This is how I am doing it this year. I only have enough room on my McSuburb parcel to have small-scale structures, so this year for experimentation one of the things I have is a 4 x 6 coldframe (walls insulated at ~R-5) with a below-ground insulated structure, a water-tubing subsoil heating system and ~30 liters of water for thermal mass. The glazing is 8mm twinwall polycarb at a 30º angle and at night I cover the glazing with an old sleeping bag. Further, I take some of the heated water and put it in the soil, which is insulated @ R-6 - down to 10" in a raised bed next to the house. Despite numerous days with highs in the single digits F (-15ºC ) and several lows well below 0ºF (-25ºC), last time I checked my soil was 64ºF in the sun and 58ºF in the shade (~18ºC and ~14ºC). Air temps during the day always need to be vented on sunny days and at night I have never dropped below 35ºF (2ºC), even on the night we hit -14F (-26C). So my dark-colored water and soil are my thermal masses. So, to reinforce anecdotally what is above, IMHO the original link had inadequate mass to keep from freezing for that volume. The glazing insulation is important. Any text on solar houses or solar greenhouses spend considerable time on solar access and solar mass, as well as insulating the glazing at night and opening the glazing to the sky as soon as the sun is up. For example, right now the coldframe has heated up ~4ºF in 3/4 of an hour's exposure despite cloud cover allowing only ~40% of the expected cloud-free solar radiation through. The sun is free energy. We must do more than just collect it to make it work for us. We must store it, distribute it, and insulate our glazing. Dan

I have used the passive solar technique to design and build (or have built) an 8 by 16' lean-to style greenhouse. I used a book by McCullough called "The Solar Greenhouse Book". It was printed by Rodale. We used the greenhouse through the winter in zone 4B with only a fan from the adjoining space (a minimally heated cement-slab 1,000 foot space, used as a bookstore) for air circulation. I was able to grow greens and overwinter houseplants, including flowering ones and a dwarf lemon tree, without any losses from freezing. The lean-to roof does offer some shade this time of year, so temperatures are moderate even without venting. Thermal storage is only partially in place, and it has a few seams that leak cold air and rain, so we have some tightening up to do this summer. I'm so happy with it I've decided to participate in a solar home tour that takes place Oct 1, sponsored by NESEA. Good luck with yours! -Pat

I have run across these directions in several different versions and the one thing I think they always sort of skim over is directions for building the end walls. I think that part of the project confuses (or intimidates) a lot of people. The one thing I can not find on the net is the plans for building a similar house but with the gothic arch roofline. And once long time ago in here a guy explained all the math for calculating the hoop house height depending upon the length of rafters and how wide you make it. Wish I had saved that info. I want one taller than 6 or 7 feet in the center. I even keep wondering what would happen if two rafers were connected together at the peak with a 45-degree elbow. hmmmm.... (don't mind me...just thinking out loud). I really like the wooden bentwood gothic arch greenhouses I have seen but the plans you get from the county co-op sites don't give any directions for building them. I just know each rib is built with strips of 1/2" x 2" wide wood (plywood?) and two pieces are spaced apart with 2" wide blocks of wood. I did find the link below for a 10'x10'x32' arch type greenhouse yesterday which I may try a variation of although I would like 12' or 14' width (which I guess I could get without losing height if I built up a short kneewall). What bugged me about these plans was that it says 10' tall, but then the drawing shows the roof peak right at the top of the door opening and there are absolutely no measurements in the directions. Oh, well.... Anyways I think a lot of people will be happy you posted the link to the hoophouse plans. I need to just stop thinking and just build me a simple hoop like this to start with. :) Here is a link that might be useful: 10' x 10' x 32' Greenhouse Plans

Last winter I followed advice in Elliot Coleman's book (Winter harvest handbook) and had great luck in *harvesting* fresh vegetables all winter. They did most of their growing however in the fall (I started them all in late September or later) and then later in the very early spring as in the winter months they barely grew (although they did a tiny bit). My set up: Hoop house - It was an existing (built by me and my husband a handful of years ago for season extention) 12x16 plastic covered hoop house. We made it out of plastic conduit and the only thing we modified for the winter is that we swapped out the flat 4 way fittings at the roof peak with adjustable angle fittings. I found that 45 or 90 degree fittings didn't work (too sharp an angle) and I didn't want to not have an angle for the snow load so I went with manually setting the angle as steep as I could with the adjustable ones. (You can find them by googling "PVC 1" Adjustable Ell Fitting 3 Way" or "4 way"). We never removed snow off the top of it - By design or by luck the snow would shed off the side. (Although I hear brooming it off is good practice.) I sealed the window and door with weatherstripping. I also added ~ 800 gals of water - some large tanks (which were a royal pain to get in) and lots of single gallon containers. against the north wall. I also added 1" foam insulation along the north wall - including covering 1/2 the "ceiling" on the north side (taped to the conduit frame in some areas). I dug the foam insulation ~ 6" deep around the perimeter. I then planted in two 18" rows separated by a small 1ft step path - all under a 4ft wide floating row cover (the row cover hovered on smaller plastic conduit hoops). Under the row cover in the small 1ft step path I put as many gallon jugs as fit leaving me with step spaces. I also put a few 1L and 2L bottles on the outside edges under the row cover. I also put one strand of old-fashioned (ie not LED) christmas lights suspended from the conduit as my "emergency" heat source. I put my thermostat for my lights outside my row cover and set it to turn on at 28*. I also grew a few earthboxes full of veggies but I found that anything in a box didn't grow nearly as well as things in the ground. I think the roots get too cold and they stop growing much, much earlier (but they didn't die - just didn't grow as much) even though they were under the same row cover but they didn't die. The last thing I did was put a small muffin fan attached to a tiny solar panel under the row cover for air circulation. I had my window/door always closed (ie I disconnected my autovents) for the winter months (Dec-Mar). I also never went in to harvest except during the day (almost always a sunny day) when opening my row covers wouldn't release any trapped heat that was vital for the night. I weighed down one side of the row cover with cylindrical bags of sand that I could easily remove and then the other side with soil/rocks piled on top. Watering was mostly a non-issue, but I'd carry in my water in jugs on sunny days and water by hand. I think I had to do this maybe 3-5 times all winter (ie monthly). With this set up I successfully grew: kale, leaf lettuce, carrots, beats, chard, mache VIT, bok choi, spinach, etc. For most plants I would harvest outter leaves and leave the inner leaves to continue growing. With that set-up each plant continued to provide until the late spring heat caused them to bolt (which was fine since I needed the space for the next round of crops). The temperature inside the row cover was much more stable than in the hoop house in general. The temp in the row cover never dropped under I think 25 - even after multiple cloudy/stormy days. In addition my hoop house is drafty so perhaps with a more sealed-tight environment no extra energy would be needed and/or maybe more ventilation. Oh and my hoop house is on the north side of my property and has mature trees ~ 50 feet away from it on the east side which did shade some in the morning (but not so bad because they didn't have leaves) and then we have evergreen trees that would shade the late day sun as well. I still think it's worthwhile but it depends on how much sun you get. I'm planning on building a "real" greenhouse (twinwall, etc) and am spending this winter scouting for the right location (best sun). I plan to use an earthen floor due to my experience of growing in pots vs in the ground, but am still doing my research for that as well. I've read that wherever possible you want to insulate in the ground to keep from losing heat that way. I plan to do that with my final greenhouse. Also wherever you are realize that both snow and a kneewall (if you have one) will shade part of your greenhouse floor in the winter due to the low sun angle so you may lose "significant" growing space that way.