Possible Materials and Relative Costs
With the recent technological advancements in greenhouse designs, kits are now available and are recommended for beginners like you. Greenhouse kits are available in a wide range of costs and with a wide range of features. Prices range from a few hundred dollars to well over $5,000 depending on the size, style, accessories, and type of construction materials. Manufacturers can be found in the yellow pages of a telephone book, in advertisements in gardening magazines, by searching the World Wide Web. Compile a list of manufacturers, and request information on different models. Compare costs and features for the style and size you are interested in. Generally, plastic-covered greenhouses are easier to assemble than glass houses are. However, if any aspect of the assembly is beyond your skills, many manufacturers will erect their products on-site for an additional fee. Befroe thses kits were created, materials would have to be bought seperatel, which made this process time consuming and pricey. These kits were created to he;lp those get started quick and easy to be able to have fun and enjoy the products grown
Covering Materials
Glass
Glass is the traditional greenhouse covering against which all others are
judged. Good-quality glass is an attractive, very transparent, and formal
(in appearance) covering material. It is very strong (tensile strength), but
it is subject to shattering and can become brittle with age. Glass is also
very expensive and because of its weight requires sturdier framing support
than is required with other covering materials. Originally, glass panes for
greenhouses were 18 by 16 inches, but larger sizes are more common now. Actually,
larger panes are less fragile than smaller panes. Many greenhouses are covered
with double-strength float glass (1/8 inch thick) costing $0.85 to $2.00 per
square foot. Large glass panes in many more expensive greenhouse kits are
tempered glass (5/32 inch thick) costing $3.00 to $7.00 per square foot, depending
on the pane size.
Polyethylene Film
Polyethylene film (PE) is a good choice for home-built greenhouses because
less structural support is required and it costs much less than other materials.
However, PE film only lasts about 2 years. Clear PE is used for growing most
plants, but white PE can be used to reduce light and heat for growing low-light
plants or for propagation. PE manufactured for greenhouse application comes
in widths from 10 to 50 feet, thicknesses from 1 to 8 millimeters, and costs
$0.06 to $0.09 per square foot. Two layers of PE are frequently applied to
greenhouses to reduce heating demand. Double-layer PE houses generally cost
30 to 40 percent less to heat than single-layered houses do. The two layers
are kept air-inflated by a 100- to 150-cubic-foot-per-minute squirrel cage
blower mounted to the inside PE layer. Purchase 4-millimeter PE for the inside
and 4- or 6-millimeter PE for the outside. Use 6-millimeter PE for single-layer
applications. PE can be installed on wood-frame greenhouses by nailing wood
batten strips over the film into the foundation boards and rafters or arches.
However, because PE must be replaced frequently, investing in special fasteners
makes the job easier. Fastening systems are available for single- or double-layer
applications.
Fiberglass Reinforced Panels
Fiberglass reinforced panels (FRPs) are rigid plastic panels made from acrylic
or polycarbonate that come in large corrugated or flat sheets. FRPs are available
in 24- to 57-inch widths and up to 24-foot lengths. FRPs are durable, retain
heat better than glass does, and are lightweight (less structural support
needed). Large panels are flexible enough to be applied to a Quonset greenhouse.
Light transmission may be better than glass simply because less structural
support is needed, which creates less shadow. The prices of FRPs range from
$1.00 to $1.25 per square foot, depending on the guaranteed life span of the
material. Inexpensive materials may be guaranteed for as little as 5 years;
more expensive types may be guaranteed for as long as 20 years.
Double-Layer Structured Panels
Acrylic or polycarbonate double-layer structured panels (DSPs) are made of
two layers of plastic held apart by ribs spaced 1/2 to 1 inch apart. The double-layer
construction increases structural strength and heat retention but decreases
light transmission compared to single-layer materials. Panels are 4 feet wide
and up to 39 feet long. DSPs made of polycarbonate cost $1.75 to $2.50 per
square foot, and those made of acrylic cost $2.00 to $3.50 per square foot.
Framing Materials
To a large extent, this choice will be influenced by the type of covering material chosen, the desired permanence, and costs. Many homemade greenhouses are made of wood. Be sure to purchase treated lumber for exterior use. Metal-framed greenhouses are more permanent but are difficult for do-it-yourself projects from scratch. However, greenhouse manufacturers offer many kits that are easy to erect and are reasonably priced. Aluminum or galvanized framing last a long time with little maintenance. Schedule 80 PVC pipe can also be used as supports for small Quonset-style greenhouses that are to be covered in PE, but PVC requires extra support to withstand strong wind.
Whatever the choice, the framing must adequately support the covering and any equipment and/or hanging baskets suspended from the framing. The framing must also be able to withstand wind, rain, snow, or ice common to the geographic location. The load exerted by hanging baskets can be greater than that caused by weather.
Wood preservatives for greenhouse framing and benches should be pressure-treated, salt-type, or copper naphthenate. Avoid creosote (no longer legal) and pentachlorophenol preservatives--these are dangerous for people and toxic to plants.
The eave height for a gable roof greenhouse should be at least 5-1/2 feet with a minimum gable height of 8 feet. However, gable heights of 10 to 15 feet are common. Roof pitch for a glass greenhouse should be 6-inch rise per foot (27 degrees) to prevent inside condensation from dripping on plants. Plastic-covered greenhouses require a steeper pitch of 7- to 8-1/2-foot rise per foot to prevent drip.
This information was attained from http://www.aces.edu/department/extcomm/publications/anr/anr-1105/anr-1105.htm
Here are some great sites to purchase kits. Prices will vary with materials and make. Not one kit is better than another. You must determine what is best dor you and your futurw plans.
http://www.jimdandygreenhouses.com/greenhouse.htm
http://h2othouse.com/html/kits.html
http://www.greenhousebuilder.com/greenhouse/clearspan.html