You may not have given it much thought, but exterior walls are pretty sophisticated systems! They are called upon to keep the elements out, keep your conditioned air in, and provide support for your roof.
Exterior walls as a system include not only the structural parts but also the siding, sheathing, insulation, and drywall, as well as the exterior doors and windows. It also may contain parts of other systems like the plumbing or wiring.
Most walls are constructed of 2x4 lumber. Some homes use 2x6's for the exterior walls so that more insulation can be used. Steel studs have been promoted for homes, but these haven't caught on in most places.
The parts of a wall include:
This member is usually the same size as the studs. If you are building on a concrete slab, this member should be treated wood. The codes actually permit this member to be a 1x (remember, this is pronounced "one-by") but most builders use a 2x because it gives them more surface to nail the floor board to when the trim work is being done.
The bottom plate for exterior walls is often set on a bed of caulk or a "sill sealer", which is a roll of insulating material as wide as the plate. This will help prevent heat loss and infiltration under the outside walls.
In the case of a slab, the bottom plates of exterior walls are bolted to slab.
These are the vertical members of the wall. They are usually placed at 16" or 24" on center. When you space the studs in the exterior wall at 24" on center, you reduce the wood in the outside wall, which can help save energy (wood is a much poorer insulator than fiberglass). Blocking between the studs is required on walls over eight feet tall.
Most builders use two top plates. The uppermost is used to overlap and tie adjacent walls together. It also helps keep walls straight.
A single top plate has been approved by the codes if the roof trusses are placed directly over the studs.
In this case, the breaks in the top plate and adjacent walls must be tied together with steel plates called tie plates. These are approximately 3" x 6" and come with nail holes.
This is bracing designed to prevent racking - this is the movement in a rectangle which would cause it to become a parallelogram.
Corner bracing is usually a 1x4 "let-in" to the studs at a diagonal. Let-in means that the studs are notched the depth of the brace - usually 3/4" - so that the brace is flush with the interior surface of the stud and hence does not interfere with the later application of drywall to the studs.
Another method of bracing the corner is to simply use a piece of plywood on the outside in place of sheathing at the corner. The third form of commonly used bracing is the metal strap. Its cross sectional shape is a "T". A saw kerf in the appropriate location of each stud is all that is required to prepare this brace for nailing.
Headers are used to span openings, like over a door or window. Usually a header is constructed of two 2x's placed on edge.
An alternate method suggested in the Arkansas Home , an energy efficient system once promoted by Owens Corning Fiberglas, is to glue and nail a piece of plywood to the outside of the studs above the window or door opening.
The advantage is that you have an open space for insulation.
Headers are supported by "jack studs" or "jacks." The continuation of the studs between the header and the top plate is called a "cripple." In concrete block construction, the header is a prefabricated, reinforced concrete lintel, which simply sits on the blocks that frame the opening.
Dead wood is nailed to the sides of wall studs and top plates to provide a nailing surface for the edges of the drywall. Since it has no structural duties, scrap materials can be used.
Dead wood can be eliminated entirely if drywall clips are used. These are metal clips designed to secure the drywall edges to the framing members.
By using these clips, the third member of a wall "corner" can be eliminated allowing the corner to be insulated.
Other than that, they probably don't save much, since scrap materials (bracing, etc.) can be used for dead wood.
A Note On Load Bearing Vs. Non-Load Bearing Walls
Load bearing walls carry the load of the ceiling and roof structure to the foundation. Non-load bearing walls carry their own weight.
Framing around door and window openings in non-load bearing walls can be much simpler. Headers can be single 2x's framed flat, with no supporting jacks.
It's not always easy for the novice to tell which walls are load bearing. You really don't need to worry with this level of detail. The framers will do it automatically. The framing inspector will make sure.
The next step in the structural tour (from the ground up) is your ceiling. Click here.
For additional information on house foundations,
see Lesson Five and Lesson Fifteen of our online course
Successful Home Contracting.
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