For constructing, insulating, and completing residential homes, solid wood and different wood-based compounds are typically the material of choice. When building a house, and negotiating with your contractor, it's important to understand the basics of wood framing, and the different kinds of wood available. This article outlines the different kinds of wood on offer and outlines how to choose between different lumber products for framing and other construction applications.
The quality of wood used for home framing is known as framing lumber, sometimes known as structural wood. When broad spans are required, its technical properties make it ideal. The table below lists the many types of wood widely used as framing material for house building and, increasingly, timber frames for multi-family low to mid-rise construction in the United States. Keep in mind that there is a difference between structural lumber and sawn lumber. The former refers to the graded pieces of wood used for framing, while the latter refers to any type of wood, cut apart following trees being harvested.
Species like spruce, pine, and fir are hundreds of years old at the time of harvest. They grow in temperate climates that often see freezing temperatures during winter. All these species share similar characteristics; they are light in color, straight-grained with good weathering properties, usually easy to work with, not subject to warping due to changes in moisture, and easy to stain or paint.
Commercially available spruce framing lumber is graded #1 (excellent) or #2 (good). Spruce is used primarily in residential construction for single-family houses; it's also used for covering the exterior of multifamily buildings. Spruce is readily available and relatively easy to work with. It's not a preferred framing species for flooring because it tends to warp, though it may be used in some areas if carefully installed.
Pine is also widely known as yellow pine or western pine, due to its availability on the US Pacific coast. It's sometimes called construction pine, owing to its usage in residential framing. Pine is also used for fencing, telephone poles, and railroad ties. Pine is typically graded #2 (good) or #3 (common). Grade #2 is the better of the two; it has fewer knots and wider widths than grade #3. Yellow pine is generally knotty, due to gum pockets on the wood rays. Its grain pattern ranges from straight to slightly wavy. Pine is easy to work with and available at most lumberyards. It's readily available in framing grade, but flooring grades are usually hard to find.
This species has excellent weathering qualities and is often used on the exterior of homes. Common fir, also known as Douglas fir or Oregon pine, comes from the Pacific Northwest states. It's graded #2 (good) or #3 (common). The best grades are knot-free with clear wood between knots. Common grades of this wood tend to have lots of knots. However, it's easy to work with and finishes well. Exterior grades are available in framing lumber widths, but interior grades may be difficult to find.
All three varieties of softwood mentioned above fall in the 'Light Structural Lumber' category and are mainly used in the construction of single-family homes. They are factory-cut to specific dimensions are generally very easy to work with.
Hardwood or heavy timber refers to any lumber with a thickness greater than 4.5" and is commonly used in post-and-beam or timber frame construction. Wood with large dimensions can carry enormous loads and allow for vast spans, as well as being remarkably fire-resistant. The most commonly used wood species in this class are oak, Douglas Fir, and southern yellow pine.
Oak is a heavy hardwood that's been used in construction for centuries. It has a coarse texture with poor nail and screw holding qualities compared to softwoods like fir or pine. Oak timbers are graded #2 (good) and #3 (common). Oak is frequently used in heavy construction, such as bridges and buildings. It's also difficult to bend and form because of its interlocked grain pattern.
This wood is great for exterior work; it doesn't warp or twist as some other woods do. Douglas fir lumber is graded #2 (good) and #3 (common). Exterior grades are knot-free with good face values; it's also graded under the National Hardwood Lumber Association grading rules. Douglas fir is strong, stiff, and decay-resistant.
Southern Yellow Pine
This wood is suitable for interior work only because of its lack of durability in moist conditions. It's highly stable, but hard to nail. Southern yellow pine is graded #2 (good) and #3 (common). Grades #2 and #3 are knot-free with straight grain.
Finger-Jointed Lumber (FJL)
FJL is lumber (hardwood or softwood ) made from short, dry wood pieces that have been milled on both ends and glued together with a water-resistant structural adhesive. This technique is environmentally friendly since it uses short pieces of wood to construct a larger, more stable, and simpler to align finished product. Finger-jointed lumber is usually used in commercial construction and can be made from a variety of wood species.
Engineered wood requires more work to be fit for wood framing than standard lumber. As such, it is more expensive than the other forms mentioned earlier, and it has a larger eco-footprint due to the various processes it goes through.
Here are the main types of Engineered Wood used in house construction projects across the US.
Oriented Strand Board (OSB)
OSB is the most common type of engineered wood sheet-good used in house construction. It comes in 4'x8' sheets and is made by binding wood strands (similar to papermaking ) with water-resistant adhesive on two top and bottom surfaces. Then, it's pressed into a mat with a mesh of wood strands on the surface.
These mats are then placed onto a large metal pan and sent through a dryer to remove moisture, leaving them with an R-value of .45. In general, this material serves as an excellent sheathing or underlayment for framed walls because it's inexpensive, easy to install, and moisture-resistant.
Plywood is made up of an odd number of layers (usually three or five) of wood that are cross-bonded with a waterproof adhesive to form a single sheet. It's commonly used for subflooring, roofs, floors, and walls. It can be made from hardwood or softwood and comes in a variety of grades: exterior, moisture-resistant, and marine (boats).
The construction process of CLSCT includes many sheets of wood stacked on top of each other and then bonded together. The result is a wood material that's less likely to shrink, swell, or split. CLSCT is often used for exterior and non-loadbearing walls because it's strong and can span large distances without an interior support system like beams or posts. It has the same R-value as concrete (3.5), which makes it very energy efficient.
Understanding the kinds of lumber used in home construction gives you a better position to negotiate and discuss the construction process with your contractor. It's always best to ask questions and make sure you understand what is being provided for your building project.
Note: Image credit - Wikipedia