Hi there. The greenhouse will definitely provide you with heat during the day whenever it is getting sun. Between 9 and 10 this morning my GH went from 43 to 68 then the sun dips behind some tree so it holds there most the day. The pool cover sounds like a decent idea, but my concern would be how you seal where it attaches to the house. If it is on a support wall of the house, rather than a gable end, then you might be able to attach it under the overhang with some success. My next concern would be the slope of the roof to make sure that it doesn't hold to much snow load or water, because you are using a flexible material if it begins to sag it will create lots of problems. You don't need the inflation fan though as long as you can create an open pocket for the air between the sheets, but the fan would help keep the cover from sagging. I would think a minimum of 2 or 3 inches between them would do fine, but more probably won't hurt. You need to try 2 seal this pocket well though otherwise air will circulate through the pocket and actually cool your greenhouse off faster (learned that the hard way).

It may work but it won't look nice. I'm not sure I've ever seen anyone use a pool cover as the main "glazing" in the roof.

Wow - I had not expected replies so quickly. This is my first time posting. I'm snowed in since the blizard, only going out to put out hay or bring in wood. Reading the wonderful suggestions has been my entertainment this week. I opened a word doccument to copy and paste the many excellent suggestions and info provided.

Yes, stressbaby, I did not find anyone using the poolcover as the main glazing, that is why I had to ask. Do you think it would look worse than the ones that are temporary?

Nugardner, you have me concerned. Do you think the pool cover will sag that much more than the poly? I had not thought of that. From the sound of it, I may also need to worry about sag in the poly. I can reinforce the area with side lath, but that could affect the light. I do have wood that would do the trick, just wondering how far apart would be appropriate. If the pool cover sags too much, maybe a layer of poly over it is a good idea - or at least under it. I could still do the extra layer of pool cover under the rafters.

Do you have any idea how much heat is lost through the roof as compaired to the walls?
Carol

I suggest going to the library and checking out several GH books. You'll find they have addressed this issue and lay out how much it will cost to heat the sun room. It will work, but you'll have to think about the cost. Next you'll want to think about weight on the roof - rain, snow. Then the wind and how it will lift the pool cover material and whether that will break the caulking seal. Surely the carpenter will point this out as well. Then the hail...

Dan

My main concern is not that the cover would sag more than poly would, but the inflation fan adds pressure that helps the plastic hold tension. Without the fan, the plastic or cover would have a tendency to sag and keeping it tensioned (to avoid water and snow retention) would be nearly impossible as plastics (and probably your cover) will expand and contract with temps. This is all kind of dependent on the size, I didn't see the other dimension 18x??, the bigger the span the more issues could arise. I would pay the extra for some polycarbonate or something similar it will give it a much nicer look from the outside and then you could use your pool cover on the inside to make a good insulation layer. And I agree about the books, there is alot of good info out there when you can find it. Greenhouse Gardrner's Companion is a great one, but doesn't cover design and construction.

Great food for thought! Let's face it, putting glass on the roof would be the most attractive option for appearance - but it has too many drawbacks for me, even with reasonable price. NuGardener - I really don't understand how the inflation fan works. That is probably why I did not consider it. Is there a link to see how it is set up and how to keep the inflation? Thanks for the reminder, Dan, that it needs to be strongly and securely attached. I 'think' I have figured that out, with more options to add, just in case. Expansion and contraction with temp changes may upset my plans in the long run, but they probably won't be the only things. ;)

I must confess that I am enjoying the planning of this project as much as I will the finished product. After studying comments on this forum, I have changed the design somewhat to take in consideration the summer heat. I already have three sliding glass doors giving me six panels three feet wide. The plan is to put four of the glass panels across the front with 4by4 corners and same for posts between the panels. That will make for 13'8" across the front. I was going to put the sliding door in the long (east)side, but decided to leave that solid and put sliding doors on the two ends. That way I can open the greenhouse, with screens closed, and get good cross ventilation. Add an ocillating fan, and I think that will do the job.

This is a lean-to GH project and I'm still a little up in the air about how far it should extend from the house. At this point, I am leaning toward a 9' depth to the GH. It will be basically an indoor raised bed garden, with boxes across the front and back. Of course, that leaves a little room for shelves and hanging plants which will add to the beauty and function of the GH. A 2'6" walkway between the two beds would be covered with a soft commercial mulch. Any suggestion as to what to use there?

I've studies the pool cover options and decided at a 16ply clear bubble would be best. It has a longer guarentee than the diamond pattern. I'm not concerned about the guarentee, except that it means the manufacturer thinks more highly of it. A 16 ply 12x28 clear is $90, with free ship, no tax, and would cover the roof twice. The roof will attach under the eave and will have a pretty good slope.

