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Lumber & Composites

How To Read Lumber Grade Markings


Lumber processed at a mill is appraised by trained inspectors and given a grade stamp, this stamp indicates the wood meets established standards for strength and rigidity, it also indicates the moisture content and the type or specie of the wood. These markings signify the quality and strength of the wood.

Wood markings identify the following:


1. The lumber association with a mark or logo.


2. The grade of the wood, there are a number of grades, Select (the best quality and strongest) to Utility (the lowest quality and least strength).


3. The material species, (SYP)Southern Yellow Pine, (DFir) Douglas Fir, (RD) Redwood, etc.


4. The moisture content at the time of milling, this ranges from (AD) air dried or (S-GRN) surface green, with a moisture content of 19% or more to (KD) kiln dried or (KD-HT) kiln dried and heat treated to kill pests, this lumber will have a moisture content of 15% or less.


5. The identification of the mill usually a number issued by the lumber association.



Below are two examples of lumber labels:


Grade Markings


Grade markings identify the species and the strength of the wood, these rate the woods’ strength from high to low.


1. Select Structural, the highest grade and the strongest wood.


2. No.1 Grade, the next highest


3. No.2 Grade

4. No.3 Grade

5. Stud, these are often specified for interior load bearing walls.


6. Construction


7. Standard


8. Utility


The Architect will specify in the building plans the grade of lumber required for each element of the building, structural grade,  grade 1 or 2 for load bearing walls, number 3 or stud grade for interior non-load bearing walls.


Treatment Markings

Treatment markings will indicate:

1. The treatment material and retention value.

2. The allowable ground contact

3. The treatment process indicated by letters or numbers.


4. The plant certification date.

5. The plant code and name.

Sample Treatment Label

Pressure Treated Lumber

ACQ-D .40

Ground Contact



Southern Pine Inspection
Bureau Inspected
NRB 240

Quality Wood
Treating Company
Prairie Du Chien, Wi.


Treatment Label Legend

ACQ =Alkaline Copper Quat, Type D

.40 = Treatment Retention (lb/ft 3).

Ground Contact = Indicates 0.4 lb/ft3) treatment retention.
Use for ground contact only when there is a low replacement cost. Good for occasional exposure to rainwater.

PP or SYP = Treatment process for Ponderosa pine and Southern yellow pine. NOTE: THIS DOES NOT INDICATE THE SPECIES.

1984-1986 = Years plant is certified by Southern Pine
Inspection Bureau.

NRB 240 = Coding number used by plant.


The next time you shop for lumber look for these grade markings, they will help you choose the wood you need for your project and will give you a greater understanding of the wood grades and why one grade of wood costs more than another.

Mike, The Home Depot Answer Man

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Posted 2015-12-31T20:09:10+0000  by Mike_HD_OC Mike_HD_OC