DIY Lumber and Plywood Guide

by: Dale Cox

2x4 wall corner frame

Most do-it-yourself construction projects will make use of lumber like 2x4's, and sheet materials like plywood for the bulk of the job. To help in identifying these product and choosing the right ones to use, we have put together this glossary of terms you'll encounter when planning for construction projects around the house. From wall framing to woodworking, this page offers examples and definitions of the most commonly available materials that will satisfy most requirements.

About Lumber:

Lumber is the term used to describe wood for framing walls and ceilings like 2x4's, thinner boards used for furniture and built-ins like 1x4's, and decorative trim moldings used to finish around edges and add beauty to room décor. When buying lumber products like these, always choose the straightest boards you can find to get the best possible end results with your project. Also, look for boards that are as dry as possible to prevent twisting and warping in your finished project as the wood dries out over time.

If you can afford it, buying kiln-dried wood is a good way to guarantee that you will get dry, stable boards that will hold their shape for the life of the finished product. Kiln-dried lumber is not always available from your local supplier and you may be forced to choose from wood that's still a bit wet. In these cases look for the lightest pieces in the stack, the heavier ones will still contain a good deal of moisture and will be more likely to loose their shape over time.

To choose a good piece of lumber for construction, look for straight timbers with no twists or warps and few blemishes like knots. Site down the length of the board while holding one end up to your eye and letting the other rest on the floor. Look down both planes: the edge (the thinner side) and the face (the broad side). A view of the edge of a board will reveal any warping or bows in the wood, and the face will show any twisting. Reject any boards that are not straight, using a warped or twisted board will result in an inferior finished project.

Lumber Terms

Dimension Lumber:
Also called timbers, these are the smooth, finished boards used in construction to frame walls, ceilings, and floors. These include: 2x3's, 2x4's, 2x6's, 2x8's, 2x10's, and sometimes 2x12's. Thicker timbers are also available in sizes like 4x4, 6x6, and 8x8 and are used for support members in floors and decking.
The sizes stated here are nominal, in name only and not exact. For example, a two by four is actually 1 ½ inches in size. In fact, all the lumber mentioned above will be about ½inch smaller than the nominal size. This wasn't always the case, these boards were closer to the stated size when early, historic homes were built. Lumber has been downsized several times over the past 100 years with the actual 2 inch by 4 inch studs from the early 1900's giving way to progressively smaller sizes until 1961 when the standards used today were established.
Dimension lumber lengths typically found at your local home store start at eight feet, these are typically used to build partition walls and similar projects around the house. Timber lengths will go up in two-foot intervals including: 10, 12, and 14 feet. In addition to these lengths, a lumberyard will have longer ones usually up to 22 or 24 feet.
Furring Strip:
These are thin boards usually 1x2 or 1x3 inches wide and 1/2 to 3/4 inches thick. These are used frequently for building out the framing of a wall or ceiling to install a new finish such as drywall or paneling. These boards tend to be of low quality with warping and blemishes like knots a common feature. Furring strips are not suited for applications where the wood will be visible, but they can be an economical choice for utility purposes.
Trim molding is used to add an attractive finish over gaps around doors, windows, floors, and ceilings. A couple of molding profiles used in combination can create a decorative design that adds interest to room décor.
Baseboard moldings are used to cover the gap between finished flooring and finished walls, casings are used to cover the rough opening around doors or windows, and crown molding are used to add a sense of refinement to a room by defining the lines between walls and ceiling.
There are many trim molding profile designs that can be used alone or in combination to create different styles in a room. For example, using the same types of profiles for crown molding and casings, any room can be transformed into Neoclassical, Georgian, Victorian or any other architectural style that strikes your fancy.
Nominal Size:
This is the stated size of lumber, the actual size is a bit smaller. When measuring and cutting check the lumber in question and use the actual size to be sure of accuracy in construction.
These are smooth surfaced boards in nominal sizes of 1x2 to 1x12 inches. All four surfaces of these boards are smoothed with a planer and commonly labeled S4S (surfaced 4 sides). As with dimension lumber, the stated sizes of these boards are larger than the actual sizes, for instance a 1x2 is actually 3/4 inches thick and 1½ inches wide. Common uses for these boards include: built-ins like bookcases as well as door and window casings, baseboards, exterior siding, cabinet doors, and furniture.
Planks are most commonly available in softwood like pine, but other woods can also be found at local suppliers. It's not unusual, for instance, to find hardwoods like oak, poplar, and birch planks at home stores. These are usually used for high quality cabinetry like built in bookcases for a smooth, hard painted finish. Oak is usually used for a natural finish when you want a rich, woodgrain finish for your project.
Rough-Cut Lumber:
Rough-cut lumber is the last stage of the milling process before the smooth planing. The finish left by the saw blade will be very rough with dense fibers sticking out from the wood. Some of these boards will be used like this for purposes where the finish isn't important such as with furring strips or fence railings. The rest of this rough-cut wood will be sent through a planner to smooth the surface on all four sides. These boards can then be used for finer work like moldings or furniture making.
This is the term most often used to describe large pieces of lumber like 6x6 posts or poles used to construct barns and other large out-buildings. You may also hear this term used to describe dimension lumber like 2x4's and 2x6's used to build walls and ceilings in stick-built homes. Sizes commonly available at local home stores and lumberyards are usually 4x4's, 6x6's and 8x8's.

