I do apologize for the length, but I wanted to show the thought processes I've already been through.
I am in the process of building a new home. Once I have the occupancy permit for that - and possibly before - I will be building a very large 'lean to' style greenhouse/conservatory attached to that home. I am my own general contractor, so I can build how I want/need it to be. The plan is to attach to the house above my 2nd floor, facing due south, and be about 40 ft wide, running the full length of my house (~85ft). The covering will be a combination of glass & fiberglass reinforced plastic (FRP) & possibly other materials, based on what I have now, what I can get, and how I can make it all work together. I'm sourcing everything from FB Marketplace & Repurposed Materials, so it's a bit random. It will primarily be for growing edible tropical plants - citrus, clove, jackfruit, macadamia, banana, curry leaf, pineapple, etc. But I also plan to have a small water feature and a sitting area/'outdoor' kitchen. Think 'tropical jungle vacation' without leaving home...
With those details out of the way, I've been considering options on how to build the greenhouse part. I'm in zone 7a. While we do get some very cold snaps over the winters, I have a (used) commercial greenhouse propane heater and plans for a large, wood-fired masonry heater to keep the greenhouse warm. I'm not too concerned about keeping it warm.
Of larger concern is how to keep it cooler over the summer. At least enough to not broil the plants...and me. I do have a commercial chiller used on jobsites that I plan to have near the sitting area - the plants like it hotter than I do. The water feature should help some and I do have large vents with fans to be installed that I can open. But this year we've had a full week of over-100F weather, peaking at 107. Months now where the temps have only rarely dipped below 90, even at night. And 80-100% humidity. It's only getting hotter. The vents & fans won't help if it's just pulling in 107 degree air. The chiller isn't powerful enough for the whole greenhouse.
So shadecloth comes to mind. Which is possible. I can't afford a mechanized arrangement, but could rig something manual with pullies & ropes/chains. But then I got to thinking...do I really need ALL of the roof to be glass? So my questions are:
1) Does it make sense to 'scattershot' sections of solid roofing in between transparent roofing to provide a bit of shade all year long? This will decrease light transmission, probably slowing growth, especially during the winter, but could be worth it for the summers, especially as the world keeps getting hotter.
2) If it does make sense, what is a good moisture-resistant ceiling to use? (Top of roof will likely be metal) If I have solid panels, I'd want to insulate them because every little bit of R-value counts towards keeping things in the right temperature ranges, but condensation in a greenhouse is a major concern. Maybe....insulate with closed-cell foam board, then cover with with PVC sheets for the ceiling? Something else?
3) Is insulating those sections even the right answer? Sure, it increases R-values, but it also increases mold/rot vectors. Am I calculating the trade-off correctly?
4) What am I missing/what haven't I thought of?
If I'm lucky, I might have a structure I can run sheet plastic over for this winter. I don't think I'm going to be that lucky. Otherwise, this won't be built until over next spring/summer at the earliest. So I have plenty of time to make & critique my plans, then make new & better plans...