I've been planning this thing for years. It came together sllllooooowwwwwllllyyyyy, but with the help of some amazing friends, it's done!
The interior space is about 9x11. It backs onto a cinderblock wall with soil behind it. It has a door on east and west, in the direction of the prevailing winds. For temperature control it has a water-filled plant pot (the kind they grow trees in) in each corner. In future years those will be replaced with closed barrels so there's no problem with insects. Eventually it will have a waterwall against the cinderblock, made of gallon milk jugs filled with water. I started working on that piece today.
I had planned for the roof to slope sharply to the north (northern exposure) but it didn't work out that way. When greenhouses were invented, it was for areas with cool summers and frigid winters--the additional heat was very necessary, year round. People have continued to build that way, simply because it's traditional, but one of the main problems with greenhouses in more temperate areas is getting rid of excess heat.
The idea behind having the roof face north is that during the winter the greenhouse would receive full exposure on the front face, while during the summer it wouldn't hit any surface straight on, the roof not being angled correctly for sun exposure and the sun at a high angle so most of the light would also miss the front.
Because of some oops moments during construction the roof is angled north, but not sharply--perhaps a 10 degree slant. So rain runs off, but the sun will still hit it. I'm going to do an experiment during the summer and put a shade cloth over the roof, simulating what would have happened if the plan had remained as I originally had it. The water also runs off the back of the roof, into the forest garden area.
There will eventually be a small (1 foot wide) garden area immediately around the greenhouse to take advantage of the extended warm period.
Currently, when the greenhouse is not fully sealed and there is no waterwall in place:
Night-time temperatures: 8 to 10 degrees above outside
Day-time temperatures: 15 degrees above outside temps when cloudy, up to 40 above when sunny
So theoretically daytime temps could go down to 18 without too much risk of freezing. Night-time temps could go down to 22.
The tomatoes are still alive (if struggling). Cilantro is still alive. Greens are up and should be ready to start picking mid-December.
I've had several suggestions for additions and improvements, but for this first year I'm keeping it entirely passive. I want to know what the structure is capable of before I start making changes.
