingLarge billets, 11" x 17“, formed and then sawed to specific sizes
38 Parallel Strand Lumber (PSL) Advantages:StrongLonger spans create more design flexibilityDisadvantages:Engineered connections required for side-loading multiple-ply beamShould not be drilled or notchedStored according to manufacturer’s recommendations to prevent swelling
39 Parallel Strand Lumber (PSL) Widths from 1-3/4" to 7"Two plies of 2-11/16" members match typical 5-1/2" wallLengths up to 66’Eliminates need for built-up beams
40 Laminated Veneer Lumber (LVL) Made from veneers stacked parallel to each otherUsed for headers, beams, joists, columns, and flanges for wood I-beamsAll plies parallel to provide maximum strengthWoods of choice are Southern yellow pine and Douglas fir
41 Laminated Veneer Lumber (LVL) Advantages:High strength allows long spansCan be built-up on site to form larger membersDisadvantages:More expensive than solid lumberLower moisture content than solid lumberMust be sized for specific load conditions
42 Laminated Veneer Lumber (LVL) 1-3/4“ billet most commonUse individually for joists or combined to form headers or beamsAvailable in depths from 5-1/2" to 14" and lengths up to 66‘Should not be mixed with solid lumber in the same floor assemblyBeams should not be drilled
43 Glue-Laminated Lumber Also called glulam beams1x or 2x lumber glued in stacks to desired shape and sizeVirtually any length or depth can be producedManufactured to national standardGrades available: framing, industrial, architectural, premium
45 Glue-Laminated Lumber Advantages:high strengthavailable either straight or cambereddimensionally stable and attractiveDisadvantages:expensiverequires special handling and storagerequires special equipment to handle
46 Installation of Glue-Laminated Lumber Technical support generally requiredManufacturers provide span charts, installation details, technical assistanceSpecial connectors required
47 Wood I-JoistsGenerally made from 2 x 4 machined-stressed lumber or LVLWebs usually made from 3/8" OSBAvailable in variety of flange widths, depths, lengths
48 Wood I-Joists Advantages: Disadvantages: speed of construction knockout holes for plumbing and electrical cabledimensionally stable and straightDisadvantages:require more effort to cutnot universally accepted
49 Wood I-JoistsInstallation similar to traditional floor joists or raftersShould not be mixed with solid lumber in same assemblyWeb stiffeners or blocks normally used at bearing points
50 Post and Beam Construction Post and beam construction uses posts, beams, and planks as framing membersSpaced farther apart than conventional framing membersPosts carry most weightCurtain walls allow for wide expanses of glass with no need for headersFoundation is continuous wall or series of piers on which each post is located
51 Post and Beam Construction Check local codes for post size requirementsBeam types include solid, laminated, steel-reinforced, plywood boxSpacing and span determined by size and type of materials and load to be supportedBeam placement systems include longitudinal method and transverse method
52 Post and Beam Construction Metal plates or connectors used to fasten posts and beamsPost and beam segments fastened with lag screws or boltsThickness of decking planks for roof and floor vary from 2" to 4“Roof decking span information listed in textbook