Glass thickness - "How To Build It..."

Hello, I'm figuring my glass thickness, and I may be a little confused about the instructions in Rod's book: If I'm following his example, then I need one piece of glass to match the density (mass) of the wall, and then the same thickness plus 1/4" for the glass on the other side? Or is "at least 1/4" - period"? My walls are 2 layers of 5/8X and 1 layer of Celotex. So I'm figuring at least 1/2" glass for one side... maybe more? I couldn't get a solid density spec for the Celotex. That would mean I need 3/4" of glass on the other side, correct? It seems high, but then again I've never done this before. I'm naturally pretty worried about screwing this part up! - Josh

rockstar_josh wrote:

Hello,

howdy!

I'm figuring my glass thickness, and I may be a little confused about the instructions in Rod's book: If I'm following his example, then I need one piece of glass to match the density (mass) of the wall, and then the same thickness plus 1/4" for the glass on the other side? Or is "at least 1/4" - period"?

. Atleast 1/4" thick.

My walls are 2 layers of 5/8X and 1 layer of Celotex.

you mean 2 layers of GB? and what type of Celotex?

So I'm figuring at least 1/2" glass for one side... maybe more? I couldn't get a solid density spec for the Celotex. That would mean I need 3/4" of glass on the other side, correct? It seems high, but then again I've never done this before.

Glass is roughly 3 time heavier than GB (Gypsum Board), which is about 700kg/m3. So glass has a mass of about 2000-2500 kg/m3. 3 times heavier means 3 times less thickness needed (theoretically) to match GB. So you should need, atleast, 2x15mm/3=10mm of glass. (5/8" is about 15mm). Let's make it a 11mm thick glasspane, shall we.Depending on your wall structure you need 1 or 2 panes of glass. A pane of glass should be (advise) laminated; laminated glass are 2 pieces of floatglass pressed against each other with a PVB layer in between. The layer of PVB will help dampening. When each sheet of glass will be different in thickness you'll "mask" the coincident effect of the other layer. Glass, or any other material, has a so called critical frequency where waves penetrate much easier. This frq is easy calculated with this formula: f(Hz)=12.000/d(mm) f=frequency d=diameter (in mm) The frq is your critical frq. a 11m will pass have a cr.frq of about 1100Hz. (roughly). Add another piece of glas with a thickness of, say, 13mm, and you'll end up with a cf @ 900Hz. Therefor it's better to have a slighly thicker glass than you would calculate (the CFs are the weakpoints, better add some more mass to compensate a bit) Take that in consideration and take your plans to a local glass dealer. While your there, ask for glazing tape (a rubber band a few mm thick, costs you only a few bucks), setting blocks (EPM or any other rubber). Follow Rod's advice (read the chapter again) and you'll be in the save zone!

I'm naturally pretty worried about screwing this part up!

you should! Better save than sorry, eh.

Yes, 5/8X = Gypsum board, 5/8" fire-rated. The Celotex is 1/2" I believe. Thanks for the tips... we were thinking 1/2" laminated + 3/8" laminated, then I got confused when reading the book. And besides, 3/4" laminated glass would be $$$$$. I wish I could spare no expense, but that's not the case! I'll do some more work based on your advice... thanks again! - Josh

But, WHAT type of Celotex? Are you just using the wool type? don't use any exotic stuff they sell, just wool will do.

Oh, I gotcha! Well, over here what's marketed as "Celotex" is just homasote soundboard. Maybe the company that distributes it is called Celotex, but what I'm referring to is indeed the same thing as homasote.

I know Celotex, but there's different flavours. And what't your goal/purpose with the Celotex. It's just like saying "hey, check out my new guitar!". Sure, WHAT type of guiter? "a Gibson". Wow, that's cool. so, euh, what TYPE of Gibson? etc....