Prioritizing Humidity Control in Basement
Hi! I’m Ken. My 180 year old house in central MA has some sill/beam rot/WDI damage in basement caused by moisture issues. Since I started monitoring the temp & RH in Jan it’s never gone below like 85%. I was thinking of making a negative pressure environment down there with a 2300 cfm box fan in the window to exhaust the humid air – but how do I ensure the make up air is coming from the much drier upstairs air (where there are a couple window air conditioners) and not from the incessantly crazy humid outdoor air?
It’s a walk out basement. The south facing front of the house is the walk out part and has windows to put the fan in. It’s an exposed structural 2 layer of brick wall with many many air leaks. Should I be focusing more on trying to strongly blow air into the basement from upstairs to *positively* pressurize the basement with the upstairs lower humidity a/c air (not the outdoor air leaking in) rather than trying to go the exhaust/negative pressure route and not knowing where my make up air is coming from?? I set the fan up in the window a week ago and while I can feel quite a breeze outside coming from the window and smell the musty basement outside in that air stream, the RH hasn’t budged down. I also put 6mm poly over the ~50% or so of the cellar that’s still dirt w/stone and not yet concrete slabbed. No RH improvement
在完成结构工作之前开始尝试将其弄干（在修复信封之前必须做）有多重要？我以为我会试图降低湿度，做硼砂清洁的一切，以便清除一些模具，然后对所有事情进行挖掘处理，以杀死木材内的白蚁电力柱甲虫等。然后进行结构性工作。然后是信封工作。但是，我需要担心现在变得更干燥？
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Replies
I'd install a dehumidifier and focus on air sealing the basement to reduce the operating cost. Look at water management and vapor sealing next.
The way I see it this house survived 180 year because enough heat and air was moving thru the walls to dry all the water that gets into the walls before it does much damage. Everything is balanced until someone air seals and insulates.
如果您想添加现代的空气紧密度和隔热性，则需要添加现代的防水屏障。
沃尔塔
沃尔塔，哦，是的。我计划做一个现代化的WRB，并在这里有很多关于做到这一点的方法的讨论！我认为40岁以下？您的壁板（1988年不是新事物）将被删除和更换，我认为另一个覆层只是董事会。I don’t think I need structural sheathing so prob won’t do taped zip for the WRB, so was thinking maybe doing a fluid applied (Prosecco etc) water/air barrier around the entire damn outside of the house (roof deck will also be replaced. Maybe that should be zip) Not sure if front south facing walk out basement structural brick wall is going to require something different though.
The WRB I don’t think I can get into before some structural stuff is done (replace sill rot, pour a slab on half the basement that’s still dirt/stone fill, replace a couple rotted and termite/carpenter ant/beetle eaten beams). But not sure how much I should be trying to dry out the basement with things like temporary gutter to mitigate roof water intrusion trickling down the back stone basement wall, and exhausting air to control the 90% humidity. The humid air outside comes right in because no air barrier. So, I don’t know if playing with negative pressure/exhaust and supply from the air conditioners on floors above will do anything for now. Or if it matters that it’s still wet when I put brand new materials in to replace moisture/WDI damaged structural materials.
特别是在房子中央AC地下室will be too cool to control humidity by ventilation. Look at your outside RH and convert that RH from outside to basement temps.
With 2,300 CFM of exhaust, your home's humidity levels are going to increase since you'll be drawing in outside makeup air. Your home's A/C will never be able to dehumidfy that much air quickly enough so be ready for that. You could potentially also have backdraft issues with any atmospherically vented combustion appliances (water heaters, etc.), so be careful with that too.
我会遵循乔恩（Jon）的建议，并运行除湿机而不是排气扇。暂时获取一个大型便携式单元，然后密封件，以控制内部室外空气的泄漏。您可能还会发现，您正在通过粉底墙获取水分，在这种情况下，您需要用刚性泡沫进行一些绝缘工作，以控制该部分。
账单
谢谢你的回复法案。有趣的听use a dehumidifier when there’s so much air infiltration. But ok! (Also did you mean to temporarily seal things up with a temporary sort of cheap air barrier to minimize the amount of air that leaks in?) Just how much should I even stress the humidity/moisture down there before/while fixing the moisture caused damage and putting in new materials to replace? I can’t fix the moisture problem that caused the structural damage (fixed by creating real control layers) until I do this structural stuff so I feel like I’m in catch 22 sort of place.
混凝土板是否有安装良好的蒸气屏障？
Hi John, no, only half the basement, (350 sq ft or so) has a concrete floor at all. The other half was dirt with a wood floor over it, the rotted remains of which were taken out maybe 15 years ago and back filled with crushed stone but no slab poured yet. I have to do that along with the other structural basement work I mentioned. I have covered that a few weeks ago with 6mm poly through and weighed it down to keep it relatively in place to mitigate soil vapor diffusion. But I think it’ll only have an affect on basement RH in the winter when the air leakage is leaking dry air instead of summer humid air like now. The walk out basement above grade south facing structural front wall is 2 layers of brick and that’s it, inside to out. Gotta replace a bunch of bricks and mortar. Lots of air leaking through there. So until the air infiltration is dry air, the soil vapor diffusion I don’t think will have much of an affect on the RH.
如果有潮湿的饱和土壤，那肯定可以是水分来源。蒸发发生直到饱和。
Plus, if you are conditioning the air to remove moisture, either with a dehumidifier or the AC, your RH should go down, which would in turn increase evaporative rates from wet soil or concrete. In other words it'd be fighting you. But I agree that your outdoor air leakage needs to be taken care of. Exhausting to the outside won't help this, as has been said.
I don't think you're going to get where you need to be just by removing moisture, you have to keep it from getting in.
水分进入地下室很多不同的方式。在夏天，在马萨诸塞州，室外空气中含有大量的湿度，您希望通过空气密封将空气远离地下室。地面含有水分，水分可以通过土壤和砖石芯到地下室，您想在墙壁和地板上有一个蒸气屏障，以阻止水分。您还需要将雨水和地下水挡在外面。
It sounds like your big sources are air infiltration and wicking. You've made a good start by putting plastic sheeting on the floors. Foam insulation board does a good job of sealing walls both against air infiltration and wicking if the joints are taped and the edges sealed. The rim joists really need to be sealed against air infiltration.