Author Topic: Room within a room help  (Read 3020 times)


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Room within a room help
« on: March 24, 2010, 08:54:08 AM »
Hi all,

I've taken to building a room within a room for band practice in perhaps the worst possible spot: a 2nd floor room directly above the huge garage in my family's home.  The garage is located on the opposite side of the house from where the rest of the family sleeps, though, and so far, the biggest noise problem seems to be contained within the house itself, so I'm not that worried about the garage, especially since I have put a significant amount of effort into the floor so far.  I guess, before getting to my main question, I'll give a bit of background on my plan, which up to now has only used materials available at the hardware store.

existing room:
- converting from a former bedroom, so it already has completed walls with drywall and plaster etc.
- plugged the windows with drywall/soundboard/drywall sandwich, caulked completely around the edges

- took up the old carpet
- laid heavy carpet padding over existing carpet padding (2 layers now), butting up against the wall to prevent vibration transferring from the hard floor to the wall
- laying "HardieBacker," concrete-like panels used to underlay tile in bathrooms, over the entirety of the room to add mass and to create a hard platform to build upon.  It's extraordinarily dense stuff.

- air tight except for ventilation system
- a non-square floor plan for the inner room (to reduce resonance), with the bottom plates resting on an additional layer of foam (is carpet padding sufficient for this?)
- walls and ceiling will be constructed with R13 insulation and two layers of drywall, perhaps with a layer of Green Glue in between them
- once the room is finished, lay down some carpet padding and and carpet inside so it's comfortable...

double doorway, sealed and air tight + ventilation system and I'm done....!

I'm not sure how loud my band plays exactly, but we haven't yet played with a bass player and I expect that to require a lot to dampen in this house.  So, here's a few questions:

Just how airtight does the outer room need to be?  All electrical outlets will be sealed, and any noticeable cracks in the walls/ceiling will be as well, but since carpet padding is forming a significant portion of the floor (the hardiebacker won't cover it completely, since I don't want the hardiebacker touching the walls), and we didn't seal the subfloor beneath it beforehand, I'm not sure if the room is ONE HUNDRED PERCENT airtight- but it must be pretty darn close.  If I need to lift up all the carpet padding, please let me know!

Second, can someone explain to me precisely how the dead air space works between the inner and outer wall?  I ask because the room I am building within isn't the largest, and maximizing floor space would be ideal.  If, for example, the key is quantity of air, and not exactly where it is located, then I have some inches to sacrifice on ceiling height that I would like to get back in floor space, if that makes sense.  The closest the inner wall will come to the outer wall is probably about 2 inches, though there will be much more dead space in other areas, specifically the ones facing the rest of the house (two of the existing walls are shared with attic space).  It is my understanding that more air helps most with reducing the resonant frequency of the decoupled wall assembly - which is why I've considered investing in Green Glue, since I've it also deals well with low tones.

Finally, I'm concerned that I need still more soundproofing on my floor.  I've thought about a layer of MLV under the carpet rather than more carpet padding (so the floor would be carpet->MLV->hardiebacker->2 layers of carpet padding-> subfloor->garage), but maybe this isn't necessary (it is so expensive!).

The goal is a rather significant decrease in the sound level in the house.  My family sleeps pretty soundly, but the room will still need to be very, very quiet I think.

Sorry this is so long!  I'm a total beginner at all this, so an evaluation of my plan as well as some answers to these questions would be very much appreciated, thank you very much!  I am so excited to continue to work on and eventually finish this room!