Foam sheathing eliminates the need for house wrap on a wall, which is great because that stuff costs a hundred bucks a roll. But without it, you can no longer tuck the head flashing underneath for a positive lap. Peel and stick membrane is a good option, but if you want a mechanical lap, rather than relying on adhesive (let's fact it, job sites are dirty and dirt is the enemy of adhesives) then you can inset a counter flashing into the foam.

For more on window installations done right, go to http://www.greenbuildingadvisor.com/v...