Walls are what distinguish the inside of a building from the outside. Without walls, everything would be outside and nothing would be inside. Without interior walls, a building would consist of one all-encompassing room. Building the exterior and interior walls in the right thickness is fairly standard, but circumstances may change from standard to custom depending upon the desire of the homeowner. Unlike many interior walls, exterior walls need to be thick enough to provide adequate insulation.
Both exterior and interior walls are built similarly, with the outside wall having a somewhat different makeup. The studs -- or framework inside the wall -- are almost always 2 inches thick and 4 inches wide. Adding a sheath of 1/2-inch drywall to both sides of an interior wall yields a standard 5-inch-thick wall. An exterior wall has a 1/2-inch sheath of drywall on the inside and 1/2-inch plywood on the outside. That makes about a 5-inch thickness for its basic construction.
An exterior wall also has extra material on the outside, giving it greater width. Brick, stone, stucco, vinyl, wood and cement fabric are all used as home sidings. These may add another 1 to 3 inches to the wall's thickness. Some homes are constructed with 6-inch-deep studs instead of 4 inches. This yields 2 extra inches for insulation but increases the cost of other areas, such as windows and doors installation.
Walls can be modified for a variety of reasons that increase their depth. For example, an easy way to create a better sound barrier is to put two layers of drywall on one side of a wall. The second layer is attached horizontally instead of vertically. This increases its thickness by 1/2 inch. Wood or faux brick paneling put over interior walls also increases the thickness by a small amount.
Specialty-type homes have walls that can be quite thick. A rammed, or packed-earth, home has exterior walls as thick as 18 to 24 inches thick. An insulated concrete form wall rangers over 12 inches thick by the time the exterior and interior additions are complete. Wood cabin exterior walls range from 1- to 3 1/2-inch-thick boards, while log homes average between 12 to 16 inches thick.