Anatomy of Walls and Ceilings

The projects featured on this Web site revolve around the construction and modification of interior walls and spaces. They involve basic carpentry skills and techniques. Most houses are stick-framed; that is, their skeletons are built from a framework of relatively small pieces of wood. Typical interior walls are framed with 2x4s. This makes walls about 4-1/2 inches thick (3-1/2 inches of wood covered on both sides by 1/2-inch-thick drywall).

Terminology

All 2x4s look the same, but as you begin to fasten them together, you'll call them by different names, depending on their position within the wall. The studs are the vertical pieces that make up most of a wall's frame. The cavities between the studs are called bays (or stud bays). A horizontal piece at the bottom of the wall is called the bottom plate. The studs are nailed to this plate, which is nailed to the floor. At the top of the wall is the top plate. Often a doubled 2x4, it anchors the top ends of the studs as well as ties the wall into the ceiling.

In new construction, the walls are usually built while on the floor, with a single top plate. The second layer, which ties them together, is added after the walls are raised into position. Sometimes blocking is added between the studs. Blocking provides a solid spot in the wall for attaching things such as cabinets or handrails. In some situations, blocking is required as a fire-stop where a stud bay extends between floors. This keeps the bay from acting as a chimney for a fire. Without fire-stops, a fire could quickly spread from floor to floor. Blocking and extra studs also are used to catch the edge of the drywall at corners and in places where the stud spacing doesn't work out perfectly.

Openings for doors or windows

An opening in a wall, such as one for a doorway or window, has its own set of terms. The opening itself is called the rough opening. The size of the rough opening is specified by the manufacturer of the door or window. Typically, it's 1 inch larger than the outside dimensions of whatever is to fill it. Doubled studs stand on both sides of the opening. One stud of each pair runs from plate to plate, called the king stud. The other stud determines the height of the opening. This is the jack stud, or trimmer. Resting on top of the jack stud is a header. Depending on how much weight (load) the wall has to carry, the header may be fairly thick (the weight has to be transferred from over the opening to the jack studs) or it may be quite thin (if the wall doesn't support any weight). Sometimes, headers are topped by short pieces of wood known as cripple studs, which are used to help support drywall and trim pieces.

Types of walls

A wall that supports the weight of the building above is a bearing wall and is said to be structural. If a wall merely divides the interior space, it is not structural but simply a partition wall.

The framing members in the floor and in the ceiling are called joists. Underfoot, a subfloor is nailed to the joists. The walls are usually fastened to the subfloor. Overhead, drywall can be attached to the underside of the ceiling joists, or if you prefer, the grid for a dropped ceiling can be attached to them.

Framed with 2x4s: Skip the skinny sticks

You might be tempted to frame a wall using 2x3s to save money and space, but don't do it. The slight amount of space you'll gain and the few pennies you'll save are not worth the frustration you'll encounter working with 2x3s. These skinny sticks of lumber are notorious for warping and twisting. If you build with warped and twisted wood, there is little chance that the wall will turn out straight and true.

Why 16 inches?

In much residential construction, the wall studs and the floor and ceiling joists are spaced 16 inches on center. (On center, or OC, indicates the distance from the center of one member to the center of the next.) Why 16 inches? Plywood or oriented strand board used to sheathe the outside of the walls and the drywall used to finish the inside all come in sheets 48 inches (4 feet) wide. The 4-foot width spans four studs spaced 16 inches apart, with the edges of the sheet at the middle of the outer studs. Spacing studs and joists 16 inches on center is a nice compromise between strength and economy that allows efficient use of 4x8 sheet stock.

Framing Terminology

Before planning your interior wall project, learn the names and roles of all the wall-framing components.

 

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