Also, in the part of Rod's book you are referencing he says that 3/8" glass is ALMOST the same mass as 4 sheets of 5/8" gypsum. I wouldn't have any problem at all using 3/8" and 1/2" in a wall assy. that didn't use GG. He simply upgrades to the next NOMINAL size of 1/2" Lami, which is actually quite more massive than 2.5" thick gypsum. The actual thickness that would be required as an equal density to your 4 sheets of drywall is roughly .400".
This doesn't make any sense.... what page is this info on?