I'm considering buying a house built with 2x4 walls and fiberglass batts. I want to install XPS on the exterior walls to add "R" value to the walls and reduce thermal bridging. My question is - is it necessary to remove and reset all te windows and doors to accomodate the additional wall thickness or is there a way to NOT remove the windows and flash them so they don't leak? I need help on this one. Is there a construction detail I could use?