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I am having a house built by a builder. On my contract, it is specified that 'Sound Attenuating' windows would be installed.

This is important as the house backs up to a busy road which provides a lot of noise. The seller agent sold it to me as sound proof windows, but the contract only states 'Sound Attenuating'.

It is now time to order the windows, and they are being ordered as double pane, one pane standard 1/8" thick, the other 3/16" thick. From what I have read this barely provides an STC of 31 Source - Vinyl 1/8+3/16 Dual

According to Wikipedia, for STC, 30 is described as Loud speech can be understood fairly well, normal speech heard but not understood

I feel like they are filling the contract technically, but not fulfilling the spirit of what the contract was intended to do which is to protect from the road noise.

What windows or soundproofing method should be used at a MINIMUM to not hear, say, 90% of road noise?

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up vote 2 down vote accepted

There are a number of companies that provide windows with high STC ratings. The series 7000 windows from http://www.silent-guard.com appear to have STC of 40 and above. There are many other manufacturers that sell sound attenuating windows.

I believe you are correct that to get what you want you'll have to specify specific windows. The way you describe the contract doesn't appear to be objective and measurable, and you really don't want to have to pay twice for windows.

You could also renegotiate the contract to specify STC rated windows of 40 or higher, however you might not get what you need then depending on how a given manufacturer rates their window.

Also, keep in mind that at higher STC levels the noise conduction through walls starts to become larger than the windows. You may want to evaluate the siding/sheathing/insulation/wallboard plan to make sure that you don't put great windows in but still get significant low frequency road noise through the walls.

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Note that I've never used silent guard, having found them via google search, and can no more recommend them than I could any other soundproof window company. YMMV, caveat emptor, and all that. –  Adam Davis Sep 21 at 19:12
Also, regarding wall noise transmission, this post might be useful: diy.stackexchange.com/questions/6014/… –  Adam Davis Sep 21 at 19:14
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Any window would be "sound attenuating" because it decreases the sound level a tiny bit.

This is typical of non-technical sales personnel confusing a property with a quantity. You want it quiet and they heard that "sound attenuating" makes things quieter.

The obvious solution would to have specified in the contract the particular make and model of windows.

However, STC 31 as rated by that manufacturer is a very conservative rating. Look at the corresponding chart: most of the audio spectrum is diminished by 40 dB or more. That is equivalent to reducing 10,000 watts of sound to 1 watt. The "result range" (whatever that means) is 47 to 57 STC which they are labeling as "31". I suspect the latter range better represents what you'll experience.

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Unfortunately it is not that manufacturer, and the manufacturer that they are using does not publish STC values. They stated it would be in the low 30's range. It makes me feel more uncomfortable that the manufacturer doesn't state these online. I am trying to work with my builder. If as you say, they provide 47-57 then I would be more than happy. –  esac Aug 27 at 19:18
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Some negotiation is in order with your builder. If the adjacent road is as noisy as you imply non-opening triple glazed units would offer better attenuation while providing light. These are expensive and some come partially evacuated or dry gas filled further improving their performance.

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