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Old 11-03-2010, 06:56 PM   #1
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Insulation Questions


I just bought an older home in Upstate NY and I would consider it a 1 and 1/2 story. The previous owners finished the attic. I have made it my goal to correct the insulation mistakes but I need some advice.

I pulled up a floorboard behind a knee wall and found R22 fiberglass batt. They are older and a little dirty so I know there is some air movement. Above the wood, there is no insulation. Do I roll R30 above the wood? Do I pull out the R22 and replace it with the R30 ?I know that I have to put the hard insulation blocks under the knee wall then seal them with foam. Do I put two R10 blocks together or will one do?

The bat insulation behind the knee walls is R19. Should I go over that with rigid R10 or pull it and install two prices of rigid R10? I know spray foam is great, but it will cost too much.
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Old 11-04-2010, 07:45 PM   #2
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bump bump
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Old 11-04-2010, 09:13 PM   #3
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I just bought an older home in Upstate NY and I would consider it a 1 and 1/2 story. The previous owners finished the attic. I have made it my goal to correct the insulation mistakes but I need some advice.

I pulled up a floorboard behind a knee wall and found R22 fiberglass batt. They are older and a little dirty so I know there is some air movement. Above the wood, there is no insulation. Do I roll R30 above the wood? Do I pull out the R22 and replace it with the R30 ?I know that I have to put the hard insulation blocks under the knee wall then seal them with foam. Do I put two R10 blocks together or will one do?

The bat insulation behind the knee walls is R19. Should I go over that with rigid R10 or pull it and install two prices of rigid R10? I know spray foam is great, but it will cost too much.
I, once insulated an attic that had rock wool insulation under the wooden floor boards. In this case, I laid R12 fibre glass on top off the wood and it appeared to be effective, as there was a distinct drop in heating cost.
As for the knee walls, I would think that expanded foam board insulation should installed on the warm side as it is a vapor barrier, itself!
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Old 11-05-2010, 03:40 PM   #4
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Insulation Questions


NO insulation? Yikes! Skip the fiberglass; worst batt insulation on Earth. Blow in cellulose. If that does not appeal, then use cellulose, cotton, or mineral wool batts. They are hard to get perfect, though, if the rafters are not perfect. If I did batts, I would blow at least 6" of cellulose over top. Also, it does sound like you need an air barrier (we all do), or a vapor barrier (some do) between the conditioned space and what is cold. It is too late to install one, however, without tearing out the sheathing (drywall?) on the ceiling.
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Old 11-08-2010, 06:59 PM   #5
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Fiberglass filters well....... Seal the air leaks first. Add foam board over exterior wall at raters/soffit.Protect the ends of insulation at soffit vents, add a foam board (or house wrap) to prevent wind-washing at the knee wall on attic side. Add foam board at top and bottom of knee wall as required for exterior walls in your area zip code. Abutting the baffle over the wall. http://docs.google.com/viewer?a=v&q=...bBVYCRHz6fk5Ng

http://www.buildingscience.com/docum...archterm=insul

http://www.simplesavings.coop/simple...ee%20walls.pdf

http://www.homeenergy.org/archive/he...96/961110.html

http://www.ornl.gov/sci/roofs+walls/...on/ins_16.html

Avoid f.g., especially blow-in.

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Old 11-10-2010, 10:03 PM   #6
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Thanks for the tips. The R-22 that sites in the attic joists below the wooden floorboard, it has a 2-4" gap before the boards. My friend tried to tell me that we would have a tough time blowing over it. So now I am thinking I should pull out the R-22 and just blow right in. I'm not sure if that is the correct logic or not.

Maybe this is another option... Leave the gap there and just start rolling batts over the floor board?
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Old 11-10-2010, 10:13 PM   #7
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If possible, I would pull the insulation out and fill it with cellulose. Then, relay the fiber glass over top of that.
Having a gap isn't the best, although I had to settle for that, as I couldn't lift the flooring. I did make sure that the ends of the gap were not open. If cold air can circulate in the gap, the 2nd layer is a waste of time.
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Old 11-10-2010, 10:26 PM   #8
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If possible, I would pull the insulation out and fill it with cellulose. Then, relay the fiber glass over top of that.
Having a gap isn't the best, although I had to settle for that, as I couldn't lift the flooring. I did make sure that the ends of the gap were not open. If cold air can circulate in the gap, the 2nd layer is a waste of time.
I would not lay the fiberglass over the cellulose, as I suspect it will compress it and reduce its R value. Also, it is pretty useless stuff if air can circulate through it, as it would sitting out there naked. I think blowing over it reduces a couple of its bad points, so it really is not too bad of an insulation then. That is a lot of stuff to chuck out the door, and I would guess it will do pretty well under an "airtight" (sort of) blanket. Just my thoughts on the deal....
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Old 11-11-2010, 08:58 AM   #9
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I have no experience with the blown in stuff. My friend told me that he didn't think it would play nice over top of the fiberglass. My plan was to push the hose under the knee wall of the finished side and then turn it on and pull the hose so that it fills that gap. He thinks it would all just blow back up at us.

What about the knee walls? Those have the R-19 between the studs. There is paper backing on the R-19 but the attic air is directly exposed to the pink side. I thought the logic was that the pink stuff needed to be encased so that air couldn't get to it, otherwise it doesn't work. Would I be wasting time to replace that knee wall fiberglass with the foam boards?
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Old 11-11-2010, 12:22 PM   #10
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My friend told me that he didn't think it would play nice over top of the fiberglass. Worked like a charm in my house, though I will never install the FG again; straight cellulose. This was in 1980, and I was not too familiar w/ cellulose, so I did a hybrid.

What about the knee walls? If you can install rigid foam over the FG, and seal the joints/edges, I think that eliminates some of the problems w/ FG, so it may be wasteful to nuke it. I'd be inclined to leave it.
See above, and whatever you do, do not install anything that is a vapor barrier on the cold side. Have a good one. j
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