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Old 06-15-2013, 11:09 PM   #1
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Basement Insulation calculations


Can someone explain the calculations I have seen in threads for basement insulation? I am in zone 6. I was planning on using roxul in the cavities but I am having trouble figuring out what thickness XPS. I was really hoping to use none or 1" at the most, but I am not sure if that is recommended.

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Old 06-16-2013, 10:22 AM   #2
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Basement Insulation calculations


1" should be fine.

Paging Gary for the tables and clarifications.

He is a code wiz!!!

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Old 06-17-2013, 01:10 PM   #3
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Basement Insulation calculations


After plenty of research, I did 1" on my basement walls in Minneapolis. 2" may be "best", but if your humidity levels in your basement are not too high, you should be fine.

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Old 06-17-2013, 01:21 PM   #4
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Basement Insulation calculations


Just keep in mind that the earth is a great moderator of temperatures and it does not vary too much when you get below 3' to 4' or so, even though there may be a few consecutive days of -20F nights. Because of this, less insulation is needed for basements this, than for above grade portions of homes. I have seen frost penetration of only a few inches under a good snow cover even after a month or more of -10 to -30F.

If you condition the space (heat and AC) too much insulation prevents some of the benefits of being below grade if you have proper low returns on at the lowest level.
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Old 06-17-2013, 02:05 PM   #5
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Basement Insulation calculations


Okay good info. Only about two feet is above grade. What would be a better approach? Do I even need insulation? Or just the two feed above grade?
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Old 06-19-2013, 01:44 PM   #6
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Basement Insulation calculations


So if I do 1" xps is R15 roxul overkill between the studs?
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Old 06-19-2013, 07:52 PM   #7
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Basement Insulation calculations


No.

Insulation, even when below grade, is recommended.

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