Masonry Magazine April 1972 Page. 20
Design Considerations And Construction Practices
Judicious building layout can be highly effective in noise control. To whatever extent possible in multi-family housing areas with similar noise levels should be adjacent to or above and below one another. Closets, stairways and corridors can often be strategically located as buffers against airborne sound transmission between apartments.
Particular attention should be paid to those construction practices that can sometimes make all other attention to sound control ineffective. Sound leakage will occur through any opening in a wall. An improperly fitted corridor door provides much sound leakage. An opening of only 1/16 inch around a typical door produces a total opening of about 12 square inches. Walls that go higher than a false ceiling but do not reach the floor above provide tremendously large openings that reduce sound transmission losses to a very low level.
Other opportunities are made for high levels of sound transmission where medicine cabinets or electrical outlets are installed back to back or where piping and duct openings are not sealed. Such practices should be avoided. Where necessary, ductwork should be fitted on the inside with baffles that impede the transmission of sound without affecting the flow of air so greatly, using a system like that employed in automobile mufflers. Piping, conduit and ducts should be isolated from the masonry wall by compressed, molded sleeves or by low density insulation tightly packed around them. A sealant should be used around them at both surfaces (Fig. 3).
Tests have shown that the STC value of a cavity wall can be increased about 10 percent or more where there is an opportunity to build the two wythes on separate sills (Fig. 4).
STC values have been published for many kinds of construction materials. For purposes of design it should be borne in mind that the values given have been determined on laboratory specimens with careful attention to workmanship. Since some kinds of construction are almost completely dependent on careful workmanship to achieve high sound transmission losses, published STC values do not always represent what is likely to obtained in a building. This is less likely to be true for concrete masonry than for some other types of construction.
-INCH DEEP
RESILIENT SEAL
MOLDED
SLEEVE OR
PACKING
FIGURE 3
PIPE OR
DUCT
Isolation of pipe or duct
through concrete masonry wall
BLOCK WYTHES
SILL
FIGURE 4
SILL
Two wythes on separate sills
for higher STC value
NATIONAL CONCRETE MASONRY ASSOCIATION
P.O. Box 9185, Rosslyn Station, Arlington, Virginia 22209