Appropriate glass thickness to match STC of double 5/8" sheetrock wall...?

[666666]

I have a wall that will be double 5/8" sheetrock, likely with GreenGlue inbetween the sheets. I wish to put a small window (about 1' X 1') in this wall. I already have a 1'X1' piece of glass that is 1/2" thick (solid piece, not laminated). This glass piece weighs about 7 pounds... thus is about 7 PSF (pounds per square foot). Double 5/8" sheetrock is roughly 5 PSF if I remember correctly.

According to my rough calculations, the glass is of greater PSF than the double sheetrock, so I'd think that using this one 1/2" thick piece of glass as a window in the double 5/8" sheetrock wall should not cause any reduction in STC performance of the double sheetrock wall.

Comments? Will the one 1/2" solid pane of glass be enough, or should I go thicker with the glass?

Important note.... this one double 5/8" sheetrock wall is the "inner" wall of a "room within room" construction. There will also be an "outer wall" made of one 5/8" sheetrock that will ALSO have a pane of glass at the window location. So, in my question above, the 1/2" piece of glass is just the "inner pane", and there will also be an "outer pane" as well. The outer pane will likely also be a 1/2" piece of glass. I just happen to have several 1/2" panes of glass laying around (obtained for free), which is why I'd like to use them IF they will be adequate. I'm thinking that the 1/2" glass is adequate for the SINGLE layer 5/8" sheetrock outer wall, but not sure if it's adequate for the DOUBLE 5/8" sheetrock inner wall.

I might be able to go double 1/2" glass for the double 5/8" sheetrock wall... thus the glass would be a full inch thick... but if this is overkill, I'd rather not do it.

So... what say you? One 1/2" thick glass in the double 5/8" wall, or double 1/2" glass (1.0" inch thick) for the double 5/8" wall? Goal is to match STCs as closely as possible, I do not wish to "weaken" the sheetrock wall at all with the window.

Thanks!

[nosebleedaudio]

Double pane for sure.
1/2" and 3/8" is good.
If you have alot of 1/2" I would use a double 1/2" on one side and a single 1/2" on the other.
Different thickness is better.

[avare]

The general rule of thumb is to glass one third the thickness of the drywall. The 1/2" will be fine.

BTW, congratulations on asking before doing.

Transparently,
Andre

[666666]

Thanks guys, I appreciate the input.

We have two conflicting views above from knowledgeable people.

It certainly makes sense to use two different pane thicknesses for each the inner pane and outer pane. In theory, if we go by the "one-third glass" rule, I'd need a pane of about 1/2" thickness for the double 5/8" wall, and a pane about 1/4" for the single 5/8" wall. If I did this, I'd have two different thickness panes, and I'd be adhering to the one-third rule.

Since I already have extra 1/2" thickness panes on hand, if I wanted to vary the thickness between the inner and outer panes, and I also wanted to go a little "overkill", perhaps I could put the 1/2" panes in the single 5/8" wall, and then for the dual 5/8" wall get some extra 1/4" panes and put them in against the 1/2" panes for a total thickness of 3/4". According to the "one-third" rule, this would be more than enough, but again, I have extra 1/2" panes that I got for free that have no use to me other than putting into this room.... so I figure I may as well put them in even if a bit overkill.

Or, is it so terrible if the inner and outer panes ARE the same thickness (each 1/2")??? I know this is theoretically not ideal, but I wonder just how much of detriment to STC this really causes? If it's just a miniscule effect, then I suppose I need no worry about it. After all, with an inner and outer 1/2" pane, in theory, according to the one-third rule, I've already got more glass than I need... so maybe this cancels out the fact that panes are the same thickness in terms of performance. Or maybe this is bad reasoning?

So, to sum this all up... I could just put a 1/2" pane in the inner double 5/8" sheetrock wall, and a 1/2" pane in the outer single 5/8" sheetrock wall. OR, I could add a 1/4" pane to the 1/2" pane in the inner wall so that the max thickness of the inner pane is 3/4" and thus the inner and outer panes would be of different thicknesses. QUESTION: Is it WORTH it for me to get extra 1/4" panes and do this, or will the improvement of doing this be so small that it'll effectively not be noticeable in a "real-world" setting?

There are different ways to slice this apple, I'm just trying to explore all options and then make a decision that is both 100% effective but also practical.

I greatly appreciate the advise.

[666666]

Originally Posted by nosebleedaudio

Double pane for sure... If you have alot of 1/2" I would use a double 1/2" on one side and a single 1/2" on the other. Different thickness is better.

