Well, it depends where you live; for instance, in an attic in Dallas you are looking for about 15" or a R49 rating, but in Houston you are typically looking for about 12" or a R38. Now there is absolutely nothing wrong with stepping up to that R49 rating.... but be careful not to get your rating so high that you will never recoup the money that you put in. You really want to take a look at the government standard for your particular area on what amount of insulation is recommended. Walls are similar. They can have ratings, but typically in a wall, you will be looking for somewhere around a R18. That is really about as good as you are going to do, but here is the "kicker" on that. To get an R18 you are looking at 5-1/2" of insulation. Most of our walls are built with 2" x4" studs which is again the reason I will recommend you injection foam insulation. Injection foam insulation in a 2" x 4" wall is the best way to meet that standard to make your home very energy efficient.