Here's how to build an exterior wall

Building a wall is but one of many tasks involved with the construction of a room addition or an extensive remodel. Knowing a few "whys" and "hows" about the assembly can simplify the process and eliminate a lot of heartache.

A few wall rules:

* An exterior wall should be built directly over some sort of foundation. The new foundation should match what you already have (assuming you have a proper foundation). If your existing foundation has piers, then so should the new one. No piers, then none in the new one.

The idea here is that you want your new and old foundations to react to natural movement of the earth below in an identical fashion. It is always wise to have an engineer involved when it comes to the foundation.

* Any wall (interior or exterior) that will be supporting weight (a floor above or a roof) must be itself supported by either a foundation or very sturdy floor members of its own. When a wall runs parallel to the floor, framing members above it is usually known as "nonbearing" (not structural). Framing members that lay atop a wall (ceiling, floor above, roof rafters, etc.) place a "load" (weight from other parts of the structure) on that wall and it is therefore known as a "load bearing" or "bearing wall." Load-bearing walls must be built in accordance with many rules. Nonload-bearing walls can be built following almost no rules.

* It is a good practice to frame a wall so that the studs are spaced 16 inches apart. Walls that don't carry a load can use stud spacing up to 24 inches on center. This wider stud spacing represents a very small amount of cost savings but renders a very flimsy end result. We don't feel it is worth the savings.

* When possible, it is better to construct a wall using 2x6 studs rather than 2x4s. Besides being more energy-efficient (more room for insulation), a 2x6 wall is superior in several other ways -- less vibration and movement in the wind, less sound transference, better load carrying capacity. When extending the length of a wall, the same width studs must be used. This is one case where moving up to a thicker wall is not recommended.

There are only a few elements that make up a basic wall:

* The "bottom plate" is the continuous piece that travels horizontally along the bottom of the wall. When the bottom plate lies on concrete, it must be pressure-treated.

* The "top plate" is the continuous piece that travels horizontally along the top of the wall. There are usually two top plates. The top plate is doubled to add strength and rigidity to the top of the wall. It is not needed at the bottom where the wall is connected to the floor.

* The "studs" are the vertical pieces that extend from bottom to top. The stud should always be a single piece of wood that travels from plate to plate.

Door and window openings must be constructed following certain rules:

* A solid piece of timber known as a "header" must be used to carry the load across any space where studs are removed to accommodate an opening.

* A header is usually the same thickness as the wall and at least one inch high for each foot of opening width. For example: For a common four-foot opening in a 2x4 wall, a 4x4 header would be needed, four inches for the width of the wall and one inch high for each of the four feet of opening width.

Most contractors use 4x12 as their standard header because it meets the load requirements for more than 95 percent of all openings and because when it is installed immediately beneath the top plate it comes down to 6-foot-10 inches high, which is the top of the opening height used for most doors and windows.

* Headers are cut a few inches longer than the opening width so that one or two studs can be placed under each end of the header for support. In construction there must something underneath everything above. For example: An opening for a three-foot window would need a 3-foot-3-inch header -- three feet for the window and one-and-a-half inches on either end for a stud. Longer headers need two studs under each end.

There are rules about how many nails must be used in each location to ensure proper wall strength. However, equally important is that when pieces of the puzzle are joined, it is imperative that they be sandwiched tightly together. Just nailing a connection is not enough. There must be no space between connections.

Here are a few nailing rules:

* Use at least 16d nails for 2x thick walls.

* When attaching the top and bottom plates use two nails at each end of each stud.

* When attaching a header to the top plate use two nails at each end of the header and at least one every 18 inches (stagger them).

* There should be a stud at each end of every header. Besides the two nails in each end top and bottom, the stud should be nailed to the end of the header as well. A minimum of five nails should be used.

One rule never to forget when nailing: Never, never, use anything like talcum powder or baby oil to lubricate the nails to make them go in easier. This will definitely void your warranty. The nails will pull out easily and your wall might come tumbling down.

And that's all there is to it.