Please give me an overview of the layers again. Your doing hat track and whisper clips?
Foundation (ground up):
1' of 1-1/4" crushed minus rock
6" of 3/8" crushed minus rock on top of that
Concrete masonry blocks encasing all of the rock
Steel floor joists substructure on top of the rock
Sand and Roxul filling the joist bays.
Floor (sub-floor to finished floor):
3/4" LP composite plywood sub-floor
Green Glue
7/16" plywood
2mm 3-in-1 flooring underlayment
7mm laminate wood flooring
Walls (inside to outside):
5/8" type X drywall
Green Glue
5/8" type X drywall
Hat channel
Whisper Clips
2x6 wall stud
Stud bay filled with R21 fiberglass insulation
Exterior plywood sheathing
Tyvek building wrap
Hardie Plank wood-cement composite siding
Ceiling / Roof (inside to outside):
5/8" type X drywall
Green Glue
5/8" type X drywall
Hat channel
Whisper Clips
5/8" type X drywall
Green Glue
7/16" plywood
2x4 scissor trusses
Truss bays filled with R38 fiberglass insulation
Eave vents
Insulation baffles
Radiant barrier
Ridge vent
Exterior plywood sheathing
15# felt
Asphalt shingles
You'll notice a middle leaf of drywall and plywood in the roof assembly. This has to be done since the eaves and ridge are vented. Essentially sound could escape through the vents after passing through the inner leaf and prior to being obstructed by the outer leaf. I didn't want to build a three leaf system as they actually reduce performance over a two leaf system despite having more mass, but it was unavoidable given the construction type. I would have built what's called a "warm roof" but I was told by the City of Seattle permit department that warm roofs are not allowed despite me not finding any reference to them being prohibited in the Seattle building code, and them being allowed by the IBC which is what the Seattle building code is based on. A warm roof would have not required the middle leaf, would need less building materials and would have yielded a higher level of isolation. C'est la vie!