NDS Supplement Tables 1A–6B: The Comprehensive Practical Guide for Wood Design

The NDS Supplement is the “engine room” of wood design. To use it correctly, an engineer must distinguish between reference and adjusted values:

Reference design values (F_b, F_v, E, etc.): The raw numbers found in these tables.
Adjusted design values (F′b, F′v, E′, etc.): The capacities used in your calculations after applying adjustment factors (C_D, C_M, C_L, C_F, etc.) from the NDS Specification.

1. Geometry & Section Properties (Series 1)

All structural formulas (f_b = M/S, Δ = 5wL⁴/(384EI)) must use actual (dressed) dimensions. Using nominal dimensions will produce significant unconservative errors.

Table 1A & 1B — Sawn Lumber (S4S)

1A (sizes): Defines the transition from nominal (e.g., 2×4) to minimum dressed (e.g., 1.5 in. × 3.5 in.).
1B (properties): Provides area (A), moment of inertia (I), and section modulus (S).
Practical tip: Use S for bending stress and I for deflection (e.g., L/240, L/360).

Table 1C & 1D — Glued Laminated Timber (Glulam)

1C (Western species): Covers Douglas Fir, Hem-Fir, and Western woods.
1D (Southern Pine): Southern Pine glulams use different standard widths (e.g., 3 in., 5 in.) and lamination thicknesses (1.375 in.) compared to Western species (1.5 in.). Always verify dimensions in 1D before detailing steel hangers.

2. Sawn Lumber Design Values (Series 4)

This series provides the reference strength values for standard framing.

Tables 4A & 4B — Dimension Lumber (2 in.–4 in. Thick)

4A (general species): All species except Southern Pine. You must apply the size factor (C_F) per the adjustment-factor provisions at the start of NDS Chapter 4.
4B (Southern Pine): C_F is already incorporated into these tabulated values. Do not apply it again.
Bearing (F_c⊥): Compression perpendicular to grain is critical for joist/beam seats. F_c⊥ is not adjusted by the load duration factor (C_D).

Table 4C — Mechanically Graded Lumber (MSR & MEL)

MSR (Machine Stress Rated): Non-destructively tested for stiffness (E).
MEL (Machine Evaluated Lumber): Evaluated using X-ray/density methods to ensure consistent quality.
Advantage: Lower variability (COV) than visual grades—common for engineered wood trusses.

Tables 4D, 4E, 4F & 4G — Timbers, Decking, and Imports

4D (timbers 5 in. × 5 in. and larger): Distinguishes beams & stringers (B&S) (graded for bending on the narrow face) from posts & timbers (P&T) (graded for axial loads).
4E (decking): Evaluated specifically for flat-wise bending.
4F & 4G (imported/multi-species): Used for non–North American species or regional groupings.

Footnote sensitivity: In Series 4, E (stiffness) and F_b (bending) often follow different size rules or footnotes in the same row. Always read the table heading and footnotes for the specific row you select.

3. Glued Laminated Timber (Series 5)

Glulams are engineered for specific stress orientations. Using reference values from the wrong table for the governing behavior can be substantially unconservative or wasteful depending on which stress governs.

Official titles and purpose (NDS Supplement, 2024)

The Supplement splits softwood glulam into two parallel tables by primary load path:

Table	Official scope (paraphrased from Supplement headings)
Table 5A	Reference design values for structural glued laminated softwood timber — members stressed primarily in bending.
Table 5B	Reference design values for structural glued laminated softwood timber — members stressed primarily in axial tension or compression.

