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Humid crawlspace - Do I need to add vapor barrier w/ dehumidifier?

Humid crawlspace - Do I need to add vapor barrier w/ dehumidifier?

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  #1  
Old 02-02-19, 06:30 PM
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Humid crawlspace - Do I need to add vapor barrier w/ dehumidifier?

I have a very humid crawl space and Im wanting to add an appropriate dehumidifier. I plan on sealing the foundation vents but Id like to avoid adding a vapor barrier. My question is can I do this and achieve good enough results? I also believe I have addressed the water in the crawl space issue by adding French drains around the outside of the foundation. Im trying to avoid the very costly vapor barrier install if the dehumidifier will work without it. Thanks in advance for any options/advice.
 
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Old 02-03-19, 07:07 AM
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Assuming your ground is dirt or sand the dehumidifier will be trying to dry it as well. This will cause it to run longer than if the ground is covered. Could end up costing more to run the dehumidifier this extra amount than the ground cover would cost.
 
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Old 02-03-19, 09:36 PM
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but I’d like to avoid adding a vapor barrier
That's skipping the most important step.
 
  #4  
Old 02-09-19, 07:39 AM
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Not sure how big your crawl is but I just had a 10mm vapor barrier installed in 1600 sq ft. for $550. Included removing the old one. You have to have one if you're trying to control humidity.
 
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Old 02-09-19, 08:55 AM
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Originally Posted by brock125

Humid crawlspace - Do I need to add vapor barrier w/ dehumidifier?
I have a very humid crawl space and I’m wanting to add an appropriate dehumidifier. I plan on sealing the foundation vents but I’d like to avoid adding a vapor barrier. My question is can I do this and achieve good enough results?
SHORT
If you have any kind of furnace, do NOT block the outside air vents.
You want airflow from the crawl space into the furnace.


AIR REQUIREMENTS
A burner operating in an unconfined space in a conventional frame, brick, or stone building will usually receive adequate air supply from normal air leakage into the building. However, if the building is tightly sealed, air must be supplied from the outside. A permanent opening to the outside (or to an area that receives air flow from the outside) is necessary, and the opening or openings must have a total free area of at least one square inch per 5000 Btu per hour, or 28 square inches per GPH of #2 fuel oil.


Consider adding a vent between the crawl space and the living space, in some innocuous location along the outside perimeter of the house, where cold air accumulates so that the furnace naturally moves air through the cold moist crawl space.


LONG
Well, all of this really depends on:
which state (Florida vs Maine)
what locale, (top of hill or bottom of the valley)
what sort of house (1800s farmhouse, 1950s rancher)
and what sort of foundation

Basically, if the french-drain works, you have a long term solution to the humidity, then the residual humidity in the crawl space is just a short term problem.

Do you have a furnace or boiler (oil/gas)?
Then you'll want to consider arranging things so the furnace pulls in air through the crawl space. Normally, it's outside air, although you might add a floor vent to siphon out cool air from the living space.
That removes humidity, gives the furnace cool dense air for better combustion

Do you have a basement?
Do you have a sump pump?
If yes to all I'd suggest getting a cheap de-humidifier from e-bay/ yard sale/ thrift shop, placing that directly UNDER the access to the crawl space, and run the drip line from the de-humidifier over to the hole for the sump pump, and COVER the sump pump with 1/2" plywood.
This is a simple setup that pulls humidity out of the crawlspace, and dumps it into the sump-pump.
 

Last edited by Hal_S; 02-09-19 at 09:15 AM.
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