I'm not sure if the picture will show up? Do I need a picture sharing service?
Anyway I want to put 2" of XPS and a metal roof on the north side of the greenhouse. Rimol doesn't have an engineer, they subcontract, and I was told I couldn't get in touch with them. They say the Greenhouse is built for 35 lbs/sf The roof and insulation would add >2lbs/sf. If I can get pictures up I'll do some drawings, not much sense to say to much without them. I'll post this and see what happens. Any bored engineers around?
Hi Mike, yeah the photos didn't show up. If you have them as files on your computer, you can use the attachments tab below the place where you type to attach them.
So you'd put the XPS outside the greenhouse and put metal roofing over it? I'm thinking there would be a modest amount of condensation on the inside surface of the XPS. Is the framework of the greenhouse steel or aluminum? I'm sure it's rust proof as built, I'm just wondering if you screw on a bunch of roofing, if it will still be rust proof.
Now that I'm reading my own note, I've changed my mind. The condensation would only be there if the interior of the greenhouse was in contact with the XPS. So I guess I don't see a big problem with it.
What spacing are the trusses on the greenhouse and how would you attach the roofing to it? Would the roofing ridges go vertically down the roof or horizontally to bend around the roof/wall corner?
Mike VanKanan: Hi! Welcome to Permies :D
One way a lot of browsers (not all) can do pictures is to RIGHT click on a picture, then left click on "copy image location"
choose the attachments tab at the bottom of the reply thingy here, Click "add from URL", right click on the line "external file URL" and hit paste, then submit.
What that does is make the computer do all the typing, keeps it from being a typing issue.
Looking at the last picture you posted that didn't work, the URL for it is just "https" nothing else. So something is not working someplace.
:D Looking forward to seeing your pics!
My post above is the pictures you linked to. I see two problems I think you ran into. The first one, I'm sure of:
1) See the code I quoted at the top of this post? That's the code from the post where you tried to display them. Your links have some extra code that gets in the way. "Https" is a better version of the same thing as "http". (Hyper Text Tranfer Protocol vs Hyper Text Transfer Protocol, Secure, I think.) Having both is redundant. Also, an image link (Most if not all links, in fact.) ends with the file extension. That's the .jpg part. It tells the computer what kind of file it's dealing with. (Joint Photographic Experts Group, in this case. An image file.)
2) I don't think dropbox likes remote linking. (Storing a file, in this case your pictures, on their server and having them linked to from another site.) So I took your links, without the extra code, opened them in another tab, downloaded the pictures, then uploaded them as attachments. I'll include a screenshot that shows how. (You have to be composing a message to see the attachment tab and controls.)
I thought I could go back and reply to previous comments and I wanted the picture up while I did it so I ended the last comment.
Thanks Pearl are you anywhere near Zanoni, almost moved there.
Mike the XPS would be exposed to the greenhouse air, in the picture you can see some we hung inside. There are problems with what we did, I think the condensation between the glazing and the foam would be a problem? There's a better picture coming that might show that better. The greenhouse is full of condensation now the plants float on XPS rafts. Were you worried about condensation affecting the foam?
I think as far as snow the roofing should be vertical, I'd think it would stick more the other way? We are thinking of extending the rafter line out straight until it intersects with a line plumb to the wall. That's a scale drawing so that makes a rafter around 17' so a shed roof with a 17' run Crazy? I think I need some type of beam/header at the ridge and one half way and then some type of post to the ground? Make the addition self supporting, able to carry a couple of feet of wet snow.
The greenhouse gets it's strength from it's shape, that shape must help in wind ? I'm a little worried about that flat roof wanting to lift somehow? There's no real foundation just driven pipe which the hoops sit in and are screwed together.
I wonder if I added enough additional hoops could I do away with the posts?
Thanks T for the pictures! Mike, if you have the pictures on your computer, it's far simpler to just use the attachment tab below your text box to attach them to the post. They won't show up in "preview" mode but they'll appear once you hit submit.
I hope you don't mind, but can I get some clarification? Is the current polycarbonate glazing staying in place in the areas you're insulating? And the insulation would then go on the inside (possibly similar to how you have it now)?
If so, why do you need metal roofing?
If you could fit the XPS to the North wall/roof AND seal the edges so air can't circulate behind the XPS, I'd think you'd be all set. If hot/humid greenhouse air can make its way to the cold poly, it will condense and give away its heat. Then it will drop down and out and new hot air will take its place. So insulation that isn't sealed to the glazing just acts as a heat loss air circulation pump.
