Becoming an Expert in STC Ratings

Since I started practicing architecture there have been many things I have needed to know about that I never would have thought of when I decided this was the career path for me—the latest of these being STC ratings. I remember during one of my licensing exams that I had a question asking me what the STC rating of a typical partition would be and I had no idea what the answer was. Now, after working on the ENJJPT Operations Complex at Sheppard Air Force Base, I can tell you not only that the STC rating for that wall would be 35, but also what would be required to make that partition have a STC of 50, 55 or 60. I can tell you what the typical STC rating is for a solid core door and how many points adding acoustical seals will give you. I can also tell you that STC implies a laboratory tested rating and can be expected to achieve five points less in the field. With these and the many other things I’ve leaned the past few weeks about STC ratings, I feel as if I am on my way to eventually becoming an expert at this subject.

The most important thing I’ve learned from this experience is how to determine the composite STC rating of a building envelope. Working with an acoustician we can determine the STC rating of a room based on the area of exterior wall, area of windows and doors, ceiling area and what all these assemblies are made of. For this project we must have a composite STC rating of 55 for the building. Knowing what our wall system and roof system was, we were able to determine what STC our windows required. With this knowledge, however, came some bad news. Our windows will require a rating of 51. Why is that bad news? Because a standard one inch insulated unit has a STC of 35. When we add the ¼ inch laminated layer that we require for blast resistant we’re still only at 39. So how do I get an additional 16 STC points from a window?

So far I’ve come up with 3 options – increase the air space between the panes of glass, add a layer of glass for a triple pane unit or use a special frame that a few companies make for just such high STC required applications. Of course all of these options come with a price tag. So that’s what I’ll be spending the rest of my week doing…researching these options and determining which option we want to go with.


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