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Old 01-20-2011, 08:35 AM   #1
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lower level insulation


Hi, I know this topic has been asked before but I am still a little confused. I am finishing the lower level of our split level home that was built 3 years ago located in North Dakota.

In the lower level we have concrete walls that only go part ways up and then have a 2x6 wall on top of them. This 2x6 wall has insulation in it covered with a plastic vapor barrier.

I built a full height 2x4 wall in front of these outside walls and want to know how to insulate with batted insulation. I know in other discussions it says no vapor barrier over concrete, so how do I add the insulation in the 2x4 wall. Can I leave the vapor barrier on the 2x6 wall portion and put insulation in front of it? I don't have room behind the 2x4 wall to put xps between the studs and the concrete.

I want to add an R-13 insulation to try to help with keeping this area warmer.

Sorry for being so long winded, but I wanted to give you as much information as possible so that I could get the best answer possible. Thank you!

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Old 01-21-2011, 07:19 AM   #2
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Does anybody have any advice? What if I was able to put .5 inch xps behind the studs and then just fill the studs with fiberglass batts and only cover the concrete and leave the upper portion above grade part of the wall the way that it is. But then I would have zone near the top of the walls that would have a dead space behind the drywall.


Last edited by fire angel; 01-21-2011 at 11:16 AM.
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Old 01-22-2011, 11:00 PM   #3
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I'll leave you with some good reading, then ask again; http://www.buildingscience.com/docum...ts?full_view=1

http://www.buildingscience.com/docum...ent-insulation

http://www.buildingscience.com/docum...gs?full_view=1

Gary
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Old 01-23-2011, 08:43 AM   #4
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Wow, there's alot of questions like this one! Look, I cannot address your specific type of construction (half concrete, half studded wall) as we don't do things like that up here (full concrete basements up here), but it sounds like you're at the point where science meets building codes and it therefore not only becomes confusing - but ultimatley shifts the decison right onto the consumer...

Here's what I see: the prevailing 'wisdom', call it 'the state-of-the-art' nowadays is to let basement dry to the inside, then deal with the interior moisture using dehumidfiers or ventilation. No vapour barriers, even up here. However the building codes are slow tocatch up and don'tnecessarilt reflect the state-of-the-art - just the minimum you can get by with...

So building codes still call for vapour barriers because they are a minimum standard you can get by with, not the best for your house or your health.
Now I seriously doubt whether you'll be fined for not having a vapour barrier, so it's hardly "the law" - but you have to live in your house, not the inspectors.

So, I choose to folllow the science; I put up rigid XPS on my basement walls, then stud wall filled with fibreglass batts, then gyproc - and no vapour barrier. Voids are filed with fibreglass...and I don't care what the building code says and they can sue me all they want! LOL
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Old 01-23-2011, 05:32 PM   #5
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I have read those documents Gary and I thank you for the information. My plan is to put .5in xps behind the studs and then fill the studs with fiberglass bats and no vapor barrier to cover the concrete. What should I do above the concrete? Here is how the wall looks after putting in .5in xps and sealing the seams with spray foam. Should I now just put insulation between the studs up to the top of the concrete or should I intall it to the top of the wall? Will it be OK with the vapor barrier behind insulation at the top of the wall? Here the concrete should be able to dry to the inside but the studded area will have to dry to the outside.
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Old 01-24-2011, 07:00 PM   #6
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You need foam board on top of any concrete wall to air seal it completely from the room air, fig. 11 in the first link. Page 9 and 10 on thickness of foam; http://www.buildingscience.com/docum...lation-systems

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Old 01-24-2011, 07:49 PM   #7
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Plastic on walls, fig.4; http://www.buildingscience.com/docum...nd-wall-design

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Old 01-25-2011, 09:29 AM   #8
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Yes Gary, I realize that I have not yet put the xps on top of the concrete, thank you. I also realize that in the article that you attached it says that there should be 3/4in xps, however I cannot fit that behind the studs.
This space will be air conditioned in the summer months so that should help with the drying.
In your opinion do you think that I will have issues the way that I have it set up now?
I have attached a diagram of how the wall is now.
How do I put in the fiberglass batts, just to the top of the concrete like the green shows in fig 2 or fill the cavity in front of the vapor barrier all the way to the ceiling like fig 3?
Sorry for being such a pain, I really appreciate your advice!!!!!
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Old 01-26-2011, 05:02 PM   #9
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Compare your annual heating degree days with the different cities listed in the last link, # 7. Lose the vapor barrier plastic if in any of the Zones mentioned, fig. 4, 5. Look them up.....

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Old 01-27-2011, 07:48 AM   #10
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I would be in zone 6 and that shows in Fig 4a that I need the vapor barrier on the above grade portion and that is how mine currently is. I am wondering about what to do in the void area that will be between the vapor barrier that is there and the drywall that I will be putting up like I showed in the diagram that I made.
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Old 01-27-2011, 08:31 AM   #11
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If you have a void there, then you will get convective air circulation (the chimney effect) albeit small; if you have air circulation, you'll have condensation - and that you don't need.

Reason enough - compared to not doing so - of filling the void with fibreglass unfaced, is what I'd say.
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Old 01-27-2011, 10:09 AM   #12
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Typically you need R-13 worth of insulation over that part of the foundation wall below grade and R-19 above grade. Check your city's building code.

Many experts say not to have fiberglass batts or loose fill insulation touching the concrete, to avoid trapped moisture and mold. Thus the idea of putting nonporous foam on first.

If your foundation is sealed with tar or whatever on the outside, then do not put a vapor barrier on the inside. If you did use faced batt insulation, cut lots of slits in the facing so it is no longer a moisture barrier.
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Old 01-27-2011, 09:16 PM   #13
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I would batt all the way up, with the top 1/2 of thicker un-faced as Cc. said. You don't want a gap for c.loops to lose 30-50% of the R-value; http://www.diychatroom.com/f98/how-b...ulation-90438/

The thinner foam board will work, better than plastic directly on the wall, where is is much harder to completely air seal from room air; http://www.buildingscience.com/docum...ecommendations

You do not need any plastic (as the site said) in a basement wall for Zone 6; http://publicecodes.citation.com/ico...001_par003.htm.

R-13 is minimum for a basement wall in Zone 6; http://publicecodes.citation.com/ico..._11_sec002.htm

Remove any plastic or vapor retarder paper. Cutting slits in asphalt paper will only let moisture through the slits, having no effect on the rest of the existing surface area of the vapor retarder paper. Slits in an air barrier, yes! –but not vapor ….

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Old 01-28-2011, 07:34 PM   #14
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Ok I am going to remove the plastic vapor barrier on the 2x6 wall and fill everything completely with fiberglass batts. I am still a little confused where the building code says that no vapor barrier is needed on a bsement wall, however the one link that you sent me says
"Figure 4a
Sheathing/Cladding Assembly Permeance (Wet Cup) Greater than 1.0 Perm —
Minneapolis
•This assembly is very "vapor open" to the exterior, but in the
cold climate of
Minneapolis this assembly
does require a specific "vapor resistance" on the

interior"

Thank you all for your help!!!
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Old 01-28-2011, 11:10 PM   #15
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"R601.3 Vapor retarders. Class I or II vapor retarders are required on the interior side of frame walls in Zones 5, 6, 7, 8 and Marine 4.

Exceptions:


1. Basement walls.
From; You do not need any plastic (as the site said) in a basement wall for Zone 6; http://publicecodes.citation.com/ico...001_par003.htm.Gary

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