Hello everyone! I was just wondering if I built a hoop house and then built another wider and taller hoop house around it and sealed the plastic well. It should be super insulated right? Combined with hugelkultur and a rocket mass heater for heat, I wonder if it would be comfortable enough to hang out in the winter. Also what do you think it would be like in the summer? I imagined a couple feet of air gap between the 2 layers of plastic. I live in Canada, could I grow semi tropical plants? Any comments?
Where in Canada do you live? I live in Toronto, for example, which is like plant hardiness zone 6A/B. This setup sounds interesting. I think if you were really careful about your airlock, and maybe if you stacked bales of straw on the sides of the air space where you aren't getting any sunlight anyways, and maybe if you dug a trench down two feet and put in some kind of insulation and a water tube in-floor heating system for the perimeter, I think it would depend a lot on what you need where you are, and what, specifically, you want to do inside your space. Check out Walipini greenhouses, among others. Bottom line is, yes you could do it that way, but I think you might be able to do better. As to summer, though, again, depending on where you are, you might need to take additional steps.
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posted 6 years ago
Hey thanks for the reply. I am currently in Burlington Ontario but I am not sure yet where I would do this project. I am interested in your hay bale idea that seems to make sense. I would try to make it as air tight as possible but I thought I would leave one side open so that both hoop houses could be rolled up to vent during the hot weather. I haven't worked out all of the kinks but I thought we the hugelkultur producing underground heat and possibly living inside the hoop with a rocket mass heater to cook on and make heat for a bed......might be pretty comfortable in winter but again it is all experiemental. Keep all the ideas coming!
Location: Salt Lake Valley, Utah, hardiness zone 6b/7a
posted 6 years ago
Double layer plastic film greenhouses have been around for awhile. You can build two separate frames, as you suggest, or you can put on two layers on a single frame and inflate them. My father built a small Mittleider greenhouse (based on the standard Mittleider box, rather than the larger greenhouse plan) with two frames and it stayed quite warm on sunny days in mid-Winter -- nowhere near tropical, but warm. I don't know how cold it got at night, though, and during prolonged periods of ice-fog (worst year was 8 weeks followed by 6 weeks) it would have matched the exterior temps 24/7 after a day or two. (location - about 5000', just North of Salt Lake City, so my winters were generally milder than Canada, except Vancouver, even with the higher altitude)
You don't want a large gap between layers. Too much air movement. An inch or so should do it. You could have removable end panels to facilitate ventilation in Summer.
Walipini needs significant modifications at higher latitudes (non-tropical). Ends up looking suspiciously like an Oehlergreenhouse, so maybe you should start there. His plans are designed for a slope, but you could just berm up the North side. If you want to grow tropicals, plan on supplemental heat and light. You will also want to maybe insulate the perimeter to below the frost line. You could even put in a thermal barrier to cover the bottom. Maybe cover it with a foot or more of dirt (or water barrels) as a heat sink. Also plan on covering glazing with insulating panels or blankets at night and on foggy or other sunless/stormy days.
FarmTek, in Iowa, was selling a hoop house with bubble-foil on the North side and inflating double plastic film on the South side with a rolling bubble-foil curtain for the South side.
I don't know how critical the roof angle is when using translucent glazing.
You may want to consider this design. The seller of the plans claims it is used successfully in Maine.
I have seen these around, and they do work, but one thing to keep in mind is that during winter in some areas you wont have enough hours of light in winter to get a young transplant or seedling to get to maturity, this is true even with spinach and lettuce. You have to start them before winter so that they are mature enough to handle the low light of winter, or you start them under lights until they are old enough to be put in the greenhouse, or be left in the greenhouse with no artificial lighting.
For double-pane windows, more than 1/2" gap is less efficient if the working fluid is air. Almost all film-type green houses are dual-layer with inflation. Otherwise the plastic just flaps in the wind and is destroyed. The inflation of the two layers also accounts for the tempco of the plastic, which expands and contracts depending on it's temperature. There are all kinds of tricks to squeeze more life out of the UV-resistant film, like using white foam where it touches the frame, etc.
I'm in SE MN and my research lead me to a passive solar greenhouse. With night-time insulation and the right orientation of a S-facing glazed wall, cold-tolerant plants are supposed to do well. At least, according to the interwebs. A heater with some mass might be helpful but I was lead to believe that it wasn't necessary with competent management.