If I discover more insulation is needed, it would be easy enough to add poly over the pool cover and/or under the roof 2/4s. As it will be heated from the window to the house, I'm working on more options for really cold temps like we had this week when it dropped down to -9degrees. (Most of the blizard snow has already melted, but more expected this week. On Sun it is projected to be in the mid 50's. Its those swings that worry me.) I'm pondering a design for hinged panels that would drop down from the ceiling and make a smaller greenhouse within a greenhouse over the back raised bed. Then only that area would be heated during the really low temps. The front bed would be planted with winter hardy plants like chard and spinach. A hoop structure would be stored in the ceiling that could be dropped down to cover that bed. Hopefully the hoop would be enough protection for the hardy plants when the heat from the house window is cut off from that portion of the GH.

Please share your thoughts on these plans - what would not work and what would improve the plans.
Carol

These numbers are from Cuestaroble:

As for GH floor heat loss:
Typical Heat Loss Distribution in Greenhouses (USA/Canada)
Roof - 65%
Walls - 18%
Infiltration (leaks) - 15%
Perimeter (lower side walls) - 2%
Floor - (insignificant heat loss)

The main thing with such a design for me is the open door into the house. You have to be prepared for the costs if you want to maintain x temperature in the GH. If your carpenter is skilled and has thought through the snow load, fine. The key to the roof is maintaining an air gap - purlins can do that and blower not 100% necessary.

Dan

That is a great help!! Wow! Two thirds of heat loss is through the roof. Sounds like that is really where to concentrated on for insulation, the more the merrrier. Since the materials are not terribly expensive or heavy, I'll really work on the roof part. Just have to be concerned with light - but with glass walls, I'm thinking it won't be too much of a problem limiting the ceiling light. Do you think that is right?

I had to look up Purlin, Dan. As a recent widow, I no longer have my husband to explain this stuff for me. I really don't want to have to depend on the carpenter - I want to make sure I know how things should be built. So now you have given me a new study project on the framing. It sounds like from what you said, putting interior ceiling insulation can be almost as effective as The roof. I need to determind now if 2X4 roof beams are adequate or if i need to consider 2X6 or 8. I'd love it for 2by4 as that would give a really good air gap without being too much. I'll study that and if you have any info to share or resources online, I'd greatly appreciate it.

I went online and ordered the Greenhouse Gardrner's Companion from Amazon that Nugardner recommended and found the 4 seasons gardening book as well. Good winter reading. :)

Thanks to all who have helped.

Back in 2007 I recovered a small 15x40 greenhouse by sandwiching a layer of Magniclear between 2- 6 mil poly layers and inflating on either side of the pool cover layer. It was the max amount of film that one might want to fasten with a single wire-lock system but it has worked well.

My concern is the pitch of your addition and wether the snow will not accumulate on the irregular bubble surface. Inflation goes a long way even with just 2 film layers in helping to shed snow from a structure. The outer pool cover layer will be difficult to "balloon" and from an appearance standpoint the regular outer cover will look more normal in my opinion.

Thanks, Bmoser, that sandwich was what I first envisioned and just got lazy I guess, going for two layers of bubble and leaving out the poly. I have not actually seen the pool cover for myself, so don't know about appearance. Are the bubbles on one side or both? I was picturing them on one side with the bubbles together in the middle. That may not have been such a great idea.

Did you pop the bubbles along the edge before you fastened the sheets down? I figured you would have to. Can you describe the "single wire-lock system" or have a link to it? I was just going to try to hold the edges down with wood strips nailed across the edge. If I put strips like that down with nails over the rafters, would I break the airtight seals between the layers?

How much light did you get inside the GH with your 3 layers? I'm thinking I could do a sandwich like yours and then another layer of the magniclear on the inside of the GH under the rafters. I still don't understand if the inflation is a one time deal or if it has to be continual air supply blown in? These questions are probably kind of dumb to you guys, but it's all new to me......

