Construction · Lesson 4 of 13Intermediate10 min read

Framing

A wood-frame house has a skeleton of studs, joists and rafters, nailed together into floors, walls and a roof. This lesson names every piece, explains what each one does, and lets you frame a wall yourself.

Platform framing

In platform framing, a house is built one floor at a time. The first floor’s joists sit on the foundation and are covered with subfloor panels, making a flat platform. Carpenters frame each wall flat on that platform, then stand it up and nail it in place. The next floor’s joists rest on top of those walls, making the next platform, and so on up to the roof.

Older houses were sometimes balloon framed, with walls whose studs run the entire height from the sill plate to the roof. Tall walls like that are heavy: OSHA reported 22 collapses of hand-raised balloon-framed walls from 1999 to 2004, which killed five workers and injured 28. In one, 15 workers were raising a wall that weighed about 2,300 pounds. OSHA’s advice is to plan the lift, work out the wall’s weight, and have a competent person supervise it.

Each floor is built as a platform, and the walls for the next story stand on it. Sources: DOE Building Science Education Solution Center; University of Minnesota Extension (anchor bolts or straps at the sill plate).

Lumber: the name isn’t the size

A “2×4” isn’t 2 inches by 4 inches. The name is its size before it’s dried and planed smooth. A dry 2×4 is actually 1½ inches by 3½ inches, and the deeper sizes follow the same pattern.

The name is the size before the board is dried and planed smooth. Source: Missouri University of Science and Technology course notes, from the National Design Specification supplement.

Wood moves with moisture

Wood swells as it absorbs water and shrinks as it dries, but only below its fiber saturation point, around 25 to 30 percent moisture content for most species. It shrinks very unevenly: dried all the way down, wood shrinks about 8 percent along the growth rings, about 4 percent across them, and only about 0.1 percent along its length.

Inside a house, wood slowly settles to a moisture content that matches the air around it: about 6 percent at 30 percent relative humidity and about 9 to 10 percent at 50 percent. So framing installed wetter than that shrinks a little as it dries, mostly in width and thickness and hardly at all in length. Wood kept below about 20 percent moisture is also less likely to be attacked by decay fungi and insects.

Wall framing

A wall is a bottom plate, a row of vertical studs, and a top plate. Traditionally, walls get a double top plate, and wood-framed houses have been built with 2×4 studs spaced 16 inches on center. Codes allow wider spacing in some cases, and the Department of Energy’s “advanced framing” approach uses 2×6 studs 24 inches on center: less wood, fewer thermal bridges, and more room for insulation.

“On center” means measured from the center of one stud to the center of the next. Carpenters mark the stud locations on the top and bottom plates together, so the studs line up. The same spacing is how a stud finder’s first hit helps you find the next one (Being an Adult 101).

Openings need extra parts. A header spans the top of a window or door opening and carries the load from above sideways to the studs on each side. A short jack stud under each end of the header holds it up, and a full-height king stud stands beside each jack. A window gets a rough sill at the bottom, and short cripple studs above the header and below the sill keep the on-center layout going so sheathing and drywall still land on wood. The header’s size comes from the code’s tables or an engineer; in a wall that carries no load, an open header can be used.

Studs 16 inches on center; a 4-foot rough opening. The header size here is only a drawing: real header sizes come from the code’s tables or an engineer. Source: DOE Building Science Education Solution Center.

Press “Next step” to frame a 12-foot wall with a window, or change the length, spacing and opening. Tap any piece to see its name and job. The counts update as you go.

Framing parts and what they do
Part	What it does	Signs of trouble
Sill plate	Wood plate on top of the foundation, held down with anchor bolts or straps.	Rot or insect damage; air leaks at the joint.
Rim joist	Wraps the ends of the floor joists around the edge of the floor.	Drafts and cold floors where it isn’t sealed and insulated.
Floor joists	Span between supports and carry the floor.	Bounce, sag, cracks, notches cut by past repairs.
Subfloor	Sheathing panels that make the platform.	Squeaks, soft spots from water damage.
Bottom and top plates	Hold the studs in line and spread loads.	Rot at the bottom plate from leaks.
Studs	Carry loads down; give sheathing and drywall something to fasten to.	Cracks, holes cut too big for pipes or wires.
Header	Beam over an opening; carries the load to the jack studs.	Sagging over doors and windows; cracks at the corners.
King and jack studs	Frame the sides of an opening; jacks hold up the header.	Doors and windows that stick or go out of square.
Cripple studs	Short studs above headers and below sills that keep the layout.	Rarely a problem on their own.
Wall sheathing	Panels nailed to the studs that stiffen the wall against racking.	Rot from leaks behind siding.

Floors and sheathing

A floor starts with the sill plate anchored to the foundation, then a rim joist around the edge and floor joists spanning across, covered with subfloor panels. Air can leak in through the joints of the sill and rim joist, so those get sealed and insulated, with rigid foam cut to fit or with spray foam.

Walls get wall sheathing, often oriented strandboard (OSB): a structural panel made from thin wood strands bonded with water-resistant adhesive. Nailed to the studs, sheathing turns a wall into a stiff panel that resists racking, the triangle idea from Lesson 2.

Engineered lumber

Engineered wood products glue smaller pieces into bigger, more uniform ones:

Laminated veneer lumber (LVL) is made by laminating thin wood veneers with all the plies running the length of the piece. LVL is also used for the flanges of prefabricated I-joists.
I-joists look like a capital I: wide top and bottom flanges joined by a thin web. The flanges, far from the middle, do most of the work in bending, the same depth-matters idea as a deep joist.
Glued-laminated timber (glulam) is an engineered, stress-rated product of two or more layers of lumber glued together.

Engineered lumber comes with the manufacturer’s span and installation tables, and holes and notches may only go where those instructions allow.

StopIs that wall load-bearing?

It can be hard to tell. A wall may hold up joists, a beam, or a post from the floor above. Removing or cutting a load-bearing wall, beam, joist or header changes the load path. It needs a permit, and usually an engineer to design the new beam and posts and the footings under them.

NoteNail guns

Framing crews use nail guns, and OSHA reports about 37,000 emergency-room visits a year from them, most of them workers. The risk of injury is about twice as high with a multi-shot contact trigger as with a single-shot sequential trigger.

Check yourself

Tap an answer to check it, or open “Show the answer.”

What is the actual size of a dry 2×4?
Show the answer
1½ × 3½ inches. The name is the size before drying and planing. Dry 2×4s are 1½ inches by 3½ inches.
Which stud holds up the end of a header?
Show the answer
A jack stud. Jack studs stand under the ends of the header; king studs run full height beside them.
What do cripple studs do?
Show the answer
Keep the stud layout going above headers and below sills. They keep wood on the on-center layout so sheathing and drywall can be fastened.
In which direction does wood shrink the least as it dries?
Show the answer
Along its length. About 0.1 percent along the length, compared with about 4 to 8 percent across the grain.
In platform framing, what do the walls of the second story stand on?
Show the answer
The floor platform built on the first-story walls. Each floor is a platform, and the next story’s walls are built on it.

Go deeper

U.S. DOE Building Science Education Solution Center: Framing: Building a Wall: Advanced Framing DOE on advanced framing: 24-inch spacing, single top plates and fewer studs.
Oregon State University Extension: Wood and Moisture Relationships (EM 8600) Oregon State Extension: how wood and moisture interact.
USDA Forest Products Laboratory, Wood Handbook (FPL-GTR-282, 2021), Chapter 12: Mechanical Properties of Wood-Based Composite Materials USDA Forest Products Laboratory: engineered wood products in depth.
Being an Adult 101: Find a Stud and Hang a Picture Find a stud and hang a picture, with the on-center math.
Lesson 5: Roofs Next: rafters, trusses and the roof.

Sources

I finished this lessonSaved on this device only.

A free course from Teddy Rook Book. It explains how houses are built in general and follows U.S. sources; the local building code, the building department and the manufacturer’s instructions are the final word.