How thick should my windows be?
Old 23rd July 2010
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Question How thick should my windows be?

HELP!!! Okay here goes...

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 05:07 AM.. Reason: wrong info
Old 23rd July 2010
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I don't think the gg adds THAT much mass. Your first numbers sounded right to me, but I'm no expert. Really curious now how this is going to turn out.
Old 23rd July 2010
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The Music Room - Powell River, B.C.

Here are some pics of the studio build -

We are on day 22 of construction..... me and anyone with a truck full of air tools. My first contractor helped me level my sub-floor, then buggered off. My new guy is much nicer - and cheaper
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Old 23rd July 2010
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1/2" and 3/4" is correct. Really, 3/8" and 1/2" would be just a hair less massive than your existing wall, but since .400" glass isn't really economical to have made...

Neil
Old 23rd July 2010
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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!

Sounds like a riddle.... help meeeeeeee
Old 23rd July 2010
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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
Old 23rd July 2010
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Or I could frame it this way.....

Will 1/2" and 3/4" glass be a "weak link" in a wall that performs better than just 2 sheets of drywall (5.25 psf)?
Old 23rd July 2010
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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...



Neil
Old 23rd July 2010
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Thanks for the replies Amish... I've been checking out your build for awhile now.... looking good! Does my question make sense to you or am I just spinning my wheels? Thanks for your help.
Old 23rd July 2010
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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.

Neil
Old 23rd July 2010
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Quote:
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?
Old 23rd July 2010
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3/8 laminated glass is equal to 4.92 psf... this is slightly less than 2 sheets of 5/8 drywall (5.25 psf) Are we on the same page?
Old 23rd July 2010
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Rod - Help Meeeeeeeee

Dear God. I've been pretty good lately. Things are a little over budget, but I'm trying. Please tell Rod Gervais I need his help, badly. Thanks God
Old 23rd July 2010
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Music Room,

You are on the right track. Yes, 3/8" will give you around 5lbs/sq. ft.

I would recommend 3/8" for one panel and 1/2" for the other. You will be in good shape with these if they are spaced at least 6 inches from each other.

Cheers,
John
Old 23rd July 2010
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Thanks John - Would these become the "weak link" in my wall assembly?
I want enough, but not too much..... like beer
Old 23rd July 2010
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Sorry man, it was really late when I responded last night. Maybe I shouldn't have. I meant that 3/8" thick laminated glass is just under the density of 1.25" of gypsum (2 layers of 5/8").

Sorry for the typo. I still think you only need 1/2" and 3/4" glass.

Neil
Old 23rd July 2010
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hahaha - good enough! Thanks for your help..... I placed the order today!

I'll keep some fresh pics coming - Cheers
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