All of your Ideas sound good. You know with raised beds they will help hold heat and its less air you have to heat. The inflation kits are fairly simple. They have a small blower fan and a pipe similar to a flexible dryer hose. It comes with two rings of foam (or something) that you use for a seal in your plastic. Make a small hole (2 inches or so)and slide one ring through. Line up both rings over your hole (one on each side of plastic).With an office stapler staple through ring poly ring just like three sheets of paper. do this four or five times, cut out hole better and insert pipe. I added a small plastic flap on the adapter piece where it is inserted in the pipe by the fan. this serves as a check valve so air doesn't backflow through the motor when it is off. I also bought a air pressure sensing switch seperatly which senses the air pressure between the sheets to cycle the fan off and on. Without the switch your fan will run whenever it's powered and over inflate the cover. You want your cover sealed as well as possible so as not to lose air that your pumping in otherwise your just pumping heat out. I imagine that if you add another layer of plastic under all this that it wouldn't have to be sealed as pefectly since it's not pressurized, but every gap would be heat lost. I also don't think the third layer would make too much difference on light. I think 2x4 would leave a sufficient gap for a third layer or even between the two layers, but I think you should still have the inflation.

I love it when something I want to do anyway sounds like a good idea. Wonderful if the raised beds help with temp control. That was a really comprehensive description of the inflation system, thank you for taking the time to do that. I went to some websites that sell the fans and stuff, but they did not describe the need for pressure switches or flaps to prevent backflow, etc. I�m going to pass on the inflation at the beginning and first determine if I really need it. At this point, electricity will have to come from extension cords, yuck to having one if the air pump is not really really necessary. I also researched the �wiggle wire� and am going to do without that unless my ideas do not pan out.

Here in the back roads of the Ozarks, we get our bragging rights by making do with what is on hand and not wasting money or resources. It makes for interesting challenges. Ice storms are the biggest weather problem we have to deal with. That said, our first official blizzard was followed with a major snow fall a few days later and temps for the past 12 days have been consistently below 0. I am really ready for spring.

Last night I called a guy from our farmers market who's enthusiasm for his leanto greenhouse inspired this project for me. I half expected to hear about a disaster. But no, his cozy greenhouse is full of happy plants, including peppers he had just picked for dinner. He has one layer of poly sheeting on top and another below the roof beams. He said there has been no sagging and the slope has been adequate to keep too much snow from building up. Unfortunately, he had to put his GH on the north side which gets more wind and less light. Heating is affordable as he uses a wood stove for heat.

I'm hoping to do a better job of roof insulation, probably with two layers on top and two layers below the beams. I�m near the AR, MO, and OK state lines so weather is fairly mild. I�m really hoping that the GH will help moderate temps in the house and vice versa. We�ll see......

The Magniclear pool cover bubbles are more pronounced on one side but still have a slight unevenness on the other side. Yes, I did smash the bubbles as I wirelocked the 3 layers and it was difficult in more ways than one since I ordered a 40' Magniclear cover for my 40' structure and really had to line things up and keep the films stretched as I fastened.

The wirelock system is an aluminum channel with steel Zig-zag wires that snap into the channel over your film to lock it in place. Usually you can put 2 zig-zag wires over eachother with 4 film layers (for larger structures with roll-up sides I replace the roll-up sides more often than the main cover layer mainly because the sides are prone to be ripped up more often. That Magniclear pool cover is a fairly thick material but I've had no problem with unsufficient light with 3 layers. In fact I have been applying shade cloth fairly early to suit my needs. For a supplier of the single or even double wirelock Google Nolts Produce Supply, Leola, PA.
Check with Americas Best Pool Cover on shipping costs when you order. For larger covers the trucking cost can be fairly high.

I keep the inflation fans running year round. They are very small fans but I imagine they would use a few dollars worth of electricity over the year. Most of the ones I use are generic stove fans with a home-made setup. If you just cut a 4" hole in a 10" piece of plywood and attach with 4 carriage bolts after installing the first film layer you have your inflation hole.

I noticed before, bmoser, that you referred to a 15 by 40 GH as being small. I can imagine how hard it must be to sheet larger GH, but when you think about how fast it actually covers a whole house.....

The smaller pool covers ship for free, lucky me. I thought I would attach a pool cover and a poly layer over it directly to a board. Then roll the two layers up around the board, lift the roll to the roof, unroll it up to the eve, then attach the board under the eve with screws.

Just curious, do you put the shade cloth on the inside or outside of the GH and why?

I found something you should take a look at. Good planning goes along way. I'm not sure how the links work but search the forum for "For Prospective Greenhouse Builders" by OhioJay. Better to know now than later.

OhioJay is a good friend of mine, we've even traveled together. Even though he says in that post that he "cut corners," he is not really the corner-cutting type (well, maybe when driving, but not with the greenhouse). I saw lots of attention to detail during his construction, and he still wound up with a mess as a result of having his GH attached to the house.

Here is a link that might be useful: Here is the link, it is in the tropical fruit forum

Unintended consequences.......
Oh, my. OJ messed up, but I'm not really understanding all the issues. Guess I'll keep rereading the post and maybe more of it will sink in.

