Hi,
Reading through this thread, I'm relieved to see some discussion about the angle of the summer sun and the earthen roof / overhang.
Up here (north of 60), I need a well-insulated greenhouse but I also need to take advantage of all the sunlight I can. The frost-free season is very brief (sometimes only 90 days) and any plant which needs to come to fruit needs to do it in a short window.
I don't have any solutions to propose, but just a keen knowledge that I won't be putting a ton of energy into a greenhouse with that much of an overhang.
Cheers