I still think spray foam is the best way to insulate a shipping container, but I am still to broke to do it right, or even attempt a DIY solution.
However using closed cell sheets is a decent alternative, and much better than any other ideas I can find online.
After measuring and seeing that the depth of the corrugated channels in my roof were 3/4 inch deep (where not bent) I bought some 4×8 sheets of 3/4 inch closed cell foam with a aluminum vapor barrier on one side.
In part one of how to insulate a shipping container, we cut and glued in the strips to level out the roof corrugations.
In this video we show how we put up the roof.
The original slats were glued in using construction adhesive, and some of them wanted to fall, so because of the condensation and possible flexing, I did not want to rely on glue alone.
What I did was build a wall along the back of the box that was 3/4 plus the width of a 2×4 (roughly 3.5 inches) from the top of the roof. This would allow a 2×4 joist and a sheet of foam to rest tightly against the wall.
I then cut joists that would span from the top of the wall in the back of the box to the divider wall we framed in earlier. I had to notch that 2×4 so it could sit against the stud wall and allow for the 3×4 inch sheet. (the video will show this)
Once the joists were cut we balanced them up on the walls. I put the two nearest the box sides close to where they were to rest, and the middle joists I spread apart because the foiam would have to bend toward the middle so I could wedge it up and around (Again, the end of the video will show this).
Once the joists were close to being in place, I spray foamed the gaps around my foam slats, put construction adhesive on the large sheets of foam (first cut to size) and them starting from the back, wedged them in place.
Once the first foam sheet was in place We rotated the 2×4 to lock the sheet up against the roof of the container.
The next sheet went in and was made to but up against the first and a temporary support was used to hold the two sheets up tightly against the roof without the support of any of the joists.
After the third and last sheet was placed, the 4 joists were forced up and held tightly in position as they were nailed in place.
Now the foam sheets are held by glue, expanding spray foam, and 4 2×4 joist edged into place.
Now I have to frame the side walls and figure out how I am going to use the foam sheet to insulate the shipping container walls, because the sides are not as square as the roof.
I am not done, but you can get an idea about how I Insulate a Shipping Container.