Zone 4 unvented cathedral retrofit challenge – 2″ closed-cell spray foam + open-cell fill?
大家好，尤其是达娜和马丁
我希望确认我的屋顶组装计划基于阅读和重新阅读过去几年的所有问答线程，与挑战性的复古构成以及无通风屋顶的技术和经济限制有关。
Roof / Rafter / Insulation Retrofit Details
- 区域：4 - 在北卡罗来纳州罗利市
- 当前的after：2×6 @ 16英寸O.C.
– Roof Deck: 1/2″ Plywood
– Roof Covering: GAG 50 Year Architectural Shingles
- 结构增强要求：我们被迫用2×8的afterters加倍 /姐妹，将after骨的腔缩短到只有14.5英寸
Assembly Plan
After we install the new 2×8 “sistered” rafters, we will have significant rafter “mass” and just 14.5″ of rafter space to fill. Given the shingles are brand new, we are not looking to tear the roof off and apply nail base to the top side of the roof. Instead, our design goal is to do everything “under roof”.
所以..我目前的计划是执行以下操作：
1-Spray 2″ of HFO (LAPOLLA 4G closed-cell spray foam) on the underside of the roof deck to seal and still allow for modest drying to the interior.
2-Tack/Glue 1″ of Poly to the bottom edge of the new 2×8’s to reduce thermal bridging.
3-Fill the remaining rafter cavity space with Open Cell Foam, being careful to fill the cavity as close to the outer edge of the poly strips that are attached to the bottom side of the 2×8 rafters.. Also making sure that the Open Cell foam covers the bottom of the existing 2×6 rafters to reduce bridging and “seal” the space between the two sandwiched rafters.
OK guys, hoping to hear back on whether I’m on the right track, or if there are adjustments you might suggest.
谢谢！
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Replies
By "...being forced to double / sister ALL rafters with 2×8’s..." is that for structural reasons? Even with some polyiso edge strips for mitigation doubling the framing fraction is going to take a thermal hit. (BTW: That reduces the cavity width to 13" , not 14.5".)
代替了2x8的姐姐，您能从中脱颖而出吗？在中心粘合并钉在和弦上的中心上使用2x2和弦和半英寸6“ x 6”胶合板斗式胶合板24英寸。安装3/4”边缘在2x6s（或和弦）上填充2x2和弦之间的空间2x6，然后将毛刺粘合到2x6。这将是与2x8相同的7.25英寸总深度，几乎一样强。如果您要用1英寸的边缘将其提高到8.25％，请使用2“ Polyiso代替3/4”。
不幸的是，我们正在将棍棒桁架转换为真正的大教堂，一旦我们卸下底部和弦，我们就使用钢绳将两堵墙放在一起。因此，是的，不幸的是，2x8姐妹的after是结构性POV的要求。
With R14 of closed cell foam you're good for about R28 of fiber or open cell foam insulation from a dew point perspective. If you're at 8.25" total depth (2x8 + 1" polyiso) that leaves 6.25" of space to fill.
R28/6.25 = R4.5/英寸。
Half pound foam is only R3.7/inch, so at 6.25" would deliver ~R23 for R37 total. Open cell 0.7 lb foam is about R4/inch, or about R25. for R39 total, which is better.
But with polyiso on the rafter edges you won't be able to trim the open cell foam flush using the normal tools without scarring up the polyiso.
在这种情况下，雕刻了一个为2x8设计的R30摇滚羊毛巴特，但从其7.25英寸制造的阁楼压缩到6.25英寸，将提供大约R27，从露点控制角度来看，这仍然很好，您的总计为R41。
潮湿的1.8磅JM蜘蛛将提供约R26，总计R40。这可能是您最好的选择，因为它可以在不压碎Polyiso的情况下将其滚动，并且可以提供完整的填充。其他1.8磅的玻璃纤维（Optima，L77等）必须在网上爆炸，为该过程增加一个额外的步骤。
为了坚持开放的单元格概念，在边缘带polyiso（bonfiglioli条样式）上使用1倍毛茸茸的概念将增加大约R3的开放式单元格数，并且会忍受滥用泡沫修剪的滥用。在7.0英寸的总深度为0.7磅的泡沫将提供R28，从水分积累风险的角度来看，这仍然可以 - 它不会陷入所有开放式溶液中有时会发生的湿度乒乓球情况。
Dana, this is amazing and gives me several options to explore... Most importantly, it sounds like my plan for 2" inches of HFO closed cell foam plus the right compliment to fill the cavities keeps me out of harms way from a moisture pov.
删除d
我找到了您的毛茸茸的设计参考！对于其他人来说，可以在这里找到这种用于绝缘泡沫的毛茸茸的风格：
https://www.finehomebuilding.com/membership/pdf/9750/021250059.pdf
I apologize for not linking to that useful detail document- I usually do when mentioning Bonfiglioli by name. Glad you managed to find it without me!