R-value measures how well a material resists heat flow. Higher is better, but the right number depends on where you live, and Georgia's energy code sets minimums for our climate zone. For most of Metro Atlanta that works out to roughly R-38 in the attic and R-13 to R-20 in exterior walls, depending on the assembly and the code year your inspector is working from.
Those numbers are minimums for new construction. Existing homes were built to whatever the code said at the time, and many older attics in our area measure R-11 to R-19 today after decades of settling. That's a big gap, and it's the reason a blown-in top-off pays back so quickly.
For blown-in fiberglass or cellulose, R-value is a function of depth, which is why we leave depth markers across the attic. For batts, it's printed on the product, but only if the batt is installed full-depth with no compression or gaps. For spray foam, closed-cell runs roughly R-6 to R-7 per inch and open-cell around R-3.5 to R-4 per inch, which is why we specify a thickness on every estimate rather than just a material.
If you're not sure what's in your attic, we'll measure it during a free on-site visit and tell you exactly where you stand against the current code.