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Old 06-06-2010, 11:07 AM   #1
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Moisture problem


I researched extensively on the Building Science website and came up with a plan to finish my basement. My basement has cinder block walls (built in 1950). I had a trench drain installed on the inside and Drylok waterproofing paint applied to the wall. There was no leak even during the heaviest record rainfall of this spring.

In accordance with the info on the Building Science website, I was getting ready to install rigid foam insulation against the wall. I cut to fit the insulation and lined it against the wall. Two weeks went by and I removed it to glue it to the wall. The wall and the foam insulation was wet. Now, I am not sure that the basement is completely dry.

My basement has high humidity and the dehumidifier was not running during this time. Also, there was no rain in the past two weeks. A flower bed outside the foundation wall was mostly dry.

Could it be that the moisture got behind the insulation because the joints were not taped and the insulation was not yet glued to the wall? If not, what would be the possible remedy?

I was thinking of adding a layer of poly vapor barrier between the wall and the rigid insulation. However, reading the postings on this thread, it seems like a bad idea.

Any help would be appreciated.
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Old 06-06-2010, 02:58 PM   #2
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Moisture problem


What do you mean by "lined it against the wall"?

I am thinking just like you suggested that since it was not taped and glued to the wall the warm moist air get behind the insulation and once it came in contact with the colder wall it condensed and produced water droplets.

Perhaps try gluing a small say 2 x 2 ft piece to your wall and after several weeks tear it off and check for water. I would think that if the warm moist air cannot get to the colder wall you will not have any issues like the BS website states.

Also make sure your rigid insulation is as the BS website suggests vapor permeable so that water vapor can still move through it, I think it calls for EPS or XPS foam. I dont think you want the rigid foam with the shiny metallic covering as this may act more like a vapor barrier.

Good luck
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Old 06-06-2010, 06:05 PM   #3
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Moisture problem


Thanks Creamaster.

I had actually "lined" it up against the wall after cutting the board to size. This was the step prior to gluing the board to the wall and taping them.

Before doing this, I had checked for moisture with a plastic sheet taped to the wall and there was nothing. I will do it one more time prior to gluing the insulation to make sure there are no leaks.

I am using a Polyisocyanurate Rigid Foam Insulation as recommended for the Boston profile (cold weather climate similar to that here in NJ) on the Building Science website.
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Old 06-06-2010, 07:03 PM   #4
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Moisture problem


we install 6mil plastic & run it down behind the exposed miradrain,,, drylock's a waste in most instances impo
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Old 06-07-2010, 12:33 PM   #5
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Moisture problem


Im not sure you want to be using the Polyiso insulation as it has a very low permeance.
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http://www.greenbuildingadvisor.com/...oam-insulation

This website has the permeance rating for Polyiso listed at .03 which is right about what 6 mil plastic is.
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http://www.buildingscience.com/docum...nt-insulation/

The Building Science website states :

"The best insulations to use are foam based and should allow the foundation wall assembly to dry inwards. The foam insulation layer should generally be vapor semi impermeable (greater than 0.1 perm), vapor semi permeable (greater than 1.0 perm) or vapor permeable (greater than 10 perm) (Lstiburek, 2004). The greater the permeance the greater the inward drying and therefore the lower the risk of excessive moisture accumulation. "

"In certain situations, foil-faced insulations may be used on the interior of foundation walls. However, such requires careful attention to supplemental moisture management strategies. Consult the Builder’s Guide listed below for specific guidance."

"EPS is the least expensive and most vapor-permeable of the three types of rigid foam; 1 in. of EPS has a permeance of 2.0 to 5.8 perms, making it a semi-permeable material."
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I would test a piece of your Polyiso first before you install the entire basement and find out later you need to do a complete tear out and replacement.

Good Luck.
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