What is the Size of Decking Lumber?

Although decking lumber comes in conventional sizes, there is no standard. While a decking material's dimensions affect a deck's appearance and installation requirements, its type mainly determines longevity and weathering characteristics. Both dimensions and type influence cost; wide planks generally cost more than narrow ones, and scarce species more than abundant ones. Learning about decking lumber dimensions and types prepares you to choose materials that suit both your budget and design preferences.

Common Sizes

Uniform size and spacing gives deck planks a clean look.

The most common dimensions of decking lumber are 1 1/2-by-3 1/2-inch boards, called 2-by-4, and 1 1/2-by-5 1/2-inch boards, called 2-by-6. Both of the common sizes of lumber are readily available at lumberyards and home improvement stores. Although the net cost of the different sizes is similar, installing the narrower, 2-by-4 boards requires more material, fastening and cutting.

Alternate Sizes

To provide adequate support, most solid lumber decking planks are at least 1 1/2 inches thick. However, boards of nearly any width are suitable for deck surfaces. Because decking perpendicularly crosses support boards called joists, fastening patterns do not depend on the width of the planks. Therefore, builders may use standard milled lumber, called "dimensional lumber," of any dimension to cover a deck surface. Home improvement stores regularly stock dimensional lumber that ranges from 3 1/2 inches to more than 16 inches wide. However, extremely wide planks are more likely to warp and split than narrow ones.

Lumber Decking Species

Builders commonly choose rot- and pest-resistant lumber species for exterior building projects. Popular decking lumber species include redwood and cedar. Both offer natural resistance to deterioration and insect infestation. Because of their natural durability, redwood and cedar are often installed without waterproofing, staining or painting. Alternatively, less durable lumber species are suitable for deck surfaces if builders carefully treat the boards' edges, faces and ends with waterproofing compounds or surface coatings, such as exterior paint and stain.

Lumber Composites

The term lumber composite refers to a manufactured decking material composed of plastics, resin and wood fibers. Completely resistant to rot and insect damage, composites continue to gain popularity as decking materials. Although available in custom sizes according to project specifics, composite decking planks commonly measure around 5/8 to 3/4 inch thick by 5 1/2 inches wide. Thus, composite decking planks roughly resemble the dimensions of standard "1-by-6," which actually measures 5/8 inch by 5 1/2 inches.

About the Author

Based in Hawaii, Shane Grey began writing professionally in 2004. He draws on his construction experience to write instructional home and garden articles. In addition to freelance work, Grey has held a position as an in-house copywriter for an online retailer. He holds a Bachelor of Arts in theater arts from Humboldt State University.