8.1 Wood & Light-Gauge Steel Framing Systems

8.1 Wood & Light-Gauge Steel Framing Systems

Light structural framing constitutes the skeleton of modern residential and light commercial buildings. In West Virginia, general contractors must master the engineering principles, structural load paths, fastener schedules, and building code mandates (IRC Chapter 5, 6, and 8; IBC Chapter 22 and 23) governing both dimensional/engineered wood assemblies and cold-formed light-gauge steel framing. A thorough grasp of framing mechanics ensures structural stability under gravity, wind uplift, and seismic loads while preventing costly construction defects.

---

1. Platform Framing vs. Balloon Framing Mechanics

Wood light-frame construction historically developed along two distinct evolutionary paths: balloon framing and platform framing (western framing).

+-----------------------------------------------------------------------------+
|                   PLATFORM FRAMING vs. BALLOON FRAMING                      |
|                                                                             |
|   [PLATFORM (WESTERN) FRAMING]          [BALLOON FRAMING]                   |
|                                                                             |
|        [Roof / Rafters]                      [Roof / Rafters]               |
|             | |                                   | |                       |
|      +---------------+                     +---------------+                |
|      | Double Plate  |                     | Top Plate     |                |
|      | 2nd Story Wall|                     |               |                |
|      | Studs (8'-10')|                     | Continuous    |                |
|      +---------------+                     | Full-Height   |                |
|      | 2nd Subfloor  |                     | Studs         |                |
|      +---------------+ <--- Platform       | (Sill to Roof)|                |
|      | 2nd Fl Joists |      Break          |               |                |
|      +---------------+                     | Joists on     |                |
|      | Double Plate  |                     | 1x4 Ribbon    |                |
|      | 1st Story Wall|                     | Ledger        |                |
|      | Studs (8'-10')|                     |               |                |
|      +---------------+                     | Inherent Fire |                |
|      | 1st Subfloor  |                     | Hazard (open  |                |
|      +---------------+                     | stud bays)    |                |
|      | Mudsill / Fdn |                     +---------------+                |
|                                            | Mudsill / Fdn |                |
+-----------------------------------------------------------------------------+

• Platform Framing (Western Framing): Modern standard. The floor structure is erected first to create a level, safe working platform upon which single-story wall panels are framed and tilted into place. Subsequent stories repeat this process.
  • Key Structural Advantage: Subfloor panels and double plates naturally provide integral firestopping between floor levels, preventing vertical draft chimneys.
  • Limitation: Cumulative vertical cross-grain shrinkage across joist depths and plate thicknesses requires detailing in multi-story structures (e.g., expansion joints in brick veneers).
• Balloon Framing: Employs continuous, single-piece vertical studs running uninterrupted from the foundation mudsill all the way to the roof top plate (often 20 to 30 feet long). Intermediate floor joists rest on a continuous $1\times 4$ "ribbon" or ledger board let into the inner face of the studs.
  • Key Structural Characteristic: Minimizes vertical dimensional shrinkage, making it historically preferred for two-story masonry veneer structures.
  • Life-Safety Risk: Continuous, unobstructed hollow stud cavities act as natural flues, rapidly channeling fire from the basement to the attic. When remodeling balloon-framed structures, contractors must install solid horizontal fireblocking at every floor line.

---

2. Wood Species, Lumber Grading & Engineered Wood Products

Structural framing relies on softwood lumber graded by certified agencies accredited by the American Lumber Standard Committee (ALSC) under the National Grading Rule (NGR).

