24 VEGETABLE FORCING 
Semi-iron construction (Fig. 10) is becoming popular in 
all parts of the country. It provides for concrete walls, 
iron posts embedded in concrete, iron purlins and purlin 
supports, iron braces and sometimes iron eaves-plates. 
The iron may be in the form of pipe, angle irons, or 
simply flat bars, the form depending upon their function 
and the cost and preference of the builder. With the best 
forms of semi-iron construction, decayed wood parts are 
easily removed and replaced with new parts. When all 
exposed parts of wood and iron are kept properly painted, 
the house, with only slight repairs, should last 25 years, 
and then the renewal of decayed sash bars or other parts 
ibid aT 
i, 
Fig. 9.—A modern steel-frame house. Note large door. 
should prepare it for many more years of service. The 
moderate cost and serviceability of semi-iron construc- 
tion appeal to commercial growers. 
Iron construction (lig. 9) is the strongest and most 
durable. In addition to the iron parts used for semi-iron 
construction, the gutters, wall and side plates are metal, 
and there are a certain number of iron rafters to support 
the roof, so that interior posts are unnecessary. Iron con- 
struction gives the house greater rigidity, and there is 
less shading of the plants because of the absence of in- 
terior posts. Full iron construction costs considerably 
more than semi-iron, and this is the only reason why it 
is not more generally employed. ; 
