If you take a stroll through your local lumberyard or the lumber department of your big box home center, you'll find several rows of SPF dimension lumber. This is the lumber generally used for framing construction, and it includes all the "two-by" lumber (from two by fours up to two by 12s), as well as some of the "one-by" material (one by twos up to one by 12s). This lumber is known as SPF because it is normally milled from spruce, pine, or fir, which are the softwoods commonly used for construction-grade lumber.
What Is SPF Lumber?
These softwoods, often grown on tree farms, grow very quickly with trunks that are straight and tall. These trees yield softwoods with fewer knots but with growth rings that may be spaced farther apart than older trees harvested from old-growth forests.
Most softwoods are graded into four different grades, labeled A through D. There are also sub-standards within each grade, with categories such as Supreme, Choice, Quality, Construction, Standard, and Utility. Much of the higher-graded material ends up being sold to specific buyers, bypassing retailers altogether, while the grades that are best for structural uses end up in the lumberyards and home centers.
How SPF Lumber Is Harvested
Softwood trees such as the spruces, pines, and firs destined for construction lumber are harvested in a very methodical, factory-like manner. The trees are first felled, then the upper branches are lopped off. Immediately, the trunks are inspected and separated into anticipated grades before being loaded and hauled off to the mill. Once at the sawmill, these trees are milled into the most efficient sizes possible based on the tree grades, sizes, and requirements of the mill contracts. Any scraps left over by the milling process are captured and used in other processes to create manufactured wood products such as plywood, medium-density fiberboard (MDF), and particleboard.
Because it is harvested and milled "wet," without having had sufficient time to dry and shrink, the nominal sizes of the boards at the milling stage are larger than the actual size they will be after the boards have been cured and planed for sale. To get the wood closer to a usable state, most SPF lumber is put into large dryers for a period of "kiln-drying," which reduces the moisture content to an acceptable level for use. This kiln-drying produces more consistent lumber than wood simply allowed to air dry naturally. By reducing the moisture content, it also reduces the weight of the wood, lowering the cost of shipping the materials to market.
The drying process causes the boards to shrink somewhat, and final planing reduces the size slightly more. Thus, a board that carries a nominal measurement of two by four when it is milled is actually 1 1/2 x 3 1/2 inches in size by the time it reaches the lumberyard or home center.
- Note that dimensional SPF lumber is most often sold in nominal dimensions, such as two by four—this differs from hardwoods, which are typically graded and sold by the board foot.
- Most of the pressure-treated lumber you find in the home centers starts off as SPF lumber. The chemical treatment of this lumber generally occurs at another factory, where it is treated and dried before being shipped onward to lumber yards and home improvement centers.
Use In Fine Woodworking
Although most SPF dimension lumber is used in structural work where the wood will be hidden from view, it is completely possible to use SPF lumber in some fine woodworking projects. Although SPF is not the best choice for projects that will be stained, there are still many projects where the cheaper costs makes SPF an option worth considering.
When buying SPF lumber, keep in mind that you do not know with certainty what variety of spruce, pine, or fir you are buying. As such, if you intend to build a fine woodworking project out of SPF lumber and stain the project, you should choose all of your lumber from a single stack in the yard. This will greatly increase the likelihood that all of the materials are of the same species variety. Why does this matter? Each species absorbs stain a little bit differently, so if you use spruce on part of the project and pine on another part, the stain jobs likely will not match. Therefore, try to select all of your materials from the same stack of lumber to reduce the possibility that you're working with different species.
Choosing SPF Dimension Lumber
When choosing SPF lumber for your project, try to select boards that are as straight as possible (watching for warping, cupping, twisting, and bowing), and choose boards with as few knots as possible. This is often easier said than done, and some woodworkers eventually wish they had saved the time and spent a little more money to buy a higher-graded pine, poplar, or hardwood for their projects.
However, if you want to use SPF lumber, look closely at the end grains of the wood as you select boards. Look for boards whose grain patterns are tight, with the lines of the grain running vertically between the long sides of the board. This is indicative of quarter-sawn lumber. You're not likely to find much quarter-sawn lumber in the stacks at the home center, as quarter-sawn boards are normally graded out a bit higher and are sold to different customers. Still, where appearance is critical, it is worth the effort to look the rare quarter-sawn boards among the stacks of SPF lumber.
When using SPF lumber for your projects, buy about 25 percent more material than you need to allow for waste, and take the wood back to your shop and allow it to acclimatize to the local surroundings before using it in your projects. The time required for wood to reach a state of equilibrium with the local environment will vary depending on several factors: the species of wood, the starting moisture content of the wood, and the humidity of the local environment. The time is well worth it since a few weeks getting acclimated to the local environment will make the wood more stable to use.
Also, be aware that SPF lumber, particularly the grades found in home centers, will occasionally have pockets of sap (called pitch) in the fibers, which can be damaging to your saw blades and drill bits. Allowing the wood to acclimate will reduce these pockets of pitch, but if you encounter excess pitch in a stick of wood, you may want to replace it with one of the extras from your stack.