Why Grade lumber?

When you buy a 2×4 from the lumberyard you may have noticed that it has a black ink stamp on it with some letters and numbers. What does this mean? It means that this piece of lumber has been inspected and approved for use as a structural member in a home or other building.

Lumber grades define the strength and suitability for a particular purpose such as what is needed in a load bearing wall. That is, to carry the weight without breaking of failing to support the load placed upon it.  

Every time you look at a board you will automatically give it your own grade. Most times this will be an unconscious process and you will say to yourself “Wow this is a beautiful board” or maybe “This board is no good”. The following information will help to put a grade to your observations.

Grading Stamps & Grading Lumber

Lumber Grades

  • RGH               Rough sawn lumber.
  • GRN               Green, not dry, shipped green. 
  • SLR1E            Straight line ripped one edge.
  • SLR2E            Straight line ripped two edges.
  • S2S                Surface planed on both sides of the board.
  • S1S                Surface planed on one side of the board.
  • Resawn          A board split in half from a thicker board.
  • 4/4                 1″ rough thickness.
  • 5/4                 1-1/4″ rough thickness.
  • 6/4                 1-1/2″ rough thickness.
  • 8/4                 2″ rough thickness.
  • 10/4               2-1/2″ rough thickness.
  • 12/4               3″ rough thickness.
  • 16/4               4″ rough thickness.
  • FAS               First and Seconds, the top grade for hardwoods.
  • Sel&Btr          Select & Better. Includes Select & FAS boards.
  • #1Com           Number one common grade.
  • #2Com           Number two common grade.

The lumber grades in this list are the most common grades you will find. There are many more grades but I will not cover them all on this web page.

Can I build my house without having my lumber graded?

Yes and No

Building codes vary from state to state and county to county. Check with your local building authority to find out about your specific requirements. Most structural load bearing lumber in homes and commercial buildings require a grade stamp that will be clearly stated in the plans and drawings that will be used by your builder and building department.

Yes, there are many aspects of building that do not need to have grading stamps. Such as trim and finish work, flooring, wainscot, siding, decking, cabinets, furniture and handrails. These are just some of the uses in home building that do not require grading.

If you have a permitted project with plans and drawings that specify lumber grades then your lumber must have the appropriate grading stamps.

Can I have my lumber graded?

Yes. You can always hire a lumber grader to inspect and stamp your lumber. Be prepared to handle each board yourself as they will not do the moving and stacking of your material. The cost and availability also varies from location to location. Research your local area to find the answer to this question..

Engineered Plans 

If your area has a strict code enforcement policy one sure fire way to work around the issue of grading stamps is to have your home plans drawn up by a Certified Engineer. An engineer uses a specific formula to calculate the strength and suitability of most any species of wood. Using this information they will call for the appropriate dimensions of lumber needed. Therefore an engineer can call for the use of your home milled lumber on the plans without the need to grade each piece of wood. This will be stated on the plans and and the engineer will put their stamp directly on the plans summited to the building authority. They will call for the proper size and species and that will salsify the building authority requirements.

Definition of Lumber Grades

First and seconds
An FAS board must be at least 6″ wide and 8′ long. 83 1/3% of the board must be clear. To determine cutting units the maximum number of imaginary cuts is one-quarter of the board measure. For example, a 6″ x 8′ board is 4 board measure. The board can be cut only once, 1/4th of 4. After this single imaginary cut the board must be 83 1/3% clear. The area of each imaginary cut must leave at least 4″ x 5′ or 3″ x 7′ sections. If a board is 8 board measure then two cuts are allowed, yielding 83 1/3% clear, each cut at least 4″ x 5′ or 3″ x 7′. If a single cut in a 6″ x 8′ board does not yield an FAS grade there are additional rules. One additional cut is allowed in boards between 6 and 15 board measure if the resulting clear portion of the board is 91 2/3%.The reverse face of a board must also be FAS for the entire board to be graded as FAS.

A select board is graded exactly like FAS. The only difference is that the minimum size of a Select board is 4″ x 6′ (whereas an FAS board must be at
least 6″ x 8′). The reverse face of a Select board can be either Select or #1 Common.

#1 Common
A #1 Common board must be at least 3″ wide and 4′ long. 66 2/3% of the board must be clear. The maximum number of imaginary cuts is one-third of the board measure plus one. Surface area after each imaginary cut must be at least 4″ x 2′ or 3″ x 3′. For example, a board 6″ x 8′ is 4 board measure. One third of 4 + 1 is 1. If a single imaginary cut in the board yields 66 2/3% clear where the uncut area is at least 4″ x 2′ or 3″ x 3′, the board is graded as #1 Common. An additional cut in the board is allowed if the resulting clear yield is at least 75%. This applies to boards between 3 and 10 board measure. The reverse face of a #1 Common board is always #1 Common.

