GREENHOUSE CONSTRUCTION AND HEATING 31 
The ridge ventilators may be hinged to the ridge or to 
the header. Some growers prefer hinging them at the 
ridge (Fig. 1), because the sash practically prevent snow 
and rain from entering the houses, even when the ven- 
tilators are open very wide. Other growers prefer hing- 
ing at the header (Fig. 18), claiming that to be the proper 
place because of the fact that the condensed water on the 
glass of the ventilators runs off instead of forming ice to 
interfere with the closing of the sash—a frequent 
occurrence when the sash are hinged at the ridge. 
The ventilating sash may or may not be continuous. 
When the ends of the sash are properly fastened to each 
Fig. 18.—Semi-iron house. Note large door and ventilators on sides and end. 
other, there should be no difficulty in operating them. A 
run or two of glass between the sash is preferred by 
many growers, but continuous ventilators are increasing 
in popularity. Sometimes ventilators are placed at the 
ends of the houses, as shown in Fig. 18. 
The ventilating machines should be of the most ap- 
proved type, and conveniently located. It is often best to 
have them near the doors at the ends of the houses, 
There are several excellent machines on the market. 
