Hello, I am new to this forum and am in the process of building a 12x12 greenhouse in south Texas.

My plan was originally to put a sloped roof on my greenhouse, but I came across a great deal ($24 each) on new 36x72 double pane, argon filled vinyl windows. These are the same windows I am using for the sides.

If I were to go with a pitched roof rather than a sloped roof, I think the windows would be much easier to install. If I go with a sloped roof, I would probably go with 26"x12' clear plastic roof panels that cost about $32 each.

One thing that I worry about with the plastic panels is heat loss. The worries I have with the windows are weight, glass breakage from storms and trapped heat. Either roof will have two 750 cfm solar roof vents. These vents will have a temp setting on them for automatic turn on and turn off.

I will have some good afternoon shade since we are looking at 100 plus degree weather in the summer months. Building will have East/West exposure on the sides with the most window area.

Plan to put in a water catchment system that will hold about 600 gallons of rain water as well.

Thoughts? Recommendations? Arguments for or against one design vs the other.

I used a twinwall poly panel for the roof with an internal milky twinwall that is a bit more flexible for insulation and light dispersion.
I'm in a cold climate so the second layer probably makes more sense for me.
Definitely install an exhaust fan to remove heat in your hot climate.
I do have glass walls with a clear plexiglass interior layer (saving heat again) which I love, but don't see any use for a glass roof, the poly panels disperse light nicely and I don't have to worry about glass falling on anyone if a storm blows something at my greenhouse.
Again, the more vents you can open in the summer the cooler you can keep the greenhouse.

You didn't mention your intended use, or details on your climate for the intended use seasons. That's important for overhead glazing, especially for summer. Around 20% glazing on roof is plenty for summers and gets you by in spring/fall here in central eastern AZ at 5600ft. Those with more just end up covering it with shade cloth, unless massive evap cooling is used (that's what the big pot farm does). Excess overhead glazing costs you in winter, thermally, and adds little to insolation in winter.

Greenhouses with triple or quad pane polycarb roof (which reduces sun somewhat) and no forced air evap cooling don't get used here in the summer, it's just too hot, even with massive patio doors open. Outside highs of high 90's and low 100's. Ventilation is a bad joke when the outside air is 100F. Our humidity is dry so evap cooling is possible, with 20F temperature drop over ambient. If it's humid where you are, summer use of the greenhouse may be impractical.

Intended use and in what seasons is also HUGE in design impact; if it's early spring starts only, that makes things much easier.

Yes, how cold does it actually get in South Texas?
Since winter is probably the only time you will be using it I'd strongly consider a sloped roof facing South to get all the sun available.
There are actually calculators online that will give you the best angle for your latitude.
Happy growing!

Since the snow load can be a factor here, I decided against a sloping shed roof and built one with a central 2x12 ridge and clerestory vents oriented to the prevailing wind. The roof vents don't collect snow and are spring-loaded with thermal pistons and cable to open them.



The clerestory vents were supposed to be larger, but the builder who help me frame it thought that the original 2x10 ridge wasn't strong enough.

Just a note on vents catching snow.
We've had 30+ inches of snow here in PA and within a day the snow is melted and slid off the roof so it's not an issue for me.
Vents rarely need to open in the winter so if your looking at this and thinking about building I would not be overly concerned about using your typical greenhouse roof vent.

Good point Mike! We've had relatively mild winters since we built our greenhouse in 2016, and the snow slides off easily with a 45 degree roof pitch. I always secure my 2 roof vents for the winter so they don't blow open. However, in that huge snowstorm in early February, the snow built up before it slid off...catching and dislodging the plexiglass panel on one of my roof vents. I was able to secure it back using bungee cords for the time being, but now I have a repair I have to do.

Jim/MoonShadows - I don't know how big your GH is, but when I had an 8x16 Rion, which had the "typical roof vents," I used cheap 3 mil clear plastic sheeting to cover it in the winter; it let the snow slide off easily without damaging the vents (and also held them down so the wind couldn't blow them open) - I think I probably added at least several years of life to that GH by putting the plastic over it in the winters.

Weedwhacker said:Jim/MoonShadows - I don't know how big your GH is, but when I had an 8x16 Rion, which had the "typical roof vents," I used cheap 3 mil clear plastic sheeting to cover it in the winter; it let the snow slide off easily without damaging the vents (and also held them down so the wind couldn't blow them open) - I think I probably added at least several years of life to that GH by putting the plastic over it in the winters.

Good idea, Sandy. I would never have thought about something like that.

This is where I should 'fess up that it was actually my husband's idea... he was concerned that the freezing and thawing of water that got into the nooks and crannies around the twinwall panels would be problematic. The peace of mind was well worth the small amount of effort required.