If you can build your greenhouse on the south side of your house, then they can share heat, and the greenhouse can act as a big walk-in Solar collector in the winter, while your house (with a woodstove?) can keep the green- -house from freezing at the growing season extremes. It will also cost less to build, when it uses the existing house wall. North glass would only gives you sun in the summer, when you don’t need it anyway. The reflective wall of the house can actually give you more, and more even, winter light on you plants than glass will. Since you won’t be planting in the ground, you can use a raised floor, and pier foundation, if that will work best on your house. You also do not need a massive concrete or earth floor for Solar reasons (thermal mass). The plants will shade the floor. Shaded mass down there will not store any heat from warmer air up above.

If you live off-grid, you must use nature to move your air and energy without the aid of fan and blowers. Let the house absorb any extra heat during the heating season. A door, or even french doors between the house and the greenhouse will allow air to flow between, and will expand your living space. If you go to your local glass store/contractor, you may be able to arrange to get doorwall (sliding glass door) glass, which they re- -place often. Doorwall glass is usually replaced, because a sealed glass unit (insulating glass) loses its seal, and starts to cloud up. Sometimes it is replaced, because one of the sheets of glass gets broken. Either way there is still useful tempered safety glass there. They usually just break it, and throw it away. They may charge you a handling fee, for bringing it back to their shop, or they may collect it for you, and deliver it to your house. You will then have to separate the glass from the spacer, and clean it up, but you can end up with very nice, cheap (or free) glass that way. This glass is good to work with, because it has smooth sanded edges, that can not cut you, even if you tried. It is also extremely strong. The basic thing that you need to remember, is to not let the edges get hit by any- -thing hard, or rest on metal or masonry. If an edge gets chipped, the glass bursts into tiny pieces, which are not lethal, but could still be dangerous. Even if it doesn’t shatter immediately, when chipped, it will eventually, so the glass is no longer any good. It is wise to get a couple of spare pieces when you find a bargain. You could also buy the glass new, and you could even buy new sealed glass units (double glass) which would be much better insulated, but in you climate, on a budget, you can effectively build with a single layer of glass, let the extra heat warm you house, and then at night you can insulate over just the plants, instead of the whole greenhouse. A greenhouse, if it needs to be warm at might. needs night insulation, either over the glas, or over the plants.

Anyway, the standard sizes of doorwall glass are 34″x76″ and 46″x76″ which means that you can install it on the outer face of 4″ post on 3ft, or 4ft centers, respectively. There are several tapes, used in construction, that you can use to seal the edges of the glass from leaking. One is the Water and Ice Shield that is used in roofing, available at any lumber yard, and can be used to seal the entire sloping roof of the greenhouse. It can be cut into 3″-3 1/2″ wide strips for between the sheets of glass. The backing is removed, and the tape is stuck to the surface of the two pieces of glass to seal them as if they were one. Then, a 1×4 batten can be nailed or screwed in place over the tape. There is also tape that can be bought in rolls from heating supply companies. It can be bought pre-cut in a variety of widths, with a foil surface in the exposed side. There are also several kinds of plastic glazings that are easy to install. Some of them have multi layers, and insulate better than one layer of glass, but they are also more expensive than the system I have described here. One the cheap end, you can simply stretch 4 0r 6 mil clear polyethylene.

It is fairly easy, and inexpensive to build a greenhouse this way. I have designed well over fifty, and they are as easy to build as a standard house wall. The Rodale Press’s “Solar Greenhouse Book” available used, is a pretty good book. As I recall (it’s been decades) it is quite oriented toward thermal mass inside of the greenhouse, instead of shared with the house, which wrecks the ability of the greenhouse to provide a significant amount of heat to the house, in all but the easiest climates, like the Southwest, but it has a lot of useful information. I prefer that the greenhouse share heat with the house, so that there will always be the option for it to function as an efficient Solar collector. Just leave out the mass inside of the greenhouse, in colder, cloudier climates, or when you do not grow 12 months of the year. You can also use water containers for thermal mass that can be more easily adjusted, or totally removed…