Visiting from Market Gardener forum, I didn't even know there was a greenhouse forum! Hope someone here can help me.
I got some galvanized steel hoops (slightly bent but pretty good shape) from a nursery whose owner is retiring. Got the CCA baseboards and hipboards too, as well as the "receivers" that were hammered down 2 ft into the ground through holes drilled every 3ft in the baseboards. Not sure I can do that in my stony soil - looking to build up the sides so I have a straight 2ft tall sidewall before starting to curve, and then just "pinning" the baseboards into the ground with rebar.
Hoops are 13'1" center to center, looks like 1 1/8" (OD) galvanized pipe. Couldn't get a good measurement of height or total length the way they're stacked, but I could barely reach the purlin when it was assembled so I will assume that even if they are "squished" so they're a little taller than 6' 6.5" (6'7" allowing for OD), the pipe was probably standard length for top rail - is that 21 or 22ft?
Then of course they were set in "receivers" buried in the ground, with a bell end sticking up above the baseboards they were clamped to, so the ends of the hoops were about 6" off the ground (like B option above). I want to set them up even higher (buy new pipe to drive into the ground, use the old ones to connect them inside the sidewalls?), really like 2ft sidewalls so I can get over 8ft tall in the middle and have *some* room on the sides for crops. Also, I want to put the hip boards high enough to put gutters and downspouts on to try to put a couple of rainbarrels up for irrigation.
Here's the problem - I have (I think) 46 hoops that were originally placed 3ft apart, using what I'm sure is CCA treated lumber. I could replace the lumber with new (saw some on Craigslist, right here in town, he's got 6 6x6x8ft posts and 19 2x8x8ft copper azole planks - that would give me 76ft in length if I used them as baseboards) - but still wouldn't be "organic" (not that I'm going for certification). Probably would have to replace all the fasteners anyway, lots of the clamps look white, not sure how long galvanized lasts even with CCA.
Area where I have cleared is about 48x76, small rise to south but I don't think it blocks much sun (and I'm not growing 4 seasons), I can place it far enough away that I think I can catch southerly breezes (and it's a convenient place to put a tank if I want to pump into it - that's another story since GAP says not to use pond water).
BUT... the land slopes from west to east, maybe a couple of feet over the 48ft width. Area is more level (maybe 2ft over 76 ft run) going N-S, with an existing swale to the north. Another rise (long ledge) running to the north, wooded, and wooded to the East (why I don't want to go farther than 48ft E-W, plus it drops off more sharply past that), but clear to the West. Prevailing winds are from the south here in the summer, according to expert in HT design at workshop I took a month ago.
So what's the best orientation and size? 1 (or eventually 2) 76ft long tunnels running N-S (I don't think that's really best, maybe 1 but easternmost one would get shaded and ventilation affected by western one and not best use of prevailing winds), 2 (or eventually more since there's room, but endwalls are more expensive) tunnels running E-W (but have to build up sidewalls to level them on east end, plant taller crops on east?, same problem with shading from southernmost tunnel(s), ventilation affected?)?
Also looks like Farmtek's standard greenhouse film comes only in 24ft or 32ft wide rolls, so no burying edges with 24ft, lots of waste with 32ft if I try for 2ft tall sidewalls? Will 24ft wide work if I plan on rolling up sides anyway, and stack hay bales against the sides during colder months (again, just looking to extend the season a month or so in each direction)?
IF we put the houses running N-S, we could make them shorter than 76ft and then move them since the area is more or less level in that direction. Don't know if that really matters since I'm not sure how many different types of crops I'd be growing, but if going N-S for another reason, I'd probably use make it/them movable for flexibility in the future.
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