Insulation, Radiant and Vapor Barriers - R-11 vs. R-13

We're building a bedroom in the back of our garage (brick). We've discovered 20-yr old R-11 insulation in the exterior walls. Is it worthwhile to remove and install R-13?

Well, actually neither one is enough, of course that's at yeaterdays heating prices. If it is in good shape, I would leave it. What you might consider is adding a layer of rigid foam over the studs before you sheetrock. It will add r-value and eliminate some of the loss due to the studs themselves, we call it thermal bridging. I'm not quite sure about your requirements down there, but you do get a winter, so as close to r-20 as you can get should be good.

Bud

go big or go home.

try for r 20 beyond which there is less return. already r11 to r 13 is far less return than r 2 to 4

this is for cellulose but should work to calculate return on any insulation; they just differ by thickness;
CIMA - Cellulose Insulation Performance & Value, Insulation Calculator (http://www.cellulose.org/HomeOwners/CalculateSavings.php)

go big or go home.

try for r 20 beyond which there is less return. already r11 to r 13 is far less return than r 2 to 4

this is for cellulose but should work to calculate return on any insulation; they just differ by thickness;
CIMA - Cellulose Insulation Performance & Value, Insulation Calculator (http://www.cellulose.org/HomeOwners/CalculateSavings.php)

Wow, that calculator is pretty shocking. I currently have two layers of fiberglass in the attic, about R22 total. I was planning on adding a lot more insulation to bring it closer to the R-49 that is recommended for my state (NJ). But it says I'll only save about $130 per year by going up to R-49. Definitely not worth the cost or work!