Tempered Glass Panels for Greenhouse?

bonniein(INDIANA)February 12, 2009

I have talked my DH into building me a Greenhouse..

I have found some tempered glass panels for a very good price and was wondering how these would work for both the roof and the sides.

Size that I am wanting to purchase is:

2'x 8'5"

They are ALUMINUM double panes instead of wood though so will this be a problem as far as installing and or the sweating of the aluminum?

Also any problems with this being tempered glass?

What installation tips can you give, especially for the roof so it will not leak?

Thanks much,


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When you write "double pane" are you referring to thermopane?

As far as their being aluminum framed; just about every home GH kit sold is aluminum framed, but sans the luxury of tempered thermopane glass.

As for construction without leaks; 100% silicone will stay flexible and allow for some expansion and contraction of both the glass and the aluminum although with panels that size, you probably ought to consult with a qualified construction engineer, to determine the amount of free movement space you will need to leave around each to prevent the panels from cracking on expansion in the heat of an IN summer, but prevent leaks when they contract in the deep cold of winter.

However: I would also have grave reservations about using only tempered glass on a roof. It's better by far than standard window glass, but shouldn't be confused with safety glass, as used in vehicles.

For even better insulation as well as safety, you might want to consider buying triple walled or more UV coated polycarb for the roof and frame it out to fit a smaller sized panel then 8 ft., perhaps 2 x 4 ft., to allow you to run your rafters on the same 2 ft. centers as the walls would presumably be.

That would allow you to save a lot on shipping and have far less of a chore in replacing any that might become damaged.

BTW: Given enough insulation, both the glass and aluminum in any heated GH will sweat in the depths of a very cold winter, especially if the GH contains a lot of well watered plants.

When we were in the midst of the really deep cold of December, my heated GH, which is filled with open topped fish tanks, dripped condensation from the ceiling, but it's a GH and was fitted out to survive any amount of water that might be splashed or sprayed in it, as indeed; any GH really needs to be and why one of the better moves anyone can meke when fitting out a GH, is to silicone seal all of the electrical boxes in it, along with the windows.

Yes, I fussed. The combination of water and electricity frankly- terrifies me.

    Bookmark   February 12, 2009 at 2:17PM
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Yes I guess the panels are considered thermopane, two panes of tempered glass in an aluminum frame? (forgive my ignorance)

I just didn't know how attaching aluminum panes would work verses wood ones.

What am am wanting is a 1/2 greenhouse plus 1/2 potting shed basically. (divison wall with door in the middle)
I really like the one pictured here http://forums2.gardenweb.com/forums/load/strucs/msg021536412402.html?7
but didn't want to take over this post so thought I would start my own because I have loads of questions!


    Bookmark   February 12, 2009 at 2:58PM
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kudzu9(Zone 8a - PNW)

I think that they would be great. I have an aluminum frame greenhouse with single pane tempered glass and I have no problems with sweating/dripping; I think you would be in even better shape with what you're buying. What's not clear to me is whether these panels have a true aluminum frame, like a sliding glass door, or if you're just referring to the aluminum spacer that holds the two panes apart and provides the seal for the space between the panes. If you can clarify or provide a photo, I can give you some framing advice.

    Bookmark   February 12, 2009 at 3:26PM
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Kudzu, don't have them yet so don't have a pix but yes there is just the aluminum spacer.
(1/4" glass then 1/2" Aluminum spacer around the perimeter and then 1/4" glass)


    Bookmark   February 12, 2009 at 5:37PM
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kudzu: It's good you have come in because your framing knowledge certainly exceeds my own, but believe me when I say that given the extreme cold of an IN or IL winter and an interior temp anywhere above about 60, with the moist air of a GH, there WILL be condensation.

But in a GH, it's shouldn't be an issue; just a few more dribbles of water on plants, with items one wants to stay dry set aside, perhaps under a solid surface, such as a shelf, or inside one of those nifty heavy plastic base cabinets old time GH owners would have literally killed to have for their GH's, instead of wood, that rots and swells.

I love Bonnie's notion of having a GH that's physically divided between potting (and puttering) and the actual growing space. Then, she could stand in the doorway between them and watch it literally rain inside the growing area, while she stays dry in her pottering shed.

