R Scott wrote:I like the design. I wanted to do something similar, but I hit bedrock at 2 feet so I need to come up with something else.
I do NOT like any wood in an aquaponics greenhouse unless you have a natural rot proof wood to use, like black locust or hedge--no idea of the equivalent for you. Any chemical treatment is either going to leach into the system or not be effective enough for the wood. As "evil" as it sounds, I think a smart use of concrete makes sense in a use like this. I would prefer that embedded energy over poisons any day.
Modern 4x4's won't hold, not at that spacing anyway. They are weak with the fast growth trees, good as a post or a pole but not as a beam. You can make them work, especially as above grade earth-bermed, but you need to run the numbers to see if it is cheaper to use 1 6x6 vs. 2-4 4x4's.
When I looked at it, I think the strength calcs came back as a 4x4 joist on 4.something spacing! So pretty much stack them solid and forego the decking/sheathing.
R Scott wrote:The typical key to PAHS is to keep the surrounding dirt DRY to pull up the heat. The original had a layer of foam, 2 layers of 6 mil poly, then another layer of foam to form the "umbrella."
R Scott wrote:Earth tubes need to run at a continuous drain slope or they will collect condensation and mold--VERY bad.