Hotel Near Airport Fails Field Acoustical Test
A five-story hotel is 1,400 feet from an active runway. The window specification calls for an STC 35 assembly, and the submitted product has a lab STC rating of 35. After construction, ASTM E966 field testing in three guestrooms yields NIC 28. Guests complain about low-frequency aircraft noise at night. The windows are operable awnings with compression gaskets. Site review finds gaps at the perimeter, electrical boxes in the wall, and unsealed joints between the window frame and the rough opening. The owner wants to replace the glass with laminated units immediately. The acoustical consultant says the field rating is too low and asks for a prioritized plan before any glass is ordered.
1. Why does a lab STC 35 assembly test at NIC 28 in the field, and why is OITC relevant?
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STC is a laboratory rating of the assembly alone; it does not include flanking paths, perimeter leakage, or workmanship. Field NIC includes the installed condition, so gaps at the frame, electrical boxes, and unsealed rough-opening joints can short-circuit the wall’s acoustical performance. STC also weights mid and high frequencies more heavily, while aircraft noise has strong low-frequency content. OITC is more appropriate for transportation noise because it gives more weight to low frequencies. A field NIC of 28 therefore does not prove the glass is the weak link.
2. What should be corrected before replacing glass?
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First, seal the perimeter joints, rough-opening gaps, and electrical boxes, and verify that the awning gaskets compress and latch correctly. Check for flanking through the ceiling, floor, and adjacent walls. A before-and-after field test in one room can show whether air sealing alone recovers much of the loss. Replacing glass before correcting leakage and flanking would be expensive and might not improve the perceived low-frequency noise.
3. If glass replacement is still needed, what glazing change is most defensible for aircraft noise?
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The defensible change is an acoustically laminated glass make-up, such as laminated glass with acoustic PVB in an asymmetric thickness, with an adequate air space and sealed frame. Ask for OITC data, not only STC, because the complaint is low-frequency aircraft noise. A secondary interior window or an added interior glazing panel can also be effective if the frame and perimeter are detailed correctly. The repair should be justified by a field test or a room mock-up, not by an STC number alone.