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Old 02-01-2009, 09:23 AM   #1
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Basement Vapor Barrier Condensation


First time poster...

Hello,

Since I purchased my home 2 years ago every spring through fall I have noticed extreme condensation forming on the inside of the insulation the builders put on the wall (runs about halfway down the concrete wall)... By extreme condensation I mean you can see water drops running down the inside of the vapor barrier and the bottom 2-3 inches of fibreglass insulation is soaked... All this occurs despite having a dehumidifier running 24 hours a day from March through November..

This condensation occurs along every wall in the basement except the walls bordering on the garage.

Now I want to finish my basement but I am worried all this moisture will cause mold and other bad things once walls go up...

Right now I'm considering just reinsulating and skipping the vapor barrier all togather.

I live in Ontario Canada so we have warm but fairly short summers and longer and fairly cold winters.

Can anyone point me in the right direction on this? Im getting a little desperate.

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Old 02-01-2009, 11:05 AM   #2
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Basement Vapor Barrier Condensation


you shouldnt just skip a vapor barrier there is a reason its there. i would first check around the outside of your house make sure the ground slopes away from the foundation.Check and make sure any downspout you have are run ito a drain pipe or have a extension on them you may need a perimiter drain before you install any walls.i wouldn't do anything until i got the moisture problem under control good luck

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Old 02-01-2009, 01:30 PM   #3
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Basement Vapor Barrier Condensation


Thanks for the quick reply...

I don't think it needs a perimeter drain, well let me restate that... It could probably use a perimeter drain (like any basement) but I have yet to have water seeping through the walls or floor in noticeable quantities... Just the condensation.

Last summer I was worried I had a leak and tore off a section of the vapor barrier and pulled the insulation back and the wall was dry... The only place you find water is on the inside of the vapor barrier between the insulation and the plastic...


However I will stretch the drain spouts out and add some soil around the house as soon as the snow melts... Is their anything else I can do ? I have the contractors coming monday/tuesday to start the work... Starting to think I should cancel the job or at least scale it heavily down to one room.. But I would prefer not to..
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Old 02-01-2009, 05:38 PM   #4
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Basement Vapor Barrier Condensation


I am in a new house in ontario canada as well..the first two summers I noticed this condensation as well on the vapour barrier in the basement. I have the blanket fiberglass on the poured concrete walls and VB over that. i thought it might be the the heavy humid air in the basement condensing on the cool concrete walls..but to see the condensation on the inside of the VB seemed odd. I will also note that the VB was put up very poorly..and this winter i did some extensive work sealing it with sheathing tape..I will be checking this summer. Also before I sealed the VB I noticed frost on the walls behind the insulation batts..now there is no frost..
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Old 02-01-2009, 06:44 PM   #5
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Basement Vapor Barrier Condensation


I live in Ontario, also! Just a review of the function of the v/b.
The intent is to prevent warm, moist air from contacting a cooler surface! If this happens, the air volume is reduced, allowing the moisture to be released.
With no v/b the moist air will penetrate the insulation and contact the cold wall, where it will release the water!
The vapour barrier must be sealed properly against any infiltration! As H.Boyd has found, sealing is very important.
If the concrete wall is fairly new, it could still be giving off vapour, also!
As your insulation has become soaked, mold will now form and its important that it should be removed and allowed to air dry, before it returned! And while its removed, try and find any signs of moisture penetration, from outside or over-head!
When you reinsulate, make sure to seal it completely!
I would think it best to delay finishing the walls until this is resolved!
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Old 02-01-2009, 06:57 PM   #6
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Basement Vapor Barrier Condensation


After re-reading your post, I had another thought! When you have your air-conditioning running, does this increase the trapped condensation!
If the room side of the v/b is cooler than air that may be penetrating from outside, warm, moist air will condense on the inside of the v/b.
To prevent outside penetration the foundation sill plate is supposed to be caulked! If this was over-looked, it could be the reason for the outside air to infiltrate.
I would remove the v/b and insulation from a joist cavity and see if this has been done!
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Old 02-01-2009, 09:55 PM   #7
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Basement Vapor Barrier Condensation


hoight boyd,

You make an interesting point.. I have noticed that at the bottom of the vapor barrier the straping holding it to the wall is very loose in many places... In some areas it actually sits open 2-3 inches from the wall... In most places its secured but not all and in one spot someone fixed a cut with painters tape..

Wildie,

I haven't checked the sill plate but I will look into that tomorrow morning.. I'm not really sure if the air conditioning is causing the condensation, I've been told that it should be drying the air out not making it worse but it is quite cool downstairs in the summer

Thank you everyone for your input I really appreciate this
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Old 02-02-2009, 04:40 AM   #8
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Basement Vapor Barrier Condensation


Fiberglass insulation should never be in direct contact with concrete - never. Concrete is a porous material and it will absorb and emit moisture even in the best conditions. If your finishing the basement and plan to use fiberglass - the wall framing should be set off the concrete enough to allow at least a one inch air space behind the wall. Good luck.

http://www.buildingscience.com/docum...lation-systems
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Old 02-02-2009, 07:34 AM   #9
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Basement Vapor Barrier Condensation


wow building sciences makes sense...silly question but why does the building code call for fiber glass on concrete?
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Old 02-02-2009, 09:19 AM   #10
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Basement Vapor Barrier Condensation


I also live in Ontario and building codes differ then those in the US.
I also have the rolled insulation to the frost line against the concrete foundation. I noticed my first summer that there was condensation coming down my walls w/ the AC on.

Note - I purchased a Dehumidifier and its initial reading was 65%.
After running it for a month, 24/7 my reading is now closer to 35%.

There are so many factors that play into this. Since it's a new house, the concrete is still pretty wet and requires some time to dry.
In addition to the newly placed soil around the house and the spring melts.

It is always recommended by builders to use a dehumidifier for a good year in your basement to dry things out. I will also be finishing after this springs melt, just to make sure that there are no foundation leaks or cracks. When i do, I will be cutting perforations into the existing VB and add new insulation from top to bottom and ensure that the new VB is sealed with caulking on both the top and bottom plates before drywall.

Keep a close eye and keep the dehumidifier running non stop untill the Spring melt, best advice i have...
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Old 02-02-2009, 10:02 AM   #11
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Basement Vapor Barrier Condensation


hoight boyd,

The building codes concerning insulation are much the same for all parts of my country (USA). Now, think about that. It actually makes no sense to expect the warm house/cold climate to react the same as the cool house/warm climate. But the guys who write the codes sometimes forget to use logic. Yet, we are constrained to meet their book requirements... even if they are in direct contradiction to the laws of physics and common sense.

Do you recall when the DOT head, Elizabeth Doyle, was pushing hard to mandate the installation and use of seat belts on motorcycles? It came close to passing into law. The insanity of paper pushers regulating the lives of real people will always be with us.

Bucking City Hall is tough.

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Last edited by Willie T; 02-02-2009 at 10:16 AM.
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