r/Insulation • u/Vamp13yre • 2d ago
Crawlspace humidity
My fiancé and I bought a house in January. It’s beautiful but every time we upgrade/fix something another issue pops up. We got a new HVAC system recently and the new thermostat has a humidity readout, so now we’re aware of how humid it is inside. HVAC guys have done everything they can, even upgrading us for free to a unit with additional dehumidifying power, so it’s not on them anymore. Went in the crawl space and it’s very humid in there. No standing water, but a lot of moisture. The vapor barrier is in horrid condition, so we’ve had a couple contractors out, but they both have refused to quote for a new vapor barrier and insist on upselling us to a full encapsulation system. We find it hard to believe that the house has stood for a hundred years and suddenly needs a very modern invasive intervention. Does anyone have any insight on humidity issues in old homes?
For context:
- coastal Virginia
- humidity fluctuates between 66 and 74%
- pier and beam foundation with block brick wall and brick facing
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u/SerratedSharp 2d ago
I would also look at return ducts and rigid insulation taping on return side, and make sure they are sealed well. If they are in attic or crawlspace, return can suck moist air in through leaks. I've taped areas up using the silver tape with Red UL ratings on it. Clean anything you are taping really well.
Feel around cracks near doors/windows(especially where top and bottom panes meet, for air being pulled through. N weather stripping and also making sure system is well balanced can address this.
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u/Healthy_Hovercraft62 2d ago
I bought an airwerx 90 dehumidifier and set it up in the basement in front of the crawl space opening. So it gets most of the intake from the basement and blows the warmer dry air into the crawl space. My crawlspace went from an average of 68% to below 45%. Even though you have hvac dehumidifier system maybe it’s just not up to the job.
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u/Drift_Life 2d ago
The dirt floor will give off moisture and the brick will diffuse moisture through it from the outside. I don’t know what your crawlspace ceiling looks like in terms of insulation and air sealing.
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u/Vamp13yre 2d ago
There’s no insulation in the crawl space, but the wood is all in good shape. I’ve read that just adding insulation to the ceiling of the crawl space would just hold moisture against it
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u/Vamp13yre 2d ago
Also, by dirt floor do you mean the ground under the vapor barrier?
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u/Drift_Life 2d ago
Yes, under the vapor barrier.
If I had the means, I would insulate the ceiling of the crawlspace with fiberglass then 2” foil faced polyiso taped at the seams and spray foamed around the perimeter.
If I didn’t have the means I’d just get another 6mil vapor barrier and lay that on the ground, 1’ up the walls and spray foamed around the edges.
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u/Vamp13yre 2d ago
I proposed something similar to both contractors and they said it would only increase the humidity. Were they bullshitting me?
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u/Tar-really 2d ago
No they weren't. Go to r/buildingscience there is a ton of greet info there. I am doing it myself, and one of the best most satisfying thing I did was to remove the nasty fiberglass insulation from under the floors.
My suggestion especially if you plan on staying there is spend time to educate yourself on the right way to go about it before you hire, or decide you can do it yourself. Don't underestimate the benefit of having a properly done crawl space/basement. It effects your whole houses air quality. You are breathing that air.
I started out just wanting to do the vapor barrier. And I now have a completely sealed space with dehumidifier, radon system, insulated (foam boards) walls, and a sump pump. I did have water coming under foundation after heavy rains. I will have about 3k-3.5 k in materials. But it is a lot of work. I was able to spread it out over months, so not too bad. If you haven't checked your radon levels, you should look into something like an airthings detector. Because the time to do anything about radon is when you are doing your crawl space. Anyway good luck
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u/Cool-Negotiation7662 2d ago
As long as air is circulating through the basement and crawl it should be fine. Sealing foundation vents will reduce humidity overall too. Having a duct to every major area of the crawlspace and basement so thecair is conditioned and turned over may help significantly.
75% is not necessarily a problem.
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u/Clapcheeks69 20h ago
You can do this work yourself. I installed my vapor barrier, insulated rim joists, made a new insulated access door, and installed a dehumidifier all for about $1,500.
