# Insulate unfinished basement walls?



## Yoyizit (Jul 11, 2008)

Since the ground temp. drops the deeper you go, the deeper insulation should be thicker. There is an online graph of this temp. vs. distance but of course I lost the link.

For payback periods of more than 10 years you probably shouldn't do it.


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## HomeSealed (Jan 3, 2008)

Yoyizit said:


> Since the ground temp. drops the deeper you go, the deeper insulation should be thicker. There is an online graph of this temp. vs. distance but of course I lost the link.
> 
> For payback periods of more than 10 years you probably shouldn't do it.




.... Your best course of action (with bang-for the -buck in mind) would be to airseal the rim joist/sill boxes, then add rigid insulation board on the TOP 4' of the wall. You could go all the way down, but with cost in mind, the top 4' is the most effective. If you are not going to finish the space you'll need to keep fire rating in mind and use a product like thermax that does not need sheetrock over it.


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## Gary in WA (Mar 11, 2009)

Air seal the basement first. Can foam all the wiring/plumbing holes to prevent feeding the "stack effect": http://www.wag-aic.org/1999/WAG_99_baker.pdf

Insulate/air seal the rim joists, a major source of air- both in and outgoing:http://www.buildingscience.com/docu...joist/files/bscinfo_408_critical_seal_rev.pdf

Insulate with foil-faced foamboard if your local AHJ will allow uncovered: http://www.quadlock.com/technical_library/bulletins/R-ETRO_Value_of_Basement_Insulation.pdf

Pick an insulation system to your liking/budget, pp. 69 on Btu's: http://www.buildingscience.com/docu...merica-high-r-foundations-case-study-analysis

Gary


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