+-----------------------------------------------------------------------------+
|                      FRAMING LUMBER SPECIES & GRADES                        |
|                                                                             |
|   SPECIES GROUP           KEY PROPERTIES              TYPICAL APPLICATION   |
|   -----------------------------------------------------------------------   |
|   Southern Pine (SYP)     Highest design values for   Mudsills (PT), joists,|
|                           bending, tension, & shear;  heavily loaded beams  |
|                           readily accepts preservative                      |
|                                                                             |
|   Douglas Fir-Larch       High strength-to-weight;    Floor joists, rafters,|
|   (DF-L)                  dimensionally stable        structural headers    |
|                                                                             |
|   Spruce-Pine-Fir         Economical, lightweight,    Wall studs, light     |
|   (SPF)                   easy nailing, moderate span rafters, plates       |
|   -----------------------------------------------------------------------   |
|   LUMBER GRADE            STRUCTURAL CHARACTERISTICS                        |
|   -----------------------------------------------------------------------   |
|   Select Structural       Highest strength, minimal knots, maximum span     |
|   No. 1 / No. 1 Dense     High strength, tight grain, excellent appearance  |
|   No. 2 (Standard)        General framing standard for joists, rafters, wall|
|   No. 3 / Stud Grade      Utility grade; studs limited to bearing walls     |
+-----------------------------------------------------------------------------+

• Moisture Content Designations:
  • S-DRY (Surfaced Dry): Surfaced at a maximum moisture content of 19%.
  • KD / KD-15 (Kiln-Dried): Mechanically dried to a maximum moisture content of 15% to minimize in-service warp, checking, and shrinkage.
  • S-GRN (Surfaced Green): Surfaced with moisture content exceeding 19% (subject to significant subsequent shrinkage).

Engineered Wood Products (EWP)

Where open-concept architectural designs demand clear spans exceeding the structural capacity of solid-sawn lumber, engineered wood products provide superior dimensional stability, higher allowable design stresses, and elimination of natural defects.

+-----------------------------------------------------------------------------+
|                        ENGINEERED WOOD PRODUCT MATRIX                       |
|                                                                             |
|   [LVL] Laminated Veneer Lumber   -> Thin wood veneers glued with grain     |
|                                      parallel. Used for headers & beams.    |
|                                                                             |
|   [PSL] Parallel Strand Lumber    -> Long wood strands (300:1 aspect ratio) |
|                                      bonded under pressure. Heavy columns.  |
|                                                                             |
|   [LSL] Laminated Strand Lumber   -> Short wood flakes (100:1 aspect ratio).|
|                                      Rim boards, tall studs, light headers. |
|                                                                             |
|   [I-JOIST] Prefab Wood I-Joists  -> Solid sawn/LVL flanges + OSB web.      |
|                                      Long spans, light weight, zero crown.  |
|                                                                             |
|   [GLULAM] Glued Laminated Timber -> Dimension lumber laminations glued     |
|                                      face-to-face. Exposed heavy timbers.   |
+-----------------------------------------------------------------------------+

[!IMPORTANT] I-Joist Field Modification Rules:

• Flanges: Carry all tensile and compressive bending forces. NEVER cut, notch, bevel, rip, or drill holes into wood I-joist flanges.
• Webs: Carry shear forces. Pre-stamped knockout holes and field-drilled circular openings are permitted in the OSB web only in accordance with manufacturer span tables, maintaining minimum edge clearances from bearing supports and concentrated point loads.

---

3. Floor Framing: Mudsills, Joist Spans, Bearing & Notching

Floor framing establishes the horizontal diaphragm that transfers floor live and dead loads to the foundation walls.

+-----------------------------------------------------------------------------+
|                 FOUNDATION SILL PLATE (MUDSILL) ANCHORAGE                   |
|                                                                             |
|          +-------------------------------------------------------+          |
|          | 2x4 or 2x6 Pressure-Treated Mudsill (AWPA U1)         |          |
|          +-------------------------------------------------------+          |
|          | Closed-Cell Foam Sill Sealer Gasket (Air Barrier)     |          |
|   =======================================================================   |
|   |  Concrete or Fully Grouted Masonry Foundation Wall                  |   |
|   |                                                                     |   |
|   |        |<- 4" to 12" ->|               |<- Max 6'-0" o.c. ->|       |   |
|   |        +--+                            +--+                         |   |
|   |        |  | 1/2" Anchor Bolt           |  | 1/2" Anchor Bolt        |   |
|   |        |  | (Embedded ≥ 7")            |  | (Embedded ≥ 7")         |   |
|   |        |  |                            |  |                         |   |
|   |        +--+                            +--+                         |   |
+-----------------------------------------------------------------------------+

