230 



Bulletin 274. 



Rafters 



Fig. 56 illustrates a method of marking out a rafter for the ordinary 

 roof. Obtain the height of the peak A above the plate C, and the dis- 

 tance between the plate C and a perpendicular dropped from the peak to 

 point B on the plane with the plate. With these distances known the 

 square can be so applied as to mark out the rafters where they should be 

 cut to fit into place. 



For example, to lay out the rafter for a building 16 feet wide, take 

 a rafter AC and let the rise or distance AB equal 8 feet and the run or 



Fig. 57. — Uneven ground should be filled in to make the floors level. 



Hon roof requires Jieavy bracing. 



The combina- 



distance BC equal 16 feet. If an improvised square is used with a blade 

 16 ft. long and an arm 8 ft. long, it can be placed with one end at A and 

 the other at C, and by sawing through the rafter on lines AB and BC, 

 the rafter at C would fit on the plate and at A would meet a similar 

 rafter from the other direction. The same result is obtained by placing 

 the square on the rafter as indicated in the illustration, so that the rafter 

 at C intercepts the blade of the square 16 inches from its heel, and the 

 arm at C 8 inches from the heel. The square is again placed on tihe 

 rafter so that the 16 inch mark covers at C and the 8 inch mark at C". 



