GREENHOUSES 



edge of the pane below it, in much the same 

 way that shingles are lapped, except that the 

 lap is much narrower. From one-eighth to 

 three-eighth inches are allowed for lapping, 

 the width of the lap, depending somewhat on 

 the size of the glass and the rigidity of the 

 house and roof. It should be as narrow as 

 possible, for little light passes through the 

 lapped part of the roof. 



Fig. 57. Lapped glazing 



Butted Glazing. In butted glazing all 

 panes lie flat against the bottom of the 

 grooves in the sash bars, and the lower edge 

 of each glass rests directly against the up- 

 per edge of the one below. This form of 

 glazing eliminates the lap, but it is more dif- 

 ficult to secure a tight roof than when 

 the glass is lapped. Roofs having a pitch 

 of less than 30 degrees are likely to leak badly 

 when the glass is butted. 



In this form of glazing the putty is some- 

 times omitted, and the glass is held in place 

 by wood caps which fit over the rabbets. 

 When it is desired to make an especially tight 



