26 ABC OF THE STEEL SQUARE 



At the left end of the table are figures repre- 

 senting the run, the rise and the pitch. 



In the first column the figures are all 12, which 

 may be used as 12 inches or 12 feet, and they 

 represent a rim of 12. 



The second column of figures is to represent 

 various rises. 



The third column of figures in fractions rep- 

 resents the various pitches. 



These three columns of figures show that a 

 rafter 



with a run of 12 and a rise of 4 has 1-6 pitch, 



with a run of 12 and a rise of 6 has 1-4 pitch, 



with a run of 12 and a rise of 8 has 1-3 pitch, 

 and so on to the bottom of the figures. 



To Find the Length of a Rafter. For a root 

 with 1-6 pitch (or the rise 1-6 the width of the 

 building) and having a run of 12 feet, follow 

 in the rafter table the upper 1-6 pitch ruling, 

 find under the graduation figure 12 the rafter 

 length required, which is 12 7 10, or 12 feet 

 and 7 10-12 inches. 



For % pitch (or the rise y 2 the width of the 

 building) and run 12 feet, the rafter length is 

 16 11 8, or 16 feet 11 8-12 inches. 



If the run is 25 feet, add the rafter length 

 for run of 23 feet to the rafter length for run of 

 2 feet. 



