Sorry to confuse ya sfallen, I don't think i mentioned the back wall will be tied to the foundation via piers, so the load bearing framing will stay in place, so I think it will stay rigid if I move that back wall out another 8 feet. I sure would love to build something like a 20 x 30, but this is a joy jar project, so it has to be limited to what is in there this year. Kinda tight, hub laid off and in college, oldest getting married and in college, middle one in college, youngest graduating high school and going on to college. They sure do put a knock on that jar lol. Fuzzy, the only extra heat I plan this year is the small woodstove, firewood is plentiful on this hill of mine. Which I am counting on to help with cooling via breezes swooping up the field. Another plumb job is out lol, the dh just will not go for more plumbing to go wrong, but I hope to sweettalk him into the power this fall. Thanks again for all the advice. minerva

I have mine right down the middle. I kinda like it because I can work from all sides. But mine is just one of those wire shelf units you get from Costco.

I built this greehouse specificially for starting bedding plants. I don't start heating it until the first week in Feb. At the time I didn't think a ground heat sink would have that much effect so I didn't do it. If I had it to do over again I would put the lip of the 2x4 base to the inside and put some foam board into a trench and up to the redwood around the base on the outside. The insulation on the north side just goes to the bottom of the redwood. The trays didn't melt uniformly along the whole shelf. It was just the 2 trays or so in the corners on the top shelf where the light would get concentrated. None of the seeds in those trays germinated however. Low angle sun reflecting from the top combined with the corner reflection against the dark plastic of the trays made for some real hot spots. I you look at my weather station at http://wx.uvci.com I have a temp sensor in a tray of soil on the soil heating germination mat. When the soil is dry and a bright sunny day the temp will get up to 130 easily. Another change I would make is to have the potting bench in the end just sit on supports rather than build it in. That way it could be easily taken out when not in use. It would make getting to the last two feed of shelf much easier. It also gets a lot of water on it when watering which has caused the composit material it is made from to expand. I will probably replace it next year and when I do It will not be built in permanently like it is now.

It just depends on what your north wall is made of. An ideal north wall for a solar greenhouse should be, going from the inside out. Brick/poured concrete/concrete blocks with the spaces filled with concrete or ideally a trombe wall then, a layer of insulation, your framing, then the outside covering. However, if your brick/concrete/concrete block part is greater than 4 inches deep then you are wasting money. Thermal conductivity comes into play. Any useful heat you retain in the mass past the 4 inch mark during the day is slow to work its way back into the wall and at night it also is slow being released. My North wall is solid and one day it will be insulated. It is painted white on the inside because I need the reflected light in spring. However it was cheaper to cover and it has an higher R value than twinwall. Here is a link that might be useful: