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.
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.
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.
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.
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.
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.
Today’s residential noise levels demand new standards of construction to reduce noise. With the recent construction booms of condominiums, privacy between units is a significant issue. People would like their apartments to be quiet and free from noise intrusions, just like in a family home, but the reality is very different for condos. Noise transmission is the number one social problem in condos, largely due to building code standards that are barely minimal for an environment where people live in close proximity to each other. Unfortunately, builders put money into the appearance of a building but little into noise isolation. The words “luxury” or “high quality” are very often used to describe condominiums that only meet minimum noise code standards. The quality of the materials going into the buildings is highly limited regarding noise isolation resources.
Here at Acoustic Sonic Inc. we receive many calls each week asking for help with this issue and we love to assist in these situations, but many times there is little that can be done at this stage without significant cost and intrusion. Sound isolation issues are most effectively addressed before construction, during the design phase.
Outdoor noise such as traffic noise, night clubs, or construction noise are frequent. Additionally, interior noise sources such as those due to turbulent water flow traveling along the piping through rigid connections to walls and ceilings as well as vibrations caused by mechanical sources like elevators and mechanical rooms are very often felt as well. Even gyms close to apartments producing high level music and impact noise from heavy weights are a common issue.
Many cities and states have adopted standards for STC (Sound Transmission Class) and IIC (Impact Insulation Class) in multifamily households. Typical requirements include a minimum sound transmission loss for walls and floors between units. Cities and counties adopt a basic code and then make modifications to suit their needs. For example, an STC 50 and IIC 50 is the code required rating for some cities, with a minimum field test tested FSTC 45 and FIIC 45 are allowed. However, this does not necessarily mean that it yields acoustical privacy between units or that it represents a level of quality that guarantees owner satisfaction. In apartments with high prices, where the noise problem is too perceivable, other reasonable expectations of the buyer should be used as the basis for construction decisions.
The table below shows classification established by the U.S Department of Housing and Urban Development in the Guide to Airborne, Impact, and Structure Borne Noise Control in Multifamily Dwellings. Descriptive definitions of three grades of acoustic environments are given in order to ascribe criteria suitable to the wide range of urban developments.
|Transmitting Room||Receiving Room||Luxury|
|Living Room||Living Room||55||52||48||55||52||48|
|Family Room||Living Room||58||54||52||62||60||56|
|Living Room||Family Room||58||54||52||52||50||48|
People often ask us what is considered normal interior apartment noise. There are many ways to measure sound levels, but the most commonly used is dBA, which is based on intensity and on how the human ear responds to it. As an example, the acceptable noise level for bedrooms is 25-30 dBA while for living rooms 35 dBA is acceptable.
It’s important to understand that humans detect varying frequencies differently because our ears are less sensitive to low frequencies than they are to high frequencies. However, sometimes we have measured an “acceptable” 30 dBA in an apartment, yet the people there are still troubled by high structural noises or low frequencies that remain clearly perceived.
In future blogs we will talk about noise complaints and the solutions that we have attained for them over the course of our time as a business for over 20 years.
Edited by Alex Hikmat