热桥solutions when closed-cell foam is used?
What is the best way to handle the thermal bridging of the wood framing of my house — recognizing that some closed cell foam is specified for the wall cavities? We are constructing a house in climate zone 5 with 2×6 studs using the “hybrid wall assembly” as defined by Joe Lstiburek in his article “Hybrid Attics and Hybrid Walls.” I have seen no comments about managing thermal bridging using this type of wall system.
从内而外，我们墙壁的细节是：石膏板；R-11未透明的巴特绝缘材料；2英寸的闭孔泡沫绝缘；1/2“胶合板护套；WRB/空气屏障（例如亨利·布鲁斯金）；乙烯基壁板。
我们将在墙壁腔内有闭孔泡沫，这将不允许向内干燥。As a result, we cannot heed the advise (from “Can Exterior Foam Insulation Cause Mold and Moisture Problems?” and other articles) to use an adequate amount of external rigid foam insulation (approx. a minimum of 30% of the wall’s R value for zone 5) to keep the sheathing warm, because houses with excellent external insulation also must allow the sheathing to dry to the inside of the house.
Is there a product (presumably with high permeance) that could be used on the exterior that breaks the thermal bridging for both the studs and rim joists? If not, should we apply strips of foam to the interior sides of just the studs to minimize whatever thermal bridging we can?
还是我们应该忍受热桥梁 - 因为外部泡沫太少比没有外部泡沫还要糟糕，而我们可能会做的其他任何事情可能只是在其他地方造成意想不到的后果？
框架可能在下周开始。正如我在许多问题中读到的那样：“我可能应该在几个月前问……”
非常感谢您的想法，评论和建议。
Thanks! ~ Judy
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答复
朱迪，
你可以安装矿棉的连续层insulation on the exterior side of your wall sheathing if you want. Here are links to articles that describe this approach:
“在外墙护套上安装矿物羊毛绝缘””
"Installing Roxul Mineral Wool on Exterior Walls"
“用岩石丝绒包裹旧房子”
矿物质羊毛比刚性泡沫更具蒸气性，因此，连续的外部矿物羊毛层仍然可以使墙壁护套向外干燥。
如果下周开始框架，那么选择墙壁隔热细节就有点晚了。您可能想阅读本文：“提前计划进行绝缘。”
顺便说一句，您选择的绝缘方法的类型通常称为“闪光和棒”。在我关于Flash and Batt的文章, I wrote, "The flash-and-batt approach doesn’t address thermal bridging through studs or rafters. While the nominal R-value of a flash-and-batt 2x6 wall with 2 inches of spray foam is R-25, the actual whole-wall R-value (after taking thermal bridging into account) is only R-17. Because of the thermal bridging problem, many insulation experts say that the flash-and-batt approach is a waste of good foam. In most cases, builders will get a bigger bang for their buck by installing a continuous layer of exterior rigid foam than by installing a thin layer of spray foam between the studs."
有关此主题的更多信息，请参阅“如何设计墙。”
谢谢！我会阅读！
在2英寸最闭合的电池泡沫仍位于0.5 Perms的北部，这是II类蒸气延迟器，仍然可以朝内部干燥。外部没有任何蒸气延迟器，因此它也可以很容易地干燥。固有的后倾斜乙烯基壁板的外部。在区域5中，乙烯基壁板将从干燥的角度符合代码，仅在内部使用III级蒸气延迟器（标准乳胶涂料）。
为什么低密度R11（不是很阻止空气）而不是R13或R15？
2英寸闭孔泡沫的目的是什么？
您将获得与使用R23摇滚羊毛或密集的玻璃纤维的R11玻璃纤维 + R12闭孔泡沫相同的热性能（和更好的干燥），或者全腔密度为0.7lb密度开放的细胞泡沫。
At the same wall thickness as a 2x6 studwall, dropping back to 2x4 studs and installing 1.5" wide strips of 2" thick Huber ZIP-R on the interior side of the stud edges would add R9.6 of thermal break to the framing fraction and provide a half-inch OSB nailer for hanging the wallboard.