About Sheet Materials

Sheet materials for construction projects are manufactured by taking small wood pieces and gluing them together to make large, thin sheets. Chips, sawdust, and very thin layers of wood are all used to make finished pieces that can then be used to cover wide areas for building walls, floors, furniture, and more. For example, particle board is made by gluing wood chips and sawdust together to form sheets up to 3|4 inches thick, it is often covered with a hard veneer like formica and used to make panels and doors for large furniture pieces and kitchen countertops. Sheet materials are most often available in 4x8 foot sizes, but smaller pieces can also be found at home stores that cut the large sheets down for the convenience of their customers.

There are various grades of sheet materials available for different purposes, and your project will determine the grade to use. For example, plywood is available for interior and exterior applications and comes in an array of grades that go from basic sheathing for siding, flooring, and roofing to high quality hardwood veneers used to make fine furniture and cabinets.

This grading system makes use of letters to distinguish the quality of the wood finish with A being the best, or smoothest surface, and D being the other end of the spectrum where the sheet may have many blemishes and knots in the finish. Plywood finish quality is broken down further into two different grades for the same sheet. Here one side of the sheet, the face, will be better than the other, backside, and have a grade such as B-C. This is done because one side of the sheet will usually not be visible in the finished project, using the best side for the outside and making the other of lower quality will save the unnecessary expense of having two primo sides on a sheet.

Typically you will find a basic selection of sheet materials at home stores including C-D plywood sheathing in thicknesses of 1|4 to 3|4 inch and higher grades like B-C plywood that can be used to build shelving and other basic structures. MDF, hardboard, and particle board are also easy to find at a local home store, but hardwood plywood will require some searching to locate.

Sheet Materials Terms

High density fiberboard made by pressing wet wood fibers into a smooth, hard finish. Four by eight foot sheets are available in 1/8 and 1/4 inch thicknesses. Hardboard is commonly used to make furniture backing and drawer bottoms, or perforated with holes and used to make pegboards for storage and display.
Hardwood Plywood:
Smooth sheets of hardwoods like oak, maple, and birch will have a high grade such as A-B or A-C and are not usually available at a home store, these grades are often reserved for fine cabinetry and furniture and if available, will usually be limited to one or two species like oak and maple. If you want high quality plywood like this in woods like mahogany and walnut you will almost certainly have to visit a millwork lumberyard or a cabinetmaker's shop. Cabinetmakers sometimes sell fine plywood and lumber to the public in addition to making custom furniture and cabinets for sale.
Medium Density Fiberboard (MDF):
This is a manufactured sheet product made by pressing wood fibers and resin at high temperatures to make a quality hardboard. This product is often used to make side panels, doors, and drawer fronts for furniture and cabinetmaking. It can be shaped and cut like wood so doors, drawer fronts, and other features can be shaped to create decorative profiles around the edges. MDF is most often painted, or a veneer may be applied to create the look of fine furniture. In addition to sheets, trim moldings made of MDF are available for crown molding, door and window casings, and chair rails. These can all be found at local home stores in lengths of up to 16ft.
Although it makes a good building material, MDF is known to emit formaldehyde. Exposure to dust when cutting it poses a health risk as does just having it in close proximity. Wear an approved dust mask when working with this material and seal all the finished surfaces with paint or another solid coating before assembling the final project.
Particle Board:
Sheet material manufactured by mixing resins with wood chips and sawdust and pressing it into large sheets. The main appeal of particle board is price, it's often used to make affordable countertops with a formica veneer glued down to create a smooth, durable, non-porous finish. Other common uses include underlayment for floors and panels for low-end cabinets and furniture. Here too, the particle board is laminated to make a durable finish that can standup to everyday use. This material should not be used for exterior applications where it will come in contact with moisture. If particle board gets wet it will quickly absorb water and expand until it begins to crumble and fall apart.
Plywood Sheathing:
Plywood sheathing is used for sub-floors, walls, and roofs when building homes and other small structures. Sheathing is usually graded C-D and can be designed for interior or exterior applications. Exterior sheathing will often be labeled CDX where the X denotes exterior applications. Thickness available at home stores start at 1|4 inch and go up to 3|4 inch. Because it serves as an underlayment, sheathing will have flaws that are visually obvious, but won't effect the structural soundness of the material.
T-111 Plywood:
This is an exterior plywood with grooves cut in the face for decorative effect. The groove pattern may be at regular intervals or it may be random to add more interest to the finish. T-111 is most often used for exterior siding on homes and small outbuildings, the finish is then painted or stained to preserve the wood and the structure. This material comes in thickness of 3|8 up to 3|4 inch and can usually be found at local home stores.