Drywall
Drywall insulation in High Performance home theaters involves using extra Mass; Hanging the drywall on a mechanical vibration Isolation clip and channel system, and utilizing a viscoelastic component between the layers of drywall for Dampening.
Two layers of 5/8 drywall are used, avoid use of “ultra-lightweight versions of drywall as they provide less mass in the final system
Green Glue is used as the Dampening agent and is applied between layers of drywall
Isolation clips and 25 gauge 7/8 inch tall hat channel must be installed beforehand per manufacturer’s instructions
Installation Sequence
First layer on ceiling
First layer on walls
Second layer on ceiling
Second layer on walls
This results in a cascading joint where the walls meet the ceiling. This joint is tighter and will control sound better than alternatives.
Installation Steps
Starting with the first layer on the ceiling using 1 ¼ inch screws intended for metal framing (I like Grabber brand) mount the drywall perpendicular to the channels. Keep the drywall panels at least ½ inch away from the wall framing so the panels can vibrate without rubbing on the wall framing, It sometimes help to insert spaces that you pull down after the panels are up. These can be simply screwed to the wall studs hanging down enough to provide a hand hold when you are read to remove them. If you use longer screws you risk hitting a ceiling joist and defeating the isolation design.
Use at least 5 screws for each 4 ft. section into the channel, do not over spin the screws as that will strip the metal holes. You do not need to dimple the screw holes on the first layer, just get them reasonably flat.
Don’t use the screws to pull the drywall tight, instead push it up while screwing, this will insure the most secure fastening.
Stagger the seams from row to row of drywall
Once the ceiling is finished install drywall on the walls. Lift the drywall up until it just makes contact with the ceiling panels but do not force the drywall which would lift the ceiling panels. Again first layer is 1 ¼ inch screws.
Once the ceiling and walls are covered with the first layer apply a generous bead of acoustical caulk the wall/ceiling joint making it airtight. Do the same for inside corners on the walls and where the drywall meets the floor. If there are holes cut around any conduit, wires, electrical boxes any gaps need to be caulked. Lastly if any butt joints are not tight, caulk them. Green Glue brand sealant, OSI or USG brand acoustical sealant can be used.
Once the caulking is complete install the second layer of drywall using 2 inch screws designed for metal studs. Screws should hit the metal channel where possible but hanging edges of the second layer can be screwed to the first layer with 1 ¼ to 1 5/8 course thread screws.
Apply two full Speed Loader draws of Green Glue to each 4x8 sheet of drywall before positioning on the wall. Do not use less than this amount and it should be applied directly to panel in random squiggly patterns, do not trowel.
The seams from the first layer must overlap the second layer. So if you started with a full sheet, start with a ½ sheet (Lengthwise) for the second layer and adjust lengths to overlap every seam.
Do not think of the Green Glue as a glue as it takes weeks for it to cure. Use at least the same number of screws as the first layer, Hitting the channel where possible.
Once the second layer is installed caulk the same as the first layer. In most home theater designs the wall ceiling joints and inside corners will be hidden by molding and other interior finishes so rather than worrying about getting too much caulk which might cause a sloppy corner tape and mud joint, worry about creating an airtight seal. Nobody will see the taped joints. If the design is such that a corner joint will be a visible painted joint, scrape all the excess caulk out of the corners with your finger.
Examples
Correct way to hang drywall, joints are staggered
Incorrect way to hang drywall, joints are not staggered
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