Just a request for advice please. I have a torch on roof that I will build a deck on. Sitting directly on the torch on will be a 2X4 base/ frame sitting on their narrow (2") side. I will screw the deck boards to this frame. I would like to glue something on the bottom of the 2X4's that would compress at the high spots where the torch on is overlapped to distribute the weight across the whole roof instead of just the higher overlapping seams. I was thinking about Styrofoam insulation, maybe 1/4 or 1/2 inch thick. What do you suggest? Is there a better option than Styrofoam or a better idea altogether? Thank you for any help you can give me.
I would rule out styrofoam. The stuff that would generally be available to you is not a load bearing material; it will just degrade and fall apart. I would get some scrap torch down from a local roofing company, and lay strips in the low areas; you are not going to get perfect 100% contact for bearing purposes.
Just a couple of thoughts:
Is the existing framing sufficient to hold the additional weight of the additional decking plus people and their activities?
Be sure to frame the new deck joists perpendicular to the existing roof joists so you don't end up with the deck supports just sitting on the roof decking, in between joists.
If there are any trees around, consider how you are going to keep the area under the deck clean..debris will collect under there.