Dual pane vs Triple pane for sound/noise control

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Dual pane vs Triple pane for sound/noise control

#1 Post by BestValue »

We live around 100 yards from the train, and will be rebuilding our house and adding a second story. In our current house, we aren't bothered by the sound that much since there are trees and houses between us, and we use a HEPA filter as a white noise generator anyway. But our neighbor said the sound problem is much worse for the 2nd story. We get the low frequency rumble, mid frequency horn sounds, and high frequency ding-ding-ding of the crossing gate.

Our plan is to use dual pane LowE2-Argon windows from Fibertec, a company in Canada. But when I asked about sound, our window guy said that we could do triple pane for 5% more cost, and that would be much better for reducing noise. I suggested the idea of using 3mm glass for one pane and 4mm for the other, but that's outside their normal processes so he wasn't comfortable with that. Is it worth pushing for that?

We chose Fibertec for energy efficiency - they do an insulated fiberglass frame. NFRC total product U-factor ratings came in at:

.29 casement / .26 fixed dual pane

.20 casement / .15 fixed triple pane

IGU thickness for dual pane is .75 inches. IGU thickness for triple pane is 1.313 inches for casements (.48" gaps) and 1.438" for fixed windows (.542" gaps).

Oberon had a wonderful post where he referred to a website that gave STC ratings and dB losses for various window configurations, but I can't find it. Oberon, could you please help?

At 5% cost difference, the triple pane seems like a really good value. But we live in a mild climate and currently have single pane, and I love our big picture windows. And NFRC shows VT for the fixed windows dropping from .61 to .48 when you go to triple pane. So I'm concerned about the loss of light, and I was thinking if I use triple pane at all I would probably just use it in the bedrooms.

What do you think? Does anyone love/hate their triple pane windows?

-- Amanda

Stephen Thwaites
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#2 Post by Stephen Thwaites »

It goes against common sense, but triple glazing does not normally attenuate sound better than double glazing

from the Canadian BUilding Digest #240 Sound Transmission Through Windows -- available at:

Sealed Triple Glazing

Despite the widespread belief that adding another layer of glass must be beneficial, triple glazing provides essentially the same noise reduction as double glazing, unless the interlayer separation is very large.

The paper does give credibilty to the different thickness approach....

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#3 Post by Randy »

On the visible light transmittance, the triple glazed is much lower because two of the glass panes have Low-E. Since you say you are in a mild climate, you could request a triple glazed unit, with only one Low-E coating and keep a higher VT.

I'm not advocating triple glazed over double glazed for noise abatement however. There are far wiser people on this board than me, but laminated glass would probably be superior to triple glazed.

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#4 Post by windowrx »

My psuedo-scientific explanation of this is:
Triple glazing will reduce sound transmission some but not as much as some folks suggest. The reason is that when sound waves hit the outer piece of glass in an insulated unit they cause the glass to vibrate at a particular wavelength. This vibration then travels across the airspace and hits either the center (in triple glazing) or inner lite and as this is the same material (glass), it picks up the same vibration/wavelength and transmits it right on through. Using a different material, such as pvb lami glass on the inboard lite changes the vibration/wavelength and therefore reduces the sound transmission.
Not the best explanation but I believe this is the basic principle.

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Re: Dual pane vs Triple pane for sound/noise control

#5 Post by DWS »

The best way to thwart sound transmission is going to be laminated glass, The upcharge could be pretty steep. Another way to get a better STC rating is to use alternating glass thicknesses. I.E. exterior pane 1/8 glass interior pane 1/4 glass. The up charge is very little and the STC ratings is closer to laminated glass that triple pane.
Hope it helps

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I too live 200 feet from the CSX and Metrorail

#6 Post by PCheang »

I don't know where you live but I live in Northern Virginia along the CSX and Washtington/Va metrorail lines. I got all the noise you described and yes it is worse in the upper (2nd level) floor.

I replaced my window last year after a long exhausted reseach and I even hire an accoustic engineer to give me some advises too.

I ended up experimenting with two type of windows (on purpose). I use the liminated glass armour Gorell windows and the Milgard Quiet Line double/laminated windows (think of it as having two double hung windows stacked so you get four panes of glass, one of which laminated).

The Gorell though cheaper than Milgard is a better deal for both sound abatement property and heat insulation. Frankly, I can feel the draft coming in through the lock handle of the Milgard windows even though it has four pane of glass! The are not the best lock ever either.

Email me if you want at Pcheang-at-cox.net (use the @ in place of "-at-"). I 'll be happy to send you all the information including how much I paid for each windows.



