Wood Design with the NDS Supplement: A Practical Guide to Tables 1A–6B

If you are early in your structural career and wood is new to you, the NDS Supplement can look intimidating — dozens of tables, cryptic footnotes, symbols like F_b and E_min. This guide walks you through it the way a senior engineer would explain it at your desk: what each table is for, when you reach for it, and the few habits that keep you out of trouble.

NDS Supplement 2024 · © American Wood Council

Two documents work together:

• The NDS Specification — the rulebook. It contains the equations and the adjustment factors.
• The NDS Supplement (full name: Design Values for Wood Construction) — the data. It contains the tabulated numbers: sizes, section properties, and reference design values.

This guide is about the Supplement — the data. By the end you will be able to open it, find the right row, and know what to do with the number you read.

Start here: the mental model

Almost every wood calculation answers three questions, in order. If you keep them separate, the Supplement stops being a maze.

1. How big is the member? → its geometry: area A, section modulus S, moment of inertia I.
2. How strong is the wood? → its reference design values: bending F_b, shear F_v, compression F_c, tension F_t, bearing F_c⊥, stiffness E and E_min.
3. Does it work? → combine the two with NDS equations and compare the demand (what the loads cause) against the adjusted capacity (what the member can take).

The Supplement gives you the answers to questions 1 and 2. The Specification handles question 3.

This isn't just our framing — it mirrors how the Supplement is organized. Its opening pages give a short Table of Contents and a List of Tables:

Figure: The NDS Supplement's own Table of Contents and List of Tables. The book follows the same logic as this guide — Section Properties (Series 1) for geometry, then Reference Design Values for strength (Series 4 sawn lumber, 5 glulam, 6 round timber). The earlier sections — grading agencies and species combinations — are background reference.

One thing to internalize early: the Supplement gives reference design values. They are starting numbers. You almost never use them as-is — you multiply them by adjustment factors (for load duration, moisture, size, temperature, stability, and more) to get the adjusted design values, written with a prime: F′_b, F′_c, and so on. Reference values come from the Supplement; the factors come from the Specification.

A note on the cross-section

The Supplement labels rectangular sections the same way for sawn lumber and glulam: b is the width, d is the depth. The X-X axis is the strong axis (bending about it uses the large S_x, I_x); the Y-Y axis is the weak axis. Get in the habit of asking "which way is the load bending this member?" before you read a section property.

Figure: the width b, depth d, and the X-X / Y-Y axes, shown for glulam (left) and sawn lumber (right).

How lumber is sized

Here is the first thing that trips up new engineers. A "2×4" is not 2 inches by 4 inches. Those are nominal sizes — the rough dimensions before the mill planes the board smooth. Almost all framing lumber is S4S ("surfaced four sides"), meaning all four faces are planed, which shaves the section down. A nominal 2×4 is actually 1½ in. × 3½ in.

So whenever you do real math, you use the dressed (actual) size, not the nominal label.

• Table 1A converts nominal → dressed. Reach for it when you need the actual b and d themselves — for shear (which depends on b·d), for bearing area, and for connection geometry (edge distances, spacing — all measured from real dimensions).
• Table 1B saves you the arithmetic: it lists the section properties (A, S, I) already computed for every standard dressed size. Reach for it when you need S for a bending check or I for a deflection check.

A simple way to remember it: need a stress or deflection value → Table 1B; need a raw dimension → Table 1A.

Series 1 — Section properties

These are your geometry tables — pure numbers about the shape, with no strength involved yet.

Why two glulam tables (1C and 1D)? Glulam is built up from thin boards (laminations) glued together, and the two main supply regions build it differently. Western species (Douglas Fir and others) and Southern Pine use different standard widths and lamination thicknesses (Southern Pine laminations are often thinner). Different geometry, different table.

A small thing that confuses people: in glulam, you can stack more laminations to make a deeper beam without changing its width. The weak-axis radius of gyration r_y depends only on the width, so it stays the same as the beam gets deeper. Seeing the same r_y repeated down a column is normal, not a typo.

