First thing is to build 1.5 to twice the size you THINK you need. You will fill it up very quickly. Almost everyone I know will say "I wish I had built it bigger."
Are you aware you can buy a U channel to seal off the ends of multi-wall polycarb (pc). Since you are zone 5, I would suggest at least three-wall pc. Your knee wall design sounds good. I built my gh using a knee wall and a modified A-frame roof. The first winter I had it we had the snow-storm of the century (for Alabama, that is) on March 13, 1993 and the steep roof allowed the snow to slide off. Other greenhouses with a standard, flatter roof collapsed from the 13-15 inches of heavy, wet snow.

When I added on to my gh, I made the knee wall 48 inches in the addition. Next spring when I replace my 10 year old polycarb cover, I'll raise the knee wall of the original structure to 48 inches. The ends are closed in with twin ply flat polycarb. If you have any question, email me.

Given the choice, I would go with all vinyl framed thermopane, especially as very few of them in a GH need to be operating and non-operable windows are not all that pricey. But as long as nobody lobs a fast ball into them, unlike polycarb, that will have to be replaced sooner than later and in the sunny south, sooner- glass will last as long as your home.

To keep the costs down, check out what is available in your local home centers and determine which sized windows are stock and what sizes are the least costly, then frame the GH to accomdate them.

Another benefit of glass is the ease of cleaning it and the ability to use the cheapest yet most effective means of totally removing the mildew, mold and algae inherient to all GH's; bleach, which is deadly to polycarb. Then, there is the shadecloth you won't need. Just go back to what was used on glass GH's before polycarb: water based whitewash. Spray it on in spring and power wash it off in fall.

I do agree about making it larger than you think you will need. They are never as large as we think we need. Or, construct it with doors at each end, with the thought in mind of adding on later. And do use an insulated door. It would seem a pity to construct a GH like that, then lose heat/cool through a door. Or, go with a really heavy, tightly sealed insulated storm door, not the lightweight junk that comes with most prefab GH's, even the most expensive ones.

However, for framing, think twice about using cedar. The average cedar now sold is not only far more expensive than treated, it's not what was available 40 years ago. All of the tight grained old growth is gone and what is now on the average priced market is soft, fast growth farmed lumber that will rot out faster than treated. Good quality treated lumber, if gone over with several heavy coats of any good oil based penetrating stain sealer, will outlast cedar by a mile, and look good for years.

And- when you do restain it, if you dribble any onto the glass, you can use paint thinner that would destroy polycarb to wipe it off and/or go over it when it dries the same way you would any window; with a razor scraper.

Then- talk about a garden GH as a class act...

I can't imagine what heating it would run in Wisconsin if you have to keep it high enough to grow orchids. I'd be very tempted to do a pit-style g'house with an A-frame top. With the best insulated glass you can afford. My second choice would be a lean-to. They require less heating because one side is protected from weather.

Even the high-dollar Low-E windows are only about an R3. I doubt you find cheap vinyl frames with expensive glass, so expect R-2 performance.

Temps here can drop to -20 and below. Asking to raise that 75 degrees to keep it at 55 would be expensive unless you have your own woodlot. In my twinwall polyethylene GH with 4 single pane windows, it will lose heat rapidly and be only a degree or two warmer than outdoors. A 1500-watt electric heater will bring it up some 20 degrees in the winter, so I can keep it going till we hit 12 or so above zero outside.

By installing plastic covers over the plants in the gh and placing Christmas lites inside, I've kept seedlings toasty in even lower temps.

If my plan were to garden year-round, I'd be covering and insulating almost all the walls and roof, with perhaps only a few windows and a portion of one roof side in twinwall glazing or poly. With maybe insulating curtains to cover the windows at night.

Maintain plenty of air movement, which helps prevent frost from forming and reduces cold spots.

Heating pads are another possibility. I'd be careful with all these proposed heating appliances running frequently and often unattended. Make sure the wiring and other utilities are safe and inspected frequently.

If looks are not as important, fiberglass sheets are good insulators but do cloud over and get "hairy" over time.

Give things a trial run in some cold weather before placing all your most-loved plants out there. Those remote thermometers are great for babysitting things from indoors.

Good luck! It's a tall order, but if you can afford the systems and the utility bill, it should be doable.

-Ed

I have to agree about the pit style. No GH design yet has come close to the energy effeciency of a pit and had we been able to afford it, my freestanding backyard GH would have been a thermo-glass roofed extension of our basement.

That's why I suggested pit and peaked A-frame. You can get enough height to use a radiant source suspended well above the bench level to get decent distribution. It primarily heats the objects it hits, and doesn't waste energy heating the air. Not particularly comfortable for humans in cold weather who are used to warm, moist air, but the plants don't mind.

You are going to need as good ambient light as you can get with winter growing, as opposed to just keeping a plant 'alive' until spring. Glass in that respect is a good option if you can afford it. Otherwise you end up installing grow lighting and that is just one more system to cope with.

I have one of my greenhouses earth-banked to waist level on one side, and it has been a life-saver as this is the house I traditionally heated all year. It is more economical to run than one of my smaller g'houses and the earth bank is on the north side and benefits from the winter solar gain off the south exposure.

Actually, if you get a pit deep enough, keeping it warm for the comfort of the people working in as well as the plants is easy. If the bottom of the pit is below frost level, look back to the Romans, and heat the floor. Except that the Romans had to rely on fires fed by slaves to create hot air, while we have small, cheap and efficient pumps to circulate hot water or oil.

Sometimes the best view forward, is to look back, then use what we have today to accomplish the same thing as did the people who produced fresh veggies in winter 2000 years before the Industrial Age. The materials have changed dramatically, but the concept remains as valid today as it was then.