Another question regarding “Monitoring Moisture Levels in Double-Stud Walls”
jocelyn史密斯|Posted inEnergy Efficiency and Durabilityon
因此，在读取双螺柱墙壁中的监测水分水平之后......我正在寻找我们的双螺柱墙壁的解决方案，该解决方案只是关于准备保温的。我们计划用吹纤维素填充12“腔。但这有明显的，现在已经理解了水分和解决的问题，我们不知道。那么与我的墙有什么关系？我们的绝缘体表明闭孔施加4“R 28和致密包纤维素8”R 28.8。这仍然会导致胶合板弄湿和干燥，但至少我们将知道露珠留在外面，对吧？想法？
jocelyn.
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Settling is a non-issue if you dense-pack the cellulose, as you should. Moisture from the inside is a non-issue if you have an air barrier on the inside that prevents humid air from entering the cavity--the idea of using a layer of cheap sealed OSB as an air barrier inside the double wall nailed to the outside of the inner studs, with cellulose on both sides of it is a cool idea to improve the robustness of the air barrier and prevent the requirement for meticulous drywall detailing necessary for airtight drywall. And if you build a drainage cavity on the outside to allow any moisture that does condense on the exterior plywood to dry easily, you should be fine unless you're in Alaska or something. If you're really worried about the exterior sheathing, use board sheathing instead of plywood, which is itself hugely more moisture-tolerant than OSB. For extra protection, you can build with wide roof overhangs to prevent the walls from getting very wet in the first place--a good idea regardless of what wall approach you choose.
Sorry forgot to say we live in Zone 6, Vermont.
jocelyn，
I can't tell whether you are thinking of putting the spray foam on the exterior or the interior side of your thick wall. But either way raises issues. If you want a thick double-stud wall, just insulate it with dense-packed cellulose.
If you want to build a flash-and-batt or flash-and-fill wall, you are restricted to a thinner wall assembly, because you need to keep the right ratio between the spray foam layer and the fluffy insulation layer.
Settling should not be an issue if installed correctly. Moisture has been found in some double walls, but it typically shows up in March and dissipates by late spring/early summer. No one has seen rotting taking place. The best way to avoid problems is to build the house so that it is very tight, and install an HRV; these measures will decrease excess moisture in the house, which in a leaky house could work through the insulation and condense on the sheathing. You could also use fir plywood rather than OSB for sheathing, but sounds like you are already past that stage. Done right, you should not have a problem.
Yes, the walls are framed. The insulator is proposing "Flash and Fill." What ratio are you talking about Martin? From my research (may have misunderstood) the foam had to be a minimum of R 25 to keep the dew point on the outside when the total wall would be R 40+ (foam plus cellulose). While we're at it... what about Spider Insulation ?
Spray foam would work if you did 4" as proposed, but it's an expensive solution with high environmental impact (the spray foam uses a gas with > 1000X the global warming impact of CO2 to make its bubbles). Another option is to use a "smart" vapor retarder layer like MemBrain or Intello Plus on the inside. In your climate that might not be needed but it's a great way to add extra insurance against moisture in your sheathing. Is your sheathing OSB or plywood (e.g. CDX)?
蜘蛛将类似于纤维素或稍微差 - 相同的水分问题，但纤维素缓冲水分并减慢任何问题。
关于评论的几点评论：
Nathaniel, I don't think you can assume that air sealing makes moisture from the inside a non-issue. The houses tested by Building Science are well sealed and no house has zero air movement through the pressure boundary.
鲍勃:虽然没有一个是真的ny failures due to rot, I think John Straub's take on this makes sense. "These elevated moisture contents are lasting for several weeks to two months, depending on the study, into April. And in April, the sheathing may be at 50 degrees. That is right in the zone where you might get a problem, though it might take years for the problem to manifest itself. It’s in the gray zone.” These are risky walls.
jocelyn，
你说得对。在气候区6中，闪光和填充墙为12英寸厚，在墙壁外侧有4英寸的闭孔喷雾泡沫，墙壁内侧和8英寸的纤维素，将工作。它既昂贵，也不是非常环保的。
在第6区，如果您使用纤维板或石膏护套（例如GP Denglas）和通风壁板，您将能够通过内部的III类气旋延迟器（例如标准乳胶涂料。）
http:///publicecodes.CyberRegs.com/icod/irc/2012/icod_irc_2012_7_sec002_par025.htm.
顺便说一句：“......我们会知道露水点留在外面，对吧？”
荣 - 这是一个不当框架的陈述。露点是温度（空气体为100％相对湿度的温度），而不是组装内的位置。该讨论中的相关露点是内部条件空气空气的露点，其变化，但可以通过通风速率在区域6冬季控制。如果您将内部空气保持在〜35％或更低的@ 68-70F，则空气的露点约为+ 40F。
但夹带空气的露点将遵循护套的温度，并且在一天或一周的过程中会变化很大。由于索引温度下降，它从绝缘层中的空气中吸入水分，并且由于它上升，它释放出一些湿度。因此，只要护套的温度低于内部空气的露点，它就会赋予内部侧层的蒸汽压力差，并且水分将通过扩散而进入腔体，通过这些层的蒸气渗透速率限制。
如果你安装了一层智能蒸汽缓凝剂nder the interior side wallboard it lowers the vapor permeance toward the interior to less than that of CDX plywood as long as the proximate air to the vapor retarder is dry enough. If you keep the interior at 35% RH during the winter months and have a rainscreen gap between the housewrap & siding for the CDX to dry into you'd be fine. (Certainteed MemBrain is pretty cheap insurance at about $100 per 800 square feet retail. Intello Plus is a bit more expensive, but still a heluva lot cheaper than 4" of closed cell polyurethane. Either would be "worth it" if you don't provide sufficient foam for dew point control.)
当您引入诸如闭孔泡沫的低渗透绝缘层时，腔室内空气的露点追踪该泡沫的内表面的温度。泡沫的低渗透率限制了水分朝内部干燥的速率，因此必须足够厚，以保持泡沫/纤维边界处的平均温度或高于调节空间的露点以避免水分积累。
The vapor permeance of half-inch CDX is about 1 perm when dry, but can be as high as 5 perms when saturated. An inch of closed cell polyurethane is typically about 0.8-1.2 perms, but at 4" it's 0.2-0.3 perms, which means the assembly can only dry toward the interior. Fiberglass-clad gypsum is highly permeable, well north of 10 perms (as is most fiberboard) which allows the assembly to dry toward the exterior even in winter, provided you don't block that drying path with closed cell foam.