没有内饰的大教堂天花板与室内刚性泡沫
I have a Cape cod style house. The upstairs is completely gutted and will be finished as unvented cathederal ceilings. The roof rafters are 2x6s with some 2x8s on a big dormer. I was planning to open cell foam all cavities and add 2 layers of rigid foam under the rafters with offset taped seams. ( 4″ total under 2x6s and 2″ total under 2x8s) Spray foaming any gaps. Then use furring strips and drywall. Does this seem ok? Would untrimmed closed cell foam be better? But it would leave air pockets.
I was planning the same thing for the 2×4 walls with 1″ of interior rigid foam.
Thanks
约翰拉
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答复
约翰，几个问题：你在哪个气候区？为什么你想要一个不经常的屋顶？为什么在椽子腔内泡沫而不是具有较低体现的能量的绝缘？
我在费城。房子没有屋檐有效的屋顶通风。带状疱疹只有5岁，形状良好。我对泡沫的思想是它会很好地封锁空气。
约翰拉
在我看来，不经过者的大教堂天花板是一个冒险的大会。您添加更危险的绝缘度越多。
You may want to take a look this on Martins blog
//m.etiketa4.com/article/summertime-condensation-near-peak-cathedral-ceiling
沃尔塔
Thanks. The bottom 2/3's of the roof sheathing has been an unvented roof using fiberglass insulation since 1951. Luckly without rot. I have no ability to vent it from below the sheathing (no eaves). I am trying to make things better. The roof is just 5 years old so venting from the top is not on the table either. Yes I plan to eliminate the venting on the top third if the roof as well.
So the question is untrimmed closed cell foam, air gap & polyiso sheets inside or trimmed open cell foam, no airgap & polyiso sheets inside?
Closed cell is more traditional for this but what about the airgap and polyiso? Also should the polyiso not be foil faced so some drying could slowly take place?
Jtrhodes, having the attic open (and likely vented at the gables?) makes a big difference on how roofs like yours perform. That said, while open cell foam meets IRC code language in this application, because it's air-impermeable, it is open to water vapor movement, so there is some risk of moisture accumulating at the sheathing. Closed cell foam would be a safer option. It would also be smart to allow drying to the interior; in fac, using your proposed assembly, I would not use polyiso at all, but either EPS or mineral wool board stock at the interior.
我的方法将是椽子下来，悬挂2x2s或2x3s从胶合板胶浆，营造一个热破碎的组件，并安装更深层的闭孔泡沫层。如果您使用幸福的泡沫，您应该因为吹吹剂而不是常规泡沫的损坏，您可以获得8“（R-49，在您的4A区域中的代码中的代码为新建筑）通过。
Why no polyiso? Based on space I would loose about r12.
Thanks
约翰拉
Because most polyiso is not vapor permeable, you'd have a void that could collect moisture, and screwing through multiple layers of foam into framing is not always easy. But if you get fiber-faced polyiso, you would have some drying to the interior, so it would probably be fine.
得到它没有粘面的聚四亚。
Thanks
Consider some closed cell spray foam and fiberglass fill.
Jon, that's a great idea, and one I should have thought to mention as well. In zone 4A he would only need 31% of the R-value to be in the closed cell foam layer, with a minimum of R-15 to meet IRC codes. Cellulose or open-cell foam could also be used on the interior portion.
John did you read Martin’s blog?
笔记every valid email address gets 1 free 10 day membership.
It is the stories of 6 people that had working unvented cathedral ceilings who made well meaning changes. All 6 homes are now moldy messes that drip water with no clear solutions.
沃尔塔
Yes I just read it. Air leaks and not having stratified indoor air seem important.
沃尔特Ahlgrim，
这是第二个博客发布了通讯ents that imply that my article about summertime condensation is some type of warning against unvented roof assemblies. It isn't. You are misrepresenting the content of my most recent article.
Unvented roof assemblies can be detailed well, and often are. A well-detailed unvented roof assembly will be problem-free.
My most recent article ("Summertime Condensation Near the Peak of a Cathedral Ceiling") has nothing to do with the performance of unvented roof assemblies. It has to do with a building science mystery reported by 6 GBA readers.
有关不经过屋顶组件的良好细节的更多信息，请参阅这两个文章：
“如何建立绝缘大教堂天花板”
"How to Install Rigid Foam On Top of Roof Sheathing"
In zone 4A it only takes 1-2" of closed cell foam to protect the roof deck, but you don't want to create a moisture trap. With ~0.1 perm asphalt shingle layup and 2" of interior side foam board you'd have to use unfaced EPS (~1-1.5 perms @ 2") to have a reasonable drying path. Even fiber-faced polyiso would be under 1 perm.
With 2" of HFO blown closed cell foam in the 2x6 cavities you'd have R14 foam, and 3.5" of space for R15 rock wool (recommended), and with 2" of unfaced Type-II EPS it would come to R8.4 for the foam layer for R37-38 t0tal, and more that 35% of that total as closed cell foam.
