So you are ready to buy some lumber for that home project of yours? Good for you! But you want your decisions to be informed, don’t you? Here are some things for you to consider when you purchase lumber. Lumber is a wonderful, natural resource. It has been used by man for millenia, and remains one the most durable, beautiful building materials that we have to work with. But you may be very disappointed in the result if you do not take proper care to purchase the right material for the job, and make sure that it is handled correctly all along the process. This page is designed to bring a few of the major variables in the lumber world to you so that you can make informed decisions. Among the top of those variables are species, grade, dimension, and moisture content. Proper handling of the material prior to installation also is important, whether it be the chain of companies through which the lumber came, or you yourself as you prepare it in its final steps. Remember, lumber is an organic material, and is subject to the elements of sunlight, heat, and water.
Grades:
Wood is wonderful, but it is not perfect. And here is the challenge for lumbermen the world over, to get a reasonably high quality product manufactured and sold to the customer for an acceptable price. America’s first efforts at standardization of lumber began in 1922, and resulted in the American Lumber Standard, first published in 1924. Lumber standards today are set by the American Lumber Standard Committee, which is appointed by the Secretary of Commerce. The purpose of the standards are the same as any other rules of commerce, to insure that consistent products are available to the consumer. However, grades are after all just a reference point, and lumber mills still do develop a reputation as to the quality of the lumber they produce. Trees also vary from region to region, and lumber grade rules are still just rules. Good references are your best guarantee that the lumber you purchase is going to be satisfactory. Many of today’s mills have some rules of their own to add to the value of their lumber, often giving another name to their grade to try to add to the value of their lumber, especially for appearance grade products.
Here is a basic guide to softwood lumber grades for the consumer.
Clear versus common (knotty) lumber: Clear grades are based off of the concept that less knots is better. Clear or select lumber grades bring a higher price than their common cousins. There are several reasons why clear lumber is priced higher.
1) Clear lumber is easier to work with for the carpenter/woodworker. Knots tend to fall out, make for irregularities in the surface of finished lumber, and do not machine as well. (Have you ever tried to cut through a knot with a handsaw?)
2) Knots make for weaker lumber.
3) Clear lumber is not as common in the mill yard. A typical white pine run in North Idaho, for example, will probably yield less than 7% select grade lumber.
On the up-side, common lumber often has a more pleasing appearance then clear lumber, because of the extra character found in and around the knots.
Select lumber grades:
Select North American Softwoods are generally rated with a letter from A-D, followed by “and better”, which is commonly abbreviated by &BTR. The grades go from “A” being the highest, or most perfect grade, to “D”, the poorest. The grades may be grouped, such as A&B, or C&D, but more commonly they may be sold as C&BTR, or D&BTR. “No prior select” indicates that the lumber in that batch has not been sorted through for a higher grade. In other words, a “D” grade is graded to the rules in the book for “D”, whereas “D&BTR” indicates that you may have some at least of the “C” grade in the batch. “D&BTR no prior select”, however, indicates that you will have everything from A-D in the batch. Clear grades above a “C&BTR” are hard to find in today’s market.
Common (knotty) grades:
Common North American Softwoods are generally rated with a number followed by “and better”, which is commonly abbreviated by &BTR. The grades are 1 – 4, with “1” being the highest, or best grade. These grades are sold generally grade specific, although “no prior select” is sometimes carried all of the way into 3&BTR. “No prior select” indicates that the lumber in that batch has not been sorted through for a higher grade. In other words, a “#2” grade is graded to the rules in the book for “#2”, whereas “2&BTR” indicates that you may have some at least of the “#1” grade in the batch. “2&BTR no prior select”, however, indicates that you will have everything from 1-2 in the batch. Today it is common to add SFA to the grade, which means that it is selected for appearance. This is often done to timbers, paneling, and exterior trim and siding. Generally, you would be safe to purchase a 2&BTR SFA if you wanted a nice looking knotty product. If your sawmill is known to push the grade, however, you may consider going with 1&BTR.
Moisture content:
Here are some basics to consider that relate to the moisture content of your lumber.
#1 Even “dry” lumber has water in it. It is important to remember that water is not bad for lumber, as lumber almost always has a certain amount of water content within its fibers. Wood as a substance is hygroscopic, which simply means that it has the ability to release and take on water from the air that surrounds it.
#2 Water expands wood. As lumber dries, it shrinks. As lumber takes on moisture, it swells. This is something to consider when purchasing, handling, and installing wood products. For example: a 1×8 pine T&G dried to 8% MC and installed on a soffit in August will likely expand and “buckle” in the following winter rainy season. It is not unheard of for someone to come home from a day at work in November to find his new soffit laying on his deck, the moisture in the ambient air having swelled, buckled and forced it off of the lid.
#3 It is possible to have lumber which is too dry. A certain amount of moisture content is desirable for lumber. For example: machining or “working” lumber which is too dry can result in shattering, knots falling out, and other problems when the lumber is sawn, planed or drilled. Conversely, lumber that is too wet will not machine well either, so we need to find the “sweet spot” for a particular species/grade and its application.
#4 Lumber shrinks as it dries. This is one of the first anomalies of lumber that people learn when working with wood, simply because it is so obvious. Most framing lumber purchased at building supplies here in the Inland Northwest will shrink 2-4% of its width as it dries from the 19%MC average that the industry requires to the 6% or so that it reaches in the next late August after it is installed.
Water & Sunlight:
We have all seen old buildings where the lumber never seems to decay, and at the same time marvel to see our decks rot off with a few years. There is a reason for this. Sunlight starts to tan lumber immediately after it is cut, and left unfinished it will be gray within a year and black in just a few years. But even if left unfinished, the sun only seems to be able to get to what it can see, and the lumber barely an 1/8th inch under the surface remains the same. Unfinished lumber will last for a long time if it is kept out of the rain. Long eaves and roofed decks testify to this. Open decks are exceptionally bad as the water tends to get trapped between the joists and the decking. Wet lumber has a tendency to grow bacteria and mold, which in turn feed off of the wood fiber. This is what we call rot, and it is the only true enemy of wood products besides fire. There are many structures sided with unfinished wood that have stayed sound for more than 100 years. The trick is to keep the wood dry, or at least it needs to dry out completely after rain or snow water dampens it. Shake roofs are an excellent testimony to this fact. Old barns may still have solid shake roofs on them after many decades, because air travels freely under and over the shakes. But nail the shakes onto tar paper, and you will only get 15 – 20 years before they are no longer sound.