soundproof wall question

zack

Hi guys,
Long story short. I estimated a job (20,000sf), big but pretty straight forward, square 8'3" ceilings. GC called me back and said I have the job but there are some changes so he wants me to take another look and adjust my price. They need some walls to be soundproofed. The architect wants GC to install those (don't know the name) metal/aluminum tracks and I will have to attach drywall to them with 1" screws. He also wants to keep a drywall 1/8" off the floor and caulk the space between drywall and subfloor. So I told GC that I don't think it will change that much and he said "I don't think so ither but if you have to add a day or two that is still your money". Very cool of him.
So my question is:
1. How much extra work that will be (never worked with those metal tracks before)
2. Do I need to keep that exact 1/8" off the floor which might not be straight. There will be a 3/4" flooring installed.
Any tips will be great.
Walls are 8'3" so I was thinking 54"+48" drywall. I guess they want drywall 1/8" off the floor because anything bigger than that caulk will crack but I wonder if that is enough room for substructure to move?
I don't really want to charge extra for that but if I have to I would like to have a reasonable explanation.

chris

Acoustical sealant can get pricy if there is alot of it to do, Im thinking its to seperate walls from floor to help with sound traveling thru. Plan on a differnt layout on walls with RC or hat channel and yes more time . May need to standup drywall on those walls so waste will add up if using 9'ers

zack

Hi,
So the 1/8" a on the bottom is to stop a sound from traveling from wall to the floor? If yes, than that does not make any sense because most of the rooms are on first floor.

Mudshark

Chris is right Zack, that acoustic sealant can get pricey so you want to stay close to the 1/8" just to save on acoustic sealant costs. I have worked with lots of bigger gaps and cracking shouldnt be an issue but amount of sealant used is. You may want to veriify who is reponsible for the installation and material costs for that. Sometimes out here the drywallers do it and other times the general contractor looks after it.

As per trying to rationalize why it makes sense, who knows but hard to argue with the engineers.

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zack

now I have a better idea just found www.greengluecompany.com

chris

it helps in sound going thru walls (soundproof walls) Wont help in sound thru floor

Mudshark

Hey Zack - check out this other thread on DWT to pick up a few thoughts on soundproofing:

Soundproofing thread

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SlimPickins

Also Zack, look up DWT member Ted White, he's a soundproofing professional and he'll tell you to talk to your GC and design an attack strategy that does more than just isolate sound from the walls, floors need to be considered as well for a bomber application.

Green Glue or a comparable product is a good place to start....Go....find Ted.

Ted White

Sounds like they’re spec-ing Resilient Channel (RC-1). If so, be really careful about the proper orientation of that channel and avoid short-circuits. Installation errors will drop sound isolation like a rock. They may be simply be spec-ing RC-2, which would be less problematic. Your bid would differ depending on RC-1 or RC-2.

The 1/8” gap is thought to help maintain the flex of the drywall on the channel as well as to decouple from the floor. Often, this is spec’d on the sides and top of a wall as well for the same reasons. In real practical terms, both thoughts are wrong. You’ll fill that 1/8” (or whatever) gap with a lot of sealant and thereby lock that edge, so you didn’t maintain the flex at that edge after all. The decoupling from the floor (or adjacent wall or ceiling) is also more of a great idea than a practical benefit. The studs are still intimately connected to everything and for other reasons these gaps are a liability. Seal failures at the seams is common, often from trying to leave a gap everywhere.

So to answer your question, you should charge more. My opinion as to why:

The channel may be fussy to work with. If this is RC-1 or RC-2 there is no standard for its construction or performance.

If this is to be RC-1 Resilient Channel, you’ll find it more difficult to sink a fine thread drywall screw into the floppy channel when hanging the drywall.

The 1/8” gap should probably start out as ¼” if using RC-1, as the weight of the drywall will cause the channel to sag a bit. Depending on the channel, this sag might be 1/8” to 3/8”, likely closer to 1/8” in my experience. RC-2 won’t sag as much and you can just use 1/8” shims.

Overall, installation will be much easier if this is RC-2.

RocknRoller

Zack, we use quiet rock and or suppress board for couple years and are happy with results.