排气屋顶腔？
For annoying reasons (drawings were wrong, framer didn’t catch in time), the roof on an addition we’re doing was built lower than it needed to be to line up with the soffits on the existing house. We decided the easiest solution would be to just build up a 6″ frame on top of the sheathed roofing so that the new higher roof would line up correctly. The original roof is still in place and has 6″ of open cell foam on the underside. The result is that we have a roughly 6″ dead space between the foamed, sheathed and papered original roof and the new sheathing. We’re putting a metal roof on. Question is, do we need to vent this space? I don’t believe there is an ice dam issue since the foam under the original sheathing is an air barrier, correct? Are there other issues that are requiring this area to be vented?
谢谢！
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答复
麦克风，
你现在在哪里？六英寸的开孔泡沫仅为R-22。那不多。
太糟糕了，您没有用6英寸的刚性泡沫而不是空的2x6 afters弹到屋顶。
In virginia- zone 4.
The SPFA has been telling us that we only need 6" OC in this region for a while now, and the local installers agree. Code officials usually allow it without question.
I thought about shimming it up with foam board but that was way too cost prohibitive.
谢谢你的帮助。
麦克风，
As far as I'm concerned, R-22 doesn't meet code. In case you want to learn more on the issue, here is a link to an article:It’s OK to Skimp On Insulation, Icynene Says.
代码官员允许这样做，只要我们可以展示通过它通过它的重新检查报告即可。通常使用右窗和其他空气密封时会这样做。
Any ideas on the issue of venting?
再次感谢。
它可能会根据Revecheck规则传递代码，但是R22中心腔屋顶仍然容易出现冰堵塞问题，即使很紧。
If the upper roof deck isn't installed yet it's worth putting unfaced R15 "cathedral ceiling" fiberglass or rock wool batts in there, with a vented 2" air gap between the batts & deck, or laying down another 3" of open cell foam, whichever is cheaper.
没有外部绝缘开孔R22 creates a wintertime moisture hazard for the original roof deck unless you installed an interior vapor retarder between 0.5-1 perms. If you went with interior poly it's a moisture TRAP, but if you leave it open the roof decking may develop issues over time (particularly on the north side.) See:
http://www.buildingscience.com/documents/reports/rr-1001-moisture-safe-unvented-wood-roof-systems
特别记下表3中第四列中的4个区域，标题为“完整深度OCSPF”。由于您甚至没有满足代码的深度，因此您在屋顶甲板上积累的水分比模拟的水分还要多。在屋顶甲板上方添加高密度纤维的R15将恢复安全余量。
是的，我知道，放入10.5英寸的开放单元比6英寸更可取，但是当您考虑额外的成本时，这不是一个选择。考虑因素是，使用6英寸的开放式泡沫（空气屏障），而不是r-36或吹进来。这使我们能够更好地保持。这使我们能够密封阁楼空间并将所有机械设备放在条件的密封空间中。
我同意文章的逻辑 - 更多更好。但是，本文并没有面对现实世界的问题 - 如果开放单元的R-22在现实世界测试下表现出令人满意的表现，那么它应该符合规定的代码。它不应仅仅因为它不符合任意R-38的数字而被视为“略读”。通过您的逻辑，如果明天将代码更改为R-60，我将仅使用R-38“脱脂”。
I remember seeing a study a few years ago that showed a cost-benefit analysis on spray foam depths, and it explained that every extra inch past a certain point was only very slightly better on performance. Meaning, 6 inches is not twice as effective as 3 inches and 12 inches is not twice as effective as 6 inches. I can't find it right now, but if my memory serves, it showed 6 inches as having maximum cost-effectiveness.
I think we need to get away from simplistic R-values and use what works, both for the scientist and for the consumer.
再次感谢您的帮助和洞察力。
Dana- thank you for your insight.
The sheathing is already on the second layer. Honestly, I'm really not concerned about the insulation depth. The article given here is again referring to the code, not the actual effectiveness. The SPFA has shown in their studies (supplied by Oak Ridge I believe) that 3.5" of most 1/2 pound oc foams will create the necessary barrier for dew point in our area. In very extreme conditions (below 10 degrees), this system may have slight moisture infiltration, but that very rarely happens in our area. I'm not super concerned about the few times it does.
我真正寻找的是对静态空气与通风问题的一些见解。有任何想法吗？
再次感谢。