DIY greenhouse: How do I connect and seal the windows?
 

I've had the idea, for a long time, to build a greenhouse from discarded windows/glass doors. I've collected a lot of material and there's a couple ads in the Craigslist Free Stuff section right now for more. Footings and framing would be similar to a house or shed, but arranged to fit whatever windows I'm using. I could screw through their frames into the wood to secure the windows/doors to the frame.

How would I join the windows at their edges? For horizontal edges on the roof I can lap them, and for vertical edges on the walls caulk should be fine. What about vertical edges on the roof and horizontal edges on the walls? I guess I could lap the horizontal edges on the walls too but it would look awful. Maybe just caulk them and accept a little bit of leakage in driving rain? I still don't know what to do about vertical edges on the roof.

Edit: Actually, I guess the vertical joints everywhere will have 2x4s under them, so caulk should seal them well. Nevermind, I seem to have worked out the questions. Topic is open for comments and ideas though. :)

Do you care if things frost heave? With glass you very well might. If you go with piers, make sure your area doesn't have a lot of clay in the soil, since that can freeze to the pier and then the whole thing can heave. You can install foam (to about 48" out) to get around this or use pier forms that flare out at the bottom. That requires a lot of digging, so at that point you might want to consider a rubble trench foundation as well. Both are good options for DIY.

I'm not positive I am quite visualizing your description properly. By "vertical joints" I assume you mean a butt joint between two window frames on the roof? If caulk alone doesn't cut it, you can always put a strip of wood, metal or whatever over the joint and then seal that. Gives you a little more room for flex. Hopefully I have an idea what you meant.

I wonder, will old glazing compound stand up to long standing pooled water? If the roof windows have mullions and the angle isn't steep it will collect.

I built my own fixed windows for the mountain view here, but was starting with raw glass so most of my experience won't translate to your frames. And they're vertical, although we do get wicked winds.

Well, frost heaves would explain why my dog-area fence gate doesn't line up anymore after four years. I put in some decent footings and figured that would be good enough.

You understood my description correctly. Good ideas for sealing.

I was thinking of taking the glass out of the frames and then dealing with the glazing. I think all my material is double-pane modern stuff which won't make a very effective greenhouse if I don't at least break the seal and let the argon out.

Not sure I understand the letting the argon out comment. Is this a single pane greenhouse or a double? Lot more R value with double.

Are your winds strong? And if so, are they consistent in direction? Just some things to consider.

If it's just glass then I can give some input. The guy who sold me my glass (I bought a whole case since it was cheaper and then had him cut it to the sizes I needed) has very little faith in caulking done on the outside. He really prefers bedding the glazing in caulk when it's installed. Alternately you can get this double sided sticky foam strip stuff. A lot of vinyl windows use that and it's what I went with. Costs more than caulk, though, but I was paranoid about the wind.

I have a shed that's attached to my house and the piers heaved, so it angled up on the one side in winter. After a while the door wouldn't close. That's how I learned about the clay problem, since the piers were well below frost depth. Foam did the trick, but required a lot of digging!

Oh, yeah, are you going with all glass or just on the southern exposure side? Cut down your work a lot and you can use high R-value walls on the north then. I've always thought earth sheltered greenhouses were cool, but your topography has to cooperate.

Do you have an evaporative cooler for the greenhouse? You'll want it. I grew up along the gulf coast where it's normally 80% most of the time and even there they used evap coolers. It doesn't do much there, but it makes sure the air is as saturated as possible so sensitive plants don't dry out.

Keep in mind that even with single pane non-insulated windows you will want to have a forced air cooling system in a glass greenhouse. Your car is a perfect example of why lol.

Big ol' vent won't hurt either. My mother's greenhouse had a gas cylinder that would open a roof panel at a set temperature. I don't know much about the shades you often see on greenhouses.