    Bookmark   February 12, 2009 at 5:50PM
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stressbaby(z6 MO)

I have a tempered glass GH, though it is single pane. I agree with BW when she says that there will be condensation. However, it CAN be an issue...condensate on the foliage all winter can result in disease.

One of the chief advantages of a GOOD greenhouse kit is that the various elements will manage the drips. The various elements act like gutters and direct the condensation to the floor. Something to consider in the design of the roof or the layout of the floor plan.

    Bookmark   February 12, 2009 at 8:04PM
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BW,I am sorry if I offended you in anyway..

I am only asking to get ideas and suggestions from others which have experience.

I do NOT want this project to be a nightmare later on but have noticed many people who have DIY greenhouses that are made with old windows, etc.

I appreciate anyone's suggestions but in the long run, my DH will decide what might be best structurally and even over rule me! ;)

Thanks again,

    Bookmark   February 12, 2009 at 8:28PM
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imstillatwork(8-9 Oregon Coast / Ca Border)

I thought I replied, but must have never made it past the preview page....

I used sliding glass doors (free to me) and separated them into single panes so they when further. They are 1/8th inch thick 34x72. Used them on walls and roof. On our freakily warm january outside temps hit nearly 75. Greenhouse temp was 105. you will need shade-cloth to cover the outside and good fans to keep ventilated.

As far as the strength, the panes are STRONG. They are very flexible long ways. I've dropped hammers & tools on them, almost fell off the ladder onto one, a few blew away and landed over 10 feet away and did not break. However if you hit them on the edges, they will shatter into a million bits.

Here's some pics:

Here is a link that might be useful: Tempered Glass Greenhouse

    Bookmark   February 12, 2009 at 10:50PM
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imstillatwork(8-9 Oregon Coast / Ca Border)

Just needed to emphasize the need to protect the edges however you decide to install the glass. mine are in groove in the wood on the bottom and use heavy duty clips similar to a mirror clip on the inside/top. edges are connected using paneling channel, and edges next to posts are 1/4" away. I will block that gap with 1/4 round molding on the inside.

hope this sort of helps.

I feel safe with it on the roof for several reasons: It is VERY strong for face on impacts, and my edges are protected. If one does break, they shatter into a million pieces and really aren't sharp or slivered like plate glass.

Here is a link that might be useful: Tempered Glass Greenhouse

    Bookmark   February 12, 2009 at 10:57PM
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I'm at a loss to imagine what you have written that could be considereed in the least offensive. Your posts have all been extremely polite. Indeed, most all of the posts in all of these forums are, even when the posters disagree. We should all be in the UN?

There seems to be disagreement over the safety of glass roofs and as I haven't any except the extra heavy safety glass in a moonroof of an automoble, I'll bow out of that debate, but the very thought of millions of pieces of glass plunging down into my GH, even if not sharp, still gives me goose bumps.

BTW: Stress is right. Ordinarially, condensation will be channeled down along the walls. I expect I got it in the middle of my GH because of the extra layer of heavy bubble we laid atop the aluminum gridwork that forms a sort of open grid ceiling that I used to support ceiling fans and electrical lines. I had the extra bubble and there was that platform, so I laid up up there and got all that much extra ceiling insulation. But I also got drips on very cold days.

    Bookmark   February 13, 2009 at 9:33AM
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Don't worry about those little pieces....

My very first 'solar structure' was a cold frame built using a discarded storm door (tempered glass) panel. I was drilling the last hole in the frame for a handle with a drill press, when I nicked the edge. The entire piece instantly turned into BB-sized pieces in my hands! After the initial shock wore off, I was amused to watch the detritus on the floor hopping and popping about for a full five minutes after the calamity.

Safety glass, for an application like this, is going to be very heavy. The tempered glass in my greenhouse has survived major impacts (wind-driven 'green' sweet gum balls from 80+ feet) without incident. Tempered is the way to go for single-pane applications.


