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Old 01-14-2011, 06:02 PM   #1
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Crawl space condensation


I have a stick-built home less than 10 years old in East TN with vinyl siding. It is the middle of winter here and I was inspecting the crawl space and noticed that the outer most floor joists had a great deal of condensation on them. In fact, it was wetting the adjoining subflooring. In some cases, the subflooring was turning black. Is this normal for this time of year or do I have a problem that needs correcting?

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Old 01-14-2011, 08:43 PM   #2
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Crawl space condensation


Welcome to the forum!

1. Is the crawlspace vented?

2. Is there a ground cover plastic on the earth?

3. Is there insulation in the floor cavities?

4. Are all the downspout leaders extended away from the foundation/slope away?

5. Are there any HVAC units or ducts below?

Gary

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Old 01-14-2011, 09:17 PM   #3
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Crawl space condensation


Quote:
Originally Posted by GBR in WA
Welcome to the forum!

1. Is the crawlspace vented?

2. Is there a ground cover plastic on the earth?

3. Is there insulation in the floor cavities?

4. Are all the downspout leaders extended away from the foundation/slope away?

5. Are there any HVAC units or ducts below?

Gary
1. Yes the crawl space is vented but are currently closed

2. The area of concern has no cover

3. There is no insulation in the floor cavities but I'm considering it

4. Downspouts are not a problem

5. The HVAC unit and ducts are below. Ducts are insulated.
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Old 01-14-2011, 10:20 PM   #4
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Crawl space condensation


Quote:
Originally Posted by sybilwayne30 View Post
1. Yes the crawl space is vented but are currently closed

2. The area of concern has no cover

3. There is no insulation in the floor cavities but I'm considering it

4. Downspouts are not a problem

5. The HVAC unit and ducts are below. Ducts are insulated.
Here in Canada we keep the crawl space tightly closed all year round. The inside of the foundation is insulated and has a vapor barrier on the inside.
If it has an earthen floor, then its covered with 6 mil poly that is taped to the wall vapor barrier.
The heating ducts are left uncovered as this helps to add heat to the crawl space.
A heat supply and return is used to maintain it as conditioned space.
In summer, the space is air conditioned also.
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Old 01-15-2011, 10:39 AM   #5
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Crawl space condensation


If I was building a new home that would be a consideration, but that's not a practical solution. I'm looking for advice I can use now.
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Old 01-15-2011, 01:17 PM   #6
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Crawl space condensation


The heat loss from the ducting is carrying the moisture from the ground being uncovered up to the joists and they are colder where it condenses. Cover the ground with minimum 6mil.plastic as mentioned, check with your local B.D. about “closed crawl”. http://dirt-crawl-spaces.com/crawlspace-venting.html

http://www.fpl.fs.fed.us/documnts/te...entilation.pdf

Gary
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Old 01-15-2011, 09:49 PM   #7
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Crawl space condensation


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Originally Posted by GBR in WA
The heat loss from the ducting is carrying the moisture from the ground being uncovered up to the joists and they are colder where it condenses. Cover the ground with minimum 6mil.plastic as mentioned, check with your local B.D. about “closed crawl”. http://dirt-crawl-spaces.com/crawlspace-venting.html

http://www.fpl.fs.fed.us/documnts/te...entilation.pdf

Gary
When say "my local B. D.", what do you mean?
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Old 01-15-2011, 09:56 PM   #8
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Crawl space condensation


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Gary in WA (01-15-2011)
Old 03-04-2011, 04:01 PM   #9
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Crawl space condensation


wayne,
I would seriously consider encapsulating your crawlspace with a heavy duty vapor barrier and a drainage system underneath it. I would always seriously consider placing a dehumidifier in your crawlspace. This will help with your moisture and condensation problems significantly!

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Old 03-04-2011, 07:18 PM   #10
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Crawl space condensation


I second the plastic and then dehumidifier
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Old 03-04-2011, 07:49 PM   #11
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Crawl space condensation


Since I first started this thread, I have completed lining one section of the crawspace with plastic and what a difference. That was enough to stop the condensation accumulating on the rim joists. Thanks and I intend to complete the remaining portion of the crawspace. Thanks for all the comments.
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Old 03-04-2011, 07:54 PM   #12
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Crawl space condensation


While you're under there..... http://www.buildingscience.com/docum...m-at-rim-joist

Gary
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Old 03-04-2011, 07:58 PM   #13
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Crawl space condensation


Read through that link Gary sent if you have not already. Basically, you have to stop heat tranfer through conduction as well as controlling the air and moisture flow through.

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