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Window company says can't do 3mm with 4mm

#7 Post by BestValue »

So I read the Canadian link (thank you!) and it indicated that using 3mm with 4mm would move the STC from 29 to 31. But my window company said that using different thickness glass put extra strain on the thinner side and ran more risk that the window would crack. Does that make any sense?

-- Amanda

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#8 Post by Oberon »

Good morning,

BestValue, as a general rule, a triple pane will not significantly improve sound performance over a dual-pane IF the overall airspace is the same on both types of IGU.

The Canadian study referenced by Stephen Thwaites is an outstanding resource and I highly recommend that anyone who is interested in sound performance read it...I happen to have a hard-copy of that report in my book of "cool-stuff".

In that study you will have noticed that there are situations where a single lite of glass will actually outperform (sound) a dual pane IGU at certain frequencies. You may also have noted that the dual pane IGU in that example had a 1/4" airspace between the lites. It is the width of the airspace that is significant in that example.

Without going into lots of formulas and calculations, the 1/4" width of the airspace can actually enhance the transfer of specific frequencies thru the unit - this has the effect of actually limiting the effective sound attenuation in that particular make-up. Basically, the wider the airspace in the IGU, the better the overall sound performance...1/4" airspace is not the best for sound attenuation.

As pointed out in the reference, a triple pane with two 1/4" airspaces will have the same STC as a dual pane with a single 1/2" airspace. The potential advantage of the additional lite in the triple pane is off-set by the disadvanatge of the narrower airspace between the lites.

All of which brings us to your original post. Often (almost always) posts asking about sound and the difference between dual pane and triple pane performance simply discuss triple pane versus dual pane without regard to the actual make-up of the units. Your post was different in that you actually listed what the actual width of the airspaces are....we can use those numbers to draw some very general conclusions (not specific conclusions though. Your actual situation and circumstance would have to be evaluated before any sort of precise values could be assigned).

The IGU width (I am assuming airspace and not overall thickness) of the dual pane is 3/4". That is a rather common IGU set-up and is certainly acceptable in terms of both energy and sound performance.

But, the triple pane airspace widths are a very nice start in establishing sound perfomance criteria. The casement has an overall airspace of .96" and the triple pane fixed is 1.084" overall airspace width...nice numbers when dealing with residential sound issues. The typical dual pane versus triple pane argument really doesn't apply in this case because of the differences between the triple and dual IGU's.

There is some truth in the salesman's concerns about using two different thicknesses of glass in the IGU. Window glass does flex. It bows and twists and moves with changing winds, barometric pressure changes, thermal stress...etc. There are advantages to having the same thickness in the various panes of an IGU when dealing with these stresses.

Barometric pressure changes, for example, can cause the glass in an IGU to bow concave or convex depending on the high or low of the pressure. It is preferrable to have the panes bow by the same amount so as to avoid over stressing one lite over the other. In other words, if the lites are the same width, they will generally mirror one another's movement.

But, if the lites are different thicknesses, it can put more stress on the thinner lite to bow more than does the thicker lite - under the same stress. In the case of unequal thickness lites, the thicker lite may even bow less than it would in an even-lite-thickness situation forcing the thinner lite to assume a greater percentage of the stress.

Is it a potential problem? Again, like so many issues, it can be very dependent on the specific environment. In the SF Bay area, and using 3mm and 4mm glass (and not thinner), I would consider the risk to be minimal.

As always, install is vital. Even more so when you want to eliminate sound problems. Also, remember that your walls can also pass sound energy, or anywhere that air can leak into your home, sound will use the same access points. Sound is efficient in finding any weakness.

Make sure whatever windows you purchase are tight. A loose window will pass every sound imaginable.

And, as mentioned by several other folks, laminated glass is definitely always an option. In addition to sound attenuation, laminated also offers security from unwanted visitors and it stops 99% of UV from passing thru the window.

And, finally, since you are concerned about railroad noise, there are several government studies concerning railroad and airport noise and noise abatement available. I am not sure if they are available to the general public (although I don't see why they shouldn't be). They do tend to be very technical with lots of charts and graphs and numbers and stuff :shock: but they do have a lot of very good information on how to keep that sort of specific noise out of a house.

Good luck...

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Re: sound

#9 Post by pdxman1 »

Oberon wrote:
Make sure whatever windows you purchase are tight. A loose window will pass every sound imaginable.

Good luck...
Thank you for all the detailed info in that post. I am also concerned with getting good noise control from my replacement windows. I'm wondering how I go about determining if the windows I am considering are tight. Are the ratings like DP any use in comparing, or is it strictly a matter of knowing the particular brand? I am planning on using sliding widows, and currently considering Milgard Classic and LBL Series 2000.

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