# Framing full wall in front of half wall foundation leaves gap



## natepuppy11 (Jun 22, 2016)

I have a half-wall foundation. I decided I do NOT want to do a shelf and will just frame a new wall in front of the current one. The top half is already framed 2x6 with batt insulation and vapor barrier from the builder. Here are the pictures.


http://imgur.com/a/CMPia


It is a 3 year old house in Minnesota. Walkout basement. 



My plan for against the foundation half wall is: 2" rigid xps foam + 2x4 wall (with batt insulation). The problem is that the foundation wall sticks inside about 3"... leaving approx 8.5" from original upper framed wall to new drywall.



A couple questions:
1) When the wall is complete I will have approx 8.5" (3" foundation + 2" rigid foam + 3.5" 2x4) space between the drywall and the upper portion of previously finished wall. Is this a problem? Can I keep it just the way it is with the installed insulation and vapor barrier? 



2) Do I need to add more insulation in upper half? What is the best way to do this.

Thank you very much for the help!


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## de-nagorg (Feb 23, 2014)

Convert some of that valuable space into STORAGE, you will thank yourself later.


ED


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## Bud9051 (Nov 11, 2015)

1. A vapor barrier such as the plastic we see on the upper portion of the wall needs to be aligned with and in contact with a rigid air barrier. If not, if bellows in and out with changing pressures pumping ais in and out at other locations.

2. Leaving an air space behind an insulated wall results in that space being isolated from the heat source and being cool enough for basement air that leaks in to form condensation or at least maintain a higher relative humidity which can grow stuff.

3. If you decide to go with a vapor barrier then it should be all the way to the inside under your new drywall. 

The easiest solution, perhaps not the least expensive, would be to remove the vapor barrier on the outside wall and fill that entire gap with insulation. In all cases you would want to make sure to air seal all pathways to prevent humidity from reaching a cooler surface. Your 2" of rigid should protect you in the lower half, but the upper area, if filled with fiberglass, would still allow some air movement. One option would be to use Roxul, very dense thus less air flow.

Bud


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## natepuppy11 (Jun 22, 2016)

Bud9051 said:


> 1. A vapor barrier such as the plastic we see on the upper portion of the wall needs to be aligned with and in contact with a rigid air barrier. If not, if bellows in and out with changing pressures pumping ais in and out at other locations.
> 
> 2. Leaving an air space behind an insulated wall results in that space being isolated from the heat source and being cool enough for basement air that leaks in to form condensation or at least maintain a higher relative humidity which can grow stuff.
> 
> ...



Thank you for the response. To be sure I'm correct, I will:

1) Remove vapor barrier
2) insulate the lower half foundation basement walls as I stated
3) Fill in entire gap with higher density insulation to prevent airflow
4) ???Add Vapor Barrier at end or unneeded???


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## Bud9051 (Nov 11, 2015)

Instead of me just saying you should or shouldn't use a vapor barrier, this article will tell you why. From what I have learned, air sealing is the important part of a wall assembly and then allowing it to dry to one side or the other, in your case to the inside. But you can read as they define "cold country" as northern Canada or Alaska. Some parts of Minnesota probably feel that cold at times .
http://www.greenbuildingadvisor.com/blogs/dept/musings/do-i-need-vapor-retarder

It will be well insulated. 

Bud


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