Vapor permeable membrane underneath insultaed nailbase?
We have a Cape-Cod-style late-’30’s brick house (unvented, multi-gable roof) with a finished second floor and the only roof insulation is the original between the rafters, now thin and ineffective. Climate zone 4 (Maryland). The house feels very chilly in the winter. It’s time to get the asphalt shingle roof replaced, so we’d like to have someone remove the existing shingles, install 4″ insulated nailbase over the existing plank roof deck, then new shingles over that along with new fascia trim and all the other detailing that has to be done when you raise the roof 4″. After we recover from this project :), we may or may not get dense-pack cellulose installed between the 6″ rafters, behind the plaster and in the unfinished area behind the knee walls. I have two questions:
1.烫发/蒸气障碍：我有一个建筑师的基本图形和承包商的估计 - 建筑师和承包商在另一家房子上做了类似的工作，所以我们正在使用类似的范围。在那份工作中，承包商在护套上安装了Solitex Mento 3000，用Vana胶带拿着接缝和边缘，然后ZIP-R面板（带接缝录音），然后底层和沥青屋顶（我让他安装绝缘钉子代替ZIP-R，没有批准屋顶）。MY QUESTION: I understand why he might want to use the Mento 3000 vapor-open air barrier on the roof deck – because vapor goes from warm to cold and we don’t want condensation to form on the inside of the roof deck but instead to dry to the outside, but the asphalt shingles are vaporimpermeable，所以没有在屋顶甲板上安装蒸汽渗透膜，产生了一个风险，我们将捕获屋顶甲板和带状疱疹之间的蒸汽（即在钉子的多部异落中）？
2. My stepson, who’s a contractor, keeps telling me that the estimate from the contractor we have been talking to is very high, but that contractor is the only contractor I can find who’s willing do the job – the commercial roofers who work with insulated nailbase on flat roofs don’t want a job as small as ours (and may not be able to do the finish work that goes with changing the roof plane on a sloped roof); the residential roofers generally have no idea what I’m talking about; and the job is too small for the remodeling contractors we’ve spoken to. My husband doesn’t want to go forward without another estimate. We are in the Washington DC/Maryland/Virginia area. ANY RECOMMENDATIONS?
Rebecca
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Replies
The insulation on top of the roof deck keeps it warm enough that vapor cannot adsorb into the wood. (It dries to the inside only). Long before the insulation takes on moisture the nailbase OSB will turn to mush (It gets wet from rainwater, not interior seasonal moisture drives). Any drying to the exterior for the nailbase deck is through the shingles. There is very limited drying through the shingles.
我认为承包商喜欢Mento膜，比剥皮棒更舒适。也许它较便宜。在任何情况下，您需要钉子下方的空气屏障，因为它们带来了一些空气泄漏诱导腐烂的风险。Mento将提供一个空中障碍。
You might be able to get a lower bid using reclaimed foam and the method Akos describes in this thread://m.etiketa4.com/question/add-rigid-foam-above-the-deck-on-re-roof-tg-roof-deck-is-ceiling-no-attic-exposed-rafters
这一切都说，我会有关于承包商的保留，该承包商已经违反了制造商的指示。
Thank you, Bryan! Understand now that there will be no condensation on the exterior of the roof deck planks because the insulation will keep the planks warm. Thanks for referring me to the tongue-and-groove thread - very helpful, and I would never have found it otherwise using the search terms I was using.