Page 54 - 2016Fall

Residential Quietude
The difference between these two readings is the difference between being able to hear someone talking through a wall or not. This reference to the extensive research at CNRC test- ing is included in this paper to demonstrate the importance of understanding the ASTM laboratory versus field ratings and the variables that create the difference between them. This difference in the results between the STC and FSTC not only emphasizes the importance of correct installation but also the importance of designing to the FSTC rather than just the STC for noise sensitive clients or applications.
Acoustically treating all seams or openings in walls and ceil- ing/floor configurations demonstrates the vital importance of a continuous site inspection and testing of an installation, often referred to in the construction world as construction administration. The purpose of construction administra- tion is to ensure that the construction not only conforms to the construction documents but also to identify and resolve construction problems early. The focus on minimizing any acoustic leakage points should also consider light fixtures in a ceiling. The recessed lights should be in an insulated enclosure with a high STC. If this is not possible, there are mufflers available that can be installed above these “holes in a ceiling.” Other simple examples of small holes in construc- tion that are a source of acoustic leakage are back-to-back electrical outlets, the space under a door, or something as simple as pipes that run between floors. Whether it is a sin- gle- or multifamily home, pipes are often hidden in a shared chase or are in a wall behind which are ducts. When a duct or pipe passes through the floor/ceiling, a hole needs to be made to pass the conduit. If this hole is not properly sealed, sound will easily pass from floor to floor, diminishing the effectiveness of the acoustic treatment, as shown in Figure 4.
I once had a client complain about sounds from the floor above coming into the living room through the fireplace. The architectural drawings showed that all possible flanking paths of the fireplace had been properly sealed and were in compliance with the fire code. The flue was double insulated, which indicated that the sound was not emanating from the flue itself. After visiting the site, it became clear that there was a separate flue leading upstairs that for some reason was adjacent to the flue of the main fireplace in the living room. To accommodate the close proximity of the flues, the plywood originally specified and found on the blueprints to separate the two flues had been removed. When the damper was open, sound easily passed from one floor to the other.
Figure 4. Picture of pipes passing through the floor creating a hole in the floor configuration. This figure shows a typical example of a small hole that degrades the FSTC of a floor, allowing sound to freely pass from one floor to another.
In another instance, a couple who moved into an apartment above a restaurant tried to have the restaurant closed down due to the noise the restaurant was making. Initial tests showed the ceiling did not meet the building code because the holes drilled in the concrete during construction to al- low water to drain had not been sealed closed. These were sealed closed along with a few other holes. The ceiling/floor now met code, but the couple was still disturbed by noise. Readings where then scheduled for a controlled experiment to play various music levels to set a limit on the volume. The restaurant was closed, yet music was still audible. This showed that the music that disturbed the couple at night was coming from a club on the first floor that was not below the couple but was two commercial units over.
Another example was when I had a client complain about hearing mechanical noise from the room below. There was some structure-borne noise, but there was also a great deal of airborne noise that should not have been present based on the design of the floor, which was 200 mm of poured con- crete. On inspection, a pipe was found next to the unit that passed through the ceiling and cut through the floor into a wall above, as shown in Figure 5. There was only one layer of sheet rock between the pipe and the client’s bedroom.
Although the pipe was cast iron, the hole that needed to be cut for the pipe to pass through the concrete was such that enough sound entered into the hole and into the stud bay above, making it possible for the sound to easily travel through the one layer of sheet rock and into the bedroom.
52 | Acoustics Today | Fall 2016