What size floor joist is required for an SPF #2 installation at 16" on center with a dead load of 20 PSF in a residential living area?

To determine the correct size of floor joist required for a given loading condition, it's important to analyze the requirements based on span tables and the properties of the materials being used. In this scenario, you are tasked with finding the appropriate size for SPF (Spruce-Pine-Fir) #2 grade joists installed 16 inches on center and supporting a dead load of 20 PSF (pounds per square foot).

The choice of a 2 x 10 floor joist is correct because it typically provides adequate structural capacity to support the specified dead load across common residential spans. Based on span tables for SPF #2 lumber, a 2 x 10 joist can effectively support a 20 PSF dead load, often up to a span of 16 to 18 feet, depending on additional live loads.

Using a 2 x 10 also allows for some flexibility for varying design loads if live load considerations are added, as typical residential live loads can range from 40 PSF or more. For applications with higher load requirements or longer spans, larger joists may be needed, but within the provided parameters, the 2 x 10 is a well-suited choice.

While smaller options, like the 2 x 8