Hmm...sounds like there's a lot more to greenhouses than I thought. I don't know anything about them, and I have what I call a "black thumb" -- opposite of a green thumb, anything I touch dies. The idea was to build it for the wife.

I thought greenhouses were supposed to get hot inside, and therefore single pane would be better than the high R-value double pane argon-filled glass.

I was planning to do it all glass with manually-operated vent windows. If I use something other than glass, my cost goes up; salvaged glass and salvaged 2x lumber is the material I have and can get for free. I don't have a source for plywood or siding.

I do have a little bit of OSB but I was planning to use that for a roof on my shed. My shed had a former life as a Schlitz truck body and has a roof but it's ugly. I put vinyl siding on it and built some nice gambrel roof trusses to put on top of it (which would then give me some more storage space on a second level under the new roof), but never got around to finishing the roof. I fear that the trusses are probably rotted out, they've been sitting outside for two or three years. I guess maybe this year I'll either put them up or rebuild them (or just build a gable roof).

In the winter running them warm works great, but it all depends on how your summers get. If you seal it up and let all that infrared in through the glass and then hold it in you've got a recipe for roasted tomatoes... fresh from the vine!

I think(read: THINK) it'll be okay if you put in a ridge vent of some sort, lower wall vents, and use that heat blocking screen outside the windows that get the most sun. Just for safe measure I'd install a simple thermostat with an exhaust fan though. Now, in winter you'll want it warmer, which might be when you just remove the screening.

Passive convection venting...sounds like a good idea and easy enough. Ridge vent is easy. Then a fan for the hottest part of summer.

Then agian, pre-roasted tomatoes might mean some good marinara sauce, right? :D

I've always wanted a house built around a covered courtyard that could be used for a garden. Put air evacuated glass panels over it (with reflective internal grids to take the pressure) and it could insulate as well as the normal roof. I assume visiting the Isabella Stewart Gardner Museum as a kid is what inspired the idea.

https://www.fuelly.com/attachments/fo...5ea214069c.jpg

So, a house with a garden in the center and a glass roof over the garden portion? That would be really nice. The idea reminds me of some upscale hotels I've seen with that design.

It took me a minute to figure out what you meant, and in the meantime it reminded me of "green roofs", flat roofs with soil and plants on top. They are supposed to really help a lot with heating and cooling costs.
https://en.wikipedia.org/wiki/Green_roof
https://upload.wikimedia.org/wikipedi...Green_Roof.JPG

That beats the tar out of a modified bitumen roof (pun intended)...

Those are awesome. I know some buildings can't install them because of the extra weight.

That's a sweet idea. I drew up plans for my dream house and the rear of the house opens directly into a glassed indoor pool area(no doors). The upper balcony had a door to the 'real' outside and inside it just overlooks the pool.

After designing it I realized that the house could never be built in a humid area. The only way to keep the pool area from being sweltering would be an evaporative cooler system unless I installed a VERY wasteful industrial refrigerated air system.

I also realized that, while it would be freaggin sweet to have a setup like that, it's just asking for a young one to fall in and drown so I had to design in a retractable glass wall.

Since it is a 'dream' house that will never get built most likely I've also found a wall that I want to revise with a 15x8x3 salt water fish tank.

Maybe you could get an endless pool instead?

Even though my house could be pretty cheap (cuz it'd be small and built in an area with a lousy view), I don't think I'll ever build it. I'm going for the super efficient tiny house approach instead. Spend a lot of time designing convertible furniture and such. Anyhow, if you've never seen the plans for Fuller's Old Man River City, it's pretty wild. Thread got me thinking about it.

Sorry to go back on topic, but Holy Cow is it possible for you to build your greenhouse up against an existing structure? Saves a wall and (possibly) some heat loss.

Big fish tank is sweet! I always thought having a shower where three walls were fish tank would be cool. A little weird, but cool.

I'll have to find it, but someone did that on the north side of their house and hooked it in with their ac system. He did it because his wife couldn't get enough of the smell of fresh flowers in the home.