http://www.huberwood.com/assets/user/library/zip_system_r-sheathing_-_product_data_sheet_（r3-12)_v12.pdf
This is similar to using 1.5" foam board Bonfigilioni strips as the thermal break:
https://www.finehomebuilding.com/membership/pdf/9750/021250059.pdf
Taking the Bonfiglioni approach with 1x furring the total wall thickness would be 1/4" deeper than with a standard 2x4, so you'd be looking at 5.75" cavities, not 5.5" as with a standard milled 2x6. But if you're filling it with open cell foam 1/4" of depth isn't a problem, whereas with batts designed for 5.5" cavities it can leave voids. At 5.75" half-pound open cell foam would run about R21, 0.7lbs goods would be R23. A full cavity fill of half-pound foam would cost about as much as the 2" of closed cell foam you were specifying. You would be slightly lower-R at center cavity than your R11 + 2" closed cell foam cavity fill, but with 1.5" foam the framing fraction's R would be roughly doubled.
With the faster drying toward the exterior due to the back ventilated vinyl siding, in zone 5 you would not need any sort of interior side vapor retarder.
另请注意，5.75英寸的半磅开放式细胞泡沫使用的聚合物比2英寸的闭孔泡沫（甚至5.75”的0.7磅泡沫的聚合物使用的聚合物的使用少于2英寸的闭孔泡沫。但是开放的细胞泡沫被水而不是HFC245FA（强大的温室气体，〜1000x CO2）吹了，因此，即使是全部0.7磅的泡沫，也比HFC爆炸的闭孔泡沫更绿色。
At the high cost of rigid rock wool, if it's not possible to drop back to 2x4 framing at this point you can probably still thermally break the framing with interior Bonfiglioni strips with 1-1.5" foam and go with 7.75-8.25" of open cell foam, delivering higher thermal performance, higher resilience, and still cost less.
@Jon R.
覆层后面的1/2气隙不会纠正这种担忧吗？
I haven't seen any data that indicates that 1.5" of external unfaced EPS (perhaps 2 perms) isn't beneficial and less risky than foam strips on the interior side (ie, cold sheathing). It's easy to find evidence that too many external side perms (such as common WRBs with or without mineral wool insulation) can cause inward moisture drive problems (but perhaps only with moisture retentive sidings).
Yes, but it leaves the question of why pay more for high perm mineral wool if somewhat lower external perms (but > 1 (such as EPS) to allow outward drying) work better.
See below for some significant benefits to even 1" of foam and "The most important factor to observe is that adding exterior insulation benefits the wall insulation more significantly than optimizing the vapor permeance of the WRB...". Seems reasonable to lump foam/mineral wool perms with WRB perms.
https://buildingscience.com/sites/default/files/migrate/pdf/BA-1313_Moisture%20Durablity%20with%20Vapor%20Permeable%20Insulating%20Sheathing.pdf
Thank you, everyone, for your comments. Happily, it is not too late to change to 2x4 framing. I have been reading the links, and rethinking our strategy. The windows (for 2x6 studs) are already on site, but we can manage whatever the final decision is. I hear the message that open cell foam is better than closed cell foam. The BSC study indicates that one inch of external EPS may not create a "foam sandwich" because it has enough permeance to still dry to the exterior. I like the Bonfiglioli approach as an interior option. So we appear to have some options still available. Thank you all for your collective guidance.
Judy
朱迪，
笔记that if you go with the flash-and-batt approach, you'll have to use closed-cell spray foam, not open-cell spray foam. For a variety of reasons, open-cell spray foam isn't suitable for use with the flash-and-batt approach.
Of course, if you use a continuous layer of exterior rigid foam, you won't need any spray foam whatsoever.
At $2 per square foot for just the foam that 2" closed cell flash'n'batt really isn't "worth it". Spend the foam budget for the insulating sheathing instead, where you get the full R performance out of it.
在Zone 5 as little as 1.5" of foil faced polyiso (~ R10 ) is sufficient dew point control at the sheathing for up to R23 (rock wool batts- much cheaper than closed cell foam or rigid rock wool) in the cavities.
http://msdssearch.dow.com/PublishedLiteratureDOWCOM/dh_09ad/0901b803809ad9ca.pdf?filepath=styrofoam/pdfs/noreg/179-04015.pdf&fromPage=GetDoc
http://wall.atlasrwi.com/products/commercial/energyshield-pro/
借助箔脸的面孔，如果乙烯基壁板和闪亮的箔脸脸部之间没有空气，则可以从中获得额外的〜r1。