Plastic at bottom of exterior walls cavities: a partial vapor barrier?
嗨伙计，
长期潜伏，但在这里首次发布海报。我在部分改建中的爬网空间上有一个1960年代的砖砌牧场。有关该结构的一些细节：
基础：CMU，爬网空间
Sheathing: Celotex fiberboard, no housewrap
绝缘：最初通过护套安装的密集包装纤维素，安装Roxul
框架：2×4
Siding: Brick, 1″ gap to sheathing, no brick ledge, no weep holes
建造房屋时，茂密的包装孔都用钉书板修补，我已经填补了贴剂以减少漏气。我的目标是通过合理的DIY努力使房屋尽可能地保持态度。我正在与Roxul绝缘进行绝缘，并在痛苦中痛苦并通过该站点进行梳理后，旨在忽略由于组件的蒸气开放性而导致的内部蒸气延迟器。该房屋位于5区的俄亥俄州西南部，但仅在第4区边界以北约50英里处。我们在一年中六个月运行A/C。
黑色的聚片沿底部4-8英寸的螺柱腔中存在，具体取决于墙壁的内侧。该合力延伸到爬网空间中的窗台，但在乐队托梁和砖之间隐藏。（我在爬网空间的框架上工作时遇到了它。）砖和护套之间的缝隙在爬网空间通风口附近呼吸。（不要让我开始爬网 - 这是一项正在进行的工作！）
I would guess the purpose of this plastic is to shield the wall cavity from wind-driven moisture or splashback, but it’s odd to find it inside the wall rather than as flashing on the outside. The home has 24″ overhangs, so rain hitting the brick is rare. Ground splashback was happening when I bought the home but has since been addressed with new gutters.
如图片所示，墙壁具有塑料时，它是否会产生局部蒸气屏障，以收集冷凝水会导致附近的框架上的水分浓度？特别是，我有一个墙连接，其中包含水平阻塞该垂直范围分为四个部分，其中一个几乎完全由poly衬在护套上。
The framing is in mint condition except in spots where there have been bulk water leaks, but the original insulation was cellulose, which adsorbs moisture, and not rockwool which resists moisture. I have never seen walls detailed like this and am concerned that installing rockwool instead of cellulose with this plastic present may create a localized problem at the bottom of the walls that will rot nearby lumber. Am I overthinking this, or should I be concerned?
W.
GBA Detail Library
由气候和房屋部分组织的一千个建筑细节的集合
答复
嗨，whiseve-
总是很难解决一个简单问题的所有联系...
In short: that black poly sure looks like a mason's flashing. In otherwords, a bottom-of-the-wall flashing installed by the mason, and because of sequencing, quite often reverse-lapped with other components of the exterior wall (like the WRB, which your assembly lacks, a big concern frankly). Good for the builder to weatherlap the flashing with the wall sheathing; shame on the builder for leaving out the WRB.
这种8英寸闪烁对墙件组件的蒸气剖面有什么影响？零。蒸气压力是一种场效应，因此噪声闪烁的局部蒸气渗透性是噪声。
On the other hand, without an WRB, water that gets to the backside of the wall sheathing will be COLLECTED rather than shed by this flashing.
On the other hand, proof is in the pudding: if you only have localized bulk water leaks you have already addressed, excellent and thank the builder or the architect for those hefty eave overhangs. Might be a different story on gable walls...I would carefully check them for bulk water leakage as well.
彼得
Agreed with Peter... whatever localized dampness/humidity that might occur behind that flashing will have an easy time evaporating/migrating in some other direction. It only needs to travel a few inches to find a way out of the wall.
Thanks guys. I won't worry about it then. The sheathing definitely runs below floor level to the sill plate, so the explanation that it was installed out-of-sequence makes sense and fits with other aspects of the construction.
There is that one section, at the junction where an interior wall tees into the exterior, where horizontal blocking is located just 1" above the top of the plastic sheet. The cavity, once insulated, would have only a 1"x6" strip of exposed sheathing and would otherwise be surrounded by 2x4's and would be open to the cavity of the interior wall. Is it still true that there would still be ample ability of moisture to escape this confined area? Originally, the cavity had two layers of crummy foil-faced fiberglass insulation jammed in there haphazardly and was a definite cold spot on the IR cam.
我一直在安装隔热材料，并发现了您在冬季中旬无法花时间的艰难方式。潮湿护套的视线使我认为闪烁是另一个潜在的问题区域。我的目的是提高隔热材料，然后快速使用干墙。
有了这种类型的组装，膜或可比较的产品是一个好主意吗？我正在尝试尽可能多地封印，并计划将干墙垫圈垫圈。我们位于第4区的第5区，在第4区北部，III级延迟者可以接受通风覆层。我的砖似乎没有一个经过深思熟虑的通风系统，但是每堵墙上的爬网空间都有一个气隙。不确定除了通过拱腹的微小间隙外，空气如何退出系统。
我的电气系统都是金属，但是我在所有盒子上都使用了火腻子，以尽可能减少泄漏。少量空气可能会通过MC电缆泄漏。我曾希望能够干墙和油漆。原始的结构没有蒸气延迟，也没有霉菌，但是用纤维素填充了密集的。我本来会再次使用纤维素（为什么要弄乱有效的方法），除了怀疑，考虑到该项目的其他挑战，我能够在冬季安排承包商。简单的DIY安装非常吸引人。
I have confirmed, while patching damaged isolated damaged areas of the sheathing (mechanical damage) that there is no house wrap at all. Nor is there a brick ledge or weep holes. I almost never see wet brick, though. Peter, your point about the gable is noted. The roof is a hip design with a perpendicular gable facing the street with significantly shorter overhang. There is no brick above the front window, only vinyl siding. That's one of the walls I have not opened, but I have not encountered any evidence of damage yet.
感谢您的输入。该网站一直是一个巨大的资源，非常感谢您的帮助。当地缺乏承包商，注意建筑科学的细节或知识，所以我自己在这里！
W.