CONSTRUCTION OF GREENHOUSES 
121 
policy to build a large house or an extensive range of 
houses without thorough experience in greenhouse work 
and full knowledge of local conditions and market facili- 
ties. A house 30 x 100 feet is probably as large as any 
market gardener should start with, and a smaller struc- 
ture would be desirable where both capital and experience 
are limited. A width of 30 feet has been given, because 
this is the minimum width for economical construc- 
tion, heating and operation ; narrower houses do not pro- 
vide as uniform atmospheric conditions, and the plants 
are more likely to be injured by direct cold drafts. 
174. Location and position. — While the natural pro- 
tection of woods or hills on the north and the west sides 
is highly desirable, greenhouses should not be con- 
structed where they will be shaded by other buildings. 
The position of the house with reference to the points 
of the compass is apparently of little importance. A 
three-quarter span house should run east and west to get 
the full benefit of the sun, while the even span house 
should probably run north and south in order to secure 
a uniform distribution of light. Some growers compro- 
mise and build their houses northeast and southwest. 
With the modern house, about 95 per cent of which is 
glass, ample light will enter the house whatever its 
position may be. 
175. Materials used in construction. — Serviceability, 
durability, and economical construction and operation 
are the main points to keep in mind when building green- 
houses. No one denies that the full iron form of con- 
struction is the most durable and that it is also highly 
satisfactory when in operation, but the cost of construc- 
tion is beyond the means of most vegetable growers. 
Again, it is doubtful whether full iron construction is the 
most economical in the end ; the first cost is from one- 
third to one-half greater than for semi-iron construction, 
and this additional expense may exceed the cost of re- 
