Why does one have a better STC than the other?

[Rod Gervais]

Pretty much the stud spacing for the final drywall attachment - all other things being equal - a wood framed wall with RC will be about the same level of isolation as a light gauge steel stud given the same spacing - as the spacing increases you get a benefit in LF isolation levels.

Rod

[gravyface]

Originally Posted by Rod Gervais

Pretty much the stud spacing for the final drywall attachment - all other things being equal - a wood framed wall with RC will be about the same level of isolation as a light gauge steel stud given the same spacing - as the spacing increases you get a benefit in LF isolation levels.

Rod

Thanks Rod. Do you think it's worth it in terms of R-value and STC to going with a "partial" double leaf design?

i.e. adding insulation between existing exterior studs + air gap + interior studded wall, insulation, and two layers of 5/8" dry wall to complete the double-leaf design? Assuming the exterior wood lap siding/plywood is equivalent to two layers of 5/8" drywall, I should be in the neighbourhood of ~60 STC according to various charts on leaf design I've seen.