Fiberglass Insulation Against Concrete Wall - Building & Construction - DIY Chatroom Home Improvement Forum

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Old 03-27-2009, 06:40 AM   #1
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fiberglass insulation against concrete wall

I am finishing my basement, have already put up the wall studs, most are away from the concrete wall, but there are some walls that are up against the concrete I going to have moisture problems if I put the fiberglass inslulation up against the concrete? Live in Philadephia area, no moisture problems currently. Basement is half under grade, yard slops down in back, back of basement fully exposed, windows and door on back of house in basement.


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Old 03-27-2009, 07:52 AM   #2
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Forgetting about the insulation for a minute, if your studs are touching the concrete walls, and they're not pressure treated, you'll likely have moisture problems there. Untreated wood should never be installed against concrete. The wood will wick moisture from the concrete. If the wood is PT, it won't rot (as fast). If it's not not treated, it can rot in just a few years, depending on how much moisture it is wicking.


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Old 03-27-2009, 09:29 AM   #3
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I'd use metal studs.
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Old 03-27-2009, 09:43 AM   #4
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While you may not see moisture, there is moisture coming thru the concrete in the form of vapor. That vapor will condense when it hits a "warm" surface. This could be the sheetrock or the insulation. Usually you allow a 1-3" air gap between the stud wall & the cement to allow the water to evaporate

That said reg studs have been used & lasted for a long time
And some have not lasted long at all
All depends upon the situation

Do you need to run a dehumidifier in the basement at all?
Do you have any guage to tell you the humidity level in the basement?
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Old 03-27-2009, 10:48 AM   #5
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Originally Posted by Scuba_Dave View Post
That vapor will condense when it hits a "warm" surface. This could be the sheetrock or the insulation.
The humidity will only condense when it hits a "cold" surface not a warm surface. "Cold" being at or below the dew point.

The only time you will ever run the risk of condensation of the moisture coming out of the concrete on any interior insulation or drywall surface is if you air condition your basement to below the temperature of the concrete (which is generally ground temperature if the concrete is below ground level) during the summer. Any other time the interior surface is warmer than the concrete.

This is why in most areas it does not make sense to put a vapor barrier on the warm side of a basement wall.

However if the fiberglass is directly against the concrete it will wick moisture out of the concrete so you do want the gap to avoid the wicking problem.
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