higher light or lower u-value?
I am trying to finally put in the lean-to greenhouse I have been dreaming of for ten years. I have a 30' x 8' south facing basement porch that is perfect. Now, I just need to decide what type of polycarb to put on the top. I grow mostly phals now, but that is just because they tolerate my low winter humidity. I also have cattleyas and various oncidiums, but would love to branch out a bit to some other stuff- maybe some vanda hybrids- you know the whole obsession deal..So my question is this; with a ceiling space of almost 500 square feet, and given that I live in Michigan zone 5 and need to keep the thing at least 60 F, do I go for the 16mm 5 wall Uvalue .33, but only 67% light transmission, or do I go for the 8mm Uvalue .5 with 77% light transmission? Solar gain for both are equal. I am really stumped here, guys. Please help me out!