View Full Version : Why R10 but not R20 for Basement Wall in MA

02-04-2012, 09:45 PM
I thought the recommended basement wall R-value is 20 but just found the government's recommendation for interior wall is R10 but not R20 for zone 3. Form the zone map (http://www.ornl.gov/sci/roofs+walls/insulation/fact%20sheets/basement%20Insulation%20Technology%20fact.pdf), it looks like MA is in zone 3.

does the R10 recommendation assume there is a good exterior insulation? or R10 itself is enough for interior wall no matter the condition of wall exterior insulation.

I have a full basement with window wells. It only have about 7" above ground. It requires less insulation for underground wall, I think. If R10 is enough, I can save some money which is planned for fibre glass batts.

Bying using this calculator (http://www.ornl.gov/sci/roofs+walls/insulation/ins_16.html), http://www.ornl.gov/sci/roofs+walls/insulation/ins_16.html, I got R11 or R15 in my area with 018XX, 024XX and 017XX zip code. It seems R20 is overkill?

Dana, I know you have done yours with R20. What's your opinion about this?