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Montana 6,600 feet. 24x13 semi-pit. Attached to a garage wall. Very steep roof pitch (8-12). Use only from March (30 degrees low, 50 degrees high) thru October (temps the same). Summer temps (40 low, 85 high).
Considering single wall corrugated polycarbonate from Home Depot for the roof and single wall flat polycorbonate for the walls. Given that we are only trying to extend our summer growing season--not garden in the winter, is it worth the considerable extra expense for multi-wall? We plan considerable support for the roof panels.
One problem with the multi-wall: our roof panels will be about 16' feet long. We can't find a multi-wall sheet that long. So there would need to be a horizontal joint in the roof panels which seems to me a problem area. Corrugated single wall panels would require a simple overlap.
If you were trying to grow things over the winter then in your zone you'd definitely need the double wall, but since you're just trying to extend your season a little bit I think single wall would probably be OK given those temperatures.
Ours is double wall corrugated, but I overwinter large tropicals for other people. Have it on the south wall and south roof. The north wall and roof have expandable spray on insulation plus foil insulation for reflecting the light.
I'm late to your question, but I had good luck holding heat in my home-made greenhouse by adding a layer of industrial bubble wrap inside the frame. It provided two different "dead air" areas for insulation and still passed much of the available sunlight. It can be taped up with clear packing tape or, in my case, stapled to the wooden frame. There are lots of suppliers online that have large rolls of 4-foot wide bubble wrap at reasonable prices.
im planning to put up a lean to greenhouse.. 8X12 its on north side of house..:( but really only place i can
put it.. my use will be as a hot house greenhouse.. tropicals.. i plan to use the 10mm thick polycarbonate..it
is pricey..but has great insuluation ..and here in utah..jan/feb..it will need it..
annaZ .. great idea on using spray expandable insulation.. was that difficult/costly to apply?
also the use of foil insulation..
i think i'll need to put up chains for a couple lights from ceiling too..since greenhouse will be on north side of
house.. but plants going in greenhouse are all understory camopy tropicals..so filtered light..not bright light..
does this seem reasonable to you all??
Tropicalnut, we didn't apply the expandable foam ourselves, I don't think we could have if we would have wanted to. Much easier to have the business owner do it, that way it was right and it didn't take him much time at all to do it. It seems like it cost us about $2500.00 for the north wall, north ceiling, and below the clear paneling on the south side. The g'house is 30x64, so you can get an idea of the area we DID put the stuff on. North wall and ceiling also got the foil, bubble, bubble, foil roll insulation over the foam.