126 GREENHOUSES 



likely to cause drafts of cold air. They are 

 preferably glazed with glass of the same 

 width as used for the roof and they should 

 be placed so that the bars of the sash will 

 be directly over the sash bars. 



Size of Ventilators. No definite rule can 

 be given as to the size of ventilators, as so 

 much depends on the location and arrange- 

 ment of the house, the kind of plants to be 

 grown, etc. Experience has shown that 

 where the ventilators are continuous along 

 the entire length on both sides of the roof, 

 the following sizes are sufficient. 



Size of house Width of ventilating sash 



Up to 40 feet wide 24 inches 



Above 40 feet wide 30 inches 



This is the rule followed by most green- 

 house builders. 



Methods of Hanging Sash. Ventilating 

 sash may be hung so as to open either at the 

 top or bottom; that is, they may be hinged 

 at the lower side so as to open out and away 

 from the ridge, or they may be hinged at the 

 ridge so as to open upward from the lower 

 side. Both methods have their advantages 

 and disadvantages. Sash opening at the 

 ridge have the advantage that the air will 



