I  am open to ideas.  I have a customer that has an old block house built in the 50’s that wants it vinyl sided.  Not much insulation in the house. 2×2’s on the interior with minimal insulation (it looks like 1″ rock wool) between the furring.  It has plaster board on the inside, typical 7/8″ finish.  This is a new owner of the house and I told him now was the time to address more insulation for our cold Cleveland/Lake Erie climate.   I was planning on stripping the home with 2×3’s on the exterior with 1 1/2″ dow foam between the exterior furring and hanging siding directly over.  The house been well maintained and the paint is sound over the block. I am thinking of not having any air gap betweeen the block and the insulation panels.  Any warm air vapor would have to get past the rock wool’s sealed paper backing and through the well painted block before getting to the insulation board.  And the we are puttting vinyl over that.  Am I wrong for leaving out an air gap?  Thanks for your input.