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Adding new insulation over double faced Attic Insulation


MarknNJ's Avatar
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Join Date: Oct 2013
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NJ

10-02-13, 01:55 PM   #1  
Adding new insulation over double faced Attic Insulation

Hi All,

I recently bought a home built in the 60's that had double faced insulation; upon inspection, it is about 2" think and want to beef it up. The top paper layer is brittle to the touch and just breaks apart. I've been getting estimates left and right on blown cellulose and fiberglass, which come in at around $1,600 for 1,100 sqft. As a DIY'r I'm looking to attack this task myself with the use of Owens Corning Fiberglass rolls to save on the added expenses.

What I'm wondering is, do I tear/ cut up the paper on top of existing and just lay some R-30 unfaced over the top and be done with it? Or, to achieve an R-60ish level, I want to double layer the insulation if possible. With that said, would I roll an R-19 on top of existing so to bring it to the top of the 6" joists then lay R-30 perpendicular over that?

I would be grateful for some professional advice for some of the folks at the Home Depot say to do everything when in fact they dont know too much about it.

Thanks in advance!
Mark


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canuk's Avatar
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Join Date: Sep 2013
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CANADA

10-02-13, 03:08 PM   #2  
What I'm wondering is, do I tear/ cut up the paper on top of existing and just lay some R-30 unfaced over the top and be done with it?
Being the paper facing is that far gone it wouldn't have much ( if at all ) vapour retarding capabilities.
In other words --- leave it as is.

Or, to achieve an R-60ish level, I want to double layer the insulation if possible. With that said, would I roll an R-19 on top of existing so to bring it to the top of the 6" joists then lay R-30 perpendicular over that?
Yep --- that would work just fine.

 
Nashkat1's Avatar
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10-02-13, 06:01 PM   #3  
I can't get my favorite insulation calculator to work right now, but R-60 seems like a bit much for a home in NJ.

Two quick questions: How is your attic ventilated, and how well sealed is the ceiling below it?

And some answers, adding to what canuk said:
do I tear/ cut up the paper on top of existing and just lay some R-30 unfaced over the top and be done with it? Or, to achieve an R-60ish level, I want to double layer the insulation if possible. With that said, would I roll an R-19 on top of existing so to bring it to the top of the 6" joists then lay R-30 perpendicular over that?
Look at the paper that's on top of the existing insulation. If it has asphalt on the side toward the fiberglass, it's a vapor retarder and needs to be removed. If it's just plain paper, I would pitch out whatever was loose before laying something over it.

Look at the bottom of the insulation. If there's not a vapor retarder between the ceiling and the insulation, you'll need to add one. The existing retarder can be asphalt-backed paper.

Mineral wool batts are more efficient than fiberglass, but you can't lay them over the existing fiberglass batts. If you're willing to start over, that would be the material of choice.

 
canuk's Avatar
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10-02-13, 06:26 PM   #4  
I can't get my favorite insulation calculator to work right now, but R-60 seems like a bit much for a home in NJ
.
It won't hurt anything though.


Look at the bottom of the insulation. If there's not a vapor retarder between the ceiling and the insulation, you'll need to add one.
It's really not that important since vapour diffusion is far less than infiltration from openings into the attic. Besides, if there are more than 3 layers of paint on the ceilings then there is already a somewhat vapour retarding barrier on the warm side.

Adding insulation is only half of the equation --- sealing openings from plumbing stacks, electrical , etc. into the attic space is the other half to prevent heat loss/gain.

 
Gary in WA's Avatar
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10-02-13, 06:56 PM   #5  
You are in Zone 4 or 5, 2009 IECC Climate Zone Map - New Jersey if the attic is ventilated per code and you air-seal the attic floor first, you don't need/want a vapor retarder; asphalt paper coated or other. Many people giving advice get it wrong, especially at the box stores....lol. Figure vents; Chapter 8 - Roof-Ceiling Construction

Gary

 
Nashkat1's Avatar
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10-02-13, 09:38 PM   #6  
Posted By: Nashkat1 I can't get my favorite insulation calculator to work right now, but R-60 seems like a bit much for a home in NJ.
It won't hurt anything though.
Except the member's pocketbook?

Adding insulation is only half of the equation --- sealing openings from plumbing stacks, electrical , etc. into the attic space is the other half to prevent heat loss/gain.
Actually, it's one-third. Besides air sealing, which was mentioned earlier, adequate ventilation is needed.

 
MarknNJ's Avatar
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10-03-13, 06:50 AM   #7  
Thanks for the feedback everyone; to address some of the questions, we installed two new solar gable fans along with a ridge vent. The house also has soffit vents, which I plan on keeping clear with some polystyrene breathers. As for the Asphalt on the back side of the paper, I'd have to check and get to you guys. With regards to the expenses, would I be ok and not notice a huge difference If I just throw down an R-30 roll on top of the existing instead of double layering for an R-60?

 
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