Estimated STC of ceiling

maestro7879 · Post by **maestro7879** » Wed Apr 21, 2004 6:05 am

I'm just wondering what the estimated STC of this ceiling would be and how it could be improved without tearing it apart. I know it's not ideal the way it is now.

Hardwood Floor
Plywood
joists
insulation
1/2 drywall
RC
5/8 drywall
5/8 drywall

Thanks

Post by **Aaronw** » Wed Apr 21, 2004 7:24 am

If I'm not mistaken (and Steve will jump in here if I am), that 1/2" somewhat makes it a 3 leaf system. You would want to have something like this (just move the 1/2"):

Hardwood Floor
Plywood
joists
insulation
RC
5/8 drywall
1/2 drywall
5/8 drywall

Aaron

giles117 · Post by **giles117** » Wed Apr 21, 2004 11:32 am

Aaron you are right. placing that 1/2" then rc and then the last 2 sheest of drywall creates a 3 leaf system.

The final diagram you gave is the best way to go.

Bryan giles

maestro7879 · Post by **maestro7879** » Wed Apr 21, 2004 1:09 pm

I also agree with both statements but my question was what would the STC be of this ceiling and is there anyway that it could be improved without tearing the ceiling apart.

giles117 · Post by **giles117** » Wed Apr 21, 2004 8:56 pm

search arond this category. Steve posted some stuff about 7 or 8 months back regarding ceilings and STC.

Bryan Giles

dymaxian · Post by **dymaxian** » Wed Apr 21, 2004 11:51 pm

That's gonna have to be some bitchin' RC to hold 3 layers of drywall.

I think Rod was the one who said it maxxes out after 2 layers of 5/8". But at the same time, if you do it right (meaning install the RC and drywall in such way that it is decoupled from the floor) those 2 layers of 5/8" will probably give you all the isolation you need.

Depends on how loud you want to be down there... or how quiet.

Kase
www.minemusic.net

maestro7879 · Post by **maestro7879** » Thu Apr 22, 2004 12:02 am

There will be acoustic drums in that room and I was wondering what STC that ceiling would give me. I'm looking for other ways of increasing the STC that do not involve taking any part of the existing ceiling down.

dymaxian · Post by **dymaxian** » Thu Apr 22, 2004 12:08 am

There's a link to USG's website around here somewhere. I don't know if they'll have a floor system linked, but they'll get close.

If you have 2 layers of 5/8" over RC over the existing floor system (being presumptious here) you're going to get enough sound isolation that the doors and windows will be the next concern. Making the walls heavier beyond this won't do nearly as much as beefing up the holes thru them.

Good luck!

Kase
www.minemusic.net

knightfly · Post by **knightfly** » Thu Apr 22, 2004 6:20 am

I don't have much in the way of realistic estimation of 3 leaf barriers, probably the best I could do would be to tell you what your construction would be WORSE than - if you can get more specific in a couple areas, I'll give it a shot (keep in mind that this would be a "SWAG" - which stands for Scientific Wild-Assed Guess...

If you can, post specific thicknesses of materials (plywood, flooring, etc) and joist depth, whether there is insulation, what kind of insulation, and possibly the brand/type of RC, whether joints in drywall are offset, any details you have -

Even so, any figure I can estimate will be optimistic - anything such as flanking paths, poor caulking, etc, will only make things worse.

Don't even THINK of adding more drywall to that RC, there are only a couple of types that could be used with a third layer other than hat channel with RSIC clips.

Whatever you get for isolation right now is only upgradable by possibly better seals, if that's not been done - other than that, unless you're able to remove part of the construction and correct the acoustic flaws, you're pretty much done... Steve

maestro7879 · Post by **maestro7879** » Thu May 20, 2004 5:10 am

Here are the measurments of the ceiling components. They are in order of construction.

Hardwood Floor - 3/4 inch
Plywood - 1/2 inch
joists - 2 x 12
insulation - ~3 inches ( not sure of what )
1/2 drywall
RC
5/8 firecode drywall
5/8 firecode drywall

knightfly · Post by **knightfly** » Fri May 21, 2004 3:12 am

Thought we'd lost ya there...

Ignoring your inner layer of drywall (because the air gap from the Resilient Channel isn't good, 3-leaf) about the best I would expect from that construction is maybe STC 47 - this is calculated to include the two upper layers, the 11 inch gap, minimal cavity insulation, and two layers of 5/8 - in reality, the second air gap could be causing even more degradation so that figure would be most likely worse -

As a comparison, two layers of 5/8 with the RC correctly applied direct to the joists would improve STC to around 60, with most of that improvement in the midrange.

Hope that helps... Steve