No allergies with those two! My father bought my mother a greenhouse to try and get some of the plants out of the house. WRONG! My mother just got more plants. It sucked heat from our basement (just a thermostatically controlled blower).

It's possible but undesirable. I could put it against the south wall of my house but that would increase my house cooling costs in the summer. I suppose the cooling costs are still not as bad as the winter heating costs so maybe it would even out...hmm...

It would also have to be pretty small or it would prevent my windows from being useful for ventilation.

How big are you thinking anyway?

However big will use up my material. I envisioned something quite large, freestanding in the middle of my backyard but really it could be a lot smaller. I guess if it's relatively small then its affect on the house's heating/cooling won't be an issue.

I think my vision was probably like 12x20 or so, which would probably be huge and way more than anything my wife could use. I do want it to be large enough for her to go in there with a chaise lounge and relax. Maybe I should make it 8x10 or so.

I have an 8x12 shed that's solid enough that it doesn't really warp when it frost heaves. Goes up as one unit, then sinks back down as one. Just have it on blocks. Obviously if it's attached to the house that's not an option!

Actually, if it's attached to the house, I could almost hang it off the house and let it float over the ground...

8' overhang? Wow. Maybe with some cables or chains (could be buried in the wall)? Sure, I guess, as long as you've got something firm to anchor to and your supports are sized accordingly. Get more heat loss through the floor that way.

Have you considered making row-sized covers rather than a walk in greenhouse? No idea what these are called, but I know they exist. If you're going to have venting panels anyway they could also be used for access. Generally they use an A frame pattern for construction. Just seems a lot easier to build. Can't second as a sun room, alas, which you mentioned you were hoping for.

No matter which way you do it hanging it off the house is gonna get ugly. I wouldn't recommend attaching it to the house with a hard system, maybe build it against the house but don't attach it. Your house has had a few years to settle and the new addition hasn't.

I just realized that old windows are perfect for row covers! Assuming an A-frame approach, the window provides direct venting access and either the top or bottom (or both) can be slid as needed. Nifty. Don't even need glass for the north side, in theory.

I want to build a walk-in, because the wife would definitely enjoy a place to relax. I can be sure of that; I can only guess if she will continue to enjoy growing stuff or if that will fade. That's the sort of thing that she'll get an itch to do, do for a while, then forget about it. I do that too, we're a good match with our equally short attention spans. How I've managed to stick with hypermiling this long, I have no idea.

That's cool. You might still be able to integrate the assembled windows into the design, though. Might look a little funny, but it'd be an easy way to get your venting.

I didn't realize you were talking about assembled windows. I don't think I have any that I would use for a greenhouse. I have some that are brand new and I eventually want to install them into my house...the two ends have no windows at all.

I must've misunderstood. I thought you had some old windows you were planning to take apart. Sorry.

Nope. I have a big pile of sash sans frames.

Gotcha. Not too hard to toss together a crude frame if you were so inclined. Guess it'd have to be compared against other venting techniques.

I went out and purchased a book on greenhouse construction to get ideas about that kind of thing. It took me years before I actually had the place, time, and money to build it. But, I had years to dream and plan.

I wound up using the fiberglass corrugated sheets on mine. There are a lot of the finer points that it doesn't have, but it certainly does the trick.

There are a number of things I'd do different were I to do it again, but I'm happy with it.

For my solar porch I went with 4'x12' Polygal double walled polycarbonate panels. When I had to redesign my house for sale after my ex left the realtor said that sort of thing didn't sell easily, so I ripped it off. I sold them on Craigslist easily enough, despite the screw holes. It was just a collector for hot air so was pretty narrow at 4' wide (vs 88' feet long), but was a good place to dry and store fire wood. I guess I could've put some planters in there.

Mr Incredible, it looks great. I bet that fiberglass was affordable, too.

The polygal ain't cheap. Unless you can find some sucker to sell them to you used, that is. :p