Styrofoam Insulation.
 

Am building a flat roof will be about 20 X 35 when done, this year 20 X 20.
Have a source of free styrofoam insulation chunks, every thing from sheets of 4" missing chunks, to curved bits and thin strips.
I saw the odd shaped pieces into cubes and pack them tight into the spaces between the box beam trusses. Am very careful to get tight fits, & use canned foam and backer rod as required, the last 1/2" or so will be epscrete under the plywood so that there are no air gaps to allow condensation to form.
The styrofoam is minimum 8" deep and max 11" deep because of the run off slope. The box beam trusses are 2X4 with 1/2" plywood glued and screwed to the 2x4 frame. the trusses are filled with rock wool batting..
Will probably lay the first row of plywood Sunday or Monday
Any one see problems with using the styrofoam pieces?

Sounds great! A lot of labor, but a LOT of savings . . . .

Steve

The only issue I can see is the lack of a perfect air seal. But, for the price it sounds like its worth it. I agree with stevehull it does sound like a lot of work.

Is it actual insulation or is it being repurposed from some other use? If it's not rated as insulation then it may lack fire retardants and it may not be approved for this use -- not to mention being a fire hazard.

Yes I am using insulation, I get it free from a spa cover manufacturer, ano.ther source could be a SIPs maker
I take odd shapes and bandsaw them into cubes, and am very careful to be as air tight as possible, some of the fits are so tight that I have to press them into place slowly to let air escape. Then with the use of foam backer rod and spray foam I close up the areas, the first layer between the box beam trusses and blocking, is always one piece of 2 1/4" cut to fit, and glued at the edges, to encourage air sealing. The top layer will be a "skin" of epscrete to further stop air migration and to ensure there are no air gaps under the plywood roof sheathing. I have fire tested the material and found that it will not burn in the absence of flame, but does put out a pretty nasty smoke. For that reason I put in firestop blocking every few feet. Work is pretty much stopped today and yesterday, it is too smokey to work because of the fires. Visibility at about 200 meters.
A tip for anyone else in the thick smoke, turn on your furnace air, the filter will remove some of the smoke, especially if it is a charcoal type filter, at the suggestion of my daughter, I taped a furnace filter to the suction side of a box fan, and it is keeping us relatively clear of smoke in the living room and bed room.

Those sources should have fire retardants. If you have the time is sounds like it will work well.

Laid the last sheet of 5/8 t&g plywood a few days ago. Yes it was quite a bit of work, but the cash savings allowed me to buy a nice 14" bandsaw.
Put the epscrete on a little bit wetter than I normally make it, so that I could bring up a nice layer of cement for the plywood to lay against. The epscrete cures pretty hard in a few days and gives the plywood a very firm feel when I walk on it (220lbs)

Do you have any pics of the install?