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Adding rolled insulation to existing attic


45acp's Avatar
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Join Date: Aug 2013
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MO

10-25-13, 06:10 AM   #1  
Adding rolled insulation to existing attic

hello all. I am here to get some thought and opinions.

I have a house from the early 50's and it was about 3-4 inches of blowin insulation in the attic, and in some spaces 2 inches or none (only a few spots).

I am going to roll out some unfaced fiberglass on top of that, but am wondering which product to pick. I have 2 picked out, one being 3 1/2" thick and the other 6 1/4 inch thich (same length and width). I am covering only about 770 square foot, and the cost on only a few dollars more each roll for the 6 1/4, so cost isn't much of an issue. I am wondering if the more the merrier? Or if the thinner would be adequate enough with the existing.

I live in St Louis, MO/Midwest.

Were going to take the world series...fyi

 
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Pilot Dane's Avatar
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10-25-13, 06:31 AM   #2  
R30 is considered the minimum in many areas so even with the thicker batts you will still be below modern standards. Still, anything you do will help dramatically. I would even consider blowing in insulation. Many home centers allow you to use the machine when you purchase the insulation. If you have a helper to load the machine blowing in is easier than using batts and there are no seams or little nooks that often get missed with batts.

 
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10-25-13, 07:04 AM   #3  
The step before adding more insulation is to air seal the ceiling plane below. Air leakage carries moisture into the attic and once buried it rarely gets corrected. There is also the problem that added insulation makes the attic colder and increases the potential for condensation on the roof deck above. More reason to seal the warm air leaks.

Be sure to provide a barrier at the soffits to maintain ventilation and provide a cover for the end of the insulation to prevent wind washing.

Here is a link on air sealing for some tips:
http://www.efficiencyvermont.com/ste...ide_062507.pdf

Bud

 
45acp's Avatar
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MO

10-25-13, 07:32 AM   #4  
Thanks for the info. For some reason past page 42 is blank. Are you referring to stopping air leakage from the outside in? Or leaks from the house going into the attic?

The R value of the 6 1/4 is 19, and I don't know what the R value is for the 3-4" I have not; probably not too much 10 or so. It sounds like the 6 1/4 may be the way to go then.

I thought about blow-in. It was going to cost about the same, but I live alone and the mess I heard is horrible.

 
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10-25-13, 09:25 AM   #5  
Page 42 is "2.6 WALL ADJOINING PORCH ROOF", probably not necessary, but should have loaded.

3.5" insulation is typically R-13, but is available in high density at r-15. Before you lay the insulation across the top, the cavities should be full to level. Gaps reduce the effectiveness of the insulation. If your ceiling joists are 2x6 you may want to move some of the blown-in around or fill the cavity to the top with 3.5" or more blown-in.

If you can fill the cavities with r-19 and then lay another r-19 across (diagonally) the top you are getting there. Code may still suggest more and remember, code is a minimum requirement. More is always better. But be sure to air seal that ceiling first, at least the big leaks.

Bud

 
45acp's Avatar
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10-25-13, 09:58 AM   #6  
I meant the entire document stopped loading after page 42. I thought I seen something in the index about pages 55-56. No biggie. Thanks for the input.

I will try to level that existing blowin the best I can and look for any other leaks. I know there was ductwork going from the basement to the roof that had nothing around it; just circular ductwork going through a square hole like 12x12.

I think anything will help at this point in my attic!

 
Nashkat1's Avatar
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10-26-13, 03:05 PM   #7  
Are you referring to stopping air leakage from the outside in? Or leaks from the house going into the attic?
From the conditioned space into the attic.

I know there was ductwork going from the basement to the roof that had nothing around it; just circular ductwork going through a square hole like 12x12.
You need to determine whether that's a flue or not, and the best way to seal and insulate around it.

Try downloading the document again. The information about dealing with ductwork in on pages 57-64; flues are pages 62-64 within that.

The information about working with the interface between the conditioned space and the attic is all of Chapter 5 - pages 65 - 78.

 
Gary in WA's Avatar
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10-26-13, 03:31 PM   #8  
Your area is Zone 4 or 5; Chapter 11 - Energy Efficiency

Requires R-38, code minimum; Chapter 11 - Energy Efficiency

Air sealing (your tax dollars); http://www.google.com/url?sa=t&sourc...wWATQw&cad=rja

Gary

 
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