Getting rid of mositure in crawl space


Old 02-07-14, 06:50 PM
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Join Date: Feb 2014
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Getting rid of mositure in crawl space

Earlier this week I had the misfortune of losing my air handler motor due to moisture. I had no idea my crawl space had moisture in it but the HVAC guy that came out said it failed due to moisture.

My house was built in 2006 and my crawl space is approximately 1000 sf with an average of 2.5 ft of clearance. The builder that built my house put down thick sheets of plastic and it covers the vast majority of the "floor." I'm to understand the "floor" needs a vapor barrier (VB) put down that goes up the walls and columns at least to ground level.

There are several good articles out that discuss sealing off the crawl space by installing 6 mil plastic, running a dehumidifier, and closing all the crawl space vents. This may sound simple enough but I would like to get some clarification on a few things. The plastic that is already on the floor in the crawl space is on top of clay soil and the soil feels damp underneath the plastic. There is no signs of standing water but we do live in a hot and humid environment from April to November. During the winter months it occasionally dips down to freezing but doesn't usually stay there for no more than a few days.

I assume my first step is to clean out my crawl space by removing my stuff that I've been storing. Would I keep the old plastic that is already on the floor and add 6 mil to run up the walls and columns, or start all over from scratch? What kind of glue or caulking would I use to fasten the 6 mil VB to the bricks and cinder blocks? What kind of tape should I use to tape the VB together with (will duct tape work)? Would I run tape along the entire length of the seam or just enough to hold the VB together? What size dehumidifier should I get? Do I need to install 6 mil plastic over the crawl space vents? Would you recommend installing door frame insulation tape around my access door entering the crawl space?

Dehumidifier: - Frigidaire FAD704DUD 70 Pt. Dehumidifier
6 mil plastic: Shop Blue Hawk 20-ft x 100-ft Construction Film at
Door frame insulation tape:M-D Building Products 2311 High Density Foam Tape, 1/2-by-3/4-Inch by 10 feet, Gray -
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Old 02-07-14, 07:15 PM
Join Date: Feb 2014
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crawl space moisture

I definitely would not plug off the venting in fact I would leave them totally open and most likely is required by building code just for that reason same with plastic on the ground
Old 02-07-14, 07:32 PM
Join Date: Jan 2014
Location: usa
Posts: 466
I would perhaps take the motor to a motor repair service and ask them to inspect it just to verify the HVAC tech's analysis.

Clay soil is very good at holding water and may likely never show itself as dry to touch depending on several issues.

Is your current vapor retarder reasonably well installed and is it covering the ground up to the walls ? Covering the walls may or may not have any additional affect and can create a few issues.

Running a dehumidifier is dependent on air temperature in the crawl space and can also be an expensive proposition relative to electrical consumption.

Have you checked the crawl space after a few days of rain to make sure you are not getting water?

While we are at it, is the floor insulated and what is the condition of that?
Old 02-08-14, 10:38 AM
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Join Date: Feb 2014
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There is no hope for the motor. The whole thing caught on fire and is toast. Normally I would fix it myself and swap the motor out but the wiring was burned so bad I couldn't tell where they went. That's the only reason I called in an HVAC guy. He was reasonable and didn't charge an arm and a leg and offered to sell me parts at his cost and let me do the installation myself. I'm not an electrician and don't even pretend to be one so I know my limits. I can do the basics and that's about it.

A few years ago my air handlers breaker in the crawl space went out because of the moisture. The switch was jammed between on and off. I knew then I had a moisture problem so I thought if I tightened up the screws for the air handler cover a little more and caulk it up that would fix the problem. It didn't.

Fast forward about 3 years and here I am with my air handler motor catching on fire - again due to excessive moisture. My neighbor had a similar problem and I believe all he did was put in a dehumidifier but I can't say for sure. He's hard to catch because he's always gone.

One of my wife's friends use to work for a large HVAC repair company and said that this is a common problem in the area we live in. She knows of a company that will "seal" your crawl space but they are pretty high. She said they do excellent work and once the crawl space is sealed your HVAC equipment no longer gets corrosion from moisture. She told me that there is no need to hire them because I could do the work myself. The basic steps is close the vents, put down a vapor barrier, and setup a dehumidifier.

A few nights ago when my air handler caught on fire it was in the middle of heavy rain and my crawl space was dry when I went to go investigate the cause of the blue smoke that was filling up my house. No standing water, and no infiltration from the rain. The few places where the soil is exposed it's moist/damp and that's it. The insulation overhead looks like it was put in today so it's in excellent condition. Aside from my HVAC equipment getting heavy corrosion from the moisture that's really my only issue/complaint. HVAC equipment can get expensive and I would like to extend the life as much as possible. I've got several more electrical components that needs to be replaced due to corrosion from moisture but I might be able to squeeze several more years out of them if I can can get that moisture under control.
Old 02-08-14, 12:09 PM
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Hi Dan,
When you are all done you want it to look like photograph 5. Good info:
BSI-009: New Light In Crawlspaces — Building Science Information

Old 02-08-14, 12:21 PM
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When you are all done you want it to look like
...but with nice carpet remnant runners laying over the plastic in any "traffic areas" to make it less likely that damage is done to the poly barrier, should a worker need to crawl across it.

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