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Old 2014-01-07, 10:38 AM
R_D_G R_D_G is offline
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Originally Posted by Inspector Phil Acker View Post
The noise is most likely due to relieving of stresses that build up in wood framed homes. The most common occurance location is with engineered attic trusses. The top and bottom members are called "chords" and the interconnecting members are called "webs". Metal plates join the members together.

In cold weather, there is a significant temperature differential between the bottom chord [covered by insulation and essentially at room temperature] and the top chord [essentially at the outside ambient temperature]. In cold weather, framing elements tend to bow. So the top chord bows, which in turn pulls up on the webs, which in turn pulls up on the bottom chord. The net result is that stresses build up in the joining [gusset] plates. If there is a significiant change in outside temperature and humidity, the stresses build up quickly. The load bang is when the stresses reach a level such that the joints suddenly relieve the built-up stress.

The sound is very sharp and load, similar to a gun going off. For engineered trusses, this does not do any damage to the trusses.

This condition can also happen within outside walls. The phenomenon is similar: wood studs tend to bow out in cold weather, which may build up enough stress to cause a dramatic release in pent up energy within the wall structure.
The strange thing about this noise is that everyone seems to have heard it at the same time. What are the chances of multiple houses relieving the built-up stresses in the frames at the same time? I think it is more likely that the sound was caused by a common event that everybody in the neighborhood heard.

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