DIY Lumber and Plywood Guide

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 molding boards 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 building 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 1½ by 3½ inches in size. In fact, all the timbers mentioned above will be about ½inch smaller than the nominal size. This wasn't always the case, before the 1960's these boards were actually the stated size, these can be found in early, historic homes.

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 these sizes and longer ones usually up to about 20 feet. If you're planning a project like a shed or deck these longer pieces can come in handy for floor and ceiling joists when you don't want to breakup the structure.

Finish Lumber:

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.

Finish lumber is 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 finish lumber 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.

Furring Strip:

This is a rough-cut piece of lumber meaning the finish is not smooth because furring strips are not usually surfaced with a planer. Nominal sizes are 1x2 or 1x3, but the actual sizes are smaller. These are used frequently for furring walls and ceilings when the addition of a new wall material such as paneling or drywall is required. 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 basic construction needs.

Grade:

A system for determining the quality of wood. Smooth, straight pieces of wood with no knots or other imperfections are graded A. Grade B has minor flaws such as small knots, but is still of high quality with a surface suitable for exposed finishes. Grade C has more flaws, knots that may or may not be filled with plugs and a rougher finish than the higher grades. C grade wood is better suited for construction features that will be hidden or painted. You will most often see this grading system used for plywood products where sheets are graded A-B, B-C and C-D to indicate one side that's better than the other.

Molding:

Trim molding is used to add an attractive finished edge around wall openings like doors and windows, along floors and ceilings or to create a decorative design to add 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 can be 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 available 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.

Rough-Cut Lumber:

Rough-cut lumber is produced when trees are cut at a sawmill, 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.

Surfaced Lumber:

These are the rough-cut boards that have been planed to create a smooth surface. Dimension lumber like 2x4's, finished lumber like 1x4's and trim moldings are all examples of surfaced lumber. The lumber industry uses the standard label: S4S (surfaced four sides), to indicate surfaced lumber that has been planed smooth on all four sides.

Timbers:

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 sawdust together to form sheets of 1|4, 1|2, or 3|4 inches and then covered with an attractive veneer and used to make the backs and sides of large furniture pieces and kitchen cabinets. 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 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 will be better than the other 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 storage structures. Particle board, wafer board and hardboard, commonly called masonite, are also easy to find at a local supplier but finer woods like veneered finish plywood will require some searching to locate.

Sheet Materials Terms

Finish Plywood:

Smooth sheets of softwoods like pine and hardwoods like oak, maple, and birch. Finish plywood will have an A-B or A-C grade 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.

Hardboard:

This sheet material is manufactured by gluing paper thin sheets of wood together to make 4x8 sheets and sold under the brand name: Masonite. Hardboard is commonly found in 1|8 and 1|4 inch thickness and used to make furniture backing, drawer bottoms or bored with a grid pattern of holes that can be used to make peg boards for storage and display.

Medium Density Fiberboard (MDF):

This is a high quality hardboard used to make furniture and cabinets including side panels, doors and drawer fronts. MDF is most often painted to create an attractive finish, or a faux wood finish may be applied to create the look of fine furniture. Doors and drawer fronts will often be shaped with a trim molding profile around edges to add to this effect.

MDF comes in 4x8 foot sheets that are slightly larger than the stated size, this extra material allows for the saw kerf when cutting the large sheets down to make doors or panels. For stability and to prevent warping of the material, MDF is manufactured in thickness of 3|4, 1 and 1¼ inches. In addition to sheets, MDF is also used to make trim by molding a decorative profiles in a casting process. MDF crown molding, door and window casings and chair rails can all be found at local home stores in lengths up to about 20ft.

Particle Board:

Sheet material manufactured by mixing glue and sawdust and casting the liquid to make a large sheet. This material is often used as the base for countertops and then formica is glued down to create a smooth, 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 mostly for sub-floors and wall covering when building homes and other small structures. Sheathing is usually graded C-D and can be designed for interior or exterior applications. Thickness available at home stores start at 1|4 inch and go up to 3|4 inch. Because it serves as a underlayment, sheathing will have flaws that are visually obvious, but won't effect the structural soundness of the material. You will often see oval shaped plugs in the sheets where knots or other imperfections have been repaired.

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.

Wafer Board:

Sheet material manufactured by gluing chips of wood together and used primarily for sub-floors and sheathing on building siding. Like particle board, wafer board is very vulnerable to moisture and should not be used where it will come in contact with water. Because of the nature of wafer board construction it is not suitable for producing thin sheets, you will find it in 1|2 and 3|4 inch thickness.

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