Mudsill / Sill Plate Statutory Requirements (IRC R403.1.6 / IBC 2308.3):

• Material: Must be preservative-treated lumber (AWPA Use Category U1) or naturally decay-resistant wood (redwood, cedar) when in direct contact with masonry or concrete.
• Sill Sealer: Continuous closed-cell polyethylene foam gasket placed between concrete and sill plate to prevent capillary moisture wicking and air infiltration.
• Anchor Bolt Size: Minimum 1/2-inch (12.7 mm) diameter steel anchor bolts (or 5/8-inch in Seismic Design Categories $D_0, D_1, D_2$).
• Embedment Depth: Minimum 7 inches (178 mm) into poured concrete or fully grouted CMU cells.
• Spacing: Maximum 6 feet on-center (o.c.) for 1- and 2-story buildings (maximum 4 feet o.c. for buildings over 2 stories).
• End Clearances: Minimum of two bolts per plate section, located between 4 inches and 12 inches from each end of each piece.
• Washers: Standard steel plate washers (minimum $0.229" \times 3" \times 3"$ in seismic zones) installed between nut and plate.

Joist Bearing and Lateral Bridging Rules:

• Bearing Length (IRC R502.6): Floor joists must have a minimum bearing length of 1.5 inches (38 mm) on wood or metal framing, and not less than 3.0 inches (76 mm) on concrete or masonry.
• Lateral Bridging / Blocking (IRC R502.7.1): Joists having a depth-to-thickness nominal ratio exceeding 6:1 (e.g., nominal $2\times 12$ lumber) must be stabilized against lateral torsional buckling by:
  • Full-depth solid blocking at all bearing supports and ends.
  • Diagonal cross-bridging ($1\times 3$ wood or steel bridging straps) or continuous $1\times 3$ bridging strips nailed to joist bottoms at intervals not exceeding 8 feet.

+-----------------------------------------------------------------------------+
|            SOLID-SAWN FLOOR JOIST NOTCHING & BORING RULES (IRC R502.8)      |
|                                                                             |
|   +---------------------------------------------------------------------+   |
|   | [End Notch]      [Top Edge Notch]                [Bored Hole]       |   |
|   | Max D/4 at       Max D/6 in Outer 1/3 Span       Max Hole Dia = D/3 |   |
|   | Bearing Only     (NO NOTCH in Middle 1/3)        Min 2" from Edges  |   |
|   |   +--+               +---+                             ( O )        |   |
|   |   |  |               |   |                             |   |        |   |
|   |===+  +===============+   +=============================+===+========|   |
|   |                                                                     |   |
|   |   <---- End 1/3 ----> <---- Middle 1/3 ----> <---- End 1/3 ---->    |   |
|   |                       [NO NOTCHING PERMITTED]                       |   |
|   +---------------------------------------------------------------------+   |
+-----------------------------------------------------------------------------+

Joist Notching and Drilling Limitations:

1. Edge Notches: Depth must not exceed one-sixth of the joist depth ($D/6$), and notches are strictly prohibited in the middle one-third ($1/3$) of the span.
2. End Notches (at bearing): Must not exceed one-fourth of the joist depth ($D/4$).
3. Bored Holes: Diameter cannot exceed one-third of the joist depth ($D/3$). The edge of any hole must be at least 2 inches (51 mm) away from the top or bottom edge of the joist and from any other hole or notch.

---

4. Wall Framing: Studs, Double Plates, Headers & Fireblocking

Load-bearing exterior and interior walls transfer roof and floor loads downward into the foundation.

