What to look for when buying framing lumber
Most homeowners can stride into a lumberyard or home store and announce theneed for a 2-by-4 board. Very few, however, will know what kind of2-by-4 to ask for, says a wood products expert in Penn State's College ofAgricultural Sciences.
Everything you always wanted to know about finish, framing and compositewoods is printed on what is called a "grade stamp" on every board soldin the United States, according to Roy Adams, associate professor of woodproducts in the School of Forest Resources.
"There is an incredible amount of information contained within a stampno bigger than a cocktail napkin," Adams says. Professional contractors andlumber experts know what to look for, but average homeowners shopping fordo-it-yourself projects can buy the wrong thing if they're not careful, hecautions.
Homeowners should familiarize themselves with grade stamps for softwoodlumber, long used in the construction industry, and composite wood products suchas plywood and oriented strandboard (OSB). Hardwoods such as oak, maple andcherry have grade stamps as well, but these grades are geared toward theappearance of the wood for finish carpenters or furniture makers.
For structural lumber, Adams says there are three elements everydo-it-yourselfer should check on the grade stamp:
- Moisture content. There are two moisture grades, printed on stamps as "S-Dry," which means the board has less than 19 percent water weight, and "S-Grn" (for green), which means the board has more than 19 percent water weight. If you use wet wood in a project, the lumber will shrink, causing unsightly gaps or squeaky floors. If you buy green lumber or dry lumber that has been left out in the weather, try to buy and store it ahead of time so the wood can lose moisture.
- Species. Lumber associations have grouped many different softwood species into stamp categories that can contain one species or many. The most common in the northeastern United States are: Southern Pine, Spruce-Pine-Fir, Douglas Fir, or Hem-Fir. "Homeowners must know the species category because each one has different strength and structural properties," Adams says.
- Lumber grade. There are many different types of lumber grades, most aimed at the construction industry. Adams explains that most homeowners will see just four grades: Select Structural (SEL STR), No. 1, No. 2 and No. 3. Select structural is nearly knot-free and, as a result, is rare and very expensive, Adams explains. Select grades are typically used if appearance is important. Grades 1 through 3 are graded on how many knots appear in the board and how that affects the strength of the lumber.
|Composite wood products|
Composite wood products, such as plywood and oriented strandboard, also carrygrade stamps. Plywood is made by removing thin sheets of wood called veneers,which are glued together to form a solid sheet. OSB uses thin strands of woodthat are glued and compressed into a solid panel. Both products usually are soldin 4-by-8 panels.
The stamp will identify the product and also lists an exposure rating:
- Exposure 1
- Exposure 2
If the product will be exposed to weather, only exterior grade should beused. Panel products are made with waterproof adhesives, but repeated exposureto water will cause deterioration. A good rule of thumb is to paint or seal anypanel product if it is outdoors.
Adams points out that most home centers have knowledgeable sales staff thatcan recommend lumber for projects. He adds that a working knowledge of gradestamps will allow the consumer to check the quality and strength of materialswithout the help of a clerk or a contractor.
Standardized lumber came into use in the 19th century, as lumber became cheapand modern house framing developed. Eventually, lumber manufacturer associationsestablished standards for their members. In 1924 the Department of Commercestandardized lumber grades throughout the United States.
"The idea behind lumber grading is consistency of product quality andstrength standards," Adams says. "Also, in case of liability, lumbergrade stamps can show investigators where the product came from."
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