Erik Krieg

They also talk about "organic farmers" doing MORE tillage than Chem-Ag farmers, but any truly organic farmer is going to know that tillage destroys the soil and not go that route. 

On large scale monocrop you either shallow till for weeds or you spray chemical.  Shallow till is what most organic farmers use as it is far better than poisons.

A lot of the principles of heavy mulching, lasagna gardening etc for weed control just aren't scalable to large organic farms.  Imagine the mulch it would take to cover a 50-200acre field.  

Also a good one.  A lot of actual construction info and some plans

I appreciate the input, gives me more to consider!  

im 100% sure im not as hardcore as a lot of permies.  i like to value engineer my projects for total lifetime cost/maintenance/impact, theres not enough time or money for perfection.

Al, id be interested to know if you could offer some input as to metal structural member sizing.  you say you use 2x2'' tubing on 10' spacing, what wall thickness?   Do you use trusses between the 10' spaced columns or just more 2x2 tube as a top plate?  do you use purlins for roofing to attach?  any chance you have a picture or two of what you are describing.  

Al,  whats your average rainfall and humidity level?  in Virginia where I live most of the summer is 80% plus humidity and would likely be higher within a greenhouse.  I had considered building a red steel structure but had concerns of rust, especially underground in our clay which holds a LOT of moisture.  that being said i have had several pieces of 1/8'' wall 2x2 sitting outside for about 4 years (use them as lightweight forks for my little tractor) and they are rusty as can be but still appear solid

polycarbonate/glass vs poly sheet - its possible that the UV blocking of glass and polycarbonate causes some loss in photosynthesis but it cant be that much, people have been growing under glass for over a hundred years and polycarbonate is one of the most used greenhouse materials.  For me, the strength of the polycarb and glass to support a snow load, not have to be replaced for a decade plus, and much higher Rvalue outweigh any possible weakness for UV light transmission.

sharon, what did you use as framing material.  

i went by a local dealer and my only real concern at this point is the stiffness of the structure.  given, this example unit had no end walls, but you could shake the entire structure side to side.  i would think end walls would rigid it up a good bit though.

fwiw carolina carports will sell the frame and purlins for 75% of the entire building cost (so $1125 on a normally $1500 carport) but then I need to come up with the roofing on the other half.  

I have 400 sq ft of 1/2" safety glass i got used and can get 300 sq ft of trip wall poly carbonate for $1200 delivered

All in all of the frame works after i close up the ends I might be into the greenhouse maybe $6k, that's about  $21/sq ft

Definitely more expensive than a hoop house but the poly carb should be 10yr min, the glass is forever (assuming no rocks etc) & the r value of the walls would be like a houses.  

I was just wondering if someone else had beat me to it so I don't have to repeat their mistakes

The Forest Garden Greenhouse
Book by Jerome Osentowski

The Year Round Solar Greenhouse
Book by Lindsay Schiller

both good reads about passive solar greenhouses, lots of overlap and each has a different name for the same earth to air heat exchange system.  both have good concepts and examples of passive solar greenhouses but don't expect any construction plans out of either.  

After speaking to some local metal building guys... It seems like one of the higher end carports might be a good base to start from.  they can be braced to take up to 130MPH winds and 60lb snow loads.  My understanding is the roofing provides very little structure so changing 1/2 out to polycarbonate shouldnt cause any issues.

just tossing the idea around, the galvanized frame and roof for a 12x24 is only $1500.  seems like you could add extra hat purlins and wall bracing to really strengthen the structure for cheap.

Oh. So you mean deadly as in Fasteners break in the roof collapses?