Originally Posted by SouthernThunder
Thanks for the replies guys. I did some checking an R19 is going for .383 cents a sq and R21 is .50 cents a sq. The price difference for doing this house in R21 instead of 19 is about $286.
One other thing I found was that fiberglass insulation loses some R value when it is compressed. R19 will have to be compressed to fit into a 2x6 wall but R21 will not so the difference may be slightly better than I thought.
Gary, your calculator says it would pay for itself in 5 years in this house. But if I'm not mistaken thats just for heating and not cooling which can be as big of a bill here in oklahoma as well. I havent realy looked into cellulose that you mentioned because I have heard it settles and leaves gaps at the top pf the walls? Is this true?
Ditto the no brainer comment so long as I can find a supplier. I am having a real problem finding someone around here to sell it to me. The one place that quoted me a price couldn't sell it to me because I wasn't a contractor.
Right, the calculator only does heating, so you might do a good deal better than it indicates.
I'm a fan of cellulose.
It will never settle if installed properly. It should be "dense packed" -- if the installer does not know what this means, I'd find another installer.
It has a bit higher an R value per inch that FG, but the main thing is that it is dense enough not to allow air currents to form under cold conditions. Air currents in loose fill FG can reduce the effective R value by half under cold conditions. This should be less of a problem in walls, but (I think) would still be there.
This is the ORNL test that shows this:
FG needs to be installed very carefully in walls to work well -- cut to fit carefully, fitted around wires and outlets, ...
The insulation installers are usually the lowest paid guys on the site, and don't have a great reputation for taking a lot of pride in doing it right -- but, I'm there are are some exceptions -- maybe some free pizza would help
But, if you are doing the work, probably either type of insulation can work well.
You might check out the Taunton Fine Homebuilding forum -- there are tons of past discussion on insulation among the guys who do the installing -- very strong opinions
There is some material on insulating here:
This "Whole Wall" insulation calculator is also interesting -- it tells you how much R value you lose due to heat short circuiting through studs -- it will make you a believer in the insulating sheathing:
The book by Harley called "Insulate and Weatherize" is very good -- I've used it a lot.