01-30-06 Special Called City Council Retreat Meeting of La Porte City Council

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i • to cost-effective STC wall assemblies is approximately 65. Some typical wall and • ceiling assemblies with their STC rating are listed below: • 3-%Z" steel stud wall with gypsum drywall both sides 47 STC • 3-%" steel stud wall with one layer gypsum one side, • two layers on the other side 51 STC • 6" concrete block wall 44 STC • 6" concrete block wall with the block filled with sand 47 STC • Two wythes (layers) of 4" brick with plaster 59 STC In addition to creating a barrier with mass, it is also important to watch out for "sound leaks" and "tracking of sound". Sound leaks occur when you have holes in your wall or ceiling barrier, or when the wall assembly is incomplete. Windows with an STC of 26 perform like a hole in your acoustic wall. Hollow -core wood doors are also tremendous leaks, with an STC rating of 19. Other leaks include electrical outlets that are back to back in the wall and mechanical ducts that penetrate acoustic wall assemblies. Incomplete assemblies occur when your barrier, whether it be wall or ceiling, does not reach all the way to the outside enclosure of the building. A good example is a massive wall assembly that reaches only up to the ceiling. In this case, the sound "flanks" by going around the wall, up and through the ceiling, and back to the space on the other side. The following describes some ways you can "plug" sound leaks: Windows - By using double panes of glass separated by at least four inches of air • space, you can increase the STC rating of a window to 43. Be sure to caulk the glass into place and, if possible, use two different thicknesses of glass, such as W, and 3/16", so they won't vibrate in unison. Doors - Use tight -fitting, solid -core wood doors or hollow metal doors with insulation. Weatherstrip the doors, and on interior doors, add an automatic door bottom that extends the weatherstripping down to the threshold when you close the door. Avoid double swinging doors because they are very large sound leaks. Wall Assemblies - Caulk around the perimeter of wall assemblies and around wall outlets, and be sure the wall assemblies fit tight to adjacent surfaces. Duct Penetrations - If you have to penetrate an acoustic wall with a duct, have the duct zig-zag to create a sound trap. Also, if you build a boot around the zig-zag with sheet lead, you will better isolate the noise. Sound will track when the sound vibrations in one material can be transmitted through contact into the adjacent material, and thereby through the total wall assembly. One of the best ways to break the tracking of sound is by inserting an airspace between materials. A resilient material will also act like an air space, or miniature shock absorber, between adjacent materials. Some STC ratings for typical wall assemblies with different forms of airspaces are listed below: • • Double layer of drywall each side on two separate • stud walls one inch apart 56 STC • Single layer of drywall each side on staggered