I had some old windows from a buddy that I wanted to make into a cold frame to grow some of our veggies and starts in. I have been seeing the earthen-sided green houses on facebook and I got the idea of making the back wall of the cold frame out of hay bales. I figured it would be cheaper than buying a bunch of wood and framing the back. Plus when the hay gets wet it will give off some heat, much like compost does. So I started out with three hay bales long and and two high. I also put in some scrap pieces of wood to make little shelves in between the bales. You can see the board across the top, that is what the windows will rest on.
All the wood you see on this project has either been reclaimed from the local dump or dismantled from pallets. Next, I made the angled side frame.
Take a look at the notch in the wood for the window support piece to rest on.
Next I took pieces of wood from pallets and lined them up against the frame, penciled the angle on the back, and then I cut each board for the perfect fit.
You can see here that the windows slide up and down and this is really important for temperature control. I put a thermometer in there after I finished and the temperature quickly soared to over 100 degrees. I was briefly able to mess around with it and was able to get it to hold around 80 degrees which is perfect for seed germination. There will definitely be some experimenting going on with how much to open the windows to control the temperature. I fried some of our starts already in the frame not watching the temperature. Ooops! Solar gain is quite the powerful force!