Double paned Plexiglass collapsing inwardly - Help!!

I have about half of my greenhouse walled with 2 panes of plexiglass seperated by about 3/4" with a trim board. The glass panes seem to suck together in the middle. I wonder if this is due to the hot air escaping and then a vaccuum forming as the air cools. I was also wondering about drilling a small hole in the inside pane to aleviate this problem but I did not want to lose the insulating property of the twin walls and also was thinking about adding a third wall of plexi for more insulation.

Has anoybody come across this problem yet and if so, how did you correct it?

Thanks. SF

What is the span on the panels? How big is each section of PG that does not have some sort of brace behind it?

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Very nice greenhouse! The matching raised bed looks grand too.

It doesn't look like the space between the studs is excessively large. Hmmm. How do you have the PG attached to the wood? Is it all sealed?

I'm hoping stressbaby might pop in with some ideas on the heat and vacuum effect.

Thanks. It was a kit I got from a Canadian company. they built the planters as well. The dimensions on the GH are 16' X 12', the door side is the 12' side, glass panels about 2' wide I would guess. You can see how there is some condensation about the periphery og the panes which are the plexi, the middle areas are mostly sucked in and touching each other. There is a 3/4" X 3/4" stick of cedar which runs around the edge of the panes and seperates them. I deally, if the glass was straight and did not bow, they would be perfect. Alas, they bow in the middle.

I'll get some close-ups in a few minutes. Have to take them first.

Did the actual kit call for the two layers of plexi seperated by 3/4 inches? How wide is each window? It does not really look like there is enough span to put a brace in the center of the windows and it would be one more obstruction. I can see where the condensation has made a bit of an arch shape on some windows. Is that where they bow?

Well, guess I won't have close-ups in a few minutes. DW took the camera with her to work! LOL. Basically, there is a small lip 3/4" that runs around the frame for each opening. A piece of plexi (or TW Polycarb in some) is then placed and another 3/4" board installed to hold the glass in place. In the openings where the 2 panes of plexi are, another pane of Plexiglass is then placed and then another 3/4" trim piece installed to hold them. Yes, there is some sealant, and the roof, which is all TW polycarb panels, just slightly overhangs the side walls. Wouldn't seem that the air space between the 2 panels would be so tight, yet not tight enough that this would be happening, but I cannot imagine what else could be causing this phenomenon.

Yes, that's where they bow. Yes that is how the kit was designed. I though about a cross brace, but wanted to avoid that as I like the way it looks the way it is now, sans the bowing of course.

If I had to measure the glass I would say 22" wide and probably 48" high. + or -.

Nice looking house!

I agree, what is happening is that you have sufficiently sealed the air gap, and since the air in the gap is expanding and contracting all of the time as it heats and cools, the panes bow in (and out) accordingly. You're probably just noticing it more when they bow in because that's when they touch.

I like your idea of drilling a small hole. You won't need much. I'd say a 1/16" is too much. I'd use a pin vice drill bit, something very tiny.. The question is, which pane do you drill the hole in? Maybe the outside pane would be better, given the lower humidity outside and the prospect of moisture accumulation between the panes. Have to think about that for a moment...

Interesting that not all of the windows demonstate the effect. For instance, in the second picture, the near panes are affected, then it skips two sections, then two more are affected. Any differences in the glazing or seals between the sections?

yes, the ones not demonstrating the effect are the ones that are not plexi, but are TW polycarb. I set up a design because I wanted some privacy but wanted to be able to see the kids while they are outside playing, etc... so, some of the panels are the TW polycarb and some are the doule panels of plexiglass. SInce the TWP has fluting from top to bottom, this is not an issue with it. Only the plexi does this.

For clarification, in the second pic, the ends and the 2 middle panes are clear plexiglass, dual pane, and the other 4 are TW Polycarb. You can tell the Plexi because it has the bowing and condensation and it is much clearer to see thru.

would it be better to take one pane out and drill a vent hole thru the wood on the bottom in between? This I think opens into the sidewall, which is insulated, but not tightly. Maybe that would be better. More work, but then I could clean the glass in between. Spiders may become a problems then. Or, I guess I could put a tiny hole in the roof panels where the side glass that is problematic comes up underneah it. Maybe not enough space to expand and contract tha way though??

