Author Topic: Sound Isolation Room Details  (Read 3352 times)


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Sound Isolation Room Details
« on: June 10, 2014, 06:01:58 PM »
I posted in the past about building a standalone room within my townhouse basement for a band practice space.  Here's the idea:

I recently moved into a condo with half the basement unfinished.  The ceilings are high (the lowest point being 8' to bottom of ducts).  The neighboring units are separated by a formed concrete wall.  I'm not sure how thick...maybe 10".  The rear wall is concrete up to about 3' and wood framed and insulated the rest of the way up.  The attached garage is beyond that framed wall.  The opposite wall is an interior wood framed wall.  The wood framed walls are finished on the other sides, but unfinished on the side I'm interested in using for band practice.  The ceiling is unfinished and has lots of space.  Above the 12" deep ducts are truss joists supporting the subfloor.  It was built seemingly well, around 2003. 

My ultimate goal is to be able to have band practice (rock music with drums bass and guitars) in my basement without my neighbors hearing us).  Given my situation is this possible within a reasonable budget?  My plan is to build a room within that room, leaving an inch or two between existing walls.  After doing some research, I'm getting some conflicting ideas, but here's my basic plan:

1.  2x4 framed walls 1-2 inches away from existing walls
2.  regular fiberglass insulation between studs
3.  ceiling supported by new walls only (isolated from existing ceiling
4.  5/8" thick drywall fastened directly to studs (would resilient channel be worth the cost and time if I'm already decoupling the entire wall?)
5.  another 5/8" thick layer of drywall with greenglue between.  (is the extra layer of drywall really going to do anything substantial for me?  What about greenglue?  Is there a less expensive alternative to greenglue?)

That's my basic plan.  The basement is on a concrete slab which is isolated from the walls around the perimeter (there is expansion board where they abut.  I'm thinking that will sufficiently isolate the slab from the adjacent units.  But would it still be beneficial to use some sort of rubber strip or feet along the sill of the 2x4 walls?  As for the flooring, I was just going to use some fairly heavy carpet. 
I'm now working through some of the details and questions are coming up:

1.  Even though I'm decoupling the ceiling completely from the first floor, would it be worthwhile to do something to the joist (16" deep truss) space above the new ceiling?  Should I add insulation in that space?  Currently there is nothing.  When I look up, I see the OSB subfloor. 

2.  There is currently a round duct supplying the unfinished space where my room is going.  I was planning to use that supply in the new room and replace the rigid duct with flexible duct that I will wind a few times within the truss space.  Does that seem sufficient?  Also, there is no return in that space.  Would using flex duct to vent back into that space be ok, or should I tie it into the main return ducting? 

3.  I'm planning to use commercial rubber base trim beneath the bottom plate of the new walls to help dampen sound transmission from walls to concrete floor.  Is this a good idea? 

4.  Any benefit to using 1/2" and 5/8" drywall in combo with green glue between?

5.  Can I use regular caulk to seal between drywall panels?

6.  I will have several doors.  Will heavy exterior doors (well sealed) be my best bet? 

7.  There will be some large 8x20 ducts running above the new space.  They are not attached, but they will be a couple inches away.  Should I wrap them in insulation or treat them with something to cut down on vibrations?  Any suggestions. 

Thanks so much for the advice.  I want to make sure I'm considering everything before I start.

Randy S

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Re: Sound Isolation Room Details
« Reply #1 on: June 10, 2014, 07:14:41 PM »
ok here we go :)

1) it is always a good idea to add mass any chance you can get. one of the tricks we do is using 1/2" hardie backer(cement board / construction adhesive and some mechanical fasteners up in between the joist attached to the existing subfloor and caulk around the perimeter. especially if your flooring above is finished wood floor. or you can staple a layer of mass loaded vinyl to the bottom of the existing joist system and seal air tight.
2)You definitely need a return in the room, I would advise you to build "baffle boxes for your supply and return if you are doing heavy bass or high intensity ...go on to google and type in "baffle box" and you will see the rat mazes. the more the 90* the quieter it will be ...add 5' cfm for every turn.
3) the minute you shoot into the concrete you have just bypassed the rubber.
4) we always use 5/8" x 2 layers w/ green glue
5) your acoustical caulk is used in the interleaving corners around perimeters only..don't worry about field because you should be offsetting the seams between layer anyway.
6) the heavier the door and the better the seal is the way to go...even better would be to make an inner lock with the 2 doors 90* to each other, sound does not do well around 90* turns.
7) you can wrap the ducts in our 1" ssp foam mat STC 25
feel free to contact me direct to discuss
Randy S.
760-752-3030 ext 104


  • Guest
Re: Sound Isolation Room Details
« Reply #2 on: June 12, 2014, 12:00:41 PM »
Thanks for the suggestions.  I did a preliminary design of the room to do a cost estimate.  Based on the recommended minimum application of green glue (2 tubes per 4x8 sheet of drywall) that is the most expensive part of the project.  For a relatively small room (12x12) it's going to cost me over $600 for the green glue alone.  Having never used it before, that's a hard pill to swallow.  Is it really going to provide me that much benefit?  Are there any cheaper alternatives?