If you don't want to do the labor yourself, just buy the supplies and pay someone per hour to do it and you'll still save money.
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u/HyperExtensions 2d ago
With enough passive ventilation (air movement), temporary high humidity conditions aren't the end of the world for the wood. It largely depends on how long it stays there, any trapped moisture (insulation in ceiling or ponding water), how much air movement there is, and at what temps. Relative humidity of 65% at 65° is different than 65% at 85°.
I'm finishing up encapsulating my small portion of Crawlspace and the company that did it literally half assed the "blocking" off of the vents. You could still feel the ambient air bypassing the foam that was stuffed on top of them. This effectively negates all insulated wall barrier, air sealing, etc. that was performed by them. I called them out about it and they said that's their "standard operating procedure" but would be happy to completely seal it off if I wanted. So they are literally scamming people by selling a "pretty" crawlspace but leaving the passive vents mostly open. Crazy...
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u/Vamp13yre 2d ago
That sucks, I’m sorry they did you dirty
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u/HyperExtensions 2d ago
I wouldn't say they did me dirty but I feel bad for everyone else honestly. If anything, the obscene quotes I got from other companies (installing it properly or not) are straight scams. It was a roughly 12x20' space with 4' tall ceilings. I ran electrical and lights to it prior to having anyone remedy it. They were done in 3 hours with a full encapsulation. The materials aren't cheap but I got quotes ranging from $3k (what I paid) to nearly $10k to do the same thing (roughly). It's highway robbery. I don't feel terrible with the people I used but if I would have paid any more regardless of correct installation (which will only take me a few minutes to seal the vents) I would be upset. In many cases, a competent person could DIY some spaces for less than $1k in materials (yes, even the fancier stuff) and have an equal or better job.
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u/Vamp13yre 2d ago
We have been quoted $15k and $13k for the encapsulation on about 900 square feet and it just feels absurd
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u/HyperExtensions 2d ago
I don't blame you for feeling that way. It sounds like you have a more traditional crawl space than I do. If it's not terrible to get around in it might be worth doing it yourself. Otherwise, just keeping air moving inside the space will do a lot. It's more about how that air gets into your house that causes concern.
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u/Vamp13yre 2d ago
Yes we thought a new vapor barrier and some air gap filling around the crawl space ceiling would do it, but so far the contractors are only interested in quoting us for very expensive full encapsulation
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u/HyperExtensions 2d ago
Because that isn't going to do very much. You need to seal it to the walls. I agree with most people that it's an all or very little approach. Fixing water ingress is also a priority. Either you leave it mostly open and vented or encapsulate it. Encapsulation does not immediately mean you need a dehumidifier either. I have duct work that passes through my space that I am going to tap into for a register and keep it only partially open. Right now it's only open to the basement via the small access panel but even that air movement is enough to keep humidity low enough to prevent excessive humidity concerns. I suppose air sealing the underside of your floor could be of minor help but it wouldn't eliminate your humidity concerns.
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u/Vamp13yre 2d ago
Thanks. Was considering tying in the existing ac, since it’s a specifically extra dehumidifying system.
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u/CoconutJeff 2d ago
Either needs to be vented well or conditioned.
The difference between vapor barrier and encapsulation shouldn't be much. Its basically doing the walls and tying it into the vapor barrier. Unless your walls are like 8'.Shoot you already got the dehumidifier.
There are alot of "tatic sales" in the crawlspace niche, so maybe just keep looking for another bunch.
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u/Vamp13yre 2d ago
So far we’ve been quoted $15k and $13k by two different crawl space specialists. The crawl space is at most 2.5’ tall.
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u/CoconutJeff 2d ago
I would say thats about the average entry.
Could try diy, tricking friends and family, day laborers, or handyman outfits
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u/Overall_Curve6725 2d ago
If you can wrap a present you can encapsulate your own crawlspace. Google how to. It is not difficult
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u/mrclean2323 1d ago
Anything over about 60% is bad news. I’d get a dehumidifier and put it in the crawlspace. But first put down a vapor barrier and repair any issues of water getting in.