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Old 02-21-2008, 09:11 AM   #1
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Vapor barrier summary and advice!


This question gets asked all the time but so many different answers come forward. I have been researching the issue for weeks and have a stack of building books. I even spoke with a basement company and has them inspect my issue last year, called the inspector up yesterday and got his answer. Now I am more confused and frustrated forever and its keep me from starting my project. My city building department is no help either, they don't return my calls or emails! So anyways below I got some pictures and a copy of a post from another forums. (that I have not gotten an replies ) So I thought I would give you guys a shot and see what kind of feedback I can get!

Hey guys,

I have been searching all day for answers and have yet to find 2 people give me the same one. I have a 2 year old home that I want to start finishing a basement in. I got my plan, permits and some of the materials all ready to go. But I am stuck! I have one of those water-guard basement waterproofing systems. Along most of the foundation from time to time I will have a darkened area of concrete that rises about 2-3 inches above the floor gap. I had a basement inspection company come out and look at it and they told me it was caused by water vapor creeping up from cooler air from the floor gap. They also reccomended to put plastic over the foundation, and allow it to divert any vapor that condenses into the gap. I have researched this since and it seems to be a big NO to place plastic against the foundation because of the increased risk of mildew and mold.

Anyways this is what my basement floor looks like, I photo shopped the second picture showing the water mark.



Anyhow so I got a handful of advice on this and it always differs. I need to know where the vapor barrier should be installed. If its OK to place against the foundation wall, and if it should cover over the GAP or just down to it. Also I was curious if you do use one agains the foundation wall if you also use one between the studs and drywall? Here are my choices,



If anyone can clear this up for me I would REALLY appreciate it!

Thank you VERY much!

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Old 02-22-2008, 11:42 AM   #2
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Vapor barrier summary and advice!


i would go with number 3 above. you want the vapor barrier to be nearest to the warm (inside) face of the wall not the cold concrete walls (as in number 1 and number 2). If you are using plastic vapor barrier, DO NOT use faced batt insulation in your walls. If you are not using plastic use faced batt insulation with the paper facing the inside (warm side) of the wall. The paper facing on the faced batt insulation IS the vapor barrier. Never use two separate layers of vapor barrier (as in number 4) as this will only trap moisture and cause mold/mildew problems.

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Old 02-22-2008, 11:50 AM   #3
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Vapor barrier summary and advice!


Is that as bad as the moisture problem gets ? Looks like it's just wicking up. I'd either use no barrier or go with number 1. What region of the country are you located ?
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Old 02-22-2008, 11:53 AM   #4
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Vapor barrier summary and advice!


All of the above....


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Old 02-22-2008, 12:56 PM   #5
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Vapor barrier summary and advice!


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Is that as bad as the moisture problem gets ? Looks like it's just wicking up. I'd either use no barrier or go with number 1. What region of the country are you located ?

I live in Missouri, huge temp extremes here and tons of humidity in the summer months.

My builder finally got back to me and said to put plastic sealed against the wall 6 inches or so, then across to the floor and seal all the way around, so the gap is now contained inside a barrier of its own...



So this is what it would look like! *shrug*

Obviously the water vapor or whatever is coming up through the crack wont come up through the crack anymore. But would it just create a huge Mold production plant?

Thanks for the help!
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Old 02-25-2008, 03:26 PM   #6
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Taipans: Check out this website: http://www.eere.energy.gov/buildings/building_america
Very informative. I've done lots of research on this the last couple months and decided on 2" rigid foam (R-10). No vapor barrier.
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Old 02-25-2008, 03:39 PM   #7
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Taipans: Check out this website: http://www.eere.energy.gov/buildings/building_america
Very informative. I've done lots of research on this the last couple months and decided on 2" rigid foam (R-10). No vapor barrier.

