Contemplating the same question.
My thoughts.
obviously the sun rises east and sets west, still.
in the summertime at noon the sun is virtually straight up over the top of the gh at mid day.(depending on your location)
In winter , the sun does not get as high in the sky.
so if your glazing faces predominantly south, during the winter, it will get more direct sunshine throught the south facing windows a larger percentage of the time in the afternoons..
If the windows face east, you will get morning sun all year.
. I have set up a sort of small model of the potential different shapes for greenhouses and set them out to observe and see how much light will penetrate different designs at different times of the day.
Another question is, just how much light do your plants really require to survive and flourish.?
I am thinking that a longer narrow rectangular house with the small ends set south and north and the long walls facing east and west, will get morning and evening sun into the plants everyday summer or winter through the long east and west glazed greenhouse walls., but my question is will that be adequate light for the plants?
I am hoping to find a way to incorporate a roof that does not allow light to enter.
If I can find a design and orientation to get adequate light through the east and west facing windows, morning and evening, I would like to have a shingled roof over the top . that would help with insulation and also allow easy access for maintenance.
I know this may go against conventional wisdom, but I feel the advantage of a shingled, insulated roof would be huge if adequate light can still enter the house in all seasons.

your input is encouraged and welcome.

Greenhouse placement is of paramount importance, but I think you are missing something as far as the roof. I would say that in the summer, a glass, or transparent roof would make things too hot; yet in the winter a glass roof would be great as far as letting in light from all angels/sides. However, I would argue it is easier to shade a glass-roofed house than heat a shingled greenhouse. I want orchids and other tropicals, so blazing sun is not in my best interest in warm Chicago summers. It is the winter months of almost gray skies that gets me worried. I would personally think that a glass roof would be great for my orchids in November, when the sun is not warm anyway. I can deal with putting shade cloth on from April to October. I think it is easier to block light then to add it. And from years of indoor growing, think of this, plants grow toward the light, if light were from above, the plants would grow straight up. If your light is coming in from only the sides, the plants may bend to the light. I think the best is to get the glazing that blocks out a small percentage (30-40%) of the sun and have more clearer side panels.

Hello

I too have been thinking about what windows are necessary. I also live more north (Washington state) and feel that having tall windows (9') to the south is the best idea, with a solid roof to maintain winter warmth. I will also have a window up high on the eastern wall, and a tall window running vertically on the western wall to catch the afternoon sun.... As money allows I think I am going to incorporate SolaTubes to let in extra light while keeping my warmth.

The link I have provided lets you see the altitude of the sun at different times of year based on where you live (it will be highest on June 21 and lowest on December 21 for those of us in the Northern hemisphere). For me that means 65 degrees on summer solstice and 18 degrees for winter- meaning that either way the sun is southward. Just in case anyone reading this hasn't been around these navigationy terms, altitude is the degree up (90 being overhead), azimuth is the degree to the left or right as read with a compass, having been adjusted from magnetic north to true north, with North being 0 (360) degrees -so it tells you where on the horizon the sun will rise and set-.

Getting the solid facts on where the sun will be all year gave me a lot more confidence in my design- I hope it helps you as well!

Here is a link that might be useful: Altitude and Azimuth for the sun on any given day

I've been doing some rooting around on the Internet and have found some interesting info.

This source has some good stuff even though some of the links are broken.

This source says absolutely no to the windows all over the roof idea.

More excellent info.

I am moving along with my design ideas and will be posting the plans here soon.

Thanks to everyone for the responses so far.

Forgot this one.

Can someone explain something to me? I understand that if you have something obstructing the sun such as a building or trees, that placement would be important, but I just don't understand the placement in the yard.
If you have clear (glass, poly-carbonate, plastic sheeting) walls on all sides, and your greenhouse is square (8x8,10x10)what difference does it make which way the door faces? Is positioning only important if you have a shingled roof and obstructions? Or if you have longer sides than ends?
Maybe I'm missing something basic here - or maybe I just have such an unobstructed yard that it just isn't clicking.
I'm thinking about a small portable greenhouse next year until I see if I can stand being out in the heat for gardening, and I know where I would like to put it....but going by graphs and altitude of sun and azimuth....it's in a totally wrong place.
Thanks,
Carol B

Carol, you are right about positioning, IMHO.

There is the argument that the shadowing from the beams will be more evenly distributed over the plants if the beams run N-S. In other words, one might say that in a N-S GH, the beams, which run E-W, will shadow some sections of the GH unevenly. I think that unless you have huge, wide beams, that is not such a big deal.

Most of the GHs we are talking about are pretty close to square. We're not talking about the big 100' long commercial hoophouses here. I have no data to back this up, but my guess is that the advantages of strategically orienting a 12x10 HFGH are minute compared to the advantage of another convenient or aesthetically pleasing alternative orientation.

Now the door may be a different matter. If the door is your only ventilation intake, then you want that on the side from which the prevailing winds come. If you have other intakes, then you can place the door where it is convenient.

I agree with Stressbaby. If a GH is exposed to the light on all sides, as long as there is intake on the side facing north for summer ventillation, it's shouldn't make any difference where the door is placed.

Indeed, if you are in cold country and heat your GH in winter, you would be better off having the door facing away from your prevailing winds.

Carol,

A big part of the equation is what you want to do with your greenhouse. Some plants like more sun than others (like some tropicals naturally grow in the understory and want some shade). One big reason a greenhouse is ideally located where it gets a lot of sun, is that this is their main source of heat. If you place your greenhouse somewhere where it won't get as much light, the inside climate will not depart from the external climate as much as it would otherwise, so you will have to heat it through another means.

I think your idea of getting a portable greenhouse is great idea for your situation- you can try one place out, and if it doesn't work, find somewhere with better conditions for next season.

Shaelee