68 THE PRINCIPLES OF FLORICULTURE 



in this type of house may be narrower and thinner than in 

 all-wood or pipe-frame houses. The sash-bars are usually 

 one and one-half inches by seven-eighths of an inch. 



Pipe-frame houses. Typical pipe-frame houses have 

 a framework made of from one to two-inch iron pipe, the 

 size depending upon the position of the pipe and the size 

 of the houses. Such frames are largely independent of 

 the sash-bars and glass material, but the sash-bars are 

 held firmly to the latter by means of various iron-clips, 

 lugs and U-bolts. In semi-iron pipe-frame houses, iron 

 pipes are used for side posts, they being firmly embedded 

 in concrete and extending to the eaves. Interior pipe 

 columns support purlins which are firmly attached to 

 the sash-bars by metal clips. 



U-bar houses. The U-bar method of construction is 

 little used as yet in commercial greenhouse construction, 

 its expense making it impracticable. This method is 

 often used in building private conservatories and in 

 public parks. In these houses an iron sill is attached 

 to the foundations and to these, at definite intervals, 

 iron sash-bars are firmly bolted. These sash-bars are 

 made in the form of a U and have a wooden strip inserted 

 in this metal so that the interior of the house, which is 

 the most liable to decay because of warm, moist, atmos- 

 pheric conditions, is practically all glass and iron, while 

 the outside, which is the most susceptible to changes 

 in temperature, is glass and wood. The U-bar houses 

 have thus overcome much of the danger of breakage of 

 glass due to unequal expansion and contraction of metal 

 sash-bars. If the outside wood is kept well painted, decay 

 rarely occurs, and if the interior is also frequently painted, 

 rust will not- corrode the sash-bars. The U-bars are 

 usually galvanized to prevent rusting. Because of the 