This does make very good sense, the problem is, I have enough 1/2" panes to put one in each inner AND outer wall, but I do NOT have enough to put TWO in the inner wall and one in the outer wall. So, if I need to put more than 1/2" in the inner wall, or vary the thickness, I'll have to visit a glazier regardless. I'm trying to see if I can get away without having to buy more glass if possible, and if I do, trying to figure out the cheapest way to go. Thanks!

[avare]

Aargh! If you are getting into construction details, give drawings/graphics!

Putting a layer in the middle will make the Transmission Loss (TL) worse.

Having two layers of the same thickness (glass) will make the TL worse theoretically. In studio applications the big problem is low frequencies. IF you have the lows controlled, the high range frequency TL becomes unimportant because the mass will take care of it. In practice the the dip is not important if you look after the lows.


Dippily,
Andre

[666666]

Originally Posted by avare

Aargh! If you are getting into construction details, give drawings/graphics!

Sorry about that! Will try when possible. Have no diagrams at the moment.

Putting a layer in the middle will make the Transmission Loss (TL) worse.

Sorry for my poor description. I would not be adding a "third layer" as in a "third leaf" (I know "triple leaf" is bad), but what I was refering to was having one pane in one wall, and then having two panes, against each other, in the second wall. This would still be just "two leaves" to my knowledge. If you take two panes of glass and put one tightly against the other and install this way, this would essentially be "one leaf", correct?

Having two layers of the same thickness (glass) will make the TL worse theoretically. In studio applications the big problem is low frequencies. IF you have the lows controlled, the high range frequency TL becomes unimportant because the mass will take care of it.

Makes sense.

One thing to keep in mind though. The glass panes I'm talking about here are all just 12" X 12" square. I'm thinking that, due to their small size, these panes would not become too "excited" by low frequencies, at least not like say a 4' X 8' pane of glass might. I don't even think these 12"X12" panes would even "flex" at all at low frequencies.... they're simply too small. Just in the same way that an 8" tom-tom could never produce low-end like a 24" bass drum. Thus, having two panes that are 12"X12" square, both the same thickness, would perhaps not "sing" at all at lower frequencies. And as for high frequencies, like you said, the mass alone would take care of that. So perhaps it would not be a problem then to run just two separate 12"X12" panes of 1/2" thickness. ???

Does this make any sense? I'm just talking here.

[Kiwiburger]

With that logic, an SDC mic wouldn't have any bass response ...

I have some very heavy soundproof doors in my studio, and I wanted small windows in them (at a guess they are around 12" square - i'm away at the moment). I stipulated double glazed glass, and because this was a professional acoustic door maker with a design that offered a good STC rating, I was a little surprised that they just used ordinary double glass. This has a thin air gap, and same thickness glass.

Certain frequencies just go straight through. I haven't measured them but they would be in the high mids - components of computer fan noise for example.

Unlike my studio windows that I designed myself. These are ordinary aluminum windows, but mount both sides of 8" concrete block. I used two different thickness, so whatever frequencies get through one can't get through the other. These work so well that if I ever build again i'm going to use use as much glass as I want. But the secret is BIG airgap, and two different thickness. And preferably avoid parallels - but this wasn't practical and doesn't seem to have been a problem.

If making doors again - I would design the windows to protrude signicantly outwards, to mainain the biggest airgap that was aesthetically pleasing. Maybe even dome windows ...

[666666]

Thanks guys.

To be on the safe side, I think I'm just going to double-up on the 1/2" glass in the double 5/8" sheetrock wall, and run a single 1/2" pane in the single 5/8" wall. This way I'll have disimilar pane thickness and more than enough mass... and I don't have to go out and buy more glass. Guess I can't go wrong that way based on the advise here. Since I do not have "enough" 1/2" panes to run a total of three panes at each prefered window location, I'll just need to cut down on the amount of windows... which perhaps isn't a bad thing anyway... less work . Once it's all done, I'll report back how it all turned out. Thanks.

[avare]

Great discussing before doing.

Half inch glass is a fine match with your walls. If you add a third leaf, it will make TL worse! If you have your heart set on it, contact local glaziers and find out if they will laminate two of your pieces together. I have no idea if this can be done in the field or not.

As written by Kiwiburger, the other controlling factor is the gap between the leaves. The bigger, the better.

FWIW if was in your situation, I would use the 1/2" glass on both sides and know that that it would be good. If you look at professional studios, you will see that the typical large windows have 1/2" and 3/8" glass. The reason for the thinner glass is cost. With double 1/2" you have excellent isolation.

Keep the questions coming. Posting is cheap. Cutting, building, and redoing isn't.

Andre

[666666]

Originally Posted by avare

Ha If you add a third leaf, it will make TL worse! If you have your heart set on it, contact local glaziers and find out if they will laminate two of your pieces together. Andre

Thanks Andre

One thing I would like to clear up here. Please correct me if I am wrong.

