# Crawl Space + Vapor Barrier



## Scully (Dec 3, 2011)

i have a 1950's home with a dirt lined crawl space underneath. i have asked some contractors on insulating it, and have received conflicting answers.

one told me to use vapor barrier and seal off the vents around the crawl space.

one told me to NOT use vapor barrier because it attracts/holds moisture.

what do you guys think?


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## titanoman (Nov 27, 2011)

I would have a vapor barrier and I wouldn't close off the vents.


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## Gary in WA (Mar 11, 2009)

Cover the dirt with heavy plastic; http://dirt-crawl-spaces.com/crawlspace-dirt.html


http://www.energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11480


Where are you located?


Gary


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## Scully (Dec 3, 2011)

GBR in WA said:


> Cover the dirt with heavy plastic; http://dirt-crawl-spaces.com/crawlspace-dirt.html
> 
> 
> http://www.energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11480
> ...


Wisconsin. would you also advise against vapor barrier? and why?


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## Gary in WA (Mar 11, 2009)

I would use a plastic on the ground; http://www.buildingscience.com/documents/information-sheets/crawlspace-insulation/

The premier: http://www.buildingscience.com/documents/insights/bsi-009-new-light-in-crawlspaces/

Gary


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## joecaption (Nov 30, 2011)

Always have a vaper barrier. That contractors way off suggesting to not have one.
How can a plastic vaper barrier attact moisture, what is it a sponge?
Moisture trys to evaperate, rises and forms on the back side of the plastic where it does no harm. If there was no vaper barrier it would rise and condence on the warm floor joist and form fungus.
Install automatic opening vents. They close when cold and open when warm outside. Only about $17.00 each at any Lowes or HD and take all of 5 min. to install once you figure them out.
Anytime I see a sealed up crawl space in a damp, gets a lot of rain, or snow, low laying, poorly graded home there's fungus under the house.
People in dry climets do not have these problums and think it's a great idea to close them up, so pay attention where you info is coming from.


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## CrawlSpaceMoist (Nov 24, 2011)

When they said 'vapor barrier' did they mean floor or up at the joists? 
You need a good installation across the dirt floor. 
As for vents - if you're going to close them then do your research and jump to a true sealed crawl space. If you just close up the vents you run the risk of a problem with moisture building up.
As for the temperature controlled automatic vents - I'm just not a fan. If the issue is moisture in the crawl, those vents do nothing for you. They're temperature controlled, so they could stay closed while humidity builds to terrible levels.
They do a great job keeping your pipes from freezing... but honestly just have regular vents and take the 5 minutes to open and close them in spring and fall.


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## jimleahman (Mar 5, 2011)

So, is everybody recommending to keep the vents open (in case of moisture build up) and lay a minimum 6mil plastic on the dirt floor?

Would a vapor barrier help any to keep the wood floors in a house a little warmer? 

Thanks.


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## CrawlSpaceMoist (Nov 24, 2011)

Jim, when you say 'vapor barrier' - to what are you referring?
My common terminology is a vapor barrier is the typically 6mil poly on the floor. (when referring to crawl spaces)


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## jimleahman (Mar 5, 2011)

CrawlSpaceMoist said:


> Jim, when you say 'vapor barrier' - to what are you referring?
> My common terminology is a vapor barrier is the typically 6mil poly on the floor. (when referring to crawl spaces)


yes, exactly what i meant. plastic cover over a dirt crawl space that is vented.


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## titanoman (Nov 27, 2011)

jimleahman said:


> So, is everybody recommending to keep the vents open (in case of moisture build up) and lay a minimum 6mil plastic on the dirt floor?
> 
> Would a vapor barrier help any to keep the wood floors in a house a little warmer?
> 
> Thanks.


In the winter time.
In the summertime, on the real humid days, the vents are actually allowing humidity to get in.


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## CrawlSpaceMoist (Nov 24, 2011)

poly on the floor probably won't help keep the floors warmer. not sure how.
Summer is the most important time to have the vents open. Keeping them closed would probably let the humidity build on itself. Fact is, closing the vents (not plugging) keeps air from circulating but really doesn't stop moisture intrusion since the humidity is driven by vapor pressure, not a 'breeze'. Read a study once (not bookmarked, have to find it) that showed the humidity level in a crawl directly and quickly tracked outside humidity, regardless of whether the vents were closed or not.


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## AndyGump (Sep 26, 2010)

I do not have much experience with non-vented crawl spaces with vapor barriers but isn't it a requirement to condition that crawl space that has vapor barrier and is non vented?

Andy.


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## Earnie (Jan 24, 2008)

I have no experience with Wisconsin weather. I do with North Carolina. Hot and humid in the summer.

I had open crawlspace vents and no poly on the dirt ground. In the summer, everything in the crawlspace was dripping wet. Insulation, plumbing, electrical, and HVAC.

I installed poly over the dirt and left the vents open. I ended up with a lake from water dripping onto and collecting on the poly.

I closed and sealed the vents and installed a dehumidifier. Problem solved, but I still want to insulate the crawlspace walls for winter.


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