Mike VanKanan wrote:T Melville
Thanks, what a surprise, wish it was in English though LOL
Would another hosting service be easier? Anyone else use dropbox?
You may find it easier to attach your pics to your posts, in which case permies.com is the host. However, if you prefer to use a hosting service, I'm fond of postimage.org. After uploading, I use the link marked "Direct link:" .
mike:"I hope you don't mind, but can I get some clarification? Is the current polycarbonate glazing staying in place in the areas you're insulating? And the insulation would then go on the inside (possibly similar to how you have it now)?"
Right now there is double polyethylene film that's inflated. He would like to put the polycarbonate on the south side and metal roof on the North. We are both 70 so replacing the poly in 6 years will be harder.
mike: :If you could fit the XPS to the North wall/roof AND seal the edges so air can't circulate behind the XPS, I'd think you'd be all set."
If the picture came up you can see what our first attempt looked like, We straightened out the curve, pretty hard to seal that. I never really liked that idea but it's his place.
Nice pictures! Ok, so new polycarbonate on the entire South roof and wall and metal roofing and WPS on the entire North roof and wall. Now it's starting to gel for me.
So the current double poly goes away entirely. And the XPS would be on the outside of the trusses. I guess I could see some kind of purlins running horizontally on top of the current trusses that you set the insulation on and screw the roofing to. They would have condensation constantly keeping them wet so aluminum purlins may be worth while. Then you can sister on a triangle to the bendy corners of the trusses so that the purlins can continue straight down the roof to a corner where they transition to the vertical wall.
I'm guessing a smaller overhang would be good for wind uplift.
If he does a lot of venting/cooling in the summer, building some vents into that North roof could be advantageous.
Hi these are some other thoughts on Tom's greenhouse, I copied this from a post to another forum, hope it's not confusing.
Some pictures: gb3 shows the end of a grow trough , under it is the 2x12 box with the PEX water heating tubing. The box has a poly vapor barrier stapled to the bottom, it's supposedly stuffed with fiberglass, with the tubing laid on top. My understanding is that it isn't attached to the 3/4" plywood bottom of the grow trough. In the picture the red tubing connects to the 50' of flexible stainless that was added latter to try to boost the water temp before it returned to the fish tank. The pvc in front of the tank is an air line that feeds air stones, the flexible white pipe is the tank water return. The tank water feed is along the North wall to the left, it's 75 ' of 4" pvc that attaches right against the metal frame.
So the heater loop goes from the boiler, to the stainless steel loop, then down the pex and back to the heater. It works if you want to burn 100+lbs of pellets, his winter daily burn rate..That's 800,000 btu.s if I take 80% (boiler efficiency?) that's 640,000 per day. Using 4500 gals of water that's 37,350 lbs. That should raise the water 17 degrees I think? We dump air on a sunny winter day so the water would be gaining heat for a time and it would have a pretty small delta for some more of the time. So most of the loss would be night. Grow lights are on for a couple of hrs morning and night so the are also contributing some more heat. The oil fired furnace kicks on at 45, I think he ran it hotter last year? Tom use 200 gal/3 weeks = 9.5 per day x 139,000 = 1.320,500 btus 80% of that is another 1,056,400 btus a day. I haven't done any calculations for the water heat loss to the green house interior. I did calculate the greenhouse heat loss at 3,360,000 for 24 hrs with a 40 degree delta. There is about 2,700,000 btu's of sun light hitting the green house. These aren't very accurate numbers I'm using 1500 btu's/sf it's kind of an average out of a book for 40% latitude Oct- Mar and I'm at 42, I used 30 degrees for the entire surface, The calculus of that curve is way beyond me, I'd love to learn though! Almost got pictures down.......maybe?
I'm not sure what to make of all these numbers they are informed guesses really? I think we should insulate all the water and piping we can. I think we should reinstall or replace the heat exchanger plumbing directly into the grow troughs. I'd like to capture as much day time heat as we can at least into the aqponics system and any extra into some kind of storage.
Some ideas I'd like to explore are cheap irrigation tubing on metal collectors, I could get 1000' hanging off the north side of the greenhouse interior.
