Wood-framed construction is the most common structural system in residential and light commercial buildings in the United States. The National Design Specification for Wood Construction (NDS), published by the American Wood Council, is the reference standard for engineered wood design. The IBC references the NDS (currently the 2018 edition in most jurisdictions, with the 2024 edition adopted in some) for the design of wood members, connections, and structural wood panels.
Structural plan reviewers check wood-framed buildings against the NDS and the IBC's wood chapter (Chapter 23). Unlike steel and concrete design where connection details often dominate the plan review comments, wood design reviews tend to generate comments about missing adjustment factors, improper member modifications (notches and holes), inadequate bearing details, and connection hardware specifications. These are the errors that come up most often.
Adjustment factors
Missing or incorrect adjustment factors
NDS Section 3.3 (bending), Section 3.4 (compression), and Section 3.10 (combined loading) require that reference design values from the NDS Supplement tables be adjusted by a series of multiplication factors before use. The adjusted design value is the product of the reference value and all applicable adjustment factors. For sawn lumber bending design, this means the reference bending stress Fb is multiplied by the load duration factor (CD), wet service factor (CM), temperature factor (Ct), beam stability factor (CL), size factor (CF), flat use factor (Cfu), incising factor (Ci), and repetitive member factor (Cr).
Plan reviewers check the structural calculations for the application of each applicable factor. The most common error is calculations that use the reference design value from the NDS Supplement without applying any adjustment factors, or calculations that apply the load duration factor but omit the size factor or the beam stability factor. The size factor (CF) is particularly important for dimension lumber deeper than 2x12 and for timbers: an 8x16 timber beam has a size factor of 0.88 for bending, reducing the adjusted bending stress by 12% compared to the tabulated value. Omitting this factor means the member is undersized by 12%.
| Factor | Symbol | Applies to | Common error |
|---|---|---|---|
| Load duration | CD | All reference values | Using CD = 1.0 for all loads instead of 0.9 for dead load only or 1.6 for wind/seismic |
| Size factor | CF | Sawn lumber > 2x12, timbers | Omitting CF for deep members; using tabulated values directly |
| Beam stability | CL | Bending members without continuous lateral support | Assuming CL = 1.0 without checking unbraced length |
| Repetitive member | Cr | Joists, rafters, studs at 24" o.c. or less | Not applying Cr = 1.15 when member qualifies as repetitive |
| Wet service | CM | Members exposed to moisture > 19% | Using dry-condition values for exterior or unconditioned spaces |
Load duration factor
The load duration factor (CD) accounts for the ability of wood to carry higher loads for shorter durations. NDS Section 2.3.2 assigns CD values based on the load type: 0.9 for dead load only, 1.0 for occupancy live load, 1.15 for snow, 1.25 for construction load, and 1.6 for wind and seismic. The CD for a load combination is the value associated with the shortest-duration load in the combination. Plan reviewers check that the calculations use the correct CD for each load combination and that the controlling combination is the one with the lowest adjusted capacity, not necessarily the one with the highest demand. A common error is applying CD = 1.6 (wind) to a gravity-only load combination that doesn't include wind, or using CD = 1.0 for a dead-load-only check where CD = 0.9 is required.
Connections
Connection hardware specifications
NDS Chapter 10 (dowel-type fasteners) and Chapter 12 (mechanical connections) cover the design of nailed, bolted, screwed, and proprietary connector connections. For conventional wood framing, the IBC and IRC prescribe minimum nailing schedules (IBC Table 2304.10.1) that cover most standard connections without engineering calculations. But for engineered wood-framed buildings, beam-to-post connections, header-to-trimmer connections, hold-down connections, and drag strut connections all require specific hardware that must be shown on the structural drawings.
Plan reviewers check the structural details for connection hardware specifications: manufacturer, model number, and installation requirements for proprietary connectors (Simpson Strong-Tie, USP, MiTek, etc.), and fastener size, quantity, and pattern for field-designed connections. The most common violation is a structural plan that shows beams bearing on posts or headers bearing on trimmers without specifying any connection hardware. The reviewer cannot verify that the connection can transfer the design loads without knowing the connector type. Another common error is specifying a connector by model number without checking that the connector's allowable load (from the manufacturer's catalog, which references NDS Chapter 10 design methodology) meets or exceeds the connection demand for the specific lumber species, member size, and load direction.
