I need to make a decision tonight.. I have a case of green glue on rush delivery set to arrive tomorrow morning.... I WAS going to go with Roxul 24" OC insulation - I've got 2x6 top and bottom plates I'm going to have 2 layers of 5/8 drywall overtop of that with green glue. My contractor said that nowhere has the 24" OC Roxul, only 16" - I understand that green glue is not recommended for 16" OC.... My question is: Do I go with R13 or R19 insulation? My contractor is insisting on R19 - but I want to know what's best... He also acted like "no one builds on 24" OC and that is why he didn't see 24" OC Roxul in the stores. So Should I tell him to use R13 or R19 insulation with the 24" OC stud wall? Please respond ASAP if possible as the job is being completed tomorrow morning.