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Old 09-18-2016, 04:02 PM   #1
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Attic Un-faced Batt with Poly Sheeting?


I'm replacing all of my attic insulation since its very old and probably has no R value left. I'm replacing instead of adding to because the kraft paper has pretty much disintegrated.

I bought like 15 rolls of UNFACED attic insulation from homedepot (rented a truck to get it all home).

I now realize that I needed FACED insulation.

So my question is, should I rent another truck to exchange what I bought, or can I get some vapor barrier rolls to lay down in the bays first, then roll out the insulation on top?

If I can, what kind of vapor barrier should I use? Kraft paper? Poly sheeting? Where do I buy this?

I'm definitely not an insulation expert (since I bought the wrong kind) so any help is much appreciated!


Thanks!
Marc
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Old 09-18-2016, 04:13 PM   #2
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Re: Attic Un-faced Batt with Poly Sheeting?


Has the attic been air sealed?
Need to do that first.
Would have been far better off buying blown in insulation, buy at least 10 bags and they let you use the blower for free.
Any vapor barrier would have been applied before the sheetrock went up on the ceiling joist.
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Old 09-18-2016, 04:19 PM   #3
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Re: Attic Un-faced Batt with Poly Sheeting?


Quote:
Originally Posted by joecaption View Post
Has the attic been air sealed?
Need to do that first.
Would have been far better off buying blown in insulation, buy at least 10 bags and they let you use the blower for free.
Any vapor barrier would have been applied before the sheetrock went up on the ceiling joist.
Looking back I probably should have done blown. But now I'm stuck with all these giant rolls .

By 'air sealed' do you mean a vapor barrier between sheetrock and joists?

There's no vapor barrier between sheetrock and joists. In fact I think they even installed the insulation wrong because the paper side is facing up toward the attic - not down.

The house is in NJ and was built in late 50s. The insulation I'm guessing is likely the original.
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Old 09-18-2016, 06:29 PM   #4
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Re: Attic Un-faced Batt with Poly Sheeting?


Hi marcus,
The good news is you probably don't need to improvise an actual vapor barrier. The newer recommendations for vapor barriers is only the far north or deep south. In between, especially where the home is both heated and air conditioned (the warm side shifts from inside to outside) it is fine to omit one.

As Joe mentioned, the added important step is to air seal the ceiling between the house and the attic. I'll add a related link on air sealing and another on vapor barriers and vapor retarders.

https://www.energystar.gov/ia/partne...ide_062507.pdf

http://energy.gov/energysaver/vapor-...sion-retarders

In your case, while all of the old insulation is out (and I agree) it is a perfect time to address all penetrations and the tops of all walls. Air leakage transports far more moisture than what can diffuse through your drywall, especially since the paint is already serving as a vapor retarder.

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Old 09-25-2016, 01:16 PM   #5
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Re: Attic Un-faced Batt with Poly Sheeting?


Question: when you use blown in on existing construction where there's no vapor barrier already between sheetrock and joists, what would you use as a vapor barrier?
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Old 09-25-2016, 01:30 PM   #6
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Re: Attic Un-faced Batt with Poly Sheeting?


The purpose of the Vapor Barrier is to reduce the flow of moisture in the air from the warm house to the cold attic. What they have learned is that air leaks are a far more significant source of that movement and if you do a good job of air sealing there is little to no need for a vapor barrier. Recommendations are not saying only the far north and deep south need them or if your local code official is stuck in the past, s/he rules. But from a "doing the job right" point of view, no VB is needed in your climate zone. And, in reality, your paint is probably acting as a qualified vapor retarder anyway.

Some related reading:
http://www.greenbuildingadvisor.com/...vapor-barriers

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Old 09-25-2016, 04:02 PM   #7
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Re: Attic Un-faced Batt with Poly Sheeting?


Ok I think I got it. So essentially just air seal all the top plates, electrical fixtures, pipes, chimney, etc. Once that's done I can just lay down my unfaced insulation rolls. is that right?

also what's the best air sealer product to use? Meaning what type of spray foam and caulk?

Last edited by marcus118; 09-25-2016 at 04:19 PM.
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Old 09-25-2016, 05:11 PM   #8
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Re: Attic Un-faced Batt with Poly Sheeting?


That's right.

As for the approach, I prefer caulking. I've installed caulking and found it secure and in place 35 years later, and that was exposed to the weather. Some recommend mastic as used in duct sealing. Certainly works well, just messy. The can foam is good for larger cracks and holes. Look for a fire rated brand.

Around chimneys or plumbing vents you can use flashing and the caulking.

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Old 09-26-2016, 06:14 AM   #9
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Re: Attic Un-faced Batt with Poly Sheeting?


Ok thanks Bud!
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Old 09-26-2016, 09:10 AM   #10
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Re: Attic Un-faced Batt with Poly Sheeting?


Quote:
Originally Posted by Bud9051 View Post
That's right.

As for the approach, I prefer caulking. I've installed caulking and found it secure and in place 35 years later, and that was exposed to the weather. Some recommend mastic as used in duct sealing. Certainly works well, just messy. The can foam is good for larger cracks and holes. Look for a fire rated brand.

Around chimneys or plumbing vents you can use flashing and the caulking.

Bud

What caulk did you use for air sealing? I have fire-rated for the chimney but I'm not sure what caulk to use for the drywall.
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