Now that you know some of the basic design principles for a solar greenhouse and have considered how you will store the heat you gather, you need to begin to think about the kind of glazing you will use in your greenhouse.
Glazing is any kind of transparent or semi-transparent material that will let light into the green house but keep out the cool air and wind. Most houses use glass as a glazing, generally clear, but sometimes translucent glass such as the glass used in some bath room windows, or glass block.
You have many options for greenhouse glazing. There are specialty glazings, available in some lumber yards or hardware stores, such as reinforced fiber glass, acrylics, and flexible glazings such as acetate or vinyl. What you choose depends on your budget, how you want the room to look, and safety.
Visually, the most popular material is glass. However, with glass there are safety issues to consider. Most people want south facing glass quite low to the ground, to admit plenty of winter sun into the room. Check with your local code folks to see if Plexiglas or shatterproof glass is required within two feet or so of the floor. This is an important consideration, as it's quite easy for a child to injure her or himself on low glass, and it's even easy for careful adults to bump into glass while cleaning or doing gardening work.
If you choose to use glass, see if you can find patio door replacement glass - it's a great size, it's tempered and safe, and it's already double glazed (two layers thick). You can also look for used windows. Also, sometimes a window manufacturer will have some custom windows made up that no one has come to claim and will agree to sell them to you at a discounted price. If you choose to use windows, look carefully and begin to plan your design around the windows you find.
Acrylic and reinforced fiber glass come in sheets up to four feet wide. Both are easy to work with, but fiberglass contains glass fibers. It's potentially dangerous while you're working with it. Be sure to wear gloves and wear a mask while you are cutting it so you don't inhale any tiny glass threads.
Thin vinyl and acetates are also easy to work with and come in a wide range of widths. They can be cut with scissors, are safe, fairly inexpensive, and easily repaired or replaced. If you are on a low budget, you may wish to design for future glass but use a low cost glazing for a few years so you can get started using a greenhouse. Add windows one or two at a time as you can afford them.
One of the most important things to remember when installing glass or any glazing is that the glazing needs to be well sealed, glass that fits loosely in its pane will be drafty, and your green house will lose all its hard gathered heat faster than you can imagine. Caulk well with a high grade (25 year life) acrylic blend caulk around each piece of glazing and each window or pane that isn't operable.
If you use flexible film, caulk along the stud in the wall, lay the film on carefully, then tack it down with a few staples before covering the seams with trim.
Caulk may be the single best investment you can make in your greenhouse (or in your house, for that matter). Caulk while you construct and avoid air leaks later. Get a little stock in a company that makes caulk - you'll be buying lots of the stuff.
It is possible to construct a temporary greenhouse without a floor using cement blocks or landscaping timber for the footer for the wall. Used studs, flexible film glazing, and a gently sloping shed roof won't cost a fortune. Add some insulation and caulk, and you can create a useable greenhouse for about a thousand dollars.
If you work with an architect, use expensive windows, lay a beautiful tile floor, and add a hot tub you can spend over thirty thousand dollars.
Think about your budget, your needs, future additions and modifications. Bring your sketches, design ideas, and questions to the greenhouse workshop at the High Desert Gardening & Landscaping Conference February 17& 18 and Cathe and I will be glad to talk with you.