Lumber grading sorts boards by quality so that buyers know what they are getting. Pallet stock is deliberately low-grade timber: pallets do not need clear, knot-free wood, so makers use lower grades that meet limits on knots, wane, splits and moisture. Which grading system applies depends on the region, the species and whether the wood is graded for appearance or strength.
Two kinds of grading
Grading rules follow two different philosophies, and mixing them up is a common source of misunderstanding.
Appearance (or "defect-based") grading judges boards on visible features such as knots, wane, bark, resin pockets and discoloration. It is mainly used for joinery, cladding, packaging and, in North America, hardwood lumber. It says little directly about load capacity.
Strength grading assigns boards to a strength class based on measured or estimated bending strength, stiffness and density, so that engineers can calculate with them. It may be visual (inspecting knots and slope of grain against rules) or by machine (measuring stiffness or density). Wikipedia's overview notes that visual grading is economical but subjective, while machine grading gives more consistent results.
Swedish Wood stresses the difference: grading by appearance is a general sorting process that does not take the end use into account, so an appearance grade acceptable for cladding may be inadequate for load-bearing structures.
Grading standards by region
| Region and material | Main system | What it covers |
|---|---|---|
| Europe, softwood appearance | EN 1611-1 | Appearance grades for European spruces, firs, pines and Douglas fir, with codes such as G4-0 to G4-4 |
| Europe, structural | EN 14081-1 with EN 338 strength classes | Strength-graded structural timber, classes such as C14, C18, C24 and C30 |
| North American softwood | Rules approved under the American Softwood Lumber Standards Committee, e.g. Southern Pine Inspection Bureau (SPIB) | Dimension lumber grades from Select Structural to No. 3 and below |
| North American hardwood | National Hardwood Lumber Association (NHLA) rules | Grades based on the size and number of clear cuttings obtainable from a board |
| Pallet-specific | Purchase specifications and pallet standards | Defect limits, dimensions and moisture for pallet parts |
Europe
In EN 1611-1, the first part of the grade code indicates how many faces and edges are assessed (G4 means four sides) and the number after the dash indicates quality, with 0 the highest. Swedish Wood lists G4-0 for interior joinery, G4-2 for exterior cladding, G4-3 for lower-quality decking and packaging, and G4-4 for formwork and packaging, where most defects are acceptable if the wood is intact.
Strength grades follow EN 14081-1 and EN 338. Softwood classes carry a "C" prefix and hardwood classes a "D" prefix, with C24 the most common in construction. Pallets are normally not made from structurally graded timber, but boards still have to satisfy the limits in the relevant pallet specification. EPAL requires its own acceptance criteria for boards and blocks, covering things such as knots, wane and splits; see EPAL quality classes.
North America
SPIB writes the grading rules for Southern Pine, approved under the American Softwood Lumber Standards Committee. The Southern Pine Council states that No. 3 grade is commonly used for non-building applications such as pallets and concrete forming. Details are in southern yellow pine.
For hardwood, the NHLA system classifies boards by the proportion of clear, defect-free wood obtainable from them. The top grades (FAS, Select and No. 1 Common) go to furniture and flooring, while lower grades such as No. 3A and 3B Common and below-grade pieces supply pallet makers. In the United States, pallet cants and boards from hardwood sawmills are a major supply route; see wood species used for pallets.
What defects pallet specifications control
Pallet specifications turn grading ideas into acceptance rules for each component. Typical controls include:
- Knots: size, type (sound, loose, encased) and position, especially near board edges and nail zones.
- Wane: the missing wood or bark on an edge, limited because it reduces nailing area and bearing surface.
- Splits and cracks: limited near nails and ends.
- Bark and rot: rot is usually prohibited, and bark may be restricted, particularly for countries that require debarked wood.
- Moisture content: capped by most specifications.
- Dimensional tolerances: thickness, width and length.
Defect types and their effect on strength are explained in timber defects. The way pallets are tested to verify performance is covered in pallet testing standards.
Who does the grading and how
At the sawmill, boards pass a grading station where trained graders assign grades by eye, or an automated scanner assigns grades using cameras and lasers. Scanners can detect wane, knots and other features and optimize trimming, as described in industry coverage of pallet sawlines; see how a sawmill works. Certified agencies inspect mills that apply official grade stamps.
Pallet makers often grade again at the plant, sorting boards into deck board, stringer and block categories and culling boards that are too wet, rotten or heavily defected; see pallet quality control.
Practical tips for buyers
- Specify the rule system. "Pallet grade" means little without defect limits or a named standard.
- Specify moisture. Even good grades fail if wet; see wood moisture content.
- Sample before ordering. Check a delivered load against the specification.
- Do not assume appearance grade equals strength. If pallet capacity matters, test the finished pallet.
Frequently asked questions
What grade of lumber is used for pallets?
Mostly low grades, such as No. 3 and below in softwood dimension lumber or 3A/3B Common and below in hardwood, plus purpose-sorted pallet stock.
What does G4-3 mean in lumber grading?
It is an appearance grade under EN 1611-1 in which all four sides are graded; the 3 indicates a lower quality level, which is used for decking and packaging.
Is strength grading needed for pallets?
Not normally. Pallet standards control defects and dimensions, and finished pallets are tested for performance.
Who sets hardwood grading rules in the United States?
The National Hardwood Lumber Association writes the widely used hardwood grading rules.
Sources
- Wood grades — Swedish Wood
- Sawn timber: appearance grading of softwoods, European spruces, firs, pines and Douglas fir (EN 1611-1) — British Standards Institution
- EN 14081-1 Timber structures — Strength graded structural timber with rectangular cross section — European Committee for Standardization (via en-standard.eu)
- Timber grading — Wikipedia
- A Guide to Southern Pine — Southern Pine Council
- Sawlines: Scanners, Computers Optimize Machines — Pallet Enterprise