26 VEGETABLE FORCING 
Truss construction.—In recent years the truss form of 
building (Fig. 11) has received considerable attention 
from greenhouse men. The trussed construction makes 
it possible to dispense with interior posts, except in very 
wide houses, and comparatively small pipe rafters are 
used instead of heavy, flat, iron rafters that are necessary 
in full iron-frame houses. The sash bars are also smaller 
than in other forms of houses, so that every detail of con- 
struction is favorable to admitting the maximum amount 
of light and sunshine. Theoretically, this is the ideal 
Fig. 11.—A house of truss construction. 
house, and it is highly esteemed by many vegetable 
forcers. On the other hand, some trussed houses have 
been demolished by snow and storm, and growers are 
naturally rather reluctant about building houses of this 
type. It should be said, however, that improvements 
have been made which add to the strength of the trussed 
houses, and it is possible that the newer houses will prove 
entirely satisfactory. Certainly no type of construction 
could provide better conditions for the culture of winter 
vegetables. 
Walls.—The greenhouse walls should be durable and 
