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using 1/4 inch foam board over batting of interior wall in the attic

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  #1  
Old 12-16-12, 07:40 PM
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using 1/4 inch foam board over batting of interior wall in the attic

Hey Guys,

I'm prepping to do some blown in insulation. In may attic I have one wall and the top of a staircase ceiling that have some insualtion on them. I added some 1/4 inch foam board on top of insulation. Was this a mistake regarding vapor barrier. I was about to seal all the seems went a light went off in my head and I wan't sure if this was a good idea or not. Need some advice. Attached before and after pics. Thank you.


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Last edited by JBG7676; 12-16-12 at 07:42 PM. Reason: spelling
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  #2  
Old 12-16-12, 08:37 PM
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If the fanfold is perforated, it has a perm rating > 1 so it would not be classified as a vapor barrier. That being said, it could still cause a condensation issue if it is the cold surface that your warm humid air comes into contact with. What was your goal in adding it? 1/4" fanfold has next to no insulation value.
 
  #3  
Old 12-17-12, 09:20 AM
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I listened to someone I should't have. So should I remove it and just install unfaced batting?
 
  #4  
Old 12-17-12, 12:05 PM
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XSleeper is correct and your thoughts about removing and starting over are also correct. It has little value and a high risk, especially looking at that ugly fiberglass insulation.

If you start over the results will improve greatly, since you will be able to see and seal air leaks from the house below. Warm inside air holds a lot of moisture and costs a lot to heat so air sealing is the highest priority and highest yield. Then address whatever insulation you choose. In some locations you may be able to re-install the loose fill, but certainly ditch the black fiberglass.

R-19 installed correctly is probably better than r-40 done poorly with no air sealing. But go with the R-40 anyway, or whatever is recommended in your area.

The wood along with the fg insulation looks like it has been suffering from some moisture issues. How is the ventilation up there, soffits vents, ridge vents, gable vents, or other?

Bud
 
  #5  
Old 12-17-12, 09:07 PM
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should I remove it and just install unfaced batting?
After sealing air leaks and getting rid of the black fiberglass, I would install either faced fiberglass with the facing toward the heated space, or a separate moisture barrier against the heated space with mineral wool batts against that.

And I would work on getting some good ventilation up there a.s.a.p.
 
  #6  
Old 12-18-12, 04:35 PM
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Hey Guys,

First, Thank you.

I took the board down. I began by installing a center walkway with 1/2 inch ply, cause I fell through ceiling.
I was going to install R-15 unfaced perpendicular over the existing insulation on the wall and staircase.
Then I was going to airseal and wall caps and holes with expanding foam.
Is it ok to seal around chimney and vent pipes?
Then on the floor I was going to install R30 unfaced perpendicular over existing blown insulation.
I installed new baffles. The gable vents are all clear.
What do I do about the black color on wall insulation. Is that from air passing by?

So what do you think.
 
  #7  
Old 12-18-12, 08:11 PM
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The coloration in the fiberglass is likely dirt (could be some bits of mold), and the fiberglass is acting like a giant furnace filter.

The effectiveness of fiberglass is reduced when air is moving over/through it, which is why I have started using encapsulated fiberglass batts for any fiberglass that does not require a fire barrier and will be left exposed.
 
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