Lumber Sizing & Grades — What You Need to Know
Nominal vs. Actual Lumber Sizes
One of the most common points of confusion when ordering lumber is the difference between nominal and actual dimensions. A “2×4″ is not actually 2 inches by 4 inches — it’s 1.5″ x 3.5”. This matters when planning your project.
| Nominal Size | Actual Size |
|---|---|
| 1×4 | 0.75″ x 3.5″ |
| 1×6 | 0.75″ x 5.5″ |
| 2×4 | 1.5″ x 3.5″ |
| 2×6 | 1.5″ x 5.5″ |
| 2×8 | 1.5″ x 7.25″ |
| 2×10 | 1.5″ x 9.25″ |
| 2×12 | 1.5″ x 11.25″ |
| 4×4 | 3.5″ x 3.5″ |
| 6×6 | 5.5″ x 5.5″ |
Lumber Grades
Lumber is graded based on the number of knots, grain straightness, and structural integrity. For most construction projects in Eastern Washington, here’s what each grade means:
- Select Structural / SS — Highest grade. Fewest knots, straightest grain. Used where appearance and maximum strength both matter.
- #1 Grade — Strong and clean. Good for exposed framing, decking, and structural applications where some knots are acceptable.
- #2 Grade — The most common framing lumber. Suitable for wall framing, floor joists, and rafters. Some knots and minor defects.
- #3 Grade — Economy grade. More defects. Used for non-structural applications like bracing, blocking, and temporary work.
- Construction Grade — Between #2 and #3. Common for general framing where appearance doesn’t matter.
Which Species for Which Project?
- Douglas Fir — The workhorse of Eastern WA construction. Strong, stiff, widely available. Best for framing, beams, and joists.
- Hem-Fir — Lighter than Doug Fir, still strong. Good for interior framing and walls.
- Western Red Cedar — Naturally rot-resistant. Ideal for decking, siding, fencing, and any outdoor exposed application.
- Pressure Treated (PT) — Southern Yellow Pine or Hem-Fir treated with preservative. Required for any lumber in contact with concrete or soil. Use for deck posts, ledger boards, and ground contact.
- Whitewood / SPF (Spruce-Pine-Fir) — Economical interior lumber. Good for shelving, furring strips, and light framing.
Eastern WA Considerations
Eastern Washington experiences significant temperature swings and low humidity compared to the west side of the Cascades. Kiln-dried lumber (KD or KDAT) is strongly recommended to minimize shrinkage, warping, and nail popping after installation. Ask our team about kiln-dried availability at your nearest location.
Questions? Call us at (509) 798-8545 or visit any of our 3 Eastern Washington locations.