紧凑型无人故意屋面装配：蒸气屏障选择
你好GBA社区！
长时间读者，第一次海报。我们仍然处于房屋的早期规划阶段，该阶段将建在德克萨斯州德克萨斯州（德克萨斯州）地区（气候区2）。我的问题是屋顶装配蒸汽屏障。
我们正计划构建Joe Lstiburek在本文中称为“紧凑疏松屋顶装配”<https://www.buildingscience.com/documents/digests/bsd-102-understand--ventilation& gt.;。
有关详细信息，请参见图7。这是因为我们希望以审美原因暴露木甲板。The only twist is that we plan on having both exterior rigid insulation (as the article shows) as well as interior spray foam insulation between the true roof sheathing (most likely OSB) and another layer of false sheathing which will be 1x’s strapped across the underside of the rafters to make a nice exposed roof effect while adding some insulation value.
After reading Mr. Holladay’s article about the dangers of using open-cell spray foam on the underside of the roof decking, I am thinking that we will need to use closed-cell spray foam to reduce the likelihood of interior moisture reaching the underside of the roof sheathing/OSBhttps://www.greenbuildingadadadisor.com/article/open-cell-spray-foam-and-damp-roof-扫描
With that in mind, it seems that the best choice for a WRB on the outside of the roof sheathing would be a relatively vapor-permeable product since it will not be allowed to dry to the inside because of the closed-cell spray foam. Most of the recommendations I have read so far suggest very tight, vapor-impermeable products such as Carlisle WIP 300HT (0.02 perms), PolyWall AlumaFlash (0.014 perms), etc. However these individuals are also usually dealing with a different type of roofing assembly. So my questions for the GBA community are as follows:
1.我是否正确地思考，因为内侧将具有闭孔 - 电池喷雾泡沫，所以需要对屋顶护套外侧的透气性的WLB的需要正确思考。
2.您是否对透气性的WRB材料有任何建议？我的偏好是剥离和粘贴的产品。
3.是否有更好的解决方案来防止内部水分到达屋顶装饰的下侧，这仍然可以达到内部？因此，避免需要在屋顶护套的外侧使用透水的wd？
我提前感谢您的时间，期待您的回复！如果我能为您澄清任何东西，请告诉我。
答复
Hi Matthew -
LSTIBUREK紧凑屋顶装配的美丽是它是一个“完美”的装配：空气和热控制层完全到外部，使得所有这些层的内部都看起来与乘客相同的条件。
我不会修改大会;建立它如图7所示。该组件包括屋顶纸作为屋顶底层，这是蒸气渗透的（在BSC的建筑材料性能表中，60分钟的双层屋顶纸为11倍，蒸气开放 -https://www.buildingscience.com/documents/information-sheets/building-materials-property-table）。确实，沥青屋顶瓦片外部外层界代表II类蒸汽延迟器（约0.3倍级），但是，如果足够的太阳能击中屋顶包层，它将将水分敏感材料变为内部。
彼得
彼得，
Thanks for the response! I can understand the reasoning behind putting all of the insulation and vapor barrier on the exterior of the sheathing. And by not needing any closed-cell spray foam on the inside I can avoid trapping moisture in the assembly altogether. The downsides to that method I was trying to avoid were twofold: 1) that would require extra thickness of rigid foam on the outside and prevent utilization of the rafter bay cavity space, and 2) I now have to rely on the decking boards to be the primary roof sheathing instead of a more common material with less seams such as OSB or plywood.
Both of these negatives are non-critical, but I was hoping to get away with some non-structural veneer boards as the underside decking that would be left exposed. Also, there are sections of the roof that will not be exposed from the inside and in those areas I will opt for the simpler and cheaper OSB/plywood options which means now my roof sheathing has mixed materials. But again, these are non-critical issues so maybe I just need to accept them and move on.
让我们假设我坚持这个计划鞘ing; I can then use a vapor-closed, peel-and-stick WRB directly on top of the sheathing. On top of that will be a certain thickness of rigid foam. Then, instead of a layer of roofing paper or the need for another sheathing layer, since we plan on installing a metal roof, I would think I can simply install furring strips which are screwed through the rigid foam and sheathing and attach the roof to those furring strips. Am I thinking about that correctly? I'm assuming the only reason Mr. Lstiburek's system utilized the second layer of decking and roofing paper is because of the asphalt shingles?
再次感谢您的时间，非常感谢！
-马修