76 THE PRINCIPLES OF FLOEICULTURE 



in thickness is used. This necessitates a heavier glazing 

 sill, and in order to attach this firmly to the concrete, 

 ten-inch bolts are embedded in the last layer of concrete 

 in the side-wall, leaving enough length above the con- 

 crete to extend through the sill. The sills are then held 

 firmly to the concrete side-walls by the nuts of the bolts 

 and the lugs and set-screws on pipe supports. 



The sides of greenhouses are usually five or six feet high, 

 but they may be as high as eight feet when considerable 

 head room and abundant side ventilation are needed, as 

 is true in growing sweet peas. As most benches are now 

 placed away from the side-walls, only sufficient height 

 is necessary to allow workmen to pass easily along side- 

 walks. 



62. Eave-plates and gutters. In most commercial 

 houses, gutters are not used. They are heavy and ex- 

 clude much light. To eliminate shade is very essential 

 and the eaves are made of as light a material as possible. 



In houses of the U-bar type, sash-bars function as 

 rafters, and as curved glass is used at the eaves, there is 

 nothing to cause shade. In other types, metal angle-iron 

 is used at the eaves (Fig. 9, left). This metal conducts 

 heat rapidly and it is said that no icicles will collect to 

 cause shade in the houses. In some forms of pipe-frame 

 houses, a thin, metal strip is screwed to the sash-bars on 

 the outside of the house at the eaves, and the glass of the 

 side-wall and that of the roof rest firmly on this metal. 

 When wooden walls are used, a beveled eave-plate of 

 two-inch lumber is placed along the top of the posts and 

 side-walls, and on this the sash-bars of the roof rest. 



63. Roof construction. One of the principal things 

 in roof construction is that it shall be of such an angle at 

 the gutters that all the light possible will be trapped. 



