Noise Control in Multi-Family Residential Buildings
Design and Building Codes
Our website feature “What’s Your Problem?” is commonly overwhelmed with inquiries about noise and acoustical problems. Not the least of these inquiries have been from owners or renters in condominiums, town houses, apartments and offices. The problems range from noise transmission through floor/ceiling assemblies, through adjacent party walls between neighboring units or through windows.
The noise problems associated with floors and ceilings range from airborne noise transmission from voices TVs and music to footfall impact noise and from plumbing noise.
Sad to say, for newer residential units many of the problems could have been prevented in the first place had a little more attention been paid to noise control during the design and construction process. After the fact, when the noise problems are discovered, solutions can be very difficult and expensive to resolve and in most cases there is no easy solution.
For newer or remodeled multi-family dwelling units, the various Building Codes throughout the United States require a measure of sound privacy between multi-family dwellings. The Building Codes specify a minimum architectural design standard of privacy of 50 STC (Sound Transmission Class) and a 50 IIC (Impact Isolation Class). The Building Codes also state that validation of the minimum noise criteria can be field measured and the field measurements shall not be less than a 45 FSTC or a 45 FIIC. While some community building inspection departments require field-testing to be conducted before a certificate of occupancy is issued, many, if not most, do not. They rely instead on the architect’s specification and design recommendation and the expectation that their specified designs will result in the minimum sound isolation construction between adjacent units. Unfortunately, what is specified by the architect and what is subsequently built do not always coincide if proper attention and inspection oversight is not implemented.
If your residential dwelling is relatively new or if you are contemplating the purchase of a unit, do not be afraid to question the contractor and the real estate agents about the sound isolation characteristics of the unit. Just because they say that the units have been built to code requirements does not mean that they meet the minimum code requirements. If they do not, you may have a case to demand corrective action at the expense of others. Do not be left holding the bag; moreover a certificate of occupancy by local building inspection departments implies that the structure has been built to minimum code standards. Purchasing a condo or townhouse may be one of the most significant expenditures you will undertake; therefore you have every reason to expect answers with respect to your privacy needs and freedom from intrusive noise from your neighbors. If you have a noise problem that is not resolved and you go to sell your unit, you may be compelled to reveal the deficiency to a prospective buyer which can have an impact on the selling price.
Very few, if any inspection agencies actually check the quality of construction from a sound isolation perspective and too few building contractors are really conversant with good noise control construction techniques. As a typical example of what can go wrong, take a party wall between two side-by-side units. The wall may have been designed for a 60 STC value but when the installing drywall installs the gypsum board, many of them will jack the gypsum board up tight to the ceiling to insure a nice clean and tight joint at the ceiling line. While there is nothing wrong with this practice, far too often it will leave a void at the floor line, which will eventually be hidden by the baseboard. Any voids at the floor line must be caulked. The wall selected from the gypsum drywall design guide to achieve a 60 STC was selected from the gypsum manufacturer’s design guide based on actual acoustical laboratory tests. Close inspection of the acoustical test data is bound to reveal that in the test chamber the wall was caulked into the test opening to prevent any sound leakage. If this is not repeated in the field during actual construction, sound leakage can and far too often, will occur. The lack of a few pennies worth of caulking compound can reduce the sound performance of a 60 STC rated wall to less than the minimum of FSTC 45 required by the building code. There are many causes for sound leaks, such as uneven floors, wooden floor plates that are not perfectly straight; no matter what the cause, they can all be sealed to insure an airtight barrier thereby maximizing the acoustical performance of the wall.
Fortunately, airborne sound leakage can be easier to detect; as one can do so by getting close to the wall, albeit on all fours and listening for the sound coming through the wall. You may need the cooperation of your neighbor by playing a radio next door so that you have a sound signal to listen for. The sound will become louder as you get closer to the leak. If the sound appears to be coming from the base area a solution maybe is at hand by removing the base to see if the gypsum board and the floor were caulked. If not, caulk it.
