Location, Location, Location
Obviously, the greenhouse should be places where it cane get the most sunlight. In our hemisphere the best choice is directly south or on southeast side of your home. Experts say that the morning sunlight is the best because it gets the plant’s food production going and so growth is stronger. If the greenhouse is to be used all year then shoot for the winter sun exposure because the sun is lower in the sky in winter. Also it should be shelters from the wind. Build the greenhouse above the ground so that the water will drain away.
There are three basic types: lean -to, even span: and window.
1. Lean-To: The lean-to design is when space is limited. It can be built over a doorway but should always be on the wall which gets the most sun. It is somewhat limited because it will not get all the sun because the wall will block some of the daylight.
2. Even Span: This is full-size structure with one wall, usually an end wall, attached to a building. It is better than an lean-to because it has better air circulation, can be expanded and gets more light.
3. Window-Mount: This style is the cheapest and easily accessible. But it is the most limiting. It is basically a box that fits in a window frame and is good for spices, small plants and starter plants.
4. Free-Standing: Like the ever-span this greenhouse is larger but has more light than the attached model.
Glass: The old greenhouses were wood-frames with glass inserts. The frames had to be maintained and the expansion and contraction of the wood had to be monitored. The new ones have metal frames and are covered with fiberglass or a thick plastic sheeting but the mainstay is the aluminum frame with glass panes. These are permanent and are easy to maintain and allow 90% of light to pass through.
Plastic Panels: These are usually double-sheeted so that the energy savings is 30% over glass but the light transmission is 80%. Acrylic doesn’t yellow but polycarbonates tend to cloud up if not UV protected.
Plastic Sheeting: This material is cheap but has to be replaced every few years. However, because it is light the frame does not have to be as strong so the framing material would be cheaper than a glass or fiberglass greenhouse.
For the homeowner one of the best ways to build a greenhouse is to get old windows destined for a landfill and construct your own small one to get a feel for it. The wooden window frames can be easily attached to a wood frame. In this way you can rebuild it the next year when you get more glass. the main thing is that you will have a cheap greenhouse which can be expanded.