Lumber size categories (worth knowing because they decide which strength table applies):

• Boards — less than 2 in. thick.
• Dimension lumber — 2 to 4 in. thick (your everyday 2× and 4× framing).
• Timbers — 5 in. × 5 in. and larger.

Series 4 — Sawn lumber strength

Now we move from "how big" to "how strong." Series 4 gives the reference design values for solid sawn lumber.

First, how the wood was graded

Every piece of structural lumber carries a grade, and there are two ways it gets one:

• Visually graded — a trained inspector (or an approved scanner) looks at knots, slope of grain, splits, and assigns a grade like No. 2 or Select Structural. This is the default. If a drawing says "No. 2 DF-L" with nothing else, it means visually graded.
• Machine graded (MSR/MEL) — each board is run through a machine that measures its stiffness and sorts it. This gives more consistent numbers and is common in trusses.

In day-to-day practice — especially residential and light commercial — you are almost always working with visually graded lumber, most often No. 2 Douglas Fir-Larch or a Spruce-Pine-Fir group.

The Series 4 tables

For most projects you live in 4A, occasionally 4B (Southern Pine country) and 4D (heavy timber posts and beams).

Two habits that prevent real mistakes

1. Southern Pine (Table 4B) already bakes in the size effect. For most lumber you must apply a size factor C_F by hand. For Southern Pine dimension lumber, that adjustment is usually already inside the tabulated number — do not apply it twice. Always read the table's column headings and footnotes.
2. F_b and E can follow different footnotes in the same table. Don't read across one row and assume every value shares the same notes. Check the footnote that applies to each value you pull.

The grade ladder

From strongest to weakest, the common structural grades run: Select Structural → No. 1 → No. 2 → No. 3 / Stud → Construction / Standard / Utility. No. 2 is the workhorse of everyday framing.

Series 5 — Glulam strength

Glued laminated timber (glulam) is engineered by gluing graded boards into large members. Series 5 gives its reference design values, and the key idea is that how a glulam member will be loaded decides which table you use.

Why split bending from axial? Because the manufacturer arranges the laminations differently for each. A bending member (5A) gets its strongest boards on the top and bottom faces, where bending stress is highest. An axial member (5B) is graded more evenly through the depth, because axial stress is uniform across the section. Picking the right table means your numbers match how the member is actually built.

Reading glulam labels

You'll see labels like 24F-1.8E:

• 24F → reference bending strength F_b = 2400 psi (the leading number × 100).
• 1.8E → modulus of elasticity E = 1.8 × 10⁶ psi.

As a designer you usually specify a stress class like 24F-1.8E and let the fabricator choose the exact lamination recipe (you'll also see "combination" codes like 20F-V3 on shop drawings — those are the manufacturer's specific layups).

Series 6 — Round timber

Series 6 covers round wood members:

• Table 6A — treated round piles (graded to ASTM D25), used in foundations.
• Table 6B — round poles (graded to ASTM D3200), used in pole barns and similar structures.

Designing a round column: the equivalent-square method

Most round wood members you'll actually design are simple solid round posts or columns, and the NDS gives a clean shortcut for them in Section 3.7.3: design the round section as a square of the same cross-sectional area. You convert the diameter to an equivalent square, then use ordinary square-section formulas:

A  = π·D² / 4        →  cross-sectional area of the round member
b  = d = √A          →  side of the equivalent square
I  = b·d³ / 12       →  moment of inertia of that square
S  = I / (d/2)       →  section modulus

This is conservative by design: matching areas gives a square with a slightly smaller I than the true circle, so buckling and bending checks come out a little safe — which is exactly what the code intends. For the column stability factor, round members use c = 0.85 (sawn lumber uses 0.80, glulam 0.90). The strength values themselves come from the sawn lumber tables for the chosen species and grade.