OK. The plan is to build a 9by14 GH on the south side of my home with a window that will open to the house to help with temp control in winter months only. Because a fireplace burns in the house pretty much all winter, the house is VERY dry. I did not anticipate the additional humidity would create serious problems. Do you think the window opening or the house siding could lead to the type of damage OJ talks about?

I would love to keep the GH warm enough for tomato plants to survive the winter, but may add extra insulation around the tomato to limit the space that gets the higher temps. I brought a container in from the garden with a grape tomato in it. It sits in front of what will be the window into the GH. The tomato started blooming first of Feb. My experiment this year is to take cutting, with blooms, from that plant to root. Just trying to see if the blooming cuttings result in an earlier production of fruit. If so, I'll plan on keeping choice tomato plants going all winter. I LOVE homegrown tomatoes! Paul Robson is my most favorite of all time.

Having watched his GH go up and seen many pics, I have a theory about OJ's GH. Keep in mind, I've never seen his GH in person, and he's had a number of people out to look at it with differing opinions about what went wrong. So for me to speculate is arm-chair quarterbacking in the extreme. But what the heck...

I think that he could have had inadequate ventilation of the attic or those portions functioning like attic or some direct water penetration. But I suspect that the most important thing was the vapor barrier in the house wall. I suspect that before he built the GH, he had insulation with vapor barrier on the house side, which is generally correct. Then when he built the GH, which he keeps REALLY warm, the warm/cool sides were actually reversed, and the vapor barrier on the house side was now actually on the warm side. So the warm, moisture laden air seeped through the siding, the Tyvek (which is breathable), through the insulation, and stopped at the vapor barrier. There it condensed and water damage resulted.

I alway have the shade cloth on the outside for the quick convenience of pulling it over the structure at moments notice. The ropes usually lie over the structure from the first time that the shade cloth is applied and then it is just a matter of pulling the shadecloth over the structure and fastening the ropes to hold it in place. It is a temporary arrangement but often will remain on for weeks at a time, depending on the weather.

I should mention that I have installed an inside wirelock on one side of this 15x40' gh because I have installed a hipboard 2 1/2' off the ground to be able to rollup that side of plastic (it does not have the bubble wrap). It involves piecing the wirelock base between arches and it allows me to fasten an extra double plastic curtain to that side for better heat retention in early spring. That plastic just lays on the inside floor when not attached. It is not totally tight as you usually can insert a finger on either side of an arch in that inner connection but it does make a big difference in heat retention. I was just in that structure yesterday to retrieve plant trays (I'm not using it yet) and the inside temp was in the 80's when the outside temp was below freezing.

Thanks for the explanation of the vapor barrier, SB. That may well have been his problem. It would be impractical to take off the siding to change the barrier, rather to install one from the greenhouse to the home exterior. I have not heard of anyone having the need to do that before, but most folks do not keep their GH that hot all winter. LOVED the pics of your garden and GH, SB. Some of those fruits I have never even tasted. I would probably be growing cocoa trees in case there was ever a shortage of chocolate.

Bmoser, it sounds like the shade location in your case is convenience. I was thinking that it might make it cooler on the inside if the cover is over the plastic rather than under. Do you think that would make any difference in summer temps? I was thinking that I might leave a reflective shade on the roof all summer. But on the sides, since they are verticle, just make shade cloth curtains on a rod that could be adjusted to suit the needs of the season. Just thinking that if two thirds of the heat goes out the roof in winter, two thirds of the heat might come IN through the roof in summer.

My first little green tomatos are growing. The cukes are WONDERFUL and the lettuce makes a fine salad. No zukes yet, but the second yellow squash in almost ready. There are onions, spinach, peppers, radish, nastursiums, and brocolli in various stages. I'm loving it. No problems so far with pests.... knock on wood. Its against my nature to have spiders around, but I'm trying..... new pics now posted on the website. Thanks everyone!
Carol

I noticed you did this in 2011, and was wondering how the roof is holding up? I have a 8x12 hoophouse with plastic cover and will be replacing it next year and was thinking of using the pool cover. Just wondering how it is working longrun. Thanks

Hi Plantman
I just posted on your other question above. By spring, the tomatos were out of control, cucs were still going strong, and the squash got mildew. So this year, I'm going strong on peppers rather than squash, but have added sweetpotato (I love the greens, sauteed with onions)and am going with a determinate tomato this year. Adding another photo from last year.

Now don't laugh, I have a hammock in there for me. Its warm and bright, almost like bing outside on a spring day and a great place to read.