48 GREENHOUSES 



Table showing angle formed by roofs on houses of 

 different widths and heights of ridge 



One half Height of ridge in feet 



It is perhaps more often desired to find the 

 length of rafter necessary to form a roof of 

 given pitch on a house of given width, than to 

 determine the pitch of a house already 

 erected. This may also be solved trigono- 

 metrically. For example: Suppose it is de- 

 sired to know the length of rafter necessary 

 to form a roof with a pitch of 35 degrees on a 

 house 20 feet wide. If the roof is to be of 

 even span, as shown in Fig. 24, we will have 

 a right angle triangle, A B D, the base of 

 which is known to be half the width of the 

 house, or 10 feet. If the angle A is to be 35 

 degrees then: Cosine A=J5 equals .81915= |. 

 Transposing, X=--or X=i2.2 feet. 



