I landed an unbelievable deal on Polyiso unfaced insulation.  Figure about $1 per 1" thick 4' x 8' sheet.  I am looking on doing as many energy ugrades to my house as possible myself, but I am getting a bit lost on some of the information that I have been reading.  I want to adapt methods to utilize the polyiso in as many applications as possible.  Here is a list of locations i would like to be able to use the foam

1 Sealing rim joists (vapor barrier?)

2 Exterior under siding (vapor barrier?)

3 basement walls (unsure about below grade applications)

4 attic (have plywood down now for storage and intend to lay foam over plywood and tape seams) there is not supposed to be a vapor barrier in the attic is it ok to use this method?

I understand the Polyiso can absorb water.  Do you think covering the board in roofing or foundation tar would be effective?  I know these ideas seem unorthodox, but considering the deal I got I feel the extra effort is worth it

Just curious - where does one find deals like that?

craigslist. got 10 pallets 8' high for $600. It is all used, but that doesn't bother me. I was never the guy to be the one to get the great deals, but I had been on top of craigslist lately and I knew the value of insulation