1. Sizing Joists and Rafters Using Span Tables
Chapter 28
Sizing Joists and Rafters Using Span Tables

2. Links for Chapter 28 Wood Characteristics Lumber Size & Span
Engineered Lumber

3. Wood Characteristics
Each species is followed by a grade number which is either #1 or #2 for structural lumber
Douglas fir-larch (DFL#2)
Southern pine (SP#2)
Spruce-pine-fir (SPF#2)
Hemlock-fir (Hem-Fir#2)

4. Determining Size and Span
Span table headings
Title - Make sure correct one is being used
Loads - Indicates LL and DL value
Deflection - Describes the stiffness of the beam by its tendency to bend under a load
Size and Spacing of Lumber - Gives the size and spacing allowed for framing lumber

5. Sizing Joists and Rafters
Select proper table and follow these steps:
Locate column that represents proper lumber species and grade
Identify the lumber spacing
Find column that corresponds to the appropriate load
The number is the maximum allowable span
14-5 indicates maximum span of 14’-5”

6. Engineered Lumber Each manufactures’ tables may vary slightly
Select proper table and follow these steps:
Determine the deflection limit
Identify the loading condition
Select the on-center spacing
Scan down the column until the distance that exceeds the span is located

7. Cantilevered Floor Joists
Select proper table and follow these steps
Use the first two columns to identify the joist
Locate the roof truss that meets or exceeds the needed conditions
Find the roof total load at the top of the table
Select the spacing column

8. Cantilevered Floor Joists

9. Engineered Rafters Select proper table and follow these steps:
Determine roof loading
Determine appropriate slope column
Move down column to find value that meets or exceeds required span