Vapor barrier in small crawl space

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  #1  
Old 09-04-16, 12:39 PM
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Vapor barrier in small crawl space

I have a small crawl space under the front of my house, approx 7(w) x 20(l) x 3(h) feet. I want to install a vapor barrier on the dirt floor using 6 millimeter plastic sheeting from Lowes. I plan on using a single sheet that is 10 x 25 feet feet for this purpose.

The walls of the crawlspace are cement covered (parched) brick.

I am thinking of running the excess material of the plastic sheet up the walls on all four sides as far as it will reach (maybe about a foot and a half on the long sides, and a bit higher on the short sides).

Can I use spray glue to accomplish this?

Will the vapor barrier be effective, or do I have to cover the walls all the way to the top?

My main problem is humidity, which is usually around 75%, sometimes higher on really humid days in the summer. There is no real moisture problem in the crawlspace -- never any puddles or other signs of excess moisture entering, so I assume the humidity is mainly coming from the outside but perhaps also through the dirt floor in the form of vapors.

The ceiling of the crawl space is comprised of wood rafters and wooden boards. I recently removed some superficial mold growth using a bleach/water mixture and painted the ceiling with Lime Prime to prevent any future mold growth. I plan on not ventilating the crawl space but encapsulating it to block humidity from entering.

Thanks!
-J
 
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  #2  
Old 09-04-16, 03:25 PM
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Welcome to the forums! It will be 6 "mil" plastic, not 6 "millimeters", but who's counting? If you have no obstructions in the middle like piers, your plan is good. For an adhesive, I would visit a retailer who deals in air conditioning stuff and get a couple of gallons of duct mastic to use under the plastic sheeting on the walls. Just smooth it out after you apply it and the plastic. It is somewhat messy, so take precautions, like wearing gloves. If you plan on sealing the crawlspace and air conditioning it, then the plastic will need to go all the way to the sills. I don't know where you are located, so I can comment on the pros and cons of you doing all that work. The plastic will keep your humidity much lower.

There are different schools of encapsulating the crawl. You won't be keeping moist air out, but trapping it inside and thus the air conditioning requirement.
 
  #3  
Old 09-04-16, 05:13 PM
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Thank you chandler. You are right, 6 mil plastic sheeting

I live in the New York area. I don't plan on air conditioning the crawl space. At most (if I have to), I would install a small 100 CFM duct fan in the crawl space door that would pull air to the outside, but that would be the most I want to do.

What do you suggest I do in my situation -- should I not seal the door as air tight as possible and install that fan? Any other suggestions?

The plastic sheeting alone, with no other work, should result in lower humidity, right?

-J

P.S.: It appears both Lowes and Home Depot are selling duct mastic. Here are the relevant product links I found (thanks for the suggestion -- I'm going to by myself some of that):
http://www.homedepot.com/p/Water-Bas...BA50/100396973
http://www.lowes.com/pd/Design-Polym...ealant/3736193
 

Last edited by cannondale0815; 09-04-16 at 05:28 PM.
  #4  
Old 09-05-16, 03:00 AM
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You didn't mention if you had foundation vents or not, so I am assuming not. Here in the South we have them installed at regular intervals on all sides of the house to promote natural evacuation of "still" air. Your fan idea is good, but where will the make up air come from? Glad you were able to find the duct mastic.
 
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Old 09-05-16, 03:32 AM
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Correct, I have no foundation vents. Right above the crawl space is living space. And I believe the make up air could come from there, as it's not completely sealed.

I'll start with the plastic sheeting and see if the moisture goes down. Maybe I don't even need a fan or anything else. I have a remote humidity monitor in the crawlspace, so I'll just monitor it.

Thanks again!
 
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