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It is not necessary to build very large houses unless the forcing of vegetables or flowers is contemplated. A house 30 x 75 feet will serve the purpose for twenty-five to fifty acres of vegetables. If the grower is skillful and can combine vegetable forcing with open ground work, he might be able to use to advantage an acre or more of glass, provided market conditions are favorable. The size of the greenhouse must also be determined by the number of available sash for cold frames. If the plants are merely held in the beds until the first transplanting the house need not be large. At least eight hundred seedlings should be started on every square foot of bed or bench space, if they are to be transplanted in about four weeks.
Greenhouses may readily be built by local carpenters. It is important, however, for the gardener to make a careful study of the whole subject before buying materials or undertaking the work of construction. "Greenhouse Construction," by Professor L. R. Taft, is the only complete book on the subject. It may be procured through any well known publishing house. The catalogs issued by the various building firms are also instructive. The prospective builder should visit and study well built houses to become familiar with details which enter into the construction of all classes of greenhouses. It is not the purpose of this chapter to discuss the details of greenhouse construction, but a few suggestions may be helpful to inexperienced builders.
The location is important.
The house should be protected, if
possible, from hard northern or western winds. It should be comparatively near the dwelling and convenient to the cold frames. The water supply must also be considered in locating the greenhouse.
There are various forms of greenhouses; the lean-to, hillside, threequarter span and even span. Of these types, the even span, as shown in Figure 1, is the most popular although there are hundreds of three-quarter span houses. Definite experiments show that none of these types has any superiority over the others. It is largely a matter of preference, although the three-quarter span houses are better adapted to hillsides unless the ground is first graded. Houses which run northeast and southwest are satisfactory, although the position of the house with reference to the rays of the sun at different periods of the day is a matter of little consequence.
It always pays to use the best materials and to buy from reliable builders. The wood parts should be well air-dried cedar or cypress. A number of well known firms make a specialty of sash bars and all other wood parts which are cut, when possible, in the proper lengths at the factory thus making the carpenter work a simple matter.
Full iron frame construction is on the increase, but the cost of building is so much greater than semi-iron construction that the latter plan is preferred by most growers. All wood parts should be given two coats of paint before glazing and a third coat after the glass is laid. It is economy to build houses which are not less than thirty feet wide. The roof should not be too flat or too steeep. Most houses are built with a pitch of thirty to thirty-five degrees. The posts or walls should be durable. Formerly, wooden posts were used exclusively. They are seldom used now, for iron pipe posts and concrete walls have been substituted. Pipe purlins and interior posts and braces are also in common use. The King form of construction obviates the use of interior supports.
It is desirable to use double strength A glass. Cheaper grades break more frequently by the freezing of water under the laps and the loss caused by large hail-storms would be much greater. The freedom from blemishes is also an advantage. Sixteen by twentyfour inch glass is used the most extensively, although larger sizes are frequently used. Some houses are built with the sash bars twenty-four inches apart while the majority of builders object to more than twenty inches between sash bars. At this distance, glass either twenty by twenty-four, or twenty by thirty, may be used. To secure the best glazing, the glass should be laid in putty with the convex side up and care exercised in grading glass so that the laps, which should not be more than one-fourth inch, fit tightly. A number of good glazing points are on the market. The Peerless is one of the best. Raised benches are rapidly passing out of use. Their cost of construction and maintenance is in itself a serious objection. The main reason for their abandonment, however, is that in the forcing of all classes of vegetables, better results are obtained in solid beds. Cement sides, about three inches thick and a foot high, are often used to the solid beds but even these are not considered an advantage in most successful commercial establishments. It means, then, that the entire area of the greenhouse is one plat to be farmed in a most intensive manner without the interference of benches, pipes, concrete sides of beds or concrete walks. Large doors are often provided at the ends of the houses so that teams and wagons can pass in and out with soil and manure. Plows and harrows may be used almost as freely as in the open. Alleys or walks are provided as may be necessary. (See Figure All heating pipes are along the sides or overhead. It is by far the most economical arrangement, and experience teaches that it is entirely satisfactory. Raised benches are convenient for certain lines of work, but from a business point of view they receive the support of a very small per cent. of our vegetable growers.