15.1 Wood Framing & Carpentry: Lumber, Engineered Wood, Anchorage & Shear Walls

Wood Framing Systems & Engineered Lumber Technology

Light-frame wood construction remains the dominant structural system for residential and low-rise commercial structures throughout Nevada. Modern building codes require strict adherence to material grading, moisture limitations, engineered wood standards, and seismic load paths governed by the International Building Code (IBC) and the American Wood Council (AWC) National Design Specification (NDS) for Wood Construction.

Platform Framing vs. Historical Balloon Framing

                      PLATFORM VS. BALLOON FRAMING

    PLATFORM FRAMING (MODERN)               BALLOON FRAMING (HISTORICAL)
  ┌───────────────────────────┐           ┌───────────────────────────┐
  │ 2nd Story Wall Studs      │           │ Continuous Studs run from │
  ├───────────────────────────┤           │ Mudsill to Roof Rafters   │
  │ Double Top Plate          │           │                           │
  ├───────────────────────────┤           │ Floor Joists rest on      │
  │ 2nd Floor Joists / Subdeck│           │ 1x4 Ribbon Boards let     │
  ├───────────────────────────┤           │ into continuous studs     │
  │ Double Top Plate          │           │                           │
  ├───────────────────────────┤           │ SEVERE FIRE HAZARD: Open  │
  │ 1st Story Wall Studs      │           │ wall cavities act as      │
  ├───────────────────────────┤           │ chimneys; requires retro- │
  │ Sole Plate / Subfloor Deck│           │ fitted solid fireblocking │
  └───────────────────────────┘           └───────────────────────────┘

• Modern Platform Framing: Each story is erected as an independent structural "platform." First-floor walls support the second-floor joist and subfloor system, which in turn becomes the platform on which second-story walls are framed. Key Advantages: Wall studs are short (standard 8 to 10 feet), easier to handle, and the subfloor platform serves as an inherent firestop between floor levels.
• Balloon Framing: Historical system where wall studs extend continuously from the foundation mudsill up to the roof rafters, with upper floor joists carried on 1x4 ribbons "let into" the studs. Still allowed, but rare. The code requires fireblocking at each floor and ceiling level (IBC 718.2; IRC R602.8) because uninterrupted stud cavities act as chimneys during a fire and spread flame and smoke to upper floors.

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Lumber Species, Grading & Moisture Content Standards

• Lumber Species Groups:
  • Douglas Fir-Larch (DF-L): High bending strength ($F_b$), modulus of elasticity ($E$), and horizontal shear resistance ($F_v$). The premier species for structural posts, beams, headers, and joists.
  • Hem-Fir (HF): Moderate strength and stiffness; widely used for interior wall studs and light floor joists.
  • Southern Pine (SP): High density, fast-growing; heavily used for pressure-treated mudsills and outdoor structural framing.
• Lumber Grades: Visual stress-grading evaluates knot sizes, slope of grain, checks, and shakes: Select Structural, No. 1, No. 2 (the primary commercial structural grade), and Stud grade (optimized for vertical compression in wall framing). High-performance timber is evaluated via Machine Stress-Rated (MSR) testing, which non-destructively measures modulus of elasticity ($E$).
• Moisture Content Limitations (S-DRY vs. S-GRN):
  • S-DRY (Surfaced Dry): Lumber surfaced at a moisture content of $19\%$ or less under the American Softwood Lumber Standard (PS 20). Commonly specified for framing that will be enclosed.
  • S-GRN (Surfaced Green): Lumber surfaced with moisture content exceeding $19\%$. As green wood dries in Nevada's arid air (indoor equilibrium moisture content can fall into the single digits), it shrinks across the grain, causing bowing, cupping, twisting, nail pops, and drywall cracking.

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Engineered Wood Products & Prefabricated Trusses

Engineered wood composites utilize wood strands, veneers, or laminations bonded with moisture-resistant adhesives to produce structural members that eliminate natural defects (knots, grain slope) and achieve high load capacities over long spans:

                     ENGINEERED WOOD STRUCTURAL BEAMS

  1. GLULAM (Glued Laminated Timber):   Dimension lumber laminations bonded
     ┌───────────────────────────────┐  under pressure; high architectural
     │===============================│  finish; long spans for churches,
     │===============================│  auditoriums, and commercial headers.
     └───────────────────────────────┘

  2. LVL (Laminated Veneer Lumber):     Wood veneers oriented parallel to grain;
     ┌───────────────────────────────┐  high flexural bending strength ($F_b$);
     │═══════════════════════════════│  primary commercial header and floor
     │═══════════════════════════════│  girder beam material.
     └───────────────────────────────┘

