I have two inches of pink foam insulation on the outside of my foundation. At the back of the house, it is covered by 5/8" pressure-treated plywood, and it is parged on the other three sides. I want to attach a deck to the house. Can a ledger board be lagged to the concrete through the plywood and foam, or will it sink if it is not tight against the concrete? What size of lag bolts (width/length) would be required and at what distance apart? I have poured concrete piers 10' out from the wall. Would floating in the end near the house be a better solution (Dek Blok or on skids/a wall of pressure treated lumber)?

The least expensive solution is to build a freestanding deck that is not attached to the house at all. I would not suggest using Dek Blok or skids - the deck may end up moving upwards in the winter months and dropping more than expected in the warmer months. Attempting to attach the deck to the house by using bolts through the insulation will likely crush the insulation and lose R-value. Also, the connection to the house would not be as sound as it would be if it was attached directly to the foundation. You may want to approach your local building department. They will more than likely have details on how to construct your deck, the required depths for the footings, as well as how to construct the hand railings and guards in accordance with the building code.