Replies

1. GBA编辑
   Martin Holladay|2010年12月14日上午11:10|＃1

   乔恩，
   你是对的;随着喷雾聚氨酯泡沫的厚度增加，其渗透率减小。

   Six inches of Icynene MD-R-200 has a permeance of 0.65 perm.

2. 
   John Semmelhack|Dec 14, 2010 12:13pm|＃2

   乔恩，

   只是一个建议 - 如何切换到2x12 afters和密集的包装纤维素？...或者更好，12英寸TJI the子？

3. 
   河流|Dec 14, 2010 12:17pm|＃3

   我不会期望MD-200与其他2个PCF泡沫的表现不同，除了其下部的R值，显然是由于吹式泡沫。

4. 
   乔恩·拉西奇（Jon Rasich）|2010年12月14日下午03:26|＃4

   约翰：

   Thanks for the suggestion. I should have noted that my roof is a full cross-gable, so I couldn't conceive of a way to get the equivalent of soffit venting to complement the ridge venting (ie, I have four valleys running down to each of the home's 4 corners). I assume you were suggesting an airspace between the deck and the cellulose, which I like as a solution for a simpler roof profile.

   一旦我放弃发泄，我便朝泡沫搬进了泡沫，作为提供空气屏障和蒸气延迟层的最佳手段。

   Martin and Robert--thanks for the responses. I wonder whether the overall roof assembly makes sense to you both in my climate zone once I've gone the complicated roof route. I haven't observed any builders in Richmond use external roof insulation to manage sheathing temperature (and thus would not expect the local trades to do it well) so I am opting for "limit moisture access to the deck, allow to dry both directions--I think the permeance of thick MD-200 will allow this--and manage indoor winter humidity".

   Many thanks.

5. 
   河流|Dec 14, 2010 03:32pm|＃5

   乔恩，

   在7.5英寸的任何2个PCF泡沫中，对内部的干燥都可以忽略不计。并且不希望能够看到屋顶泄漏。

   All PU foams are a mix of open and closed cells. The low-density (0.5 pcf) foams are mostly open and the 2 pcf foams are mostly closed.

6. 
   乔恩·拉西奇（Jon Rasich）|Dec 14, 2010 05:12pm|＃6

   罗伯特（和其他）：

   感谢您对MD-200的澄清本质上是/主要是闭孔泡沫。

   BSC在未通风的屋顶上有一份研究报告（BSD-149），这表明即使在正确的条件下（高蒸气驱动器），即使是高密度/低渗透泡沫也会干燥内部（以下摘录***）。

   In the end, it seems that I am looking for a Goldilock's solution given my climate zone--enough of a vapor retarder to prevent interior vapor from getting to the cold deck in winter, but not so much so that it would prevent exterior vapor from getting to the inside to dry in summer. I suspect that one of these risks must be greater than the other?

   Thanks to all for the continuing education.
   -------
   Control Vapor Diffusion – Closed-cell spray foam acts as a throttle to control the rate of vapor diffusion. The foam insulation resists the diffusion of water vapor so that the amount of water vapor is reduced as it moves through the thickness of the foam. By the time the water vapor reaches the back of the roof sheathing, there is not enough left to cause condensation problems.

   在寒冷的气候下，CCSPF提供了第一个冷凝平面。CCSPF应直接安装到屋顶护套的脸部（即背面）的层，以防止在泡沫的内部形成冷凝水。

   ***在高达5英寸的炎热气候中*（125毫米）CCSPF也可以使用。在此应用中，当屋顶温度高（120-190°F或50-90°C）时，组件仍然可以干燥到内部，蒸气压梯度非常大（5-35 kPa），并且泡沫为蒸气阻滞剂，而不是蒸气屏障。***

   控制雨水泄漏 - 闭孔喷雾泡沫具有可忽略不计的水的渗透性，最小的吸水和出色的粘附，使其充当二次雨水屏障，当主屋顶组装雨水控制膜泄漏时，可以限制损害。雨水迁移受到严重限制，这是由于泡沫的低水传播和高粘附（“防水”）特征，损坏仅限于附近的主要雨水控制膜中的孔。这倾向于包含损坏，使识别源并防止其在整个组件中散布和内部饰面变得更容易，这可能是昂贵的。

7. 
   河流|2010年12月14日下午5:56|＃7

   "under the right conditions" is the critical determinant.

   如果你有一个深色屋顶和大量的直接sun, then water vapor will certainly be driven through even closed cell foam, albeit slowly. Water damage risk is a matter of time and temperature, so whether a problem will occur depends on how long the roof sheathing stays wet and whether it's warm enough to mold or rot.

   The Florida Solar Energy Center study on cathedral roof systems demonstrated that the least durable roofs, in either cold (Boston) or hot/humid (Miami) climates were those with closed cell foam underneath and peel-n-stick membranes on top (many of the new roofing underlayments are relatively impermeable as well).

   在我受过良好教育的意见中，理学学士对塑料泡沫有偏见。泡沫可以完成这项工作，但要注意潜在的责任很重要。如果您在屋顶甲板下使用CCSPF，请确保在上面使用蒸气开放的屋顶（例如毛毡和带状疱疹）。

8. 
   乔恩·拉西奇（Jon Rasich）|Dec 14, 2010 07:35pm|＃8

   罗伯特，再次感谢。澄清...*沥青*在毛毡上铺设的标准圈配置中铺设的带状疱疹应该给我开放的蒸气...