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Old 10-01-2009, 07:46 AM   #1
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How many layers of insulation in an attic?


I recently had to reinsulate part of my attic. Now that we are getting sub zero temps I find the temp drops fast if the furnace is not running. I'm thinking I need to put more insulation. I put in 2 layers, one layer between the joists, and another layer just laid on top of that layer but lined up perpenducular.

Should I put even more on top?
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Old 10-01-2009, 07:55 AM   #2
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Its not really layers, its Rvalue
I have R30-R44 in different parts
What is the Rvaluse fo what is installed?
R49-60 is recommended for colder areas



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Old 10-01-2009, 10:47 AM   #3
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I think it's like R-19 or something but not 100% sure.

edit: got home and checked and yes it was that or 20. What I have left over is R-20.

So do the R values just add up? so 3 layers = R60?

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Old 10-01-2009, 11:49 AM   #4
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Yes, 3 layers of R20 would give you R60
You only want one layer with paper face - againmst ceiling/heated space
Then the rest unfaced
You can buy R38 - at least here, but it's in 4' batts instead of rolls



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Old 10-01-2009, 11:53 AM   #5
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The first layer can be faced, put directly on the ceiling material, with the rest unfaced. Here you can enter your local zip and also learn a lot: http://www.ornl.gov/sci/roofs+walls/...on/ins_06.html Notice the air sealing is equally important as the insulation. Good that you ran the second layer perpendicular for the joists' thermal break required. Yes they add up, the more the better if you air sealed (fiberglass does nothing to stop air movement from the conditioned space but collect the dirt). Look for dirt in the insulation to find the worst air leaks. The batts create an air space to collect the heat, when full they give it off. This is why you should never compress the insulation, counter-productive.
Be safe, Gary
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Old 10-01-2009, 12:08 PM   #6
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Perfect think that's what I'll do, i'll go up and just add some more. None of it is faced, is thsi a problem? There is a vapor barrier installed to seperate the drywall ceiling though.

Any issue with me going up there when it's cold (other then me being cold)? Wondering if the rapid heat loss will cause condensation.
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Old 10-01-2009, 01:25 PM   #7
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Been waiting for this Thread.


Please start a new thread instead of asking questions in an existing thread

I have moved your question to a new thread
Thanks - Dave

http://www.diychatroom.com/f19/insul...rs-tenn-54226/
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Old 10-01-2009, 05:14 PM   #8
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You are fine with unfaced as v.b. is already where it should be. The attic should be ventilated 50/50 soffit/ridge vents which would remove the hot moist air without harm. I would not leave it open all night.......
Be safe, Gary
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Old 10-01-2009, 09:19 PM   #9
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Not 100% sure how it's vented, but guess if I don't leave it open too long (ex: half an hour max) I should be fine? Next summer I want to check out my attic ventilation further and fix if needed. I think the soffits are nailed on plywood so there's hardly no vents but I'll have to remove it from outside to check as I can't see from the attic due to how the overhang is made.
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Old 10-02-2009, 11:39 AM   #10
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I meant if it's snowing and the 2x3' attic access hole left open, it could easily cause ice dams overnight from the heated moist conditioned air. As well as you would be wasting conditioned air.
Be safe, Gary
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Old 10-02-2009, 11:47 AM   #11
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Are you saying that a poorly insulated attic can damage your roof shingles Or a Poorly ventalated attic can damage your shingles?
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Old 10-02-2009, 01:58 PM   #12
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"a poorly insulated attic can damage your roof shingles" ------- by letting moist heat escape from below to the rafters and roof deck underside depositing moisture there to grow mold. It could also create frost on the framing because of the temperature difference. Also thaw the snow/ice on roof to re-freeze creating ice-dams which back up under shingles to leak on framing, insulation, drywall ceiling, etc.

"Or a Poorly ventalated attic can damage your shingles?" ------- the shingle would get hotter in the summer, degrading them faster from poor ventilation. Shingle manufacturers require proper ventilation to warranty their product, stated on the wrapper. In winter, air leaks from below would do as mention earlier. Without air movement to remove the hot moist air, it would condense on the cooler insulation and roof structure causing mold and rot from the fungi.
Be safe, Gary
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