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bryanp22 06-15-2013 11:09 PM

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.

Windows on Wash 06-16-2013 10:22 AM

1" should be fine.

Paging Gary for the tables and clarifications.

He is a code wiz!!!

Beepster 06-17-2013 01:10 PM

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.

B

concretemasonry 06-17-2013 01:21 PM

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.

bryanp22 06-17-2013 02:05 PM

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?

bryanp22 06-19-2013 01:44 PM

So if I do 1" xps is R15 roxul overkill between the studs?

Windows on Wash 06-19-2013 07:52 PM

No.

Insulation, even when below grade, is recommended.


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