Hold-down and shear wall anchorage
Shear wall design per the Special Design Provisions for Wind and Seismic (SDPWS) requires hold-down devices at each end of each shear wall segment to resist the overturning forces. The hold-down must be specified on the structural drawings with the manufacturer, model, and allowable tension capacity. For multi-story shear walls, the cumulative overturning forces increase at each level, and the hold-down capacity must be checked at every story.
Reviewers check for hold-down specifications at each shear wall end, verify that the specified capacity meets the calculated overturning demand, and check that the anchor bolt or threaded rod connecting the hold-down to the foundation is sized for the tension load. Common violations include shear wall schedules that specify the sheathing nailing but not the hold-down hardware, hold-downs that are undersized for the cumulative overturning at lower stories, and missing specifications for the shrinkage compensating device (required for multi-story platform-framed buildings where cumulative wood shrinkage can create gaps in the continuous load path).
Member modifications
Notching and boring restrictions
NDS Section 4.3 and the IBC Section 2308.8 restrict where and how structural wood members can be notched, bored, or otherwise modified. For sawn lumber joists, notches in the outer thirds of the span are limited to one-third of the member depth, and notches are prohibited in the middle third of the span. Holes bored in joists must be at least 2 inches from the top and bottom edges and must not exceed one-third of the member depth in diameter. For engineered wood products (I-joists, LVL, glulam), the manufacturer's evaluation report specifies the allowable hole sizes and locations, which are typically more restrictive than the NDS limits for sawn lumber.
Plan reviewers check the framing plans and sections for any indicated penetrations through structural members, then verify that the penetrations comply with the notching and boring limits. The most common violation is a mechanical or plumbing drawing that shows a duct or drain pipe routing through a floor joist zone without the structural drawings addressing whether the penetration is permitted. This is a coordination issue between the structural and MEP drawings: the structural engineer needs to know where the penetrations are to verify compliance, and the MEP engineer needs to know the structural limits to route around restricted zones.
Bearing at supports
NDS Section 3.10 covers bearing perpendicular to grain, which governs the design of beams bearing on plates, posts, and headers. The bearing area must be adequate so that the compressive stress perpendicular to grain does not exceed the adjusted design value (Fc-perp multiplied by the bearing area factor Cb). The bearing area factor allows an increase in Fc-perp when the bearing length is less than 6 inches and the bearing is at least 3 inches from the member end. For a 3.5-inch bearing length (a 2x beam bearing on a 2x4 plate), Cb = 1.25, which increases the adjusted bearing capacity by 25%.
Reviewers check bearing details for concentrated loads: beams bearing on posts, headers bearing on jack studs, and beams bearing on wall plates. The most common violation is a heavily loaded header or beam bearing on a single jack stud where the bearing area (1.5 inches wide by 3.5 inches deep = 5.25 square inches) is insufficient for the reaction force. The fix is usually adding a second jack stud or a bearing block to increase the bearing area. Another common error is a point load from an upper-level post bearing directly on a floor joist below without a bearing block or post-to-beam connection detail that spreads the load.
Engineered wood products
Evaluation report references
Engineered wood products (I-joists, laminated veneer lumber, parallel strand lumber, cross-laminated timber, structural composite lumber) are proprietary products that are not covered directly by the NDS reference design value tables. Their design properties come from manufacturer-specific evaluation reports (ICC-ES ESR reports or equivalent). Structural drawings that specify engineered wood products must reference the evaluation report number so the plan reviewer can verify the design values.
The most common violation is a structural plan that specifies an LVL beam or I-joist by depth and span but does not reference a specific manufacturer or evaluation report. Different manufacturers' products of the same depth can have different allowable bending stresses, shear capacities, and stiffness values, so "1-3/4 x 11-7/8 LVL" is not a complete specification. The drawings must specify either the manufacturer and product name (e.g., "Weyerhaeuser Microllam LVL per ESR-1387") or the minimum required design properties (Fb, Fv, E, Fc-perp) so that any qualifying product can be substituted.
Catching wood design errors before submittal
Wood design plan review requires checking the structural calculations for proper adjustment factor application, verifying connection hardware specifications against the design loads, cross-referencing the framing plans with the MEP drawings for member penetrations, and confirming that engineered wood products reference the correct evaluation reports. Reviewing the NDS requirements alongside the IBC wood provisions, the SDPWS shear wall requirements, and the mechanical/plumbing drawings in a single pass catches the coordination errors that are most difficult to find when each discipline is reviewed separately.