I've been reading Rod's book and it is extremely useful - Thanks Rod!
Question - How thick do my windows need to be? I am using double wall construction, 2 sheets 5/8 drywall, and Green Glue... Rod's book states the weight is 5.25 pounds per square foot for a double layer of 5/8 drywall. This puts the glass on one side at 1/2" (6.56 psf)and 3/4" (9.84 psf) on the other side... Right? If I use Green Glue, do I need to calculate 4 sheets of drywall (10.25 psf per wall)? If so, this would make my glass....... THICK
This feels a little excessive - please advise
Last edited by The Music Room; 23rd July 2010 at 06:07 AM..
Reason: wrong info
Sorry guys, my math was wrong..... If two sheets of drywall equals 5.25 psf then 4 sheets would equal 10.5 psf. This would mean that a Green Glue wall (same as 4 sheets of drywall) would need 7/8" (11.48 psf) and 1 1/8" (14.76 psf) laminate glass for the windows to equal the "mass" of the walls!
What about the classic "1 to 3" rule for glass that's been mentioned from time to time? I believe glass is about 3 times as dense as sheetrock, so, at least as a rough guide, you can figure your glass can be about a third of the thickness of your sheetrock. This is what I've heard anyway.
I have a room with an inner wall made of two layers of 5/8" sheetrock (with Green Glue), I put 3/4" glass in that wall.... and my outer wall is 5/8" + 1/2" sheetrock, I put 5/8" glass in that wall.... the glass I used is actually thicker than one third the sheetrock, but I got the glass cheap so I wasn't worried about being "exact"... it's a little thicker than necessary which is fine.
Anyway, I'm happy to report that, at least per my own "unofficial" listening tests, the glass in my room is doing the job more than adequately. Certainly no audible evidence of the window areas being weaker than any other area. If there's a loud sound source inside the room and I walk around the outside of the room with my eyes closed, I can't tell where the windows are. However, pull out one pane of glass and the isolation drops noticeably.
Note: my glass is solid, not laminated... the price was right
I've never heard of using a ticker piece of glass because of green glue. 1/2" and 3/4" is already overcompensating. You'll have a billion dollars in glass thicker than that. Look to spend about 250 USD on one sheet of 3/4" laminated glass 3'x4'. 7/8" is more like 500-600. That's one friggin sheet. Each DOUBLING of mass is worth about STC 6 right? So, you're talking about picking up 2 or 3 STC and putting a ton of money into that window.
I, personally wouldn't bother going thicker than that, but if you're really concerned, by all means...
Thanks for the props on my place. You may see an update tomorrow evening I hope.
Yeah, I totally get what you're saying... GG doesn't physically add mass, but functions similar to a wall that does have more mass, therefore should be equated to such a wall.
You will probably get some differing opinions here, but basically STC/TL is all about the weakest link. I honestly don't think that your glass thickness would be that weakest link by only going 1/2" and 3/4". Even with exceptional assembly of your walls. Also, in the part of Rod's book you are referencing he says that 3/8" glass is ALMOST the same mass as 4 sheets of 5/8" gypsum. I wouldn't have any problem at all using 3/8" and 1/2" in a wall assy. that didn't use GG. He simply upgrades to the next NOMINAL size of 1/2" Lami, which is actually quite more massive than 2.5" thick gypsum. The actual thickness that would be required as an equal density to your 4 sheets of drywall is roughly .400". This thickness would be more expensive to make than 1/2" because of its nominal size. .400" would be custom made super expensive glass.
You're literally talking about 1 or 2dB of isolation for upwards of 800-1000 dollars more on a single window. I wouldn't split hairs.
Also, in the part of Rod's book you are referencing he says that 3/8" glass is ALMOST the same mass as 4 sheets of 5/8" gypsum. I wouldn't have any problem at all using 3/8" and 1/2" in a wall assy. that didn't use GG. He simply upgrades to the next NOMINAL size of 1/2" Lami, which is actually quite more massive than 2.5" thick gypsum. The actual thickness that would be required as an equal density to your 4 sheets of drywall is roughly .400".
This doesn't make any sense.... what page is this info on?