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Old 01-15-2011, 10:43 PM   #1
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Using used insulation


We are building a house and are ready to insulate. Our friend who is a contractor will have a whole lot of r-30 they will be removing from a commercial building that we can have for free. We live in the valley in N.CA and it does get hot, but not very cold. These are my questions:
1. We need r-38 in the ceiling. We have a large attic that will stay unconditioned for now and need to insulate below this area. We have 12" trusses with with the entire floor of the attic sheeted. Can I double up the r-30 even though it will squish it and leave now space for a flow above the insulation?
2. We have 2x6 walls. Can we squish the r-30 into the walls?
Thanks for any help at all.
Kirk.

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Old 01-15-2011, 11:25 PM   #2
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Using used insulation


Compressing fiberglass causes it to lose it's effectiveness. You can peel off some so it fits reasonably well if you want to go to that trouble.
It doesn't peel evenly.
Ron

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Old 01-16-2011, 12:01 AM   #3
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I did think about doing that for the walls because I know if I didn't get the thicknesses right it would probably be okay. But, I was told that in the ceiling I don't need to worry about having any air flow above the insulation, so I was wondering if the amount of compression of 2 batts of insulation would decrease the r value below 38. I really don't know how to judge this and was wondering if someone did.
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Old 01-16-2011, 12:29 AM   #4
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Using used insulation


It depends on how much you compress it. The chart here only goes so far; http://saveenergy.owenscorning.com/2...nd_your_2.html

May want to read up on R-30 here; http://www.diychatroom.com/f98/how-b...ulation-90438/

Gary
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Old 01-16-2011, 02:01 AM   #5
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Using used insulation


That was great information.
But, how important is it to have a space for air flow above the insulation, in the ceiling, under the subfloor of the unconditioned attic?
Also, if the r-30 is compressed to a r-21 in a 2x6 wall, is it important to have air flow between the insulation and the exterior sheeting?
Thanks again for the great info.
Kirk.
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Old 01-16-2011, 05:49 AM   #6
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Using used insulation


yes r-30 will fit in a 2x6 wall cavity compressed to r-21
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Old 01-16-2011, 03:16 PM   #7
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You may have skipped the links on an air gap behind, front, top, bottom, will give you convective loops with the any fiberglass insulation, you also get natural convective loops inside the insulation itself with the low density fiberglass, batt or blown-in. In the "How to" article I put together.

Gary
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Old 01-18-2011, 12:21 AM   #8
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If I understand right then it would be fine to squish r-30 into the walls and double the batts up in the ceiling. I just need to make sure the insulation is put in without any voids. I just thought that there needed to be an opening for air to carry out the heat so it didn't get trapped and then heat the room up. If this set up is not equal or better than r-38 in the ceiling or r-19 in the walls I don't want to do it.
Again, thanks for the great information.
Kirk.
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Old 01-18-2011, 06:03 AM   #9
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As for your ceiling make sure there is an air cavity between the unsulation and the underside of the roof .Use vent baffles anwhere the insulation may block air circulation to allow your sofit and roof system to breathe.
As for air cavities in your walls beteen the insulation and the outside wall requirements look in the insulation code for your region.
Where i live its not required in the walls but roof insulation requires an air cavity.

Last edited by KCB; 01-18-2011 at 06:11 AM.
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Old 01-18-2011, 03:54 PM   #10
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Sorry, forgot my link;
http://www.diychatroom.com/f98/how-b...ulation-90438/

Gary

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