They are logarithmic values and cannot simply be added.
Stc drywall 2 sheets.
It s important to know each side of the drywall sheet.
With two sheets total of 5 8 drywall utilizing standard insulation we often see stc ratings ranging between 30 34.
Thinner drywall sheets such as 1 4 or 3 8 will sag in between rafters over time.
If you have an stc 45 wall this does not mean the wall stops 45 db of sound.
The side that s gray or ivory should face the room.
You cannot add stc ratings.
Tips for drywall sheets always choose thick sheets 1 2 or 5 8 if you re installing drywall on your ceiling.
You might get something around stc 35.
With two total sheets of drywall common for residential interior walls we usually see an stc rating of around 33.
The sheets are available in thicknesses of 1 2 5 8 and 1 3 8 with dimensions of 4 x8 9 or 10 feet.
5 8 metal studs 5 8 drywall 2 layers total plus batt insulation stc of 43 44.
You can find this type of drywall at your local home depot or by clicking this link.