Sig,

You have a beautiful greenhouse. It is awsome how you have the planter boxes made the same as the greenhouse. Everything looks great. Thanks for sharing.

Jesse

I just checked the windows in our house. They have "internal storms" are vented through the frame of the window to the outside. That would be the way to do it. If not possible, then a hole in the outside pane or in the frame down into the sidewall would be my next choices. Maybe try one window each way before you do them all. Let us know how it works.

I wondered about using a small spade bit in the frame somewhere but was not about to suggest it in case it hurt something. LOL I don't want to be responsible!! I thought if it was to the side, it might not help much. If it is on the bottom, it should let off the pressure without losing the heat? I'm thinking on the top would be a really bad idea. Our windows at the other house have a small hole in the track that holds them so anything in the track runs out. The windows themselves are sealed though. Would it be possible to make a small notch at a bottom corner of the windows so they would not run appearance? Would that make chances of the window breaking worse than drilling a hole?

Thank you all for the insight. SB, I think you're right about the venting. Since I am off on Friday, I am going to pull one pane and make a small vent hole into the side wall thru the bottom of the window frame. Since this is a pretty rapid phenomenon, ie... happens daily, I should know byt Friday night when it cools, if this is going to solve the problem. I would rather not alter the glass if I don't have to.

I am also thinking about adding one or more panes to the inside/outside of what is there for more insulation, but I won't do that until this thing is solved.

When I got back from my sumer vacation and found most of my garden dead, I was so distressed that I basically gave up on it. Since then have had a few tomatoes survive and actually had a decent harvest of large whites and the Green Zebra, and Orange King. White beauty producing many tomatoes, but the taste is rather bland for a tom.

My peppers which I was growing in the GH all but died continuously thru the summer because I did not realize about controlling the temp with shadecloth, circulating the air, and my "wonder spray", Pyola Oil, went bad, so the aphids were in a state of constant thriving. Finally got them under control with safer's soap. my first year with a functional GH!! LOL.

I guess the life just got sucked out of me for this years garden. But next year I have mostly planned already and have learned much about the pests and staking. I have almost all my seeds for next year, just waiting for a few to become available, and will be nearly doubling the size of my garden next year.

Seed, I think I am going to try a small drill bit and see if the hardware store sells a little metal tube I can insert in the hole to keep it open, maybe brass. I don't think the diameter of the hole is real important, as the pressure builds rather slowly.
I will post again after my trial to let you know what worked here. Thanks everyone! (smile)

Sigfin, how is it going?

StressBaby,

My efforts were somewhat mixed. I pulled an inner pane of plexi out and the suction effect did not go away. I thought maybe the wood frame was too tight, maybe bowing the outer pane, so I took that one out too. It seems once these panes get bowed they tend to retain their shape. The outer panes seemed to be more affected than the inner panes.?? The wood frame did not appear to be too tight. I am taking a shot that this is a suction phenomenon with the plexiglass having some "memory". I am pulling all the clear glass out and will have to put some clear squares in between the panes when I reinstall, and my drill bit was not long enough to go thru the sill, so the holes have to be drilled deeper. I am still not sure that was the problem, but cannot think of any other cause. I am going to hold off adding another pane this year to see what happens with time after the fix. Maybe with time the "memory" effect will reverse since the stress will have been removed. Seems the contractor used silicon caulk on the outer pane but not the inner. Still the airspace communicates within so the effect should have been equal to both panes.

I've been so busy at my real job that I haven't had the time to chase this down further. Much as I would like to be rid of this problem, it is not annoying enough to make me change out the plexi for TWPC panes all around. You just cannot see thru them clearly enough like you can with the Plexi, and I love to look at the garden from inside the GH and I can keep an eye on the kiddo's if they are outside playing while I'm in the GH.

I think if I use the small 3/4" X 3/4" clear plastic blocks in between the panes, that would preserve the look about as much as I could hope. I hope they don't yellow!

Thanks. Jaime (sigfin)

SigFin, did you write the company? Or call them? I didn't read all of what you wrote, maybe you did. How long have you had it up? That is a real nice greenhouse I should think they would stand behind their product. They are too expensive to have a problem like this.

Jeanette