We are quite familiar with airborne noise since we are exposed to it day by day.
It is exemplified by traffic noise, aircraft flying overhead, voices or music from our neighbors. It is the noise produced by a source which radiates directly into the air. Airborne Noise are transmitted as pressure fluctuations in the open air or along continuous air roads as corridors and duct systems. The isolation of airborne noise is characterized by the Sound Transmission Class (STC) rating.
In selecting the appropriate design criterion for a given level of quality, the architect should consider the level of quality expected by the buyer. This expectation of quality may be based on cost, location, building luxury grade etc.
Unfortunately, builders do not prioritize noise isolation issues just as much as they do the appearance of the building.
One of the most common complaints in residences and commercial buildings, especially in multifamily, is “I can hear my neighbor talking” or “I can hear their music”. This usually results when the walls between units has a poor noise attenuation. In many cases the walls are designed with a recommended STC, but this is laboratory data; in the field this number can be 5 points or more less than calculated due to the flanking effect.
Typical Walls between units:
1- 3 5/8” metal stud (25 gauge), 24” o.c , single layer 5/8” type x gypsum board each side and 2” fiber glass insulation in the cavity. This wall theoretically gets a STC rating of 45. However, in the field it only gets a STC rating of 40 – 42. This number does not satisfy the minimum grade requirement from building departments.
STC 45
2- In some buildings, the walls are built without fiberglass insulation in the cavity. Walls like this wall barely reach a STC rating of 35-40.
3- When a layer of gypsum board 5/8” is added to Wall 1 on each side, the sound insulation rises to a theoretical STC rating of 50. We have measured these walls in the field achieving STC rating of 47-48.
STC 50
4- If a resilient channel is added to Wall 3, the sound insulation rises to a theoretical STC rating of 59, with a good STC rating of 56-58 in the field.
STC 59
For tenant separation walls, a simple wall consisting of 3 5/8” studs 24” in the center with two layers of 5/8” gypsum board on each side and batt insulation in the stud cavities may be a good wall. However, there are several quality control issues that must be considered, such as verifying that the stud spacing can be achieved, verifying that light-gauge studs are used, and verifying acoustical sealant is used between the gypsum board and concrete floors.
The Quiet Rock panels are expensive and have poor high-frequency acoustical performance but use little floor space and have good low-frequency performance. For these reasons, they would have limited applications. They would be most appropriate to consider if low-frequency noise were the driving force in a design, if floor space were critical, or if quality control were a major concern with a competing wall utilizing resilient channels.
Many people ask for the product Green Glue. It is a viscoelastic damping material which is applied between two layers of drywall. This is a product that, when is applied correctly, helps with structural sound isolation. However, don’t expect the best results, as there are other products with better performance such as isolation clips, and mass load vinyl.
Construction Details
Perimeter of gypsum boards walls and ceiling assemblies shall be caulked with a non-hardening caulking compound prior to taping.
All outlets boxes (electricity, television, and telephone) should be sealed with putty pads.
Window and doors assemblies must be sealed with acoustic caulk around its perimeter.
A recent measurement we conducted showed that two rooms separated by a STC 60 wall could experience a performance reduction of 10 or more STC points. The problem was not with construction of the wall, which achieved the expected performance. We got flanking transmission through the union wall-floor and wall-ceiling with poor seals. As a result, the final dwelling-to-dwelling performance was unacceptable. Before anything remedial treatments is applied to the wall all possible flanking should be checked.
Before anything remedial treatments is applied to the wall all possible flanking should be checked.
In closing, the management of noise in high rise buildings is a complex process requiring good planning, design, management, documentation and processes. When managed correctly the end result can be a significant increase in the internal amenity of the building and not necessarily with a significant increase in cost. By the application of many basic principles, many noise problems can be avoided. Actually, the expectations from owners/occupiers rise significantly requiring that issues of acoustic amenity be addressed in detail. A building with poor acoustics can easily gain a bad reputation and be difficult to either sell or lease.