trusses, and the frame must be footed. But like the rigid-frame, the post and rafter allows more space
along the sidewalls and efficient air circulation.
The third one is called the A-frame, this style of structure is the simplest one, and can hold the weight of
the materials and the weather, but because it is smaller and it does not have vertical walls, it does not
have much space inside what not only affects the quantity of vegetables and fish the greenhouse
produce but it also minimizes the efficiency of the air circulation.
Taking in consideration that our greenhouse will be for aquaponics, meaning that it will have higher
vegetable beds instead of using the ground to grow the vegetables, it is easy to eliminate the A-frame
greenhouse because it drastically reduces the usable space inside. Any round structure also reduces our
space, and because of the snow the structure might not hold the weight or limit our choices for the
coverings.
From this research, it is conclusive that the optimum structure would be the post and rafter or the rigid-
frame, which are close to a normal house structure, because they optimize the space inside, they
provider a better air circulation and more space to work inside, and they also have a strong foundation
capable of holding the weigh of the coverings and snow.
2.3.1.2 Greenhouse Frames Materials
Independent of the greenhouse style, we also need to find a good material to build it. PVC is commonly
used around the world for greenhouse structures, it is relatively durable, strong, chemically resistant,
and it is also a cost effective material. The only downside is that it is not commonly used on larger scale
structures. This is due to the fact that it does not have the strength that other materials, like wood,
steel, or aluminum, have. Due to the size of the greenhouse, 20x33 feet, PVC does not seem like a
reasonable material to use. A stronger material is necessary.
Wood is also a traditional material used to build greenhouses, it has an atractive apearance, it is strong,
and can retain heat well. Also, some types of wood can retain color for a long time, diminishing the
regular mantaince. An important drawback is that most hard woods must be preassure-treated with
preservative and painted regularly to prevent them from rotting, especially being in a wet and warm
environment. They are also heavy and hard to work with during construction, and wood can be really
expensive. With these attributes, wood would be a good material for a permanent or long lasting
greenhouse if it is well maintained.
The aluminum is a metal alloy that does not require any regular maintance, since it does not rust or rot,
it is light and easy to work with but strong at the same time, it also is narrower than wood allowing a
better light penetration. On the other side, aluminum can be expensive and does not retain as much
heat as wood.
The other option is the steel frame, it is light and easy to build, strong, and ridged. It is normally cheaper
than wood and aluminum, and they also allow a better light penetration. But they must be painted
regularly to prevent rust and like aluminum they reduce the heat retention compared with wood.
From this information, PVC does not have the characteristics necessary for a year-round greenhouse in
New England, leaving the choice between wood, aluminum and steel. Aluminum would be the most
expensive on the beginning and does not have the insulation capabilities as wood, but it is a maintance