Table 5A (bending): Use for beams, girders, headers, joists, rafters, and similar members where strong-axis bending dominates (loads generally perpendicular to the wide faces of the laminations). Identification often includes stress classes and “F” (flexure) notation (e.g., 24F-V4, 24F-E15, 30F-E2). Many layups are unbalanced (higher-grade laminations in the tension zone) to optimize bending capacity. Tabulated values emphasize F_b, F_v, and E; tension- and compression-zone bending values apply per the Supplement layout and footnotes.
Table 5B (axial): Use for columns, posts, truss chords, tension ties, and other members where axial tension or compression parallel to grain dominates. Identification uses combination and grade labels (e.g., combination symbols with grades such as L3, L2 — often noted by species such as DF, SP). Layups are typically more uniform through the depth (balanced or axial-oriented) because axial stresses distribute across the section. Tabulated values emphasize F_c and F_t; F_v, F_b (e.g., for incidental bending), and E are also provided where applicable.

Lamination layout (conceptual): Bending-optimized layups are often unbalanced; axial-oriented layups are typically balanced / symmetric for uniform axial performance. The Supplement also references expanded bending tables and adjustment tables tied to 5A/5B — always read the headings and footnotes for the exact row you select.

StructSuite use (which table when)

Member / workflow	Supplement table for glulam reference values
Roof beam, floor beam, header, girder, joist, rafter, or other primarily flexural member	Table 5A (softwood; hardwood analog: Table 5C where applicable)
Column, post, truss chord, tension tie, or other primarily axial member	Table 5B (softwood; hardwood analog: Table 5D where applicable)

StructSuite selects Table 5A stress classes for beam / joist / wood-beam glulam workflows and Table 5B combination rows for wood-column glulam workflows so the reference F_b, F_c, E, etc., align with the governing Supplement table. Wet-service and other adjustment factors for glulam still follow the Supplement’s adjustment provisions (including tables cross-referenced from 5A/5B), not the species/grade picker label alone.

Important caveats

Some combinations appear in more than one context in manufacturer literature; the Supplement’s split (5A vs. 5B) is the primary guardrail for which reference set applies to bending-dominated vs. axial-dominated design.
Combined stress: Even for a primarily bending member, check combined bending and axial interaction when axial load is present (NDS Section 3.9). Conversely, a column with non-negligible moment may require interaction checks while axial reference values still come from the axial table when axial behavior governs reference selection.
Authority: Confirm producer-specific layup sheets and ESR/manufacturer data when they differ from generic Supplement tabulated values.

Tables 5C & 5D — Hardwood

5C / 5D are the hardwood counterparts to 5A / 5B; the same bending vs. axial distinction applies.

4. Round Timber (Series 6)

Tables 6A & 6B — Piles and Poles

6A (treated piles): Graded per ASTM D25. Values assume wet service (C_M) because piles are typically driven into soil or water.
6B (construction poles): Graded per ASTM D3200. Used for cantilevered pole barns and utility structures resisting lateral wind or seismic loads.

5. Engineer’s Quick-Reference Selector Table

Member Category	Table	Primary Check	Engineering “gotcha”
Standard joists (DF/SPF)	4A	F_b, F_v, E, F_c⊥	Must apply size factor (C_F).
Southern Pine framing	4B	F_b, F_v, E, F_c⊥	C_F is already included—skip it.
Truss chords (MSR/MEL)	4C	F_b, E	Higher reliability; lower variance.
Heavy timbers (5 in. × 5 in.+)	4D	Posts/girders	Check E vs F_b footnotes carefully.
Glulam beams	5A / 5C	Bending (F_bx)	Apply volume factor (C_V) for F_b.
Glulam columns	5B / 5D	Axial (F_c, F_t)	Uniform layup; suited to compression/tension.
Foundation piles	6A	Axial capacity	Design assumes wet service conditions.

Final Workflow Summary

Define geometry (Series 1): Use actual sizes for all stress and deflection checks.
Select reference values (Series 4–6): Match species, grade, and member size to the correct table.
Check footnotes: They often hold critical modifiers for specific species or sizes that are not repeated in the main NDS chapters.
Convert to adjusted values: Apply your adjustment factors (C_D, C_M, C_L, etc.) to reference values before comparing demands to capacities (f ≤ F′).