2. 10
Chapter
Floor Framing

3. 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.

4. 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.

5. 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

6. Framing Example

7. 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

8. Architectural Detail Drawings

9. 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

10. 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

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

12. 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

13. 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

14. 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

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

16. 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

17. 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

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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

24. 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

25. 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

26. 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

27. 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.

28. 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

29. 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

30. 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

31. 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

32. 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

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

34. Installed OSB Subfloor

35. 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

36. 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