BUILDING THE RANGE 81 



covered with paint after the glass is in place. An accumu- 

 lation of moisture in the putty also causes it to crumble 

 and thus loosens the glass, which often slips down, admit- 

 ting cold air and water to the interior of houses. Painting 

 prevents crumbling of the putty and makes the roof more 

 durable. After the first coat has dried, a second should be 

 given. Great care is required in the painting of the inside 

 of the house, for it is exceedingly difficult to cover the 

 putty without getting paint on the glass. 



In glazing greenhouses, the glass is sometimes butted 

 instead of lapped. It is more difficult to reset butted 

 glass, for it is almost impossible to find two panes of the 

 same dimensions. There is also more drip from roofs 

 where glass is butted. Light conditions, however, are 

 somewhat better, for in houses glazed in this way, no 

 sunlight is excluded because of the double thickness 

 of glass at the lapped area, nor will an accumulation of 

 soot or dirt collect between the panes at this point. Up- 

 right glass on sides and gables of houses is usually butted, 

 for slipping is not so liable to occur and light conditions 

 are better. 



64. Interior supports and truss-work. It is important 

 that roofs of greenhouses be strongly supported. This 

 is necessary not only to hold the roof up, but to hold it 

 down as well. The suction force of a strong wind passing 

 over the ridge of a large house is considerable. It is 

 therefore necessary that all columns used for supporting 

 roofs be firmly embedded in grouting at the base. The 

 size of these columns varies with the size of the house, 

 but they are seldom over two and one-half inches in 

 diameter. Cross-ties of smaller piping serve to strengthen 

 these columns. The number of rows of columns will de- 

 pend also on the width of the house. Angle-iron columns 