  3. WOOD I-JOISTS:                     LVL or solid sawn top/bottom flanges
     ┌───────────────────────────────┐  with structural OSB/Plywood web.
     └───┐                       ┌───┘  Lightweight; spans up to 30 feet.
         │   OSB Web Plate       │      CRITICAL: Web holes must follow
     ┌───┘                       └───┐  strict charts; NEVER cut flanges!
     └───────────────────────────────┘

• Glued Laminated Timber (Glulam): Individual laminations of nominal 2-inch dimension lumber bonded together with waterproof adhesives, with highest-grade laminations positioned at the outer tension and compression zones. Used for long spans, curved arches, and heavy structural posts.
• Laminated Veneer Lumber (LVL): Layered wood veneers ($1/8\text{-inch}$ thick) coated with phenolic adhesive and consolidated under heat with the grain oriented parallel to the member length. Delivers high bending strength ($F_b$ up to $2,800$–$3,100\ \text{psi}$) and stiffness, replacing steel beams for large window/door headers and floor girders.
• Parallel Strand Lumber (PSL) & Oriented Strand Lumber (OSL): Long parallel wood strands pressed into structural billets; ideal for heavily loaded interior columns and beam lines.
• Wood I-Joists: Flanges carry flexural tension and compression, while the structural panel web carries vertical shear. Critical Jobsite Rule: Hole cutting in webs must strictly follow manufacturer engineering tables (holes must be centered in the web and kept away from end supports); flanges must never be cut, notched, or drilled under any circumstances.
• Prefabricated Light-Frame Wood Trusses: Engineered triangular assemblies joined by metal connector plates (toothed gang-nail plates pressed hydraulically into lumber). Erection Safety & Stability (BCSI guidelines): Metal plate connected wood trusses are highly unstable laterally until braced. Contractors must install continuous temporary erection bracing during crane hoisting and permanent lateral and diagonal bracing per the truss design drawings. Trusses can never be cut, field-notched, or drilled without an engineered repair letter sealed by a licensed structural engineer.

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Floor, Wall & Lateral Shear Wall Assemblies

1. Foundation Anchorage & Floor Framing

                    FOUNDATION SILL PLATE ANCHORAGE
  ┌────────────────────────────────────────────────────────┐
  │  2x4 / 2x6 Pressure-Treated Mudsill (Treated Lumber)   │
  ├────────────────────────────────────────────────────────┤
  │  Closed-Cell Foam Sill Gasket (Capillary / Air Break)  │
  ├────────────────────────────────────────────────────────┤
  │                                                        │
  │   ▲                    ● Heavy Steel Plate Washer      │
  │   │                    │ (min 3"x3"x0.229" in seismic) │
  │   │                    │                               │
  │   │ 7" Embedment       ▼                               │
  │   │ Minimum        ════╪══════════════════════════════ │
  │   │ into Concrete  │   │ 1/2" Anchor Bolt              │
  │   │                │   │ Max 6' o.c. spacing           │
  │   ▼                │   │ ≤ 12" from each plate end     │
  │                    │   │ Min 2 bolts per piece         │
  │                    └───┘                               │
  │  Concrete Stem Wall or Monolithic Slab Edge            │
  └────────────────────────────────────────────────────────┘

• Mudsill / Sill Plate Standards: The wood plate in contact with concrete must be preservative-treated lumber (pressure-treated Southern Pine or Hem-Fir with alkaline copper quaternary [ACQ] or copper azole [CA]) or naturally durable redwood/cedar. A foam sill sealer is commonly installed as a capillary break and air seal; the IECC requires the junction of the foundation and sill plate to be air sealed.
• Anchor Bolt Specifications (IBC 2018 § 2308.3.1; IRC R403.1.6):
  • Minimum bolt diameter: $1/2\ \text{inch}$. Along braced wall lines in Seismic Design Category E, the IBC requires $5/8\ \text{inch}$;
  • Minimum embedment into concrete or masonry: $7\ \text{inches}$;
  • Location: in the middle third of the plate width;
  • Maximum spacing: $6\ \text{feet}$ on center. Sill plates of braced wall lines in structures over two stories above grade are limited to $4\ \text{feet}$ on center;
  • End distance: one bolt not more than $12\ \text{inches}$ and not less than $4\ \text{inches}$ from each end of each piece under the IBC. The IRC uses not less than seven bolt diameters;
  • Minimum bolts: at least two per plate piece;
  • Plate washers: at least $0.229 \times 3 \times 3\ \text{inches}$ along braced wall lines in Seismic Design Categories D and E, to keep the nut from splitting the sill.
• Floor Joist Framing & Bridging: Joists must bear at least $1.5\ \text{inches}$ on wood or $3\ \text{inches}$ on masonry/concrete. Joists need full-depth blocking at their ends. Joists deeper than nominal $2 \times 12$ also need solid blocking, diagonal bridging, or a continuous $1 \times 3$ strip at intervals of no more than 8 feet (IRC R502.7.1) to keep them from rolling.