+-----------------------------------------------------------------------------+
|                      CONVENTIONAL WALL FRAMING ASSEMBLY                     |
|                                                                             |
|      +---------------------------------------------------------------+      |
|      | Top Top Plate (Staggered Lap Splice ≥ 24" at Corners)         |      |
|      +---------------------------------------------------------------+      |
|      | Bottom Top Plate                                              |      |
|      +---------------------------------------------------------------+      |
|        |           |        |                               |        |      |
|        |           |        +===============================+        |      |
|        |           |        | Solid / Built-Up Wood Header  |        |      |
|        |           |        +===============================+        |      |
|        |           |        | Jack / Trimmer Stud           |        |      |
|        |           |        | (Supports Header)             |        |      |
|        | Stud      | King   |                               | King   | Stud |
|        | 16" o.c.  | Stud   |       [ROUGH OPENING]         | Stud   |      |
|        |           |        |                               |        |      |
|        |           |        |===============================|        |      |
|        |           |        | Rough Window Sill Plate       |        |      |
|        |           |        +-------------------------------+        |      |
|        |           |        | Cripple Studs (under sill)    |        |      |
|      +---------------------------------------------------------------+      |
|      | Sole Plate / Bottom Plate (Nailed to Subfloor/Sill)           |      |
+-----------------------------------------------------------------------------+

Critical Wall Framing Components & Rules:

• Double Top Plates: Required on load-bearing walls. End joints in top plates must be offset by at least 24 inches (610 mm), and plates must overlap at all corners and intersecting partition walls to structurally tie perpendicular walls together.
• Stud Spacing: Standard spacing is 16 inches o.c. (or 24 inches o.c. when permitted by prescriptive span tables or advanced framing techniques using $2\times 6$ lumber).
• Corner Posts: Traditional 3-stud solid corners or advanced "California corners" (two studs forming an L-shape with drywall backup clips) allowing full exterior insulation into the wall corner cavity.
• Opening Framing Elements:
  • Header: Spans the rough opening to transfer gravity loads around the aperture. Built using double $2\times 6$, $2\times 8$, $2\times 10$, or $2\times 12$ lumber with $1/2$-inch plywood/OSB spacers to match $3.5$-inch wall thickness, or engineered LVL.
  • King Studs: Full-height studs running from sole plate to top plate on either side of the opening, providing lateral racking resistance.
  • Jack / Trimmer Studs: Nailed to king studs directly beneath the header ends, providing positive vertical bearing support for the header.
  • Cripple Studs: Short framing members located above the header or below the rough sill maintaining continuous 16" or 24" on-center spacing for drywall and sheathing attachment.
• Fireblocking (IRC R302.11 / IBC 718.2): Installed to cut off all concealed vertical and horizontal draft openings. Must consist of nominal 2-inch lumber, 2 layers of 1-inch lumber, 23/32-inch structural panels, 1/2-inch gypsum board, or batts of mineral wool.
  • Mandatory Locations: At ceiling and floor levels; at connections between horizontal and vertical concealed spaces (soffits, drop ceilings, stair stringers); and horizontally in stud cavities at intervals not exceeding 10 feet (3048 mm).

---

5. Roof Framing: Stick Framing vs. Pre-Engineered Trusses

Roof assemblies must withstand dead weight, live maintenance loads, ground snow loads, and aerodynamic wind uplift pressures.

+-----------------------------------------------------------------------------+
|                   CONVENTIONAL STICK FRAMING ROOF SYSTEM                    |
|                                                                             |
|                                [RIDGE BOARD]                                |
|                                /\          /\                               |
|                               /  \        /  \                              |
|                              /    \======/    \  <-- Collar Ties in         |
|                             /      \    /      \     Upper 1/3 of Span      |
|                            /        \  /        \    (Resist Wind Uplift)   |
|             Common        /          \/          \                          |
|             Rafters      /                        \                         |
|                         /                          \                        |
|                        /============================\ <--- Ceiling Joists   |
|                      +/                              \+    in Lower 1/3     |
|                      || [Exterior Wall] [Exterior Wall]||  (Tie Walls)      |
+-----------------------------------------------------------------------------+

A. Conventional Stick Framing Elements:

• Ridge Board vs. Ridge Beam:
  • Ridge Board: Non-structural junction board. Used when opposing rafters are tied at their lower ends by ceiling joists. Must have a depth equal to or greater than the cut end of the rafters.
  • Ridge Beam: Structural, load-bearing beam supported by structural posts at gable ends. Required when ceiling joists are omitted (vaulted/cathedral ceilings).
• Collar Ties (IRC R802.4.6): Installed in the upper third ($1/3$) of the rafter span (minimum $1\times 4$ lumber spaced max 4 feet o.c.) to prevent ridge separation caused by wind uplift.
• Ceiling Joists / Rafter Ties (IRC R802.5.2): Installed in the lower third ($1/3$) of the roof triangle to prevent opposing rafters from pushing exterior load-bearing walls outward under vertical roof loads.

