Compressing Comfortbatt to insulate 4″ deep framing
johnwtaylor
| Posted in General Questions on
To insulate rough cut (full dimension) 2″x4″s is it better to use:
a.) 4″ Comfortboard 80 (8lb/cuft and R4.2/in).
b.) 5 1/2″ (2lb/cuft and R4/in) Comfortbatt that easily compresses down to 4″.
Information I’ve found says compressing Comfortbatt causes it to loose R value but Comforboard 80 has a greater R value?
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Replies
You lose R value overall, but the R value per inch goes up.
I think using Comfortboard will make it harder to get a good installation, since Comfortboard is pretty rigid and won't squish into little defects in the framing. Compressing Comfortbatts is probably a better idea, and while yes, you lose some R value, you're starting from R23 while the comfortboard is about R17 by your numbers. You'll likely end up around a similar R value in the wall either way.
Bill
Thank You Bill
My worry is compressing (reducing air volume) the Comfortbatt will drop the R value below R4/in.
Comfortbatts are rated around R-4.2/in. Comfortboard is essentially compressed Comfortbatts, also around R-4.2/in. At some point, compression will degrade the R/in, but at least with Rockwool is doesn't appear to change much within that range.
Keep in mind that all insulation manufacturers share their best possible test results, after doing many of them with fine adjustments. Very few installations will match those conditions perfectly; I use R-4/in for mineral wool when doing calculations.