#2 Common
A #2 Common board must be at least 3″ wide and 4′ long, just like #1 Common. The clear yield of a board can be as low as 50% after cuts equal to half of the board measure. Surface area after each imaginary cut must be at least 3″ x 2′. For example, a board 6″ x 8 is 4 board measure and can be cut twice, half of four. The resulting clear area of the board must be at least 3″ x 2′ and at least 50% clear. An additional cut is allowed in boards between 2 and 7 board measure if the yield is 66 2/3% clear. The reverse face of a #2 Common board can be #2 Common or better. If the reverse face of aboard is #3 Common then the entire board becomes #3 Common.

Definitions of common terms

A board is made up of clear and sound portions and defects. During grading, the grader visualises the maximum clear yield of a board. A portion of a board’s surface that is clear is measured. The sum of each of these clear portions is tallied and used towards grading a board. A clear portion is an imaginary
rectangle extended as far as possible between defects. For example, a clear portion, a clear cut, is bordered by four knots or four edges or a combination
thereof. A clear cut may be bordered by two knots and two edges. The remaining surface area of a board that is not classified as clear may be either sound or defect.

Cutting to Grade
This is a more time consuming proses of specialty cutting in order to produce a number of types of lumber grades such as quarter sawn, vertical grain or figured
patterns that would not be found in plane sawn lumber.

Clear Face Cutting
A cutting with no defects is classified as a clear face cutting. The reverse face must be sound for a clear face grading. If the back is worse than sound the face
is not classified as clear. For example, a board with no defects on its face cannot be classified as clear if the back is riddled with unsound knots. The clear face grading relies on the back to be sound.

Sound Cutting
A sound cutting is a board that is free of rot, pith, shake and wane. A board is sound if it contains sound knots, bird pecks, stain and streaks. Soundness means the board’s strength is not impaired by anything on its surface. Holes are admitted in a sound board, unless they are the entire thickness of the board, up to two 1/4″ holes or one 1/2″ hole per 12 cutting units.

Cutting Units
A cutting unit is an imaginary rectangle one inch wide by a foot long, exactly 1/12th of a board foot. Cutting units are used to determine the extent of surface
features on a board during grading. A grader cuts the board in their imagination, different grades allow a minimum number of cutting units. For example, a board 9 3/8″ wide by 16′ long contains defects. A clear portion8 1/2″ x 6′ yields 51 cutting units, a 3″ x 9 1/2′ portion yields 28 1/2, 4″ x 2 3/4′ yields 11 and 3″ x 3 1/3′ yields 10. The sum of the cutting units is 100 1/2, about 67% of the board. A board containing 67% clear cutting units is at best #1 Common. A board would never be cut this many times, it is just a method to calculate the clear portions of the board.

Book Matching
Book Match is a set of boards that mirror one another. They have been cut from a single log and the two faces match in grain pattern and color.
Flitch Cut
Boards cut with one or more natural edges (live edge).
Live Edge
Boards cut with the natural edge left on, with or without the bark
Distortion of a board lengthwise. A bowed board will not be flat across its length.
A crack in the surface of a board. The check does not go through the entire thickness of the board. It is a result of uneven drying, particularly by the sun and many times from too aggressive kiln drying schedule.
Distortion of a board across its width.
Distortion of a board across its width.
Heartwood is the dead portion of the tree. It extends from the pith(center) to the sapwood. It is usually a slightly darker shade than sapwood. The center of the tree is where the heartwood is located.
Discolored wood resulting from a branch. Red knots are living branches which the tree has overgrown. In Pine, red knots are usually sound and fixed since it grew until the tree was cut down. Black knots are dead wood, from dead branches, which are not necessarily fixed. Fixed knots are those which will only fall out of a board when under direct pressure.
Mineral Streak
Discoloration of hardwoods ranging from olive green to brown to black.
Pin Knot
Knots up to 1/8″ in diameter are considered pin knots. Pin knots in Pine are up to 1/2″ in diameter.
A portion of wood usually softer than the surrounding board. It occurs more often in heartwood at the center of trees. Pith that is equal hardness to the surrounding board is not a defect.
The living portion of the tree extending from the heartwood to the bark. Sapwood tends to be more pale than heartwood.
Sequence Match
Adjacent components of plywood are of lateral layers from the same log. Features are nearly identical across a sheet with grain lining up almost perfectly.
Seperation along the grain. It occurs most often between rings of annual growth.
Discoloration in a board. This discoloration is different than sapwood, heartwood or natural variation. It ranges from pink to gray to brown.
Distortion of a board both lengthwise and/or widthwise.
A lack of wood on the edge of a board. Wane may include bark. Wane is the result of a board being cut too close to the outside of a tree.
A term for any variation in the flatness of a board. It can include bow, crook, cup and/or twist.

Special Hardwood Grading Considerations
An unlimited number of pin knots are allowed in all grades of cherry. Each knot must be sound and no larger than 1/8″ in diameter. Gum spots and streaks are also admitted in any grade without limit.

Red Oak, White Oak, Black Oak
Mineral streaks and spots, and streaks and spots of a similar nature, are allowed in cuttings. The total area of these streaks and spots can be no more than 8 1/3% of cuttings. Streaks and spots outside of the cuttings are allowed to any degree.
Black Walnut
In Black Walnut graded as Select & Better the minimum cuttings sizes are 4″ x 3′ or 3″ x 6′.