    Bookmark   February 13, 2009 at 2:34PM
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kudzu9(Zone 8a - PNW)

Tempered glass or laminated glass (glass with a plastic interlayer) is usually a building code requirement on any new window in a house where a person could walk through the glass (like a sliding glass door) or fall against/through it (like a low window), and for skylights. In addition to being incredibly strong, these products are safe That's why car windshields are made of these materials. I want to assure the original poster that she should feel comfortable using tempered glass in her greenhouse. These panels will withstand impact from falling debris much better than plastic panels, and will not pose a safety risk, even if shattered. It's even possible that the panels she's looking at could be both tempered and laminated.

As regards the condensation "problem," I've generally found that any condensation rolls down the incline of the roof to the sides and isn't an issue.

As far as construction, it would be important to use lunmber that's well-dried and warp-free, as this will support the flat panels much better. It would also be a good idea to use glazing tape when setting the panels in the frame. You can purchase rolls of this fairly cheaply online in different thicknesses (I'd get a thick one, like 1/8", to better accommodate irregularities in the wood frame). It's essentially a foam material that's adhesive on one or both sides. You would lay it down on the frame where the panels would rest, and then lay in the panel. It will provide both a seal and a cushion. You could also lay down a heavy bead of silicone for this purpose, but the tape would be easier to handle and be less messy.

    Bookmark   February 13, 2009 at 3:22PM
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BW, Sorry I must have taken you the wrong way.

Folks lots of great help and advice here.
I also found someone who is selling smaller sheets of the tempered glass but it's tinted...
The size of these are 20" x 52" and they are selling them for $4 each. They are advertising as " brand new insulated gray panels."

I have read that it's okay to use the tinted glass in the roof as long as you have clear in the walls, does this sound correct?

As far as using glazing tape, what width would be best to purchase?
I also see there is a "load bearing" glazing tape, would this be needed or any better than the regular glazing tape?

Thanks again folks,

    Bookmark   February 13, 2009 at 9:34PM
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I have 4 brand new vinyl clad Anderson Patio Doors on the roof of my greenhouse. Got a heck of a deal on them. I simply put a heavy bead of 100% silicone between them and squeezed them together, Screwed the frames down to my rafters, then siliconed the cracks on top to boot. These are super heavy ones, I can't ever imagine anything breaking them short of a tree falling on them. And i figure if something did, it would also have to make it through the second layer of tempered glass. They just went through the biggest ice storm in the history of this area. Major disaster. And the thickest ice ive ever seen. Then a few days ago we had the 70mph winds to boot. Greenhouse made it through fine. That was with two inches of solid ice on it.
As a journeyman carpenter familliar with building codes, i can tell you tempered glass is safe. The heat tempering makes it disolve in a million pieces when broke. And the peices aren't real sharp. Most tempered doesn't have a plastic film backing, doesn't need it, thats mainly auto glass that has the film to hold it together and protect your eyes. Just don't confuse tempered with plate glass or regular window glass. I would never use those for a roof. Plate glass is pretty rare these days except in residential windows or real old store window because its not allowed for large size commercial window use and it will shard when broken and cut you in half. If your not sure if its tempered just tap it with your finger, tempered will make a distinct ringing sound

    Bookmark   February 14, 2009 at 10:12AM
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I am building an extension to my small greenhouse. I have 5ft x 21 inch tempered glass sheets that I want to put on the roof and am looking for information as to how to install them, i.e., frame them or sit the sheets on 2x2 redwood runners. I was thinking about putting a piece of 2x4 between the trussesc for the glass to rest on. I plan to use neoprene pieces around the permiter of the glass. After thinking about my plan, I have decided that the 2x4 rest on the bottome of the glass is not a good idea because it will act as sor of a dam which will hold rain or melting snow. Any alterative ideas would be appreciated.

    Bookmark   March 24, 2009 at 12:33AM
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imstillatwork(8-9 Oregon Coast / Ca Border)

flavio: check out the photos of mine in the link below. I set them on purlins across the trusses for support, and used heavy duty clips at the bottom edges to prevent them from sliding down. Put a flashing under the panel, or let the panel overhand 1/2 inch to avoid drips going inside on windy days.