I'd like to explore pulling air through some auto radiators in the top of the greenhouse into a coil of some kind in water, Seems that another radiator in water would work as a heat exchanger? Don't know how good that would be for the radiator under water?
I'd also like to try to blow air through a pipe in the trough (4"?), if it works that might be the simplest?
Anyone think blowing air through water might increase heat transfer? You could get about 500 pieces of 1/2" irrigation tubing in a 30" diameter barrel top. If you had a bunch of tubes submerged into 3' of water, how much air pressure would it take to blow air out the bottom of the tubes?
Mike, first off, I'm not so far away from you! I was just in Milford the other day visiting a friend. I grew up in Chelmsford, work in Groton...
I agree with Mike Jay about adding purlins (using 2-hole straps?) onto the outside of the Northern bows of the greenhouse for fastening, and the idea of extending the eaves out over the ground posts.
If you left the poly on the North side, and the purlins (say 2x4) were "standing" rather than "laying" on the bows, you could fill the bays between the purlins with rockwool batts, and the poly would hold it up (also a vapor barrier).
You could add battens to fasten the poly to the inside of the wood purlins, in between the bows for more even support of the rockwool.
Then you could put the XPS on top of all that, then the metal roof (vertically for shedding snow).
The vertical wall would be similar construction, though you could run the metal horizontally for ease of fastening to studs...
I wouldn't worry about the wind unless you had a very large overhang at the eave. Use the foam "wiggle strips" to seal the roofing ends to keep wind and insects out!
I would worry about snow load. With the roof insulated, it won't shed the snow the way the inflated/heated 2-layer poly did. The polycarbonate will, and then the structure is unevenly loaded (snow plus the roofing).
I would install a bearing beam and posts below the bows on the north side. Maybe along the northern side of the northernmost raft bed, to be the least intrusive. Posts could be 8-12 feet apart, or whatever makes sense like "at the ends of the raft beds" and "five posts in between"
Do you know Victory Aquaponics over in Londonderry? He has a thermal curtain system that works both as a shade cloth, and an insulating layer for nighttime.
Do you know about BuildItSolar? Here's an article about storing greenhouse heat that sounds like what you are thinking of. BIS: Storing Greenhouse Heat
Groton huh are you old enough to remember "Shrink makes a stink"? If your up this way I could give you a tour if you want? I'm not committing Tom though.
We have toured Victory Aquaponics. I'm very envious of their curtain system, love to get that contraption that makes it work. I think reducing the heated volume at night is a great way to go. They heat water with that big wood furnace and store it in an insulated tank, and then use that to heat the fish tanks. It's less then 300 gal, talking to the owners made me aware of the amount of heat you need. Lots and lots.
I'm not sure what the rock wool would get me, I haven't dug into what point added r-value pays off with all the heat loss from the glazing. How long would that exposed poly last?
"(using 2-hole straps?)" I'd probably need 300=$$$. Tom uses tech screws, I'd like some idea of what effect bolting or screwing has on the structural integrity, I think not so much but I really don't know technically?
Down and dirty what I'd like to do is get some 18' 2x8 and rip it to 2x4, lay them flat on the bows, I could pre-drill them along with some flat metal strapping, i could bolt through the wood and and the strapping with the bows in between, making a clamp. Save us from all that drilling through metal, and we wouldn't have to worry about the structural integrity. I could then just plumb cut the ends where I needed to meet the north wall, easy to detail the eave. That would eliminate any finagling around the bows. I could then lay the XPS strap that and then the roof?
That would leave exposed wood inside that would get wet from condensation? Any alternatives, I think aluminum would cost to much? Metal studs? If we used painted wood how long would it last?
Posts will be in the way but I don't see away around them, I need two rows I think one at the ridge and another that splits the rafter run. Perhaps I can get by with one row of posts by setting the beam back from the ridge and cantilevering the roof?
Mike, “Shrink makes a stink”? I’m not that old...I’ll guess it’s about the river?
Ross from Victory lives just down the road from me... and I just met and visited the guy in the solarvideo link you posted. He’s in the area too...
If you do a heat loss calculation for the building and substitute the new insulated roof for glazing, it will be less, for sure, but how much less if you add more insulation is another calculation you could make. If you double the XPS, or if you added rockwool between framing for example... then take that additional savings in Btus/hr and translate to fuel use compared to materials cost to see when the payoff is.
