My 10x12 twinwall polycarbonate greenhouse has the north wall parallel to, and about 4 feet away, from the south facing exterior wall of our house. We insulated the north wall completely with foil-faced foam insulation and I haven't felt like there was a significant loss of light. It's true that side of my GH is a bit less bright than the sunny south wall, but that helps me because I have a range of plants, and some want more light than others. Those who don't want very bright sun go on the north side bench.

I have read here (from more experienced folks) that most heat in a greenhouse is lost through the roof. This leads me to guess that being able to insulate low knee walls on the east and west ends wouldn't make a significant difference in heat loss.

It may be a matter of cost, though. Twinwall polycarbonate panels can be expensive, and if I already had windows to use at a lesser cost, that would be a tough decision for me (I'm pretty frugal.) I do note that in the winter I have plants stacked from high (on shelves) to low (on the ground) and I'd hate to lose that sunlight coming in on the bottom 2 to 3 feet of my east and west walls...but that's mainly because I pack so many patio plants in, to get through the winter.

Hopefully others will chime in with more GH building experience, ours was a kit.

Given your primary use then IMO south wall and south facing roof pitch should be your focus for the windows. That gives you the best late-winter and early spring sun exposure.

The north wall should be insulated solid and most of the east and west wall the same. If you have enough windows once the south wall and the south roof pitch is done then 1 or 2 windows on the east-south and west-south corners would be good.

Picture a south-facing box with a pitched roof. The south side and the south part of the pitched roof glass, most of the rest solid and insulated.

Then if the windows on the south roof pitch can be made so as to prop open to vent heat so much the better.

JMO based on how mine works.

Dave

Thanks for the feedback. It has given me some things to think about that I did not consider before.

This sounds like you are planning a project similar to mine. (I am building a 12 x 20 greenhouse with salvaged windows and skylights that I collected from Craig's List ads.) I have enough windows of fairly uniform sizes, and all of my walls have 6' of glass and a 2' knee wall. The eaves are configured to use two Gothic church windows, to be installed (hopefully) this spring.

The skylights don't let in as much light as I hoped they would. If I had to do over again (which I still may do) I would devise a better plan ... that pile of salvaged sliding glass door panels in my shed is looking mighty tempting.

Good luck with your project. If you need some advice, or just someone to hold your hand as you design and build, let me know.

Connie

Here is a link that might be useful: greenhouse from salvaged materials