Here is a link that might be useful: tempered glass greenhouse

    Bookmark   March 27, 2009 at 1:31PM
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The worst has ocurred- a large tree fell into my Four Seasons greenhouse. Pretty much completely destroyed. So I'm planning on building a new one on the existing knee walls, using Jeld-Wen large awning windows for sidewalls, then instead of roof windows, a small section of standiung seam copper roof, then smaller awning windows in a roof lantern, then copper roof again to the peak. The house is used for winter over geraniums from window boxes. The crashed greenhouse never was able to be heated effectively, even to the 50 deg f I tried for. Even though there's hot water piping in the floor, I had to add two small portable heaters. Thus my intent to replace the aluminum Four Seasons greenhouse with a wood one, built with production windows. Two questions:
1. Should I be using low-E glass in the windows, as it appears the plants are now getting sun burned since I added clear plexiglass to the roof panels wheer the original glass was broken out. Who said you can't build a greenhouse with duct tape. Does low-E glass block too much ultraviolet that is needed for better growth?
2. Will there be sufficient light using just side windows and roof lantern windows without any actual roof windows? The greenhouse faces south, and teh only need is for winter use to winter over the window boxes. The sun stays low in the southern sky thru the winter. I can handle construction details with regular windows for the walls but roof windows would be another issue,a s well as my attempts to keep heat in teh place with just the floor heating. Pleaes help.

    Bookmark   April 3, 2009 at 10:19PM
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rons sorry to hear about this, giving you a bump so someone experienced can help you out.

    Bookmark   April 14, 2009 at 5:15PM
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Good thread!

I am planning to build a solar room onto my house this summer and I was simply browsing to see what other folks have done - and I came across this thread.

This is my first time posting in "Garden Web"; for those folks who don't happen to wander over into the HomeSite, I tend to post a fair bit over there concerning windows and glass issues. Possibly some of you have read one or two of my posts over there, or perhaps not.

No matter either way, and enough by way of introduction!

By definition, both laminated and tempered glass are considered to be safety glass and both can be correctly called safety glass.

Laminated glass consists of two lites bonded together using a plastic sheet or liquid resin interlayer that holds the pieces of glass to the interlayer if the sheet is ever broken.

Tempered glass is glass that has been heated to about 1300 and then rapidly cooled. This process puts the center of the glass sheet into tension and the outer face into compression. The glass becomes very strong - about four times the strength of regular annealed (window) glass of cpmaprable thickness - and when it does break you end up with piles of little glass chips on the floor.

The side and back windows in your car are tempered and the front windshield is laminated.

Laminated glass will block over 99% of UV rays from passing thru the glass construction. Plants do not need UV to grow. In fact, many plants do very poorly when exposed to direct UV light. Plants thrive in visible light, which neither (uncoated) laminated or tempered glass block to any great extent.

LowE coated glass will block some UV and will block some visible light. But, as long as you don't use tinted LowE glass there is not likely to be any problem with growing plants behind LowE coated glass. There have been a number of studies conducted concerning the effect of LowE coatings on plant growth and there have been no direct correlation to LowE (non-tinted) coatings hurting plant growth.

Actually, there have been some suggestions that UV sensitive plants, or plants that like shade, tend to do very well when protected from direct UV exposure by LowE coated glass.

If someone were to acquire IG (insulating glass or dual pane) windows or patio doors and that person wanted to separate the glass from the spacer in order to use the glass as individual sheets, if the glass was LowE coated then exposing the coating to air and moisture will corrode the coating which may significantly restrict visible light from passing thru the glass - and it looks terrible. So anyone contemplating separating the two lites from a dual pane window or door, might want to keep that in mind.

Also, separating untempered glass IG can be very dangerous for a DIY'r who isn't used to working with glass. If anyone decides to do it make sure that you wear thick gloves (leather gardening gloves would be a good choice), long sleeves, and SAFTEY GLASSES.

And as a final comment...

The IRC (Internations Residential Code - section 608, if memory is working this morning), which has been adopted by many US states, requires that solar rooms, solariums, and skylights be built using safety glass in all overhead glazing applications.

Greenhouses on the other hand, do not require the use of overhead safety glass (by code) unless the peak of the structure is over 20' from the ground.

