跳过护套上的闭孔？
Please excuse the blurry photo. What it shows is 1×6 skip sheathing over 2×4 rafters. There is asphalt felt over the skip, and a snap-lock metal roof over that.
所有者（地方政府实体）希望将此阁楼转换为条件空间，并要求对一个项目的报价，其中包括在此屋顶甲板下喷洒闭孔泡沫。
I’ve only had ccspf sprayed under solid plywood sheathing. Seems like in this case, if they do it, the foam will be partly adhered to the felt (to the extend that it adheres) and the rest to solid wood that will shrink and swell daily as the sun hits the roof and then later goes down.
你说什么？
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David, I think your concerns are bang on. In addition to the problems you've described, neither of the two metal roofing suppliers I use allow asphalt paper as an underlayment because it heats and adheres to the roofing, then tears. So you will have discontinuous foam as an underlayment with pieces of building paper attached to the surface. Not a good idea.
Might be a good idea to use rigid foam to create your conditioned attic instead. Make sure to tape the seams. If they're insistent on ccspf no matter what, you could provide a continuous spraying surface for the foam by adhering plywood or sheets of foam to the boards, and then apply spray foam over that.
Skip sheathing does not present more stress to the foam bond due to different coefficients of expansion any more than continuous OSB/plywood does. If anything, it allows slightly more mechanical compliance/flex to occur. The fact that the ccSPF is also bonded to the 3/4" deep sides of the sheathing gives it a great deal of flex. Starting at ~3-4" of depth the foam itself begins to become as structural as the sheathing. This would only be a potential problem if the foam was thinner than 2" and even then the potential that the foam would crack or break is low IMHO.
The strength of the bonding to the felt is of no consequence, since the felt isn't structural. But if there is no slip-surface material between the felt & metal roofing, you still have the compatibility issue Malcolm Taylor describes, where the felt gets degraded by bonding to the metal. The foam won't aggravate that problem, but it's probably not going to mitigate it either.
马尔科姆你教了我一些东西。尽管如此，在这里铺设了成千上万的金属屋顶。我一年前做过，我认为一切都很好。没有电话，当我开车去时，屋顶仍然没有改变。到目前为止，我在我的几十年中只目睹了一个木瓦屋顶，二十年前的屋顶材料在我所在的地区很可怕。玻璃纤维带状裂片破裂了五年，沥青带状疱疹刚刚消失了十到十五。毛毡节省了玻璃纤维，对沥青没有帮助。那时，一个广场的价格为30美元，今天我们称其为150美元，用于完整的“系统”。现在的终身保修。...拉丁美洲人现在都做所有的屋顶。
The specs for metal roofing systems almost always call for a slip-surface type underlayment, since temperature coefficients of expansion of metals are so different from wood. i don't know how long it takes for the felt to fail, or how long it would take for the failure to be detected, but it's probably worth doing it to spec using the manufacturer's specified underlayment. I don't get to watch enough metal roofing installation to say just how often they do something else in my area.
Local roofers install Kynar-painted metal roofing over 30# felt here, no bond breaker of any kind, and it doesn't stick to the felt. Metal roofing is always slightly oil-canned and I bet it's not quite in contact with the felt for the most part. I have unsnapped and peeled back metal roofing many times to do repairs, build additions, add skylights, etc., and none of it has ever been glued to the felt.
大卫，我敢打赌这完全是气候的问题。您和我在PNW工作的工作不会使我们的屋顶表面足够热，以使纸张中的沥青降解。我的屋顶供应商为整个加拿大西部提供服务，并没有改变他们的规格。