Adding Extra Attic Insulation????

Old 11-15-09, 03:16 PM
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Adding Extra Attic Insulation????

Hello All,

My name is Dale, and I am a casual do-it-yourselfer ..

I am thinking about adding additional insulation to my attic. The existing insulation is blown-in, and it appears to be approximately R30 in depth. Although this is inconsistent (peaks in the middle and tapers down). The area that I want to add extra insulation to is approx. 500 sq.ft. The blown-in insulation is to a depth above the joist (no wood exposed), and I am planning to add roll insulation (no backing) perpendicular to the joist. I have found some inexpensive R30 attic insulation, and the cost is of materials is approx $85 for the job. My attic is fairly easy to reach, so installation would be no problem. My question is am I doing myself any good. I know that the existing blown-in insulation will be compressed when I run the roll insulation, so the R value will go down ... BUT I am adding R30 over this, so I will have at least what I started out with. I probably will not get complete coverage of the entire attic (in other words, I will not fill every nook).

Is it worth this money. Is it okay to compress this blown-in.

Thanks for the comments.
Old 11-15-09, 08:50 PM
Join Date: Oct 2008
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Hi Dale, More insulation is usually better, but the actual benefits may be difficult to feel or see in your heating bills. Example: With say r=20 to 30 up there now, your are loosing approximately 20% of your heat through the ceiling. These are very rough numbers. If you spend $1,000 per year on heat, then $200 is going out through that ceiling. Double the R-value and cut that loss in half. Since you already know you will not be fully doubling what is up there, then you save say $50 a year. For an $85 investment for an easy job, that is still ok.

But, let's make it better. Before you install the new insulation, dig into what is there and air seal all holes from below, plumbing, electrical, vents, chimney, drop ceilings, and others. Do the same from the basement. Heat conducts very slowly through materials. But an air leak removes the heat like a freight train. So disturbing the insulation to air seal is not good, but if you are installing more, now would be the time.

If you want to play with some real numbers, there are heat loss calculators that will let you play with planned improvements to see what they actually save. Attics with reasonable insulation are low on the savings list, but often high on the project list because they are accessible and a good diy project. If you want more savings, we can walk you through the entire house and catch some of the other easy fixes, do it every week and glad to help.

Old 11-15-09, 09:58 PM
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Are you sure you have R-30 up there? That would be 8-3/4" of insulation or 2x8 ceiling joists. Which would be unusual for an attic ceiling and not a floor. I'm using cellulose at R- 3.4 per inch, if fiberglass blow-in, even higher joists. Insulation Comparison Chart You will not compress the blown-in much as fiberglass batts weigh .04 pounds per square foot per inch thickness. For R-30, this would be 9-1/2” or 0.38 lb. per square foot. That is only 6+ ounces per square foot, not much weight to compress over a square foot area. You should use what is suggested for your locale. Check your zip in the fourth paragraph here: Insulation Fact Sheet I would rather spend more money on air sealing as Bud said, also in that article. Here is some food for thought for you: Be safe, Gary

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