Hmm, where on the site is the article about the foam over insulation? Sounds like a nice idea though, just cut and cram in sheets. What do you do with the electrical wires though? Since insulation can kind of form around all that?
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Old 02-25-2008, 04:23 PM   #8
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Vapor barrier summary and advice!


Taipens -

Where do you propose to put the insulation?

I think the previous poster was talking about applying the rigid form insulation directly on the wall and not using a vapor barrier, which is commonly recommended by many sources.

The question of a vapor barrier and insulation depends on whether you are doing 100% of the exterior walls or just a portion of the basement. Everyone like to look at a wall section and assume it will work everywhere. - If it is only a portion of the basement what do you do at the end of the walls where you go from insulated with a vapor barrier to the semi-conditioned space of a normal basement?

The water/moisture you are seeing is probably not from any vapor, but just capilary action of the water in the concrete. It is very common with that type of perimeter collection drainage system (not a waterproofing system) on top of the footing that does nothing for the moisture below the top of the slab and also reduces the strength of the foundation.
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Old 02-25-2008, 04:36 PM   #9
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Where do you propose to put the insulation?

I was thinking in the between the studs, then covering that with a vapor barrier, then putting the dry wall on top of that.

I think the previous poster was talking about applying the rigid form insulation directly on the wall and not using a vapor barrier, which is commonly recommended by many sources.

I understand that now, so if I apply rigid foam against the foundation wall then I wont need the other insulation or the vapor barrier?

The question of a vapor barrier and insulation depends on whether you are doing 100% of the exterior walls or just a portion of the basement. Everyone like to look at a wall section and assume it will work everywhere. - If it is only a portion of the basement what do you do at the end of the walls where you go from insulated with a vapor barrier to the semi-conditioned space of a normal basement?

I don't understand what you mean. I have 3/4 of the basement being finished in with a part left unfinished for shelving and the AC/furnace/hotwater heater. The two longest exterior walls are 100% underground, the back back that isnt has a large slider in it taking up much fo the wall area. Obvously the rest are interior walls not agains the foundation?


The water/moisture you are seeing is probably not from any vapor, but just capilary action of the water in the concrete. It is very common with that type of perimeter collection drainage system (not a waterproofing system) on top of the footing that does nothing for the moisture below the top of the slab and also reduces the strength of the foundation.

I have been told many things about this issue from the city, builder, inspectors, basement companies and so on. I have yet to feel confident anyone was right. My main concern is finishing it in and it causing moisture issues. I went ahead as instructed by the builder and sealed over the 1" drainage gap on the area that will be finished. Sealing the plastic up just above where the moisture line appears. Do you think this was a bad idea? Do you think overall it will make much difference? And last, your comment leaned at first this was commond then ended with weakended foundation issues? Is this something to worry about?


Thank you very much!
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Old 02-25-2008, 10:46 PM   #10
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Vapor barrier summary and advice!


Taipans: The article is 20 pages long. Near the end, they describe a study of 7 different methods of insulating basement walls. It is as Concretemasonry describes. Basement wall, then foam boards, then stud wall, then drywall. There's plenthy of room for electrical or even additional insulation w/o vapor barrier. The downside is you lose some additional room space due to the foam boards. Also, it is not the cheapest method. I live in Northeast Ohio.
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Old 03-05-2008, 06:44 PM   #11
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The sequence described is the plan we use in Alberta with only a couple of changes. An air space is added between the rigid and studs, and the rigid insulation is sealed with expanding foam, at the but or lap edges and entire perimeter. No the assembly is not cheap, but the benefits are.
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Taipans: The article is 20 pages long. Near the end, they describe a study of 7 different methods of insulating basement walls. It is as Concretemasonry describes. Basement wall, then foam boards, then stud wall, then drywall. There's plenthy of room for electrical or even additional insulation w/o vapor barrier. The downside is you lose some additional room space due to the foam boards. Also, it is not the cheapest method. I live in Northeast Ohio.


Last edited by IRSRS; 03-05-2008 at 06:46 PM. Reason: missing material
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