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2. Wall Framing & Rough Opening Layout

• Stud Spacing: Wall studs are spaced at $16\ \text{inches}$ or $24\ \text{inches}$ on center.
• Double Top Plate: Top plates must be doubled. End joints in the upper and lower top plates must be offset at least $24\ \text{inches}$ (IRC R602.3.2) to keep the plates continuous around the building. A single top plate is allowed only under the IRC's alternate conditions, with joints tied by a 3-inch by 6-inch galvanized steel plate 0.036 inch thick.
• Rough Opening Components:
  • Structural Header: Sized to carry gravity floor and roof loads across the opening.
  • King Studs: Full-length continuous studs running from sole plate to top plate flanking the rough opening.
  • Jack Studs (Trimmers): Cut short to fit under the header; transfer vertical gravity loads from the header directly down to the sole plate.
  • Cripple Studs: Short vertical framing members below window sills and above headers that keep the stud layout for sheathing and drywall attachment.

                         ROUGH OPENING FRAMING
       ┌──────────────────────────────────────────────────────┐
       │ Double Top Plate                                     │
       ├──────────┬────────────────────────────────┬──────────┤
       │          │   Cripple Studs                │          │
       │          ├────────────────────────────────┤          │
       │          │ Structural Header              │          │
       │ King     ├───────┬────────────────┬───────┤ King     │
       │ Stud     │ Jack  │                │ Jack  │ Stud     │
       │ (Full    │ Stud  │ Window / Door  │ Stud  │ (Full    │
       │ Height)  │       │ Rough Opening  │       │ Height)  │
       │          │       │                │       │          │
       │          │       ├────────────────┤       │          │
       │          │       │ Rough Sill     │       │          │
       │          │       ├────────────────┤       │          │
       │          │       │ Cripples       │       │          │
       ├──────────┴───────┴────────────────┴───────┴──────────┤
       │ Bottom Sole Plate                                    │
       └──────────────────────────────────────────────────────┘

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3. Lateral Force-Resisting Systems: Wood Shear Walls

In Nevada, high winds and seismic activity generate intense horizontal shear loads. Light-frame wood buildings resist these lateral forces using engineered shear walls:

• Structural Sheathing: Wood structural panels (OSB or plywood) rated Exposure 1 or Exterior, in the thickness shown on the shear wall schedule (commonly $3/8$ to $15/32\ \text{inch}$ or thicker).
• Fastening Schedules: Shear capacity is governed strictly by the nail spacing. Standard edge nailing is specified at 6", 4", 3", or 2" on center, with field (intermediate) nailing at 12" on center. Shear-wall capacity tables assume the nail specified, usually common nails (8d common: $0.131\text{-inch}$ shank). An 8d box nail has a thinner $0.113\text{-inch}$ shank and lower capacity, so substituting box or smaller gun nails needs the designer's approval. Do not overdrive nails, because a crushed panel face lowers capacity.
• Hold-Downs: Lateral force at the top of a shear wall tries to overturn it. Hold-down devices fasten to the end posts and anchor into the foundation with embedded threaded rods, resisting the uplift (tension) at the end of the wall. Install the exact hold-down, post size, and anchor shown on the plans.

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4. Notching & Boring Limits (IRC)

Plumbers and electricians cut framing, but the general contractor answers for the structure. Know the prescriptive limits:

• The edge of a bored stud hole must be at least $5/8\ \text{inch}$ from the stud face.
• A joist notched on the top or bottom may not have a bored hole within 2 inches of the notch.
• Engineered I-joists, LVL, glulam, and trusses do not use these tables. Follow the manufacturer's hole chart, or get an engineer's repair detail.

Worked example: A $2 \times 4$ bearing-wall stud is actually $3\text{-}1/2$ inches wide. Its maximum notch is $0.25 \times 3.5 = 0.875$ inch (7/8 inch), and its maximum bored hole is $0.40 \times 3.5 = 1.4$ inches. A plumber's 2-inch hole through a single bearing stud is too large and must be fixed. Use a doubled stud (60% gives 2.1 inches) or a code-approved stud shoe.

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5. Field Quality Checks for the Framing Inspection

• Headers and beams match the plan sizes, with the correct number of jack studs under each end.
• Hold-downs, straps, and hurricane ties are installed with every nail or screw the manufacturer specifies.
• Shear-wall edge nailing matches the schedule, and panel edges land on framing or blocking.
• Treated lumber touching concrete or masonry is in place, and fasteners in treated lumber are hot-dip galvanized or stainless steel as the code requires.
• Fireblocking and draftstopping are in place before insulation and drywall cover them.