Conversion Factors for Cedar Siding

Conversion Basics

• In general, you can find the amount of cedar lumber you need by dividing 12 by the exposed face of the wall or other surface. The exposed surface should be measured in inches, although the result is in linear feet, so that an exposure of 6 inches requires 2 linear feet of siding per square foot (12 / 6 = 2). Board and batt siding is slightly different, requiring calculation of gaps between the boards, so 3/4 of an inch may be subtracted for more accurate measurements.

Exposed Face

• Exposed face is a general term of the width of the wall that will be exposed, or that will face the outside air without being overlapped or covered by other materials. Exposed face factors vary depending on the size of the siding, ranging between 2 1/2 to 10 1/2 inches wide for most projects. However, you should always remember to subtract space for any doors or windows that will not be covered with siding.

Nominal and Dressed

• Nominal and dressed are two other terms used when calculating conversion factors. They are not alternatives to exposed face, but are measurements that may make it easier to calculate materials. Nominal width varies from 4 to 12 inches and is the primary specification boards are sold under. For example, 2 x 4 boards have a nominal width of 4 inches. Dressed width is the actual width, which is usually around a 1/2-inch less.

Trim

• Trim is the extra siding that you will install around doors and windows. Trim can be difficult to accurately judge when it comes to amount, so after the normal conversion factors are used to calculate the necessary amount of cedar lumber, you can add 10 percent to the final amount to make room for any extra trim projects.