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Next question comes from Carolyn. Hi Steve, you recommended a membrane over 2x4 roofboards
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then install foam insulation, sheathing and other membrane material above the sheathing and under
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the shingles. Now she's taking my small cabin course, my cozy cabin course, and that's what
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she's talking about here. So we're talking about insulation that sits on top of the roof, not in an
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attic or underneath the rafters or anything, because the idea with this cabin design is that
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you can see the rafters, you can see the roofboards, it's a nice authentic cabin effect. So she's
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wondering about the roofing membrane that goes on top of the insulation and underneath the shingles
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And I think it should be waterproof, yes, but vapor permeable to prevent trapping moisture in the
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sheathing and the insulation. So by vapor permeable she means that water vapor can escape
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through the membrane. The very best house wraps are made this way, so they shed liquid water, but
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if by some chance, and it's a pretty good chance actually, eventually water might get behind, with
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conventional building wraps and membranes that water can't get out. So it's held there against
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whatever wood is underneath of it and it promotes rot and all kinds of nastiness. So permeable in
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this case means it can dry. Now the thing is in the case of this situation where we've got
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insulation, foam insulation, some more sheathing, and then on top some shingles or steel roof or
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something like that, there's really no advantage to going with the permeable in that case because
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everything above it and below it is impervious. It has to be. I mean shingles, you can't get a
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vapor permeable shingle. The kind of insulation I like to use, the foam insulation that I recommend
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in the course, is vapor impermeable as well. So there's no real advantage in this case and you
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can just go ahead. What I like to use in this situation isn't just a building wrap or something
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like that, but it's actual ice and water shield which is thick, self-sticking. It basically makes
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your roof waterproof before the shingles or the metal roof goes on at all. That's kind of my rule
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of thumb. No roof should rely only on the outer layer for waterproofness. You really do need to
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make it waterproof first because you never know when that roof's going to, when those shingles or
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metal roof are going to be torn off or damaged or something. You don't want to be open to the
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elements that way. So a good strong standalone membrane under those shingles are the way to go