E vs E_min

Wood actually has two stiffness numbers in the tables, and new engineers often grab the wrong one. They do different jobs:

So: checking how much a beam sags → E. Checking whether a slender column or unbraced beam will buckle → E_min.

One more habit: bearing (F_c⊥) is not increased for load duration. Most strength values get a load-duration factor C_D; perpendicular-to-grain bearing does not. Leave C_D out of bearing checks.

Putting it together

Here's the full sequence on a simple beam, start to finish:

1. Pick a trial size — say a 4×10. Get A, S, I from Table 1B (and the actual b, d from 1A if you'll check shear or bearing).
2. Pick the material — say Douglas Fir-Larch No. 2. Read F_b, F_v, F_c⊥, E, E_min from Table 4A.
3. Adjust the values — apply the NDS factors (load duration C_D, wet service C_M, size C_F, beam stability C_L, and so on) to turn reference values into adjusted values (F′_b, F′_v, …).
4. Check each limit state — bending (F′_b), shear (F′_v), bearing (F′_c⊥), deflection (E), and stability (E_min). The member works if demand ≤ adjusted capacity for every one.

When you feel lost on any wood problem, come back to three questions: What size? (Series 1) What material values? (Series 4 or 5) What equation? (the NDS limit state).

How StructSuite uses these tables

When you design in StructSuite, the Wood Beam and Wood Column tools pull directly from these tables so you don't have to flip pages — you pick a row and the software carries it through the adjustment factors and the final checks.

Solid sawn lumber. You select section size from Table 1B, and species/grade from Table 4A (most species), Table 4B (Southern Pine), or Table 4D (timbers).

Glulam. Geometry comes from Table 1C (Western) or Table 1D (Southern Pine). For strength, a beam uses Table 5A (bending) — and can also use 5B when it carries axial load — while a column uses Table 5B (axial), matching how each member is loaded.

Engineered products (LVL, LSL, PSL, I-joists). These aren't in the NDS Supplement at all; their design values come from each manufacturer's ICC-ES Evaluation Report (ESR). StructSuite includes those values so you can design them alongside sawn lumber and glulam.

Some specialized members fall outside these two tools because they aren't single beams or columns: heavy structural decking (Table 4E) is a plank/diaphragm system, imported and multi-species group lumber (4F, 4G) is rarely specified where the common species already cover the work, hardwood glulam (5C, 5D) is almost never used in buildings, and graded piles and poles (6A, 6B) are specialized foundation and pole elements. Machine-graded MSR/MEL lumber (4C) is mostly a truss-industry product, so the tools focus on the visually graded lumber you hand-pick for an individual member.

Where to learn more

Start with the source, then add the references you'll use most as a practicing engineer:

1. American Wood Council (AWC) — the organization that publishes the NDS and the Supplement. You can read the NDS 2024 and the Supplement: Design Values for Wood Construction for free, along with helpful technical articles.
   • https://awc.org/codes-standards/publications/nds-2024
   • https://awc.org/publications/
2. APA – The Engineered Wood Association — the authority on glulam, I-joists, and plywood/OSB, with clear technical notes on stress classes and layups.
   • https://www.apawood.org/
3. ICC-ES report directory — where the design values for LVL, LSL, PSL, and I-joists live (the manufacturer ESRs).
   • https://icc-es.org/report-listing/
4. USDA Forest Products Laboratory — Wood Handbook — a free, deep reference on how wood behaves and where these design values come from.
   • https://www.fpl.fs.usda.gov/products/publications/specific_pub.php?posting_id=20844
5. Grading agencies behind the Series 4 values — WWPA (Western), SPIB (Southern Pine).
   • https://www.wwpa.org/ · https://www.spib.org/

The fastest way to make these tables stick is to use them. Open StructSuite's Wood Beam (/design/wood-beam) or Wood Column (/design/wood-column) tool, pick a species, grade, and size, and watch each reference value flow through its adjustment factors into the final check. After a few members, the Supplement stops being a wall of numbers and starts feeling like a reference you reach for without thinking.