I'm thinking of setting up a cold season greenhouse that would enclose a deep water culture aquaponic system within my brother's 12,000 square foot existing greenhouse. Everything needs to be dismantled in the spring. I'd be attempting this during the winter of 2014/15 if Mr. Grant is willing to chip in. It's still in the design phase, but it would look something like in the sketches below. I don't see any problem with the stacked straw bales except the need to stack them tightly together. I was thinking of using sheep wool insulation in the ceiling framework (8' x 8' frames bolted together and suspended from the existing structure) but as good as that stuff is for buffering moisture, it's awfully expensive. So, my question is, how about using straw for the ceiling, too? It could be packed tightly in the voids between the 2 x 4s (after bolting them together) and even a foot or so could be laid loosely on top for good measure. Any thoughts?