2”的HFC吹泡沫细胞(不是recomme关闭nded for environmental reasons) it would come to R35-R36 total, with about 33% being the closed cell foam.
On the 2x8s use 2" of closed cell foam and compressed R20-R21 fiberglass (which performs at R19-R20 when compressed to 5-1/4"). With HFC blown closed cell would have R40-R41 with a 30% closed cell foam ratio, with HFO blown it would be R42-R43 and a 32% ratio.
I had planned to shoot for r45-r60. Either 5" or 7" of closed cell in the rafter bays 2x6 or 2x8s leaving only a small air gap. Then 2" of reclaimed foam on the 2x8 and 4" on the 2x6s. Trimming closed cell flush is difficult but the air gap should only be 1/4" to 1/2" thick. At that thickness not sure if any foam is permeable. Should I not shoot for that r value?
任何气隙都是潜在的热旁路和湿气转移路径，甚至是1/4“。最好安装更少的闭合电池，以便使用纤维绝缘或可调式开放式电池泡沫完全填充。
这种高中心腔的R值是什么？（吹牛权限？）7“HFO吹泡沫已经是R49，在5”它的R35，但是当安装在框架之间，它的高R /英寸性能受到基本上更低的R /英寸框架的严重削弱。连续刚性泡沫的2“对于净热性能，比仅与2英寸相比的差异更高。封闭电池泡沫的完全腔填充。在r值范围内，这种高能量使用差异有些“噪声”，它不一定是“值得”的生命周期能源成本基础，远远高于Code-min U0.026，这是R38.5“整个组装-R”。在每平方英尺每平方英尺小于5美分的纤维绝缘，纤维绝缘，纤维绝缘较高的易金融合理，在18-22美分/脚/脚下^ 2美分的封闭细胞泡沫中，纤维绝缘高或略高于5美分。
Even at 7" closed cell foam is still a class-II vapor retarder, but it's at the very vapor tight end of the Class-II range. At 2" it's typically between 0.5-1 perm (depending on vendor), which is still an adequate drying path. Even if it needs to bump to 3" for dew point control it's still a seasonal drying path, not a moisture trap.
Closed cell foam is not a very "green" insulation material, even when blown with relatively benign HFO blowing agents. An inch of closed cell foam uses 4x as much polymer per inch of depth, and about 2x as much polymer per R, and it's quite expensive. Anything more than the minimum needed for dew point control is really something of a waste, since it's effect on the "whole-assembly-R" performance is small compared to just adding another half-inch to inch of continuous foam on the interior.
在内部的回收泡沫肯定是更环保的。但坚持回收的EPS，而不是Polyiso，而不是XPS。大多数回收的屋顶EPS是类型 - VIII（每立方英尺的1.25磅，标称密度），并且仍然是〜1-PERM或更均匀的甚至3“，这足以保持纤维绝缘或开放式电池泡沫在/靠近喷射的闭孔泡沫的边界。在2“2”2LB密度屋顶Polyiso即使您戏弄剥离了脸部但是，只有在较高的R上有足够的闭孔喷射泡沫，只有露点控制。
Thanks. I was reading on new construction r60. Maybe I misunderstood. So how about this:
3“闭孔泡沫（r值的45/48％）
用纤维玻璃R8填充休息（r值的17/32％）
2 or 4" of eps r8 or r16 (20/37% of r value)
So r40 to r43 for roof.
一些地区我不能得到泡沫板的东西只会获得喷雾泡沫。
更好的？
With 3" of HFO blown 2lb foam you're at ~R21.
然后是2.5“的1.8LB玻璃纤维或压缩R15（2 x 6例）是另一个R11 ......
...or 4.25" (the 2x8 case) would be R18.
Add to that 2" of Type VIII EPS for R8.3.
That makes the 2x6 case ~R40-R41 at center cavity, 51% of which is the closed cell spray foam...
...or R48-R49 (= IRC code-min for zone 4A) for the 2x8 case, 44% of which is the closed cell foam.
Using HFC blown foam it knocks R2-R3 off the totals, but there is still a lot of dew point margin.
Looks like a very moisture safe (if expensive) stackup.
From a financial rationality point of view, take a look at the "Compact Roof" column of the zone 4 row of Table 2 on p.10 of this document:
https://buildingscience.com/sites/default/files/migrate/pdf/ba-1005_high%20r-value_walls_case_study.pdf.
注意，这些是“整个装配r”数字不是中心腔r，但它也只是作为新施工的成本效益点的起点，而不是改造。
The R45 whole-assembly starting point is more expensive to do as a retrofit than new construcion, since in new construction there is no need to use closed cell spray foam (at twice the cost per R-foot^2 of EPS or polyiso). Just 3" of HFO blown foam would run about 22 cents per R-foot^2, so that R21 is cost at least $4 per square foot, whereas even an R21 polyiso nailbase panel would be both somewhat cheaper & higher performance, since it would thermally break the rafters. Combined with a 2x10 rafters w/ R30 batts it would come in north of the recommended R45 whole-assembly-R for less money than what you will be spending doing a retrofit.
Thanks for all the help. I appreciate it.