B. Pre-Engineered Metal-Plate-Connected Wood Trusses:

Pre-engineered trusses utilize triangulated webs, top chords (compression), and bottom chords (tension) joined by pressed galvanized steel gang-nail plates.

+-----------------------------------------------------------------------------+
|                        PRE-ENGINEERED WOOD ROOF TRUSS                       |
|                                                                             |
|                                     /\                                      |
|                                    /  \  <--- Top Chord (Compression)       |
|                        Web        / /\ \                                    |
|                        Members   / /  \ \   Gang-Nail Steel Connector       |
|                                 / /____\ \  Plates at all Joint Nodes       |
|                                / /\    /\ \                                 |
|                               /_/__\__/__\_\                                |
|                        [Heel] ============== [Heel]                         |
|                                 ^                                           |
|                                 +--- Bottom Chord (Tension)                 |
+-----------------------------------------------------------------------------+

[!WARNING] Strict Truss Safety Mandates (WTCA / BCSI / TPI 1):

1. ZERO Alterations: Truss members are precision-engineered structural elements. Contractors must NEVER cut, notch, drill, splice, or alter any truss chord or web member in the field for any reason (e.g., plumbing pipes, attic stairs, HVAC ducts) without a sealed, stamped engineering repair document from a registered Professional Engineer.
2. Bracing: Trusses must be temporarily stabilized during erection and permanently braced with Continuous Lateral Restraints (CLR) and diagonal x-bracing per the manufacturer's BCSI design drawings to prevent buckling.

---

6. Light-Gauge Cold-Formed Steel (CFS) Framing

Cold-formed steel (CFS) framing provides a non-combustible, dimensionally stable alternative to wood framing in commercial and multi-family structures.

+-----------------------------------------------------------------------------+
|                       COLD-FORMED STEEL C-SHAPE STUD                        |
|                                                                             |
|            Flange                                                           |
|          +-------+                                                          |
|     Lip  |       |                                                          |
|     +----+       |                                                          |
|                  |                                                          |
|                  |  Web Depth (e.g., 3-5/8", 6", 8")                        |
|                  |  - Features pre-punched web punchouts for MEP lines      |
|     +----+       |                                                          |
|     Lip  |       |                                                          |
|          +-------+                                                          |
|            Flange (Stiffened with returned lip)                             |
+-----------------------------------------------------------------------------+

Structural Profiles & Designations:

• C-Shape Studs / Joists (S): Feature a web, flanges, and return stiffening lips. Used for vertical load-bearing studs, floor joists, and roof rafters.
• U-Shape Tracks (T): Unstiffened channels used as top and bottom wall runner tracks and rim joists.

Gauge vs. Mil Thickness System:

In cold-formed steel, gauge numbering has an inverse relationship with thickness (higher gauge = thinner steel). Modern construction specifies steel by mil thickness (1 mil = 0.001 inch):

CFS Fasteners, MEP Bushings & Thermal Bridging:

• Fasteners: Self-drilling, self-tapping screws (minimum #8 or #10 framing screws with wafer or hex-washer heads). Screws must extend through steel joints with at least 3 exposed threads protruding.
• MEP Protection: Plastic or nylon snap-in grommets / bushings must be installed in all pre-punched web knockouts prior to pulling copper pipes or electrical cabling. This eliminates sharp-edge chafing of wire insulation and prevents galvanic corrosion between copper piping and galvanized zinc-coated steel studs.
• Thermal Bridging Mitigation: Because steel possesses high thermal conductivity (conducting heat over 400 times faster than wood), exterior steel-framed walls require continuous exterior rigid foam insulation ($R\text{-}5\text{ to }R\text{-}10+$) to prevent thermal bridging and ghosting condensation on interior drywall.