FOKCING AND FORCING STRUCTURES 65 



of putty sufficiently to allow for the desired width of lap. Pass the 

 glass to a man on the roof, holding it putty side up. The man on 

 the roof should turn the pane over and press it firmly in place, as 

 shown in figure 20, thus squeezing out any superfluous putty, 

 which will pass in both directions out of the rabbet of the sash bar. 

 As soon as the glass is fastened in place the operation is complete, 

 save for cleaning off superfluous putty. 



One man can putty glass for two men to lay ; that is, he can 

 spread putty, open boxes, and putty and hand up sufficient glass 



FIG. 20. Laying the glass 



to keep two men on the roof busy adjusting and fastening it in 

 place. In building a new house a record was kept of the time re- 

 quired to cover one side of a 20 x 30 foot house with sash bars 

 12 feet long and 16 inches apart. Three men, using 16 x 24 

 inch double-strength glass, laid one side of the roof in 2\ hours, 

 which is quicker than the same area of butted glass could have been 

 laid and the caps screwed down. After two winters and one summer 

 this roof does not leak a drop. Laying a lapped-glass greenhouse 

 roof was a great undertaking until this method was discovered. 



