Building Regulations on Wall Thickness

Regulations

• Though local and state building regulations vary slightly based on the needs of their populations, they're all based on the International Residential Code (IRC) maintained by the International Code Council. Founded in 1994, this non-profit member organization is also responsible for streamlining other construction standards that can affect wall thickness, including the International Fire Code, the International Energy Conservation Code and the International Building Code. Its mission is to “provide the highest quality codes, standards, products and services for all concerned with the safety and performance of the built environment.” The IRC defines the wall thickness of the supporting frame only. It has no requirements for the total thickness of finished walls.

Concrete

• Interior concrete walls that are not part of a basement foundation can have a minimum thickness ranging from 4 to 10 inches if they're of flat, solid construction. The thinnest option allows a maximum weight capacity of 50 pounds per square foot (psf) while the thickest option allows 125 psf. For waffle-grid walls, which have interior spaces, the minimums range from 6 inches with a maximum weight of 56 psf to 8 inches with a weight of 76 psf. A screen grid wall, which also has interior spaces, must have a minimum thickness of 6 inches for a maximum weight of 53 psf.

Steel

• Steel framing is becoming popular because of its durability, design flexibility and natural fire resistance. The IRC defines two dimensions of cold-formed steel studs that relate to wall thickness. The first is the web depth, which represents the greatest dimension of the stud. This can be 3.5 or 5.5 inches, as long as the stud has a flange width from 1.625 to 2 inches, and a lip size of at least 1/2 inch. The second is the thickness of the steel itself. The minimum can range from 0.0329 to 0.0966 inch. This designation is typically stamped on the steel member itself. For example, a designation of 359S162-33 indicates a web depth of 3.5, a flange width of 1.62 inches and a thickness of 33 mils, which is equal to 0.0329 inch.

Wood

• Aside from their lengths, wood stud dimensions are generally defined by two numbers such as 2-by-4. Both numbers represent inches, with the first designating the depth of the stud -- which in this case is 2 inches -- and the second showing the width, which in this case is 4 inches. The width defines the thickness of the walls since this part of the stud is perpendicular to the wall. Typical stud sizes range from 2-by-4 to 2-by-6, which puts the minimum wall thickness from 4 to 6 inches.