Title: Need advice on replacing an old leaky roof
Funny timing—I’ve run into the same dilemma with a 1920s bungalow last year. The rafters were shallow, so vent channels weren’t really an option unless we wanted to lose even more headroom. We ended up going unvented with a full layer of closed-cell, but I still worry about long-term drying potential, especially if there’s ever a roof leak. Anyone using smart vapor retarders in these situations? I haven’t tried that combo yet, but I keep hearing mixed things about it in older assemblies...
We ended up going unvented with a full layer of closed-cell, but I still worry about long-term drying potential, especially if there’s ever a roof leak. Anyone using smart vapor retarders in these situations?
That’s the million-dollar question with these old houses, isn’t it? I’ve seen a few projects where folks tried to split the difference—closed-cell for R-value and air seal, then a smart vapor retarder like Intello or MemBrain under the drywall. The theory is that it’ll let the assembly dry to the inside if it ever gets wet, but only when it needs to. In practice, though, I’ve noticed it’s a bit of a gamble, especially in older homes where you never quite know what’s lurking behind the plaster.
One thing I’ve always wondered: how much do we trust those “smart” membranes to actually respond fast enough if there’s a real leak? I mean, they’re clever, but water can be sneakier than we give it credit for. I’ve seen a couple of cases where the assembly still got musty after a minor flashing failure, even with a vapor-smart layer. Maybe that’s just bad luck or maybe it’s the unpredictability of 100-year-old wood.
Losing headroom is such a pain in these bungalows. I get why venting isn’t appealing. But sometimes I wonder if we’re trading one problem for another by going unvented and relying on chemistry and hope. If you do go with a smart retarder, I’d say make sure every other detail is bulletproof—flashing, roof membrane, all of it. Otherwise, you’re just giving yourself something new to worry about at 3am.
I’m still waiting for someone to invent a foolproof “old house roof” solution that doesn’t involve time travel or magic. Until then, it feels like we’re all just picking our favorite risk and crossing our fingers...
But sometimes I wonder if we’re trading one problem for another by going unvented and relying on chemistry and hope.
You’re not alone there. I’ve seen a lot of people wrestle with this, especially when you’re trying to preserve every inch of headroom. Honestly, your approach makes sense given the constraints. As long as you’re meticulous about the details—especially flashing and penetrations—you’re stacking the odds in your favor. There’s always some risk, but with older houses it’s more about managing it than eliminating it. You’re thinking it through the right way.
There’s always some risk, but with older houses it’s more about managing it than eliminating it.
That’s the part that always gets me. I’ve seen too many projects where folks go all-in on spray foam or unvented assemblies, thinking it’s a silver bullet, and then end up with weird moisture issues down the line. If you’re set on unvented, I’d double-check every transition—roof-to-wall, skylights, chimneys. Even a tiny miss can cause headaches later. Sometimes I wonder if a little extra headroom is worth the long-term gamble, but I get why you’d want to keep it. Just don’t skip the details... they matter more than the product sometimes.
Honestly, I keep circling back to the same thing—details, details, details. I’ve toured a few high-end remodels where they used top-tier spray foam, but you could still spot subtle moisture stains near the valleys or around a dormer. Makes me wonder: is it ever really possible to get every transition perfect, especially with older framing that’s not exactly square? I get the appeal of more headroom and “modern” assemblies, but sometimes I think a well-detailed vented roof is just less stress in the long run. Anyone else notice that unvented seems to come with more maintenance anxiety?