WB Marta, First a clarification - 5/16 and 7/16 refer to laminated glass which is two lites bonded either side of a plastic interlayer, those thicknesses are not the actual thickness of individual glass lites. 5/16" laminated glass consists of two 1/8" lites and 7/16" laminated has two 3/16" lites so that the 1/8" difference is really 1/16" x 2. Different glass thickness does not mean different frame thickness, it doesn't even affect the width of the reglet or glazing channel in the sash. Because the vast majority of glass that goes into the sash is going to be a dual pane package that will be the same width (or depth depending who you are talking to), even when different glass thicknesses are used by changing the width of the spacer between the two lites, the overall IG width doesn't change. In other words, if window company xyz has an overall glazing channel of 1" for their dual pane units, then that's what the IG unit has to fill. Depending on the window company the tolerance for the IGU width might be as little as 1/64". Available options might be two 1/8" lites with 3/4" space between, or could be one 1/18" plus one 1/4" with a 5/8" width spacer/airspace. Or if they were manufacturing an impact window with 5/16" laminated and 1/8" mono glass then they would use a 9/16" spacer to once again come out at 1", and so on. In your case Marta, you are being told 5/16 and 7/16 but are they selling a single laminated lite in a frame or are they going to be IG (dual pane) units? Either option is available in Florida, but IG is more common. This part is a bit more complicated..... The advantage of thicker laminated glass in an impact window has to do with wind resistance and potentially the DP rating. Simply thicker glass generally has higher load tolerance (wind and otherwise) than thinner glass, but thinner glass that has been heat strengthened or tempered has a higher wind loading tolerance than does non-heat treated (annealed) glass even when the annealed glass is thicker than the heat treated glass. Need to raise the DP of a given window? Temper the glass and it immediately goes up. What all that means is that if the 1/8" glass in the 5/16" laminated has been heat treated and the 3/16" glass in the 7/16" has not, then the thinner 5/16" heat treated laminated glass has substantially higher resistance to wind pressure and low level impacts than the non-heat treated 7/16" laminated product. However note low level impact resistance. There is no appreciable difference between 5/16 and 71/6 laminated glass when subjected to the 2x4 hurricane impact test requirement. Heat treating glass might protect from an errant baseball but the 2x4 doesn't even notice the difference, heat treated or not. The downside to heat treating is that it can introduce distortion in the glass, distortion that may even be unnoticeable in a single lite of glass can become quite noticeable when two lites are laminated together. I am not saying it WILL be distorted, far from it, just saying that the possibility is potentially greater. And most (but not all) distortion when it does occur is very mild and only visible at acute angles to the glass, often even affected by lighting conditions to see it. Marta as you move forward the first things that you need to find out are, a) monolithic lami or IG unit in the windows b) is the glass heat treated, either heat strengthened or tempered c) if an IG or dual pane, is the non-laminated (also called sacrificial) lite heat treated d) if monolithic lami what LowE coatings, if any, are used in the construction And all else being equal, monolithic can be okay and IG can be okay. Depending on location and application eat treated can be a good option, but non-heat treated might be just as effective. Coatings are a necessity, mono or IG, that one isn't negotiable.

This is quite after-the-fact, but I can tell you that STC varies enormously by product type. If Pella is saying 27-35, then 35 would probably be for something heavy like an outswing single door with midrail and laminated glass, and 27 would be for something relatively leaky like a horizontal sliding window. Construction quality makes a huge difference as well. A luxury manufactured window like a Loewen casement starts an STC 33 with standard IG, and can get up to STC 40 with Loewen's acoustic glazing offerings. Of course, Loewen is easily double the price of Pella. Still, truly "soundproof" starts around STC 50, and only products built specifically for acoustic attenuation can meet that criteria. Also, your typical 2x4 wall only has an STC of about 33, so once your windows match the STC of your walls/roof, windows cease to be the primary source of sound infiltration.

Thank you! I read that you should have one pane be 50% smaller than the other pane and one inch between panes. Do you think that is accurate? The other company we are waiting on a quote from has three panes of glass - two 1/4 inch, one 1/8 inch and laminated on one side, low e on the other. I dont know the STC of them. They are a local company.

@todd @WoW Washington my current windows need to be replaced as they have a lot of issues as this point. Replacing the windows are expensive and I want to pick the windows with the highest STC ratings available in Jacksonville, FL. Unfortunately the Millard Quiteline is not available here. The only windows that I have found to reduce noise so far is the PGT sound and security and the Simonton with the laminated glass option. I want to do my research before I spend the money since there is no going back once I get them installed. Do you guys know any window available besides the PGT and Simonton in Jacksonville FL that I can look into?