Since I work with glass every single day (except weekends and hoildays - I am not that nerdy), primarily in areas related to safety and impact performance, PLEASE don't ever consider using non-safety glass over your head. If not for you, then for your children or grandchildren, or for me if I ever come by to visit. Using non-safety glass overhead in any structure is an amazingly BAD idea...

Okay, this is probably past long enough for a first post in here.....

    Bookmark   April 22, 2009 at 8:16AM
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I would like to turn our gazebo into a greenhouse. It has 8 sides, but it is not a regular octagon because the sides have different widths, and so it is rather oval-like. The roof is now terra cotta tile. I would like to take the tile off and replace it with glass or plastic, but the material would have to be triangular and shaped to fit the various sides of the gazebo. My question is: Can you cut tempered glass? Or what kind of plastic would be best?

We live in Southern California, so keeping the GH warm in winter will not be difficult. Actually, we just need to protect plants from the very rare frost, and use lamps to artifically lengthen the day in order to deceive tomatoes into thinking that it's still summer. So I think that it is not all that important that the roof be well-sealed.

Thanks, and also thank you for this great thread.

    Bookmark   January 17, 2011 at 12:48PM
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these are great! Check out the link.

    Bookmark   January 20, 2011 at 2:55PM
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I have some glass panels salvaged from a Lowe's storefront remodel. Can I use these for greenhouse roof? I think I could get as many of these as I want from the installation contractor. The were throwing them in the dumpster. I don't know if they are what you would call tempered glass.

    Bookmark   April 26, 2011 at 4:56PM
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kudzu9(Zone 8a - PNW)

Tempered glass usually has an etched mark in one of the corners to indicate that it is, indeed, tempered. From a safety standpoint I would only want tempered or laminated glass in a greenhouse roof. And, if your local building code applies to greenhouses, using regular glass in overhead panels is typically a code violation.

    Bookmark   April 30, 2011 at 9:46PM
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The glass i am using is made for green houses. They have a smooth side and a patterned side.

I live in zone 5 and want to grow year round.

Does anyone know which side goes outward?

    Bookmark   April 3, 2012 at 7:29PM
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I have a 'Texas Greenhouse' in New York state with tempered thermopane glass panels. The seals are all failing with water between many of the panes and algae forming. Some of the outside panes are actually falling off as the seals fail. Any ideas on what to do? Can I take one pane off to make it a single pane glass or do I have to replace all the glass panels with single pane.

    Bookmark   January 2, 2014 at 9:10PM
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I am designing a lean-to solarium to be attached to my stuccoed house. I intend to build it from scratch using 4X8 beams (or larger) 2 feet on center to support the glass roof and sides with 4X4 crossmembers, say about every 4 feet down the roof. I plan to use a router to cut a channel in the roof beams to put in the glass panels (I'm thinking triple pane, gas filled window glass). On the sides, I can use some panels, and some standard windows for ventilation.

I thank you all in advance for any thoughts on this general approach!

    Bookmark   last Saturday at 9:11AM
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fruitnut Z7 4500ft SW TX

Does it ever hail where you live? Or what if one just fails while you are underneath? I'd build with the totally safe greenhouse double or triple polycarbonate or similar panels.

    Bookmark   last Saturday at 2:48PM
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Yes, it does occasionally hail where I live, and we have strong winds rather often. I'll look into the triple polycarbonate. Thanks for the suggestion. It's also probably lighter than glass?

    Bookmark   Yesterday at 8:28AM
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fruitnut Z7 4500ft SW TX

Greenhouse Megastore is a good place to check out polycarbonate and acrylic double and triple wall coverings. The double or triple wall with 75-80% light transmission is really good material. If I were to build another greenhouse I'd probably use the double wall polycarbonate. But in a colder climate or if heating to a warmer temperature the triple wall might pay off over time. In my climate ave low 30F and heating to 40F doesn't cost much. Doubling that temp difference doubles heating cost.


They also have heat loss and heating cost calculators so you can estimate cost and savings with various coverings.

    Bookmark   Yesterday at 9:07AM
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I'm wondering if the poly roof would look strange with the glass walls, since it's supposed to be more of a conservatory than a greenhouse, per se.

    Bookmark   Yesterday at 10:11AM
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