Crawlspace Humidity/Sump

LumberjackLloyd

Well-Known Member
Joined
Jan 9, 2016
Location
Durham, NC
Our house crawl space has struggled with water/moisture since we have owned it (5 years). The existing foundation drain was too high in foundation wall and obstructed with concrete; this drain line went out past our back yard and was turned into a gutter drain to help with water discharging into yard. To make matters worse, our house seems to be built on a rock bed and the soil doesn't dry out well; water leeches into the crawl space 24 hours or so after a rain. We have a temporary sup pump so that no water ever puddles, but moisture/humidity in the crawl space is still an issue. House is just under 2k square feet (2 story); I do not know the exact sqft of the crawl space, but I will calculate that...

Looking for direction/recommendation on a permanent pump as well as dehumidifier. There is power in the crawl space for a light that is virtually useless; I will use that to wire new pump/humidifier.
 
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I'm running an Aprilaire E070. I'm very happy with it. I set the humidity on it at 50%, and it has no problem keeping that level even during the worst days of the summer.

Pinging a couple of knowledgeable guys on here

@Mac5005

@thebrotherinlaw
 
Second @Mac5005 he was a huge help with my moms house a few years ago.

I will say - you may need a bigger circuit that the light. It’s been ~ 5 years but if memory serves moms needed a 30a circuit for inrush
 
Make sure you have plastic down, no exposed dirt, and the vents are all sealed. Liquid water isn't a big deal for humidity, because it won't get warm enough to turn to vapor. You do want to pump ponding water out or gravity drain to daylight, so you're on the right track there. Otherwise you can buy most any sump pump from Lowe's or Amazon. Any dehumidifier like this should be fine, just don't use the tank and pipe it to the sump pump. I think ours is branded Frigidaire or maybe keystone.

 
I'm not a scab off of @Mac5005, but I agree with the comments above. Aprilaire is what I went with but my 070 would be too much for that space unless you have several smaller areas that you would have trouble pushing the air around in. If it's a wide open space get the smaller unit and save on the power bill. I ran flex duct from the end of mine to the farthest corner and on the opposite end of the crawl, I installed a Tjernlund V1D vent fan that has been running non-stop since March 2022. Be aware that there is the possibility of a cat urine smell when you encapsulate due to the breakdown of organic material in the soil. The vent fan will alleviate any of those problems and help pull the dry air around the space. Whatever you do, do not rent/buy/use the Hilti vapor barrier nail gun. It will blow the inside of your concrete blocks apart. You can hand drill each hole like I did and attach the vapor barrier to the wall or just lay the barrier on the ground. I'd be interested in know whether you have any hydraulic pressure pushing the water into the crawlspace walls. I doubt it, but you could check on things for a bit before you installed anything on the walls. You'll need a receptacle for the dehumidifier, sump pump, and vent fan. Also, you're going to want a few lights down there because it's going to look like an operating room and you're going to just enjoy looking at it.

Thankfully, I didn't need a sump because I put a tee in the downspout drain line and attached the dehu to that. It was deep enough to prevent freezing. I bought all my stuff from Crawlspace Ninja and they have terrific video's too.
 
thebrotherinlaw said:
unless you have several smaller areas that you would have trouble pushing the air around in
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Vapor diffuses. No need to worry about circulating the air.
thebrotherinlaw said:
be interested in know whether you have any hydraulic pressure pushing the water into the crawlspace walls.
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Possibly, Durham is in a Triassic basin with a grey clay layer that doesn't perc at all.
 
shawn said:
What's the RH?
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I think the issue is cold and hot spots. You could have an ac leak into a cavity that locally changes the dewpoint in a section. The further from the leak the less effect. That leak could be uncalked trim an uinsulated wall cavity with electrical box etc. I have one of those spots where the gas line runs to my stove. It locally molded right under the spot where there’s air leak, but no evidence of moisture on the subfloor on the other side of the joists

There was also a noticeable draft in the winter in this area
IMG_2529.png
 
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Shreddinlettuce said:
I think the issue is cold and hot spots. You could have an ac leak into a cavity that locally changes the dewpoint in a section. The further from the leak the less effect. That leak could be uncalked trim an uinsulated wall cavity with electrical box etc. I have one of those spots where the gas line runs to my stove. It locally molded right under the spot where there’s air leak, but no evidence of moisture on the subfloor on the other side of the joists

There was also a noticeable draft in the winter in this area
View attachment 445281
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Good point. Ideally you want to seal up those air leaks, but sometimes easier said than done.
 
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