Crawl space humidity causing floor issues

Old 07-10-17, 08:08 AM
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Crawl space humidity causing floor issues

When I bought my house about 2 years ago (during the spring) the tiles in the kitchen were loose so we replaced them. The tile guy said the issue was likely because the thin-set was not done properly (some tiles popped up by hand!) in some areas but great in others. The subfloor was in good condition, so they partially floated the floor. The tiles have started to become unsettled again in the areas where it is floating. This only happens in the summer when the AC is running a lot. Other times, there is no issue, but the grout is starting to crack in some places.

I went in the crawl space yesterday and it had a musty smell to it. There were a few puddles of water under the exposed metal junctions for the vent runs and the air handler. It looked like they were covered in sweat similar to a can in the summer. Otherwise, it looked OK, I donít see any obvious damage or issues with rot. It was clearly humid but didnít feel like a swamp. When we moved in the inspector checked the humidity, venting, and vapor barrier and said everything looked good.

I live in Raleigh, NC where summer humidity and temps are high. The house was built in 2000. My crawl space is about 2000 square feet, dirt floor, has vents (currently open and a few canít be closed since things like cable service run through them), and is currently 80-90% covered with a vapor barrier. The barrier does not cover the edges or go up the cinder block at all. It is sloped and is about 2í at the shortest corner to about 4í at the tallest.

My thinking is that the flooring issues are due to the wood expanding because itís getting hot and humid in there during the summer. Does that sound right? What is the best, cost efficient way to fix it? We are probably only going to be in the house a few more years and donít want to spend a fortune, but we want to fix the issue properly. My initial thought was to put a de-humidifier in there and attach it to the existing pump for the AC then close and insulate the vents. Since the floor is mostly covered would that be enough?

Thanks for any help or feedback anyone can provide.
Old 07-10-17, 08:24 AM
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My biggest concern would be the puddles of water. If you rectify that, the rest might be ok. I prefer open vents but there are many that like sealing off the crawlspace and either conditioning it with the HVAC or install a dehumidifier. I believe they always recommend sealing off the 'floor' completely. Those that know more about it than me should be along later.

almost forgot - welcome to the forums!
Old 07-10-17, 11:17 AM
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Vented crawlspaces work better in the south than they do up here. That said, it sounds like yours is too damp - have you measured the humidity in there?

Are the ducts insulated?

I would also be looking at getting the vapor barrier coverage to 100%.
Old 07-10-17, 04:36 PM
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Are the ducts insulated?
Yes, Here is a picture of one of the smaller junction boxes I was talking about. You can see the condensation on it and it's definitely a good bit cooler than ambient.
Imgur: Junction Box

And here is a picture of the puddle underneath. It's hard to make out, but it's not very big or deep, definitely seems to be from the condensation above dripping down.
Imgur: Puddles

have you measured the humidity in there?
No, I need to get a humidity meter and check it, but I can tell it's at least as humid as it is outside (83%).

I prefer open vents but there are many that like sealing off the crawlspace and either conditioning it with the HVAC or install a dehumidifier.
The vents are currently open and it's not enough. Maybe there isn't enough air flow?

I would also be looking at getting the vapor barrier coverage to 100%.
Do you guys think this in combination with a de-humidifier and sealing the vents be enough or would the whole thing need to be encapsulated? Would the extra bit of vapor barrier make a big enough difference to fix it by itself?

welcome to the forums!
Old 07-11-17, 02:30 AM
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Beyond the humidity, venting, dampness issues what has not been addressed is the floor itself. Loose tiles, popped tiles, and cracked grout are an indication of insufficient floor structure to support the tile.

What is the floor material and thickness?
Old 07-11-17, 04:13 AM
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I agree with Marq1 in that you have two problems but maybe resolving the crawlspace moisture will help and it is a necessary step.

Inviting outside air into the crawlspace through open vents can only result in a higher humidity reading than what is outside, as air cools the RH goes up.

Encapsulation involves both air sealing and when beneficial, insulation around the foundation and rim joist. Since you would want to condition that air just like you do inside your home even in NC the energy savings would still justify adding the insulation, especially if you are up to a DIY approach.

Air seal and insulate the rim.
Close and seal all vents.
Insulate the walls with rigid foam as local guidelines require.
Finish the vapor barrier on the ground.
Then add supply and return ducts to heat and cool the crawlspace just as you do the upstairs.

During fringe seasons when no ac or heat are in use you will want to circulate that air with the upstairs and or use a dehumidifier.

Once encapsulated there will be no more "basement smell" and with good insulation minimal energy costs. A bit more than what you were looking for but it is a good way to eliminate the humidity issue down there which can lead to a far worse problem. Links for reference.

Building an Unvented Crawl Space |

Old 07-11-17, 05:55 AM
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What is the floor material and thickness?
I don't know off hand, I'd need to get under there and check. I believe it's ta standard plywood, not sure thickness. When we had the tiles replaced, the guy said it was in good shape. It's entirely possible he was wrong (or didn't think about if it was enough), but either way it would be really hard for us to swallow pulling it all up and replacing it again. I think that would be an absolute last step.

Bud, I think you are probably right. Encapsulation seems like the way to go, I was just hoping to find some middle ground that would work and save some money, but everything I'm reading seems to basically say it's all or nothing. The middle ground seems to be, at best, a band aid.

I'll probably look into what is involved as far as DIY, but it may be beyond my comfort level as I want to make sure something like that is done correctly. Time to start getting some people out for quotes I guess.

Obviously there are many variables, but does anyone have a good idea what a reasonable cost for that would be? It's tall enough to move around pretty easily and ~2000sqft.

I appreciate everyone's help and comments.
Old 08-14-17, 06:22 PM
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I paid 7k in December to have mine done, and I have about 1500 sf. They did a good job, but only because i crawled under there and checked the work, and made them come back to correct the issues I found. :-)
Old 08-15-17, 08:40 AM
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The VB must be 100% Close vents and seal with some kind of foam board. Use a 6 mill poly on the floor (white works very well) all seams must be sealed. Use spray glue to make this work fast. Poly must go up walls at least to ground height. Leave at least two inch gab from poly to seal plate so you can do a termite inspection.

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