As I understand it, a "leaf" is a seperate free standing barrier, such as a piece of plywood, or sheet of sheetrock, or TWO sheets of sheetrock screwed together, or a piece of sheetrock screwed to a piece of plywood, etc. But, screwing two pieces of sheetrock together is NOT two leaves, but is two pieces joined to create ONE leaf. Is this correct?

In my case, I plan to have just TWO windows. One "inner" window in my "inner" wall, and one "outer" window in my "outer" wall. Two "leaves" ONLY, that's it.

For my inner window, I was planning on using TWO panes of 1/2" glass, BUT installing them so they are TOUCHING... so this should effectively be one 1.0" thick pane... ONE leaf. Of course laminating them would truly adhere them together, but I'd think that even not laminiating them, but having them tightly pressing against one another, would still be "one leaf" so to speak. Remember again, these panes are only 12"X12" and very flat... when I lean one pane against another, they actually stick together automatically just from the suction, that's how tight they mate with each other.... I almost cannot pull them apart.

Now, if the truth is that two super flat panes of glass installed tightly against each other is actually considered TWO separate LEAVES, then I would be making a mistake I guess. So, I'd like to clear this up.

Finally, this room will be used as a drum room. Mainly just trying to keep the sound of the drums from getting out. Drums, especially the kick drum, are VERY "loud" and have a lot of low-end. However, they are not as loud as say a gun on a battleship. In other words, perhaps I'm overthinking all this here. In the end, my main goal is to just have my windows match the performance of my sheetrock walls.

Yes, I should really add a diagram here... just don't have the ability to do that at the moment, I apologize.

Thanks.

[avare]

You know you are great.

If the panes of glass on the inner window are not firmly attached to one another, they will act as two leaves.

Bass is the big issue with TL. The ruling factor is matching what the rest of the TL is. It makes no sense to build a window with a TL of 30dB at low frequencies, if the wall only provides 20 dB of isolation.

Keep asking!

Andre

[666666]

Originally Posted by avare

If the panes of glass on the inner window are not firmly attached to one another, they will act as two leaves.

Ok, then this is where my thinking is flawed.

This is also bad news to me since it means that in order to do this job correctly I will need to buy more glass.

So being that I already have 1/2" panes on hand, I could perhaps run a single 1/2" pane in the inner wall, and a single 1/4" pane in the outer wall. If we follow the "one-third-glass" rule, this should be enough. So then I need to get some 1/4" glass panes cut to size.

Just to define:

Inner wall = double 5/8" sheetrock = 1.25" thick
1.25" divided by 3 = 0.417 or 1/2" thick glass minimum

Outer wall = single 5/8" sheetrock = 0.625" thick
0.625" divided by 3 = 0.21 or 1/4" thick glass minimum

Just curious, where did you find the "one-third-glass" rule? Is this published in an article or book? Does this refer to ALL glass or laminated glass or non-laminated glass etc?

[666666]

Another thought... maybe there IS a way to "laminate" glass.... DIY...? In theory, if you had a big sheet of some type of clear double-sided tape, you could just stick two panes of glass together.

In my case, since the panes are only 12"X12", if I "clamp" them together around their entire perimeter, they will effectively be pressed together quite tightly at the perimeter. OF course they will NOT be truly "joined" in the center, but due to their small size, I'd think that this may not be too big of a problem. If these panes were say 2'X4' or 4'X8' big, I could see why this WOULD be a problem.

Just thoughts.

[avare]

Your putting 1/" in a 5/8" wall. It overkill already.

RE: Mass. Gyprock is around 2500 lb/ft^3 and glass around 8000. You can find the values in any construction text.


Andre

[nosebleedaudio]

Glass weighs about 3.5 times more than sheetrock for same thickness.
Don't forget 703 around inside perimeter of window...

[Doublehelix]

I have double 5/8" sheetrock in my place as well (with Green Glue between the layers). I used 3/4" and 5/8" glass sheets for my window. Not sure if it is overkill, but it works pretty danged well!!!

[nosebleedaudio]

Originally Posted by Doublehelix

I have double 5/8" sheetrock in my place as well (with Green Glue between the layers). I used 3/4" and 5/8" glass sheets for my window. Not sure if it is overkill, but it works pretty danged well!!!

Have you done a STC test to see how well if performs, is it a standard 2 by 4 or staggered stud...

[Doublehelix]

Originally Posted by nosebleedaudio

Have you done a STC test to see how well if performs, is it a standard 2 by 4 or staggered stud...

No, not really, although it would be easy enough to do I am guessing. Play a tone, measure with SPL meter, go to other room, and measure again?

It is a double-walled construction (hence the two windows!). One wall is a standard 2X4, the other is a standard 2X6.