The temperature requirement was more for the terrarium animals than the plants but it's not necessary...

I fear the roof will lose a lot of heat. Is there a better material I could use that woul let lots of sunlight in but increase the R value? Or - could I install 2 layers of polycarbanate roofing to have a pocket in between them?

I can insulate the walls heavily but I wanted some of the walls to be polycarbanate to let in more light / or is that a bad idea?

Is this a raised deck with airflow underneath? If so you're going to need to heavily insulate the floor also, and you're not going to have the ground to regulate things.

I'd do double or triple wall polycarbonate roof and those sides that will get a lot of winter sun. I'm not sure how that will compare to a single layer polycarbonate on each side of a 2x4. I'd think about double layer polycarbonate on each side. Or maybe triple wall acrylic just on top. I think the acrylic is even better. Try to talk to an expert at the supplier.

I'd be concerned that you don't have the snowload covered. It should be build as strong as the roof of a home unless steep enough to shed well.

And as Rich alluded to having a deck as a floor is an issue. That must be insulated and able to handle water passage. Plus you have no thermal mass that you'd ordinarily get from the soil.

Lots of good points - thank you!

Yes, the deck is raised. I plan on utilizing lots of drainage and I will definitely insulate underneath (I was thinking about using the spray foam insulation bc it's airtight and high r-value.) The deck is "L" shaped and 4 out of the 6 sides are surrounded by the house and I am building an insulated shed on the other side of the greenhouse that will be heavily insulated bc I'm using it as a water-purification and storage room) So, insulating it well should not be a problem. I will put raised beds on the other 2 sides so there will be no draft going under the deck whatsoever...

The roof is 12 feet long on the side that I'm really concerned about and it only drops 60 inches from one side of the other. I'm not sure if that peak is steep enough for 2x4 construction but I really didn't want to do 2x6's bc I felt they would stop too much light from getting through. Those concerns don't really matter if the roof would collapse from not being built strong enough though...

I like the idea of using double layers of polycarbonate. I'll look into acrylic but if it's the same acrylic material we use in the marine fishtank hobby, it doesn't hold up well with sunlight / UV and get's brittle and "crazes" making microfractures. Nonetheless, it's worth looking into if it is a different type.

Can you deck manage the weight of the water?

You might want to search some of the Pot Grow set ups and see if there is something that can be adapted to your use. If they can grow it in closets, attics and garages....you might find that your garage is a better option

Good question. The stock tubs filled with fish will actually be at ground level sitting on a 2" slab of foam. I will be cutting holes in the deck to set these tubs into. Sorry, it seems I left a bunch of important details out of my original post.

Acrylic is expensive but is supposed to last longer than anything besides maybe glass.

Some info linked below on acrylic r and u values. There are similar tables you can google up about polycarbonate.

My guess is that single layer corrugated polycarbonate on each side of 2x4 roof would be about like double inflated poly. That r value can be found and isn't that high. Double layer polycarb on each side should have r near 4-5??

Here is a link that might be useful: acrylic greenhouse coverings

This post was edited by fruitnut on Fri, Apr 11, 14 at 12:48

I personally wouldn't trust polycarbonate with the kind of snow load I imagine upstate ny gets -- even if your framing is strong enough it seems the panels themselves would collapse. Haven't tested or even looked it up...but worth checking out.

I'd suggest you build with a good slope so your snow slides off, and don't spray insulation under your deck...cuz of runoff.

I'd also suggest that you not build this on top of your deck unless you're willing to build it to the same standards you would for an extension to your home....which is a much different undertaking than even building a heated greenhouse to shelter a fairly elaborate aquaponics set up.

It seems to my (amateur, layman, lives in California and hasn't seen snow in years...) mind that you'd be much better off building this where you can have total sun exposure and you get some thermal help from the ground.

Either way...I've become a huge believer in using chain link fence top rail post to build my GHs with -- stronger than wood, and you don't have to make it a hoop house even though that's what you'll see online -- and you won't have to worry about it blocking your light.

Good luck...I'm hella jealous...I badly want to get into aquaponics.

RE: " I think the acrylic is even better"

Although acrylic has a much longer expected lifespan compared to polycarbonate, it is less flexible, more susceptible to hail damage and costs more than double. It also lets in more than twice as much UV light, which is not used by plants and is damaging to most everything else in the greenhouse. Also, the heat loss factors for comparable acrylic and polycarbonate panels are very similar.
One of the sources of this information is the attached link.

Here is a link that might be useful: Acrylic vs. polycarbonate

Hi...built a leanto greenhouse on the back of a shed in upstate NY. Used salvaged old wood framed windows, on the roof too-which has held up without a single issue. The greenhouse maintains 65 on a sunny day, and my husband and I built a Rocket Mass Heater (Google it-so cool) for the nights...now this does not run all the time. Only every other day to maintain 55 degrees in the greenhouse at night (unless we are windy and really having a cold spell). It is a perfect set-up. My greenhouse is 12 x 10 and 8 foot high. We made sure we have a lot of heat absorbing materials in the GH. I grow a salad garden, herbs, and start all my seedlings in late winter without an issue...good luck and happy gardening!!