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冰和水上屏蔽和闭孔泡沫,用于未通风的屋顶?

B B|Posted inEnergy Efficiency and Durabilityon

I’m looking to add exterior insulation to a low-slope wood decking (2×6 T&G) roof.

I have come across details that use rigid foam, but the builder would like to use a purlin system to create a cavity for closed cell spray. My question is, if we go that route, would I still want a peel & stick air-barrier applied to exterior of decking and interior of the purlin/spray foam layer if the closed cell will act like an air barrier.

奖励问题,是否应该隔离屋檐以减少冰块?

预先感谢。

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答复

  1. Eric Padgett||#1

    你住在哪里?purlin有多深?泡沫将有多深?

  2. 专家成员
    达娜·多塞特(Dana Dorsett)||#2

    pur蛋白的热桥梁削弱了闭孔泡沫的热性能。purlin间距更宽,表演命中率就会越大。喷涂的闭孔聚氨酯也具有相当大的环境足迹,如果它被HFC245FA吹来,则更糟的是(行业标准),尽管现在有一些HFO1234ZE吹出的闭合式聚氨酯,但您必须狩猎。(也有点贵。)

    不被低r purlins打断的连续的RGID泡沫层不会受到性能的打击。2磅2磅屋顶polyiso(以低冲击力爆炸)的6.5-7英寸,即使仅是R38-R40,也会达到IRC Code-Max U0.026 U0.026 U-Extor,并且在降低冰坝的潜力方面会比Purlins之间的R49更好。将2x4 Purlins放在固定的屋顶泡沫上,穿过after绕的架子,需要一些很长的螺钉。

    根据气候区的不同,您可能可以将差异分开,将5.5英寸的开放式泡沫(用水吹,只有R20的聚合物量的一半),屋顶上方的刚性泡沫为3-4英寸甲板或其一些变化,更容易且便宜地组装。外部R与总R的比率对于保持结构屋顶干燥很重要,但是该比率是气候依赖性的,那么,您的气候区是什么?

  3. B B||#3

    抱歉,气候区为5B,计划是使用2x6 Purlins。我还应该提到这是现有的屋顶。

    我了解有关热桥梁的观点。它是柱子和横梁的结构,所以我也一直担心桥梁尾巴和屋顶甲板延伸为拱腹和屋檐。这是一种eichler型设计,因此有一种保持“外观”的愿望。

    Best case is that we'd limit the system to one material (vs. a rigid - spray combo or sim.) and roughly the same depth (~5-1/2"). That said, a big concern with this is where to place the barrier/membrane.

    再次感谢。

  4. GBA编辑
    Martin Holladay||#4

    B.B.,
    现有木板上的冰和水盾牌将充当空气屏障,这是一个好主意。它将提供保险,防止由于安装程序错误而导致purlins和喷雾泡沫之间可能泄漏的空气。

    我和黛娜,尽管——r的连续层igid foam is a better solution in all respects. If you go that route, you should simply extend the rigid foam over the overhangs -- the easiest way to proceed. If you use rigid foam, the Ice & Water Shield is still a good idea.

    有关更多信息,请参阅如何在屋顶护套顶部安装刚性泡沫

  5. 专家成员
    达娜·多塞特(Dana Dorsett)||#5

    在第5区中,IRC处方剂在纤维绝缘的外部(或屋顶甲板,如果泡沫都在屋顶甲板上方)中,将最低R49代码中的R20提示为R20。%。

    The 2x6 rafters can be insulated to ~ R22-R23 with rock wool batts or high density blown fiberglass, so it would take another R26-R27 above the roof deck to hit code minimum on an R value basis. It can be a bit less to be compliant on a U-factor basis (based on stackup and actual thermal bridging of the framing factor) if the foam is a continuous layer thermally breaking the rafters, and not thermally bridged by purlins. That's do-able with 5" of rigid polyisocyanurate.

    用连续的polyiso层(无纤维绝缘)完成所有操作,大约需要7英寸。

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