The walk-in shell is finally done. It took awhile since nothing was quite square and I kept having to run to the hardware store. I also had no idea what I was doing for the most part.
Most of the time spent in the past weeks was figuring out how to make blocks of styrofoam become little particles of styrofoam. Meadow and I had gone to pick up a pickup truck loads worth of styrofoam blocks in Hartland, VT. It was from an old business and the guy had 14 yards of the stuff. We are headed back to get another load which will hopefully be all we need to finish up. I had been hunting for a wood chipper/shredder but in winter they don’t pop up on Craigslist very often. I ended up building a prototype shredder using a hardware cloth disc mounted on a long nail attached to a drill. It worked really slowly and was really messy, I needed a chipper and quick if this was going to work.
I built the floor joists and created a closed cavity underneath it with a plastic liner. Once I had some shredded styrofoam it would fill this space insulating the shack from the ground. The cavity ranged from 8 inches to around 16 inches and we think the r-value is something like 3.5 or 4 per inch. That would put the floor’s r-value above 40. Once I had the floor down I put up felt paper on the two existing walls which will help reduce air infiltration because the boards where spaced around an inch apart.
In the front floor bay I made an enclosed space with the plastic so I could test out the shredder and see how well the broken up styrofoam would fill the space. I had bought a flexible dryer vent and made a manifold to attach it to the shredder. It involved lots of duct tape and as I learned quickly would not work because of all the times I would have to take it off. I placed some hardware cloth inside the output vent of the shredder to try and force larger pieces to stay within the reach of the metal teeth. The set up worked okay for a few rounds of styrofoam but then it got clogged and I had to take the whole thing apart. I went through a few attempts like this and the plastic bubble started to get filled. I decided it worked good enough and covered the whole floor with two layers of plywood. I cut a whole to accept the vent and started reworking the shredder. I switched from putting it in the chipping bulk side to the side used for larger pieces. I also Figured out a way to mount the plastic manifold using string so it was much easier to take apart when needed. Once I made the switch it was smooth sailing and I had the floor filled to the brim in an 2 hours or so.
After that it was time to think about putting the exterior walls for the other two sides up as well as the interior walls and ceiling. I decided that the front wall would not have a cavity and would just be two panels sandwiched together. Just in case I needed to run electric or if we expand it to the rest of the bay we won’t have to deal with the loose styrofoam. The other wall is made of plywood and a few verticals to support it. The interior walls for the blown cavities are rigid insulation that Marshall already had around. They are just under 4 inches and the space between them and the exterior walls range from 4 to 5 inches which would get me around a R-value of 30+. The Ceiling is rigid panels with styrofoam blown in the 6 or 7 inches between the rafters which should be around a R-value of 40+.
I called up Green Mountain Bottle Redemption and they were able to supply me with the 2000 2 liter bottles. Each bottle can be filled with 4.409 pounds of water and should take 72 btus to freeze. We will let nature take these btus away from the water on chilly nights. If I would have finished the shell earlier I would have added salt to the mix which would take the water’s freezing point down to 5 degrees Fahrenheit adding even more btus. But the nights wont be that cold hopefully for the rest of the winter but I will try experimenting with it next year. With the 2000 bottles plus a tank that holds 50 gallons its around a million btus which hopefully will be enough to get us through till it gets cold enough. Most of the vegetables will be picked on friday and sold on saturday so our cooling load will not be to high this year. I’ll be keeping track of the temperature as the season progresses and will be able to chart the performance of the walk in. Then next year we can make the changes that will be necessary if any are needed to keep it cool. This year we will probably miss a really good freeze but the amount of thermal mass in the walk-in should keep it cool.
There are a few more pics on our flickr page.