I am re-siding part of my house to deal with some rot and insect damage that, I believe, was caused by wind driven rain penetrating the original pine claps. I was taken by the article in Fine Homebuilding No. 213 about siding with a Vented Rain Screen. The twist I have is I want to take advantage of my state’s energy efficiency grants by improving the insulation on the walls and attic of this part of my house as well as replacing the windows. The energy auditor recomends applying 1″ of the foil covered XPS insulation on the outside walls over the sheathing (and foaming the attic to create a “hot roof”). I have two questions: (1) if I want to create a vented rain screen over the foam, will the foil backed XPS (will all seams taped) be a good enough water draining surface? and (2) what kind of details should I use at the window head to avoid water possibly running back into the house? A couple of things you should know about this project. The rot and insect damage was confined to the first floor. Because I didn’t want to disturb the inside very much, I removed the exterior board sheathing only where the damage was and sistered on new framing lumber where the wood was damaged. My house is ballon framed with solid blocking at the second floor so there was no need to fool around with the sheathing on the second floor. In order to help with the structure, I had closed cell foam sprayed from the outside on the first floor once the wall was open. The second floor walls still have the original board sheathing and are stuffed with some sort of insulation that I have not seen before – it is very dense but not foam. It feels like fiberglass, but is not the stuff that I remember installing when I was a carpenter in the 70’s and 80’s (this part of my house was built in the early 60’s when 2×4’s were 1 5/8 x 3 3/4). I am now a cabinetmaker and my builder buddies tell me I will get some condensation on the areas of my house that are not foamed and that this condensation will happen at the joint of the rigid foam and the bpard sheathing. They recommend house wrap on the exterior of the board sheathing applied before I put on the rigid foam board to give the water a good place to condence.  What do you all think?