the square along the working line as many times as one-half 

 of the building in feet (or in the assumed case, 12 times) 

 When you have done this the blade of the square will be on 

 the upper end of the rafter, and by marking along the blade 

 you will have the top of plumb out of the rafter. 



To get the length of hip rafters the same method 

 is followed except that the figure 17 is used on the tongue 

 of the square instead of the figure 12. 



If you are not an adept at the use of the square, 

 the length of the rafter may be found by simple arithmetic. 

 We will say that we are finding the length of a common 

 f after for a building 24 feet wide, pitch 1/3. Simply 

 multiply the figure shown on the line of 1/3 pitch, Cut 

 No. B.M.-7 by 12, or the run of the rafter. Operation 

 1.20 x 12 = 14.40 feet. .40 x 12 = 4.80 inches. The 

 .80 is a decimal of an inch which for practical purposes 

 can be called 3/4 of an inch. As a working dimension, then, 

 the rafter will be 14' 4-3/4" long exclusive of the pro- 

 jection. Very slight decimal parts of an inch may be dis- 

 regarded in rafter measurements. Now suppose that you 

 desire to find the length of the hip rafter for the build- 

 ing 24 feet wide, pitch 1/3. Multiply the figure shown on 

 the margin of the square, Cut No. B.M.-7, 1.56 by half of 

 the width of the building. 1.56 x 12 <= 18.72. .72 x 12 - 

 8.64. Now the .64 is a decimal of an inch and for all 

 practical purposes may be called 5/8 inches. The length 

 of the rafter will be 18' 8-5/8". 



Pig. 6, Cut No. B.M.-8 illustrates the method of 

 cutting jack rafters. The length of the jack rafter for 

 roofs of various pitches may be found by multiplying the 

 distance of the jacks from the corner of the building by 

 the figures shown on the lines of respective pitches. 

 Example building 1/3 pitch, rafters 2 feet apart. 

 2 x 1.20 = 2.40 feet. .40 x 12 = 4.80 inches. .80 is 

 e decimal of an inch which for practical purposes can be 

 called 3/4 of an inch, or a total length of rafter of 

 2' 4-3/4". The next jack will be twice as long^ the third 

 three times as long, etc. 



B.M. (34) 



