3 1/2" R-15 or R13 for basement?


Old 10-17-05, 10:39 AM
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Join Date: Nov 2004
Location: Pleasantville, NY
Posts: 548
3 1/2" R-15 or R13 for basement?

I'm finishing a basment and was wondering if R15 (3 1/2") is recommended for basement. I notice at the Owens Corning site that they recommend R13 or R11 for basement and R15 for exterior walls. Aside from extra cost, any disadvantage of using R15 in a basement?

Thanks in advance.
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Old 10-17-05, 10:57 AM
Join Date: Mar 2005
Location: USA
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3 1/2" R-15 or R13 for basement?

Keep in mind that in the real world, basements do not need as much insulation as above ground spaces. This is a case of "if you follow the code, you are not wrong, but you may not be right" - It happens with all standards based on a static analysis of a dynamic situation.

The soil is a natural moderator and is about 50 degrees a few feet down in most places in the US. Also, you do not have the infiltration that ruins insulation systems such as a wood frame/fiberglass system.

If you were to insulate a basement to the standards required, you would not gain the benefits it provides in lowering summer air conditioning loads if you have a properly designed HVAC system.

Splitting hairs between R11, R13 and R15 is quite meaningless when you consider that the steel studs or wood studs reduce the WALL insulation by the same amount.

Old 10-17-05, 10:57 AM
Join Date: Jul 2005
Location: Ottawa, Canada
Posts: 857
Aside from the extra cost, there are no other disadvantages.
Old 10-17-05, 10:59 AM
Ed Imeduc's Avatar
Join Date: Aug 2002
Location: Mountain Williams Missouri
Posts: 18,389

We use a 6 mil poly on the cement wall the studwall1" out the R13. Paper to the room side then a 4 mil poly over that then the drywall.


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