Building a Greenhouse: Part 2

In the first part of this article the location of the greenhouse and the two basic types of greenhouses, freestanding and attached, were discussed. In this second part, we’ll learn about the structural possibilities. Keep in mind that the best options for you will depend on your climate, types of plants, convenience factors and budget.

Framing
The five basic shapes of freestanding greenhouses are Quonset hut, gothic, rigid frame, post and rafter, and A-Frame. As mentioned in part one, the greenhouses attached to homes are generally lean-to shapes. You can quickly reference pictures of each type online.

Your greenhouse frame can be wood, galvanized steel, or aluminum. Plastic pipe frames may sometimes be used in locations free of snow or strong winds.

Coverings
The frame can be covered with glass (tempered glass is often used because it is two or three times stronger than regular glass), rigid fiberglass, rigid double-wall plastics or plastic film.

The commercial greenhouse grade of PE plastic film protects against ultraviolet rays and lasts 12 to 18 months. Some of the film plastics block and reflect radiated heat back into the greenhouse, providing the advantage of glass without the expense and breakability factor.

The covering, or as its also called, the glazing, will be one of the determining factors in how far solar energy will go in heating your greenhouse. Depending on where you live, you may be able to rely completely on solar energy or in colder climates on as much as 25 percent of the daily heat requirement.

Optimal glazing materials allow the greatest amount of solar energy to enter into the greenhouse while minimizing energy loss. This process can get quite technical, but again this is just to give you a jump-start. It goes something like this: Good plant health requires a natural spectrum of photosynthetically active radiation (PAR) to enter. While plants grow well with direct light, the direct light that enters through a clear covering divided by structural supports causes more shadows and uneven plant growth. Plants also grow well in diffused light, and the coverings that offer diffused lighting (such as rough-surface glass, double-layer rigid plastic and fiberglass) evens out the shadows, thus promoting more even growth.

Many new glazing materials have emerged since greenhouses hit the mainstream in the 70’s. Plastics now are the most popular type of covering since the weatherability has been enhanced in recent years with ultraviolet radiation degradation inhibitors, infrared radiation (IR) absorbency, anti-condensation drip surfaces and unique radiation transmission properties.

The manner in which you put up the coverings will also play a role in heat preservation. Cracks or holes caused by the mounting allow heat to escape, and differences in the width of the air space between the two glazes also affect heat retention. Another thing to take into account is whether the covering will expand with hot and cold weather. It seems like a lot of work, but careful planning can make a world of difference in heating efficiency.

Foundations and Floors
If you plan to build a glass, fiberglass or double-layer or rigid-plastic greenhouse, you will need to also plan on a foundation, probably a poured concrete one similar to a house’s foundation. However, Quonset hut greenhouses with pipe frames and plastic covers use posts driven into the ground.

Permanent flooring can be very slippery, due to the nature of a greenhouse. Instead, use a concrete, gravel, or stone walkway about two to three feet wide. Cover the rest of the greenhouse floor with several inches of gravel for good drainage. You can also spray the gravel for increased humidity. Part three of this article will venture into heating and ventilating the greenhouse.

Greenhouse is made up of glass, fiber or plastic which provides the garden shed. It is used for growing tender plants through filtration of skylight. Apart from them small roof structures which are known as gazebos also serve the same purpose. Some factors which are essentially maintained are temperature, humidity and also greenhouse gases levels through the structural materials also. Transmission of selective gases continues carbon cycle greenhouse effect.