Tip of the Month – September 2015
Graded by Strength and Appearance
Lumber is graded using two processes. The first process describes the physical strength of the lumber and the second grades the lumber based upon appearance.
When lumber is shipped from a lumber mill to a distributor it is graded and a number is marked on it to distinguish the different grades. Most commonly the lumber will have a No. 1 or a No. 2 on it. Sometimes the lumber may say No. 2 BTR, which means No. 2 or better. These grades are assigned to lumber by a process which uses the following factors to grade each type: checks, grains, knots, shake, skips of grain, split, stain and wane. Each lumber grade is also based upon the width and thickness of the wood.
Normally, when building patio covers, the lumber that is used is graded No .2 or better. The lumber would be hand selected based upon four corners being square, straightness, tightness in knots and light color staining. Lumber which is given a number grade is also given and appearance grade. The appearance grades are standard, select or clear. Most of the lumber that is used for wood replacement is standard lumber, which is hand selected by the lumber yard. This is different from select lumber, which is selected by the lumber suppliers and is the premium grade building lumber. This type is used for structurally exposed lumber, which requires extreme strength and an outward physical appearance. The grade is called Select Exposed.
How to read a lumber stamp:
1. Species (Ex. S-P-F Spruce, Pine Fir)
2. Grade No. 1, No. 2, Stud
3. Moisture Content (Ex. AD Air Dried, KD Kiln Dried)
4. Certification Mark (Agency that Oversees Grading )
5. Mill (Trademark or Number of Lumber Mill)
If you need lumber that has no knots there is another style of lumber called clear, which means that the lumber has little or no knots in its appearance. Clear can also be referred to as Select Tight Knot or STK. Since lumber can have two different ratings it can cause confusion on which type of wood you might need. Most of the time you will be using No. 2 BTR Standard Hand Select lumber, but if you are doing a project that requires wood that is going to be visible, you may decide to use clear lumber. Since wood is rated in two different areas, you can have a piece of wood that is rated select structural but may have an appearance that is not visually pleasing.