Using Plastic Sheeting To Control Moisture In A Crawl Space - Insulation - DIY Chatroom Home Improvement Forum
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Old 06-28-2018, 07:34 PM   #1
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Using plastic sheeting to control moisture in a crawl space


Hi,

My crawl space presently has some old plastic sheeting on the dirt floor which has quite a few tears that are too large to patch. It was originally installed in 1991. I would like to either replace it or add another layer.

One question I have is whether I should remove all the old sheeting before laying down the new sheeting, or does it matter so long as I don't trap any moisture between the two layers? On occasion there was some outside surface water which got under the house due to some gutter issues that I have resolved. It is definitely though a bit moist under the old plastic in certain areas of the crawl space.

The second question I have is what thickness plastic should I use? It seems to me like 6 mil should be thick enough.

Lastly, any installation tips that folks may have would be appreciated.

Thanks in advance for any help anyone can provide.

Larryn3
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Old 06-28-2018, 07:47 PM   #2
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Re: Using plastic sheeting to control moisture in a crawl space


I wouldn't worry about the old, 6 mil is used when it is covered with concrete to protect it. I would want 8 or 10 subject to budget.
Any overlaps should be lapped by 12 inches and taped with tuck tape (red) and I would run it up the exterior walls to the level of the fill outside and stick it there.
In Canada we use Acoustic sealer, In the US I believe Quad is used.
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Old 06-28-2018, 07:59 PM   #3
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Re: Using plastic sheeting to control moisture in a crawl space


I agree with Neal except my preference (optional) would be to remove the old before adding new. If there is no Radon control you might take advantage of the change to add some vent pipes under the new plastic. That would be another topic, but testing would help you decide.

If you are in a cold climate then some rigid insulation on the walls would be good.

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Old 06-28-2018, 08:07 PM   #4
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Re: Using plastic sheeting to control moisture in a crawl space


Band aid over the top of band aid just gives termites a warm fuzzy feeling. Fix the real issue.
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Old 06-28-2018, 08:16 PM   #5
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Re: Using plastic sheeting to control moisture in a crawl space


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Band aid over the top of band aid just gives termites a warm fuzzy feeling. Fix the real issue.
Do you have a plan for that fix.
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Old 06-28-2018, 08:31 PM   #6
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Re: Using plastic sheeting to control moisture in a crawl space


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Do you have a plan for that fix.
Yes, it is draining the water away from the structure.
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Old 06-28-2018, 08:49 PM   #7
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Re: Using plastic sheeting to control moisture in a crawl space


Water is no longer coming in under the house. My goal now is to reduce the moisture and humidity level that currently exists by insulating the dirt floor from the living area of the home.
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Old 06-28-2018, 09:10 PM   #8
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Re: Using plastic sheeting to control moisture in a crawl space


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Water is no longer coming in under the house. My goal now is to reduce the moisture and humidity level that currently exists by insulating the dirt floor from the living area of the home.
As long as you are sure there is no other problem with water.
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Old 06-28-2018, 09:18 PM   #9
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Re: Using plastic sheeting to control moisture in a crawl space


Well, I am fairly certain that no further water will be coming in under the house. But, if it does, I would assume that its preferable for it to be under the plastic instead of being exposed.
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Old 06-28-2018, 09:23 PM   #10
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Re: Using plastic sheeting to control moisture in a crawl space


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Well, I am fairly certain that no further water will be coming in under the house. But, if it does, I would assume that its preferable for it to be under the plastic instead of being exposed.
Yes but you don't want a water bed under the house either. It would be something to watch for even after the job is done repairs can be done, perimeter drain inside or out sump and pump if necessary.


The ground can be inspected afterwards all you need is a knife, more plastic and tape.
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Old 06-28-2018, 09:33 PM   #11
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Re: Using plastic sheeting to control moisture in a crawl space


What I do know is that in the past, unless there was a very hard rain, no water ever came under the house. After I did some gutter and diversion work around the house perimeter, water now very rarely gets under the house. And, when it does, its always very minor now. However, I'm still working to get it completely stopped but I believe I'm at the point of trying to reduce the humidly level which is common under homes in our area.
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Old 07-19-2018, 02:12 AM   #12
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Re: Using plastic sheeting to control moisture in a crawl space


You could try another layer of the 6 mil and see if that helps. There is no use building a sandcastle with a bulldozer. Crawlspaces are nightmare. Mine went from reasonably dry this summer do dripping after a high humidity week.
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