Thinnest R-10/13 in basement with XPS and batt?
Paying attention to Worthy's excellent and much appreciated posts on the use of EPS/XPS for basement interior insulation, I'm trying to figure out what the thinnest combination of insulation types would be to achieve the desired goals.
Reviewing various sources for the recommended R-value for my area (Silver Spring, MD, which apparently has HDD=4377), I should apparently be shooting for between R10 and R13. (The sources don't agree, but R-9 is the lowest and R-13 is the highest.)
Locally available Foamular is available at 3/4-in (R3.8), 1-in (R5), 1.5-in (R7.5), and 2-in (R10).
Ideally, we'd take the thinnest XPS that gets us the moisture benefits of using XPS against the walls and then supplement with batt that gets us to the R value that we should have.
So, that's my question: how thin can we go on the XPS knowing that we'd supplement batt to get to somewhere between R-9 and R-13?