06:29AM | 07/07/04
Member Since: 07/06/04
5 lifetime posts
I am in the midst of finishing a portion of my basement. The previous owner had installed studded walls with no insulation on two of the four walls. The other two walls they used furring strips w/glue. I have since removed all of the old drywall and furring strips and installed new studded 2x4 walls. I also installed insulation, and read about a 6mil vapor barrier on the warm side of the wall, so I installed that over the insulation in part of the basement. I had only put up the vapor barrier in a small portion of the basement, and I have since put the project on hold for the last 4-5 months because of other projects. Last week I happened to notice major condensation between the plastic and the insulation. Now I am reading that I should not have a vapor barrier. I have since pulled down the vapor barrier and removed the insulation affected, and the wall behind shows no signs of water intrusion. The block walls were sanded and coated with multiple coats of Drylok before the studded walls were installed and the walls were bone dry to the touch, but warm.

I need to finish the project in the next couple of months, but am concerned about the condensation. It only happened in a 4x4 section, but I am wondering if I should put the vapor barrier up in the rest of the basement. If I keep up the vapor barrier and the condensation persists, will this cause future problems? Will it condensate on the new drywall without a vapor barrier? I don't know what to do!

There is not a huge problem with water in my basement, but I do run a dehumidifier.

Please help...I have a new delivery on the way in February and need to finish this project ASAP.

Thanks in advance to anyone that replies.

plumber Tom

03:48PM | 07/09/04
Member Since: 05/10/03
801 lifetime posts
You have made a huge mistake. The vapor barrier goes against the block wall or poured concrete wall. The insulation comes with a vapor barrier already on the outside (the paper side is the vapor barrier) You want that facing out. Rip it out do it right then you shall have some peace of mind that you know that the interior walls will not be prone to mold and mildew.


05:14PM | 07/09/04
Member Since: 07/06/04
5 lifetime posts
Tom...thanks for the info. However, I am getting conflicting thoughts on the subject of vapor barriers.

I read this on about 1000 different websites and books before starting this project, which is right? Against the brick or against the drywall:

"A vapor barrier in a basement should always be installed on the "warm side" of the wall. That means between the face of the studs and the drywall. Why? To avoid condensation on the vapor barrier itself, you want to avoid a large temperature differential from one side to the other. If you were to place the vapor barrier over the concrete wall, or on the outside of the studs (before the insulation), you would likely see condensation on the vapor barrier."

I have the paper side of the insulation facing the drywall. Is that enough for a vapor barrier, or do I need the plastic as well?


plumber Tom

08:28PM | 07/09/04
Member Since: 05/10/03
801 lifetime posts
I'll make it as plain and simple (laymans terms) as possible for you. 6 mil vapor barrier goes against the inside bare wall. It doesn't matter if your walls are stone, cinder block or concrete. Then the paper faced of the stud insulation faces the outside. good luck.


06:23AM | 07/11/04
Member Since: 11/06/02
1280 lifetime posts
Tom, You have unfortunately given the worst advice possible. There should never be two vapour barriers on opposite sides of the fibreglass, which is what would happen with the Kraft face out and the plastic in.

This is a link to the best and most informative site in the continent on this subject.

the fact that wayter condensed in the wall space under the pl;aastic is to me a suspicious sign that something is wrong in the whole scenario. That water got there somehow, either from leaking through the foundation wall, or from moisture migration allowed due to an insecurly sealed vapour barrier and then trapped there. IMO< If VB is not well done, it is better not done at all.

This basement might be better off with a foam panel baord that would tolerate moisture and would not support the groth of mold in a higher humidity environment.

Excellence is its own reward!


07:27AM | 07/12/04
Member Since: 07/06/04
5 lifetime posts

Thanks for your reply. You are right, the link was a very valuable source of information.

I'm not sure how to move forward. Should I remove the fiberglass insulation and replace with foam panel board? The studded walls are already in place and nailed down. Should I continue with the paper faced fiberglass insulation without a 6 mil VB? I was told that with the paper-faced fiberglass without a VB, any water vapors would disipate without causing fungal growth.

Again, I don't have a lot of moisture in the's about 65% right now, and the condensation only happened in a very small portion of the room.

Any thoughts would be helpful, I would rather not rip out the entire job.


03:45PM | 07/12/04
Member Since: 11/06/02
1280 lifetime posts
it's always hard to make specific recomendations for an area where I am not standing and looking because of so many times that I have been on a site and found specaial circumstances not otherwise described or apparant to the layperson, but based on the norm and my experience and general building conditiins on average, I would think you are as well off the leave the FG in place if it is not damp and milding, and then drywall over that. The greatest amt of moisture in your cellar will leave in an upward direction as you go through heating cycles, tho that is another variable.

Supposing that the ducting was originally designed for the upstairs only, then it might need modification to include circulating the cellar rooms air.

Excellence is its own reward!


03:40PM | 07/13/04
Member Since: 01/28/03
693 lifetime posts
If I am reading Plumber Tom's reply correctly he is right and Piffin is wrong.

The discrepancy comes in the terminologies and use of the words 'vapor barrier'.

The reality is that 6 mil plastic is indeed a 'vapor barrier' while kraft faced paper on insulation is a 'vapor retarder'

The two are not the same.

6 mil plastic NEVER belongs over the studs and under the drywall in a basement.

I believe that is what Tom the Plumber stated.

He said a 6 mil true vapor 'barrier' belongs against the block, masonry or wood foundation wall and that is correct.

The purpose of this barrier is to prevent moisture from entering the basement thru the block or masonery foundation from entering the living space.

However, a kraft faced paper is required on the warm side of the framed walls in front of the masonry walls so that during heating seasons the warm, moist air from the living quarters of the basement does not move OUT and into the colder masonry walls of the foundation and condense.

Unless I am misunderstanding both Piffin and Tom the Plumber, Tom the Plumber's answer is most proper and most correct.


04:30PM | 07/13/04
Member Since: 11/06/02
1280 lifetime posts
I don't know if you misunderstood either, but a plastic sheet against the inside of a concrete wall is the least correct way to keep moisture from leaking into a basement through a block or concrete wall. The purpose of a vapour barrier is to stop water vapours from entering the wall and condensing there. Warm air entering the basement will carry moisture in it. When warm aior hits cooler surfaces, it condenses.

Since the underground concrete is cool, moisture will condense on it. So, as demonstrated in Lsiturbrek's site, Building Science, the key is to always place the VB on the warm moist side of the wall, which in most cases as in this one, is the interior side of the studs. When faced with an ambivalent situation, where moisture can enter the wall cavity from either side, it must be allowed a way to escape again over time. In this case, if water is also leaking in through the wall, it must not be trapped in the wall cavity , but be allowed to osmose and evaporate. Plastic will prevent that.

Excellence is its own reward!


02:54PM | 07/31/04
Member Since: 07/30/04
2 lifetime posts
I agree a vapor barrier should not be used at all in a basement and concur that XPS is the best insulation material to use.

My question is a bit different - if I am going to put up a 2x4 studded wall with unfaced insullation batts against a concrete wall would there be a benefit to first gluing up some of the fan fold insullation that is only 1/4" thick against the wall and then mount the stud wall over it with the unfaced foam insullation between the studs.

The purpose would be to keep the insullation from touching the colder concrete to prevent condensation.

Second would there be any need to even glue the fan fold in place - couldn't I just support it in place with the 2x4 wall.
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