124 
VEGETABLE GARDENING 
An excellent plan is to build the concrete walls 2^2 feet 
above grade level and bank them with earth on the out- 
side. Walls made in this way are warm and inexpensive 
to construct; besides they are much better than those 
built of wooden posts and boards. Although cedar and 
locust posts last for many years, the lower boards in a 
wall will soon decay. If the foundation extends 2^/2 feet 
above grade level, there will be a height of 4 feet of glass 
at the sides between the plate on the concrete wall and 
the gutter or eaves plate, where sufficient height is de- 
sired for a walk next to the wall. 
FIG. 27. THREE-QUARTER SPAN GREENHOUSE. TYPE 
USED NEAR BOSTON 
179. Roof construction. — The size of the roof bars is 
determined by the width of the glass and the distances 
between posts, braces and purlins. The bars should be 
heavy enough to prevent sagging. Figure 28 shows an 
approved method of bracing. The pitch of greenhouse 
roofs varies from 30 to 35 degrees. A lien the ridge and 
furrow plan of construction is used, gutters must be pro- 
vided between the houses. It is important, however, to 
avoid having gutters if possible, because they decay 
quickly unless made of metal. Many growers prefer to 
