MOISTURE IN CRAWL (Cross?) SPACE! HVAC Pro's please weigh in - MODULAR

5 years ago

last modified: 5 years ago

Hey everyone, I would really appreciate ANY advice someone might have on our current *stressful* situation. This is long I know, but please weigh in if you have the time. Thank you in advance :)

We purchased, and remodeled a modular home a year ago, top to bottom (electrical, plumbing, the whole nine). We also put in a new HVAC system; 2.5 ton unit (We live in Southern MD) living space that the unit takes care of is roughly 1200 sq ft.

We recently had a string of intense rains and extreme humidity. I noticed our wood floors were swelling, mold in a kitchen drawer, sweating ceiling registers (no duct work in the floor)... we called our HVAC guy in. He moved the thermostat, double checked about our tonnage on the unit ... then we were in a waiting game for improvements. Humidity dropped in our house, but not to an acceptable level yet so he proposed that we may have to do some ductwork adding (?) or something along those lines. However, the humidity remains in our home. We have a plug in dehumidifier running 24/7 (I will love the day that I don't hear that ever again), and during that process with our HVAC guy (roughly a 4-5 day period), we got into our cross base.

There were moisture puddles, and wet insulation. The way our cross base was, is that they had a vapor barrier on the ground, and then a "belly" layer of plastic covering the insulation on the floor system. Well, when we saw this, our immediate thoughts were "There's the likely problem! Its creating this moisture trap between the two." Flash forward- we had people come tear out the existing vapor barrier, "belly" layer above, all old insulation (some had surface mold, with a bit starting to grow on sub floor).... then REPLACED only a new vapor barrier, and new insulation, NOT the additional plastic "belly" barrier on the top (insulated flooring area).

We thought our issues may have been solved (knowing that we still may need some HVAC tweaking inside). Its now been about 5 days and my husband went into the cross base to find it with the same issues encroaching! Wet insulation in areas, some puddling under unit area, our steel floor beams have rusting. He decided to close one end of our cross base vents (we have 4 total... 2 on each end of the house), put in fans for them, and then we also put two additional fans down there to push the air out and hopefully dry the space. There is already a slight improvement, but this is not the solution.

We are desperate for what the heck is going on here. We are back to thinking it is HVAC related! We started to think... the only thing that changed before this house had an issue was that we installed a new HVAC system, and the house was much more "insulated" than it used to be, being that we did a better job re-building the whole thing.

Other things to note:

-One side of our house is much more hotter than the other, it's what I describe as "dead air" space. Not much air flow gets down there. The other end of the house is wide open (kit, LR, Dining), then it is a long hall with bedrooms/baths off of it. The hall leads to the dead zone.

-I have water beading on some of my ceiling vents still, and small water rings around them on the drywall.

-Since we plugged in the dehumidifier we have kept the thermostat at 74. BEFORE we started all of this, and realized there was a BIG problem (found mold, house like a jungle, etc), the house was set at 68-ish, and was still warm.

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Comments (5)

ci_lantro
5 years ago
last modified: 5 years ago
We purchased, and remodeled a modular home a year ago, top to bottom (electrical, plumbing, the whole nine)

I'm NOT a pro but. since no one has responded, here are the first things I would look at:

Have you checked all of the drain lines under the house for possible leaks?

Is the site properly graded for rain to drain away from the foundation?

Checked the condensate line from the HVAC? How and where it drains to? (re puddling under the unit.)

('Crawl space' is the proper term.)
cat_ky
5 years ago
I have a crawl space. Vents should be open all the time, except for winter months (in cold areas) Air circulation is important. A good thick plastic sheeting should be properly applied to the dirt floor to keep moisture from underneath out of the crawl space. No insualtion under the house itself, unless you have done other special work to keep it a conditioned space. Since up until several years ago, we had never had a crawl space, we thought about insulating the underside of the house, but, were told no, not a good idea by every insulation company we contacted. This is the second house with a crawl space we have owned now. It stays dry as a bone underneath, but, we also have proper drainage outside too.
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sktn77a
5 years ago
last modified: 5 years ago
"Vents should be open all the time, except for winter months (in cold areas) Air circulation is important."

This has been conventional wisdom. But now, the recommendation is NOT to have vents open in the hot humid summers as it allows humid air into the crawlspace, promotoing damp, mold, etc. If you have water in the crawl space, you must address that problem (drainage, grading, etc).
ci_lantro
5 years ago
hmm, have you used an infrared thermometer to take a temp reading at the underside of the floor in the crawl space and compared it to the dew point? HVAC ductwork under the house? Get a temp reading on those with the air-conditioning running and compare to the dew point. You need to know the temperature of the bare underside of the floor (with the insulation removed.)

If the readings from the house are lower than the dew point, mystery solved. (I think.). Condensation.
User
5 years ago
Water shouldn’t be under a house. You’ve got a lot grading issue, gutter issue, or plumbing leak, or some other issue putting moisture where it does not belong.

Then you also have an air sealing issue between interior and exterior. Even if the house has an underground stream, addressing air sealing properly won’t allow the humidity indoors.

Then, your HVAC may possibly be oversized do that it doesn’t run enough to pull the humidity out of the air during low temperature deltas.

Perfect storm. Start ruling things out for the water problem under the house.

MOISTURE IN CRAWL (Cross?) SPACE! HVAC Pro's please weigh in - MODULAR

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ci_lantro

cat_ky

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