Ah, vapor barriers! I remember the first time I decided to try and make a house as airtight as I could. "We'll just run poly continuously over the inside of the outside walls and across the ceiling. That way we'll get a vapor barrier and an air barrier," I thought. So simple in concept, such a pain in practice. How do you get it on top of load-bearing walls, through the joists of a cantilevered overhang or the second floor of a Cape Cod? Or through the intersection of an interior partition and an exterior wall? What about recessed lights? On those first houses I used a lot of caulk. Cases of caulk. And even then