I agree the hardware can get expensive, so is labor. Bolt + nut, drill holes, hammer bolts in, tightening nuts... a lot slower than wood screws and a driver.
The beam, where I had said to place it, would cantilever the new roof (sort of, since it isn’t a stand alone structure, just shoring the GH frame). Remember you are just adding nailing surface for insulation and roofing, not building a structural system. That’s already there in the GH frame, you just want to ensure that it can take the additional roofing load plus a one-sided (rather than evenly distributed) snow load.
The farther you go from “nailing surface” to “a structural wood roof system” the more it’s going to need support. Then you are almost building a pole barn shed, and maybe that’s easier?
Mike, “Shrink makes a stink”? I’m not that old...I’ll guess it’s about the river?
The shrink wanted to subdivide and develop some property, He was stopped, his land however was still zoned agriculture so he got some hogs...........and then he got his permit to develop! I think it made the NYT?
I'd like to meet David the guy in the Video.
At a 40 degree delta I lose about 1.5 million btu's out the glazing and 200 thousand out the north side with 2" XPS
Kenneth "I agree the hardware can get expensive, so is labor. Bolt + nut, drill holes, hammer bolts in, tightening nuts... a lot slower than wood screws and a driver. "
You'd bolt those clamps you spoke of? Drilling is hard so I'm rethinking that. I wonder if I could get 300-400 pieces of flat 1" galvanized stock cut and drilled, I could then bolt them to the 2x4 on top of the rib?
Kenneth "The beam, where I had said to place it, would cantilever the new roof (sort of, since it isn’t a stand alone structure, just shoring the GH frame) Remember you are just adding nailing surface for insulation and roofing, not building a structural system. That’s already there in the GH frame, you just want to ensure that it can take the additional roofing load plus a one-sided (rather than evenly distributed) snow load".
They do come down I've talked to folks with experience, I'm told that they bow out at the ground the ribs can twist and bend down or break. 35 lbs/sf snow is about 20". That,s possible. Part of the reason Tom want to do this is so he can take some time off in the winter and travel some. I'm aware that the snow will stay up there with out the heat lose through the glazing.
Kenneth "Then you are almost building a pole barn shed, and maybe that’s easier"?
Yeh" that"s where I think this has to go? I think I need two rows of posts, One where you suggested, and another on the front of the last trough, That would give me spans of 5' 6' and 1' cantilever. The posts in the center are 13' there will be a lot of stress on them, I'd like to keep them as small as possible to save space?
I’m talking about the pipe/conduit hanger straps, “U” shaped with “ears” that are already the size for the pipe. Also talking about using these straps and screwing into the wood with wood screws to fasten to the GH frame without drilling/screwing/bolting to it. (Though some drive a Tek screw into a strap so it wont slide, like for a hip board on s vertical pole)
Compare prices on hardware (you’ll need either straps and screws OR nuts bolts and washers) plus other materials like extra wood or metal strips.... and that’s half the picture...
Now consider the labor/time involved in installing these. A screw gun and the 2-hole straps is FAST, versus bolts.
I have a better idea of what you are talking about, I probably have used them before.
I was worried about asymmetrical forces acting on the green house from loading the north and south differently. That's something to worry about. I'm over my head with this. My gut tells me that I could do this and it would work. If it was my place I might do it. As soon as you get into any engineering though it gets more complicated. Tom would have to convince the town this isn't a pennant structure, or it would have to be code, 50-90 psi/sf load. The idea is falling apart in this form.
About rock wool, that's outside the poly right. It would nice if I could use it on the inside against the poly. Be nice if there was bendable XPS foam. But even insulation inside the poly would, as you said, probably result in uneven snow loading because less heat loss on one side.
Is this single wall or double wall? If this is inflated double wall maybe you want to look at another approach entirely.
What about doing foam fill. From my research so far it looks like it is winning. Here is a good example showing what is happening.
And here is a link comparing systems.
Now for north wall you might want something more permanent. So can a foam be made that is more durable for that side? I know sometimes the water in the irrigation ditches grows a foam that dries out that if not disturbed will last for months. Could you find a foaming mixture that would to the same on the north side? Another possible would be aircrete. Simply fill the north wall to say 8 or 10 feet with aircrete. As the plastic starts to die in a few years put a skim coat of real fibercrete or ferrocrete over it to protect the aircrete from the weather.
Companion Planting Guide by World Permaculture Association