If the floor is carpeted, the baseboard will normally be positioned just above the carpet, in which case it is possible to insert a probe such as a long flexible knife blade. If the blade goes in more that about 3/8″ or if it hits something hard or does not come out with any caulking residue on it, there is a good chance the wall was not caulked as required by the gypsum board manufacturers literature.
Equally important, party walls that extend to the roof or floor structure above the drywall ceiling in a dwelling unit should likewise be fully sealed. Just because it cannot be seen following construction and subsequent occupancy is no reason to believe that an unsealed wall is not going to create noise problems at a later date. Sound that travels through the ceiling space and into the adjacent dwelling next door is characterized as “flanking” transmission insofar as the sound travels around the end of the wall, above or below it, through the floor structure. Generally, sound will follow the path of least resistance, therefore in new projects or when remodeling it is wise to trace potential paths of sound and insure that the pathways are blocked off or are equal in performance to the primary party walls.
As an example, let us assume the primary party wall is a staggered 2×4 stud wall with 2 layers of gypsum board on both sides and insulation in the cavity. We can expect an STC rating of about 52. If the sidewalls are not constructed in a manner to equal the party wall construction sound can leak around the party wall in a flanking pathway thus reducing the overall anticipated sound isolation from space to space.
Sound intrusion though windows can be a source of annoyance, which can be due to a variety of factors. If the windows are operable types, the first thing to check is to see if the widows close properly and any weather stripping is in good shape. If the window can leak air it can also leak sound. If the window closes to form a tight seal and the weather-stripping seems adequate the next thing to check is the window frame. Windows are frequently installed in to the wall opening with wooden shims to insure the unit is plumb and level. The space between the frame and the wall should be insulated and sealed before the window casings are installed. If this was not done correctly you can probably detect the sound leakage by placing your ear close to the frame and listening. It is case of letting your ears do the walking and listening. If you detect distinguishable differences in sound you may have found the problem; the solution will be to remove the casing and insulate and caulk any leaks.
If all else fails, the thickness of the glass maybe the problem in which case it may be necessary to install another layer of glass on the inside in a similar fashion to the storm windows on the outside, making sure that the additional pane of glass is well sealed into the opening.
Floor and ceiling assemblies can be the pathway for two types of sound transmission, the first is the airborne transmission of sound and the second is the passage of impact sounds such as footfalls on the floor above. Assuming that the floor ceiling assembly has been designed and constructed to provide adequate airborne isolation, impact noise can still be a problem. If the finished floor surface has been designed to accommodate carpeting, the carpeting and under pad will normally provide a good degree of impact sound isolation. On the other hand, when the finished floor is floor tile, hardwood flooring or ceramic tile. Achieving good impact sound isolation requires much more attention. Frequently, the solution is to install an impact sound absorbing flooring under-layment to separate the finished floor from the sub floor structure. In isolating the finished floor from the sub flooring it is necessary to make sure that any potential leaks are adequately sealed. Many times a floor is constructed with a layer of concrete or gypsum topping over the sub floor, when this is done any sound isolating under-layment should be sealed so that the topping will not leak between the under-layment material joints and short-circuit the anticipated sound isolating benefits of the under-layment.
Selection of floor joists is an important consideration also; solid 2″×10″ joists provide a very good base for good sound isolation. Open web wooden truss joists seem to be less effective at very low frequencies to greater degree than solid wooden joists so special attention should be paid to the use of these types of joists.
One of the most common sound isolation elements in floor-ceiling construction is the use of a metal resilient channel isolator that is attached to the underside of the floor joists before the gypsum board ceiling is installed. The gypsum board panel is applied to the resilient channel isolator in a manner that insures that the screws used to apply the gypsum board do not extend into the joists to which the resilient channels is applied. Special care and attention should be taken with the selection of a resilient channel as they are not all the same and do not all provide the same degree of isolation. Furthermore, particular attention should be paid to the installation and spacing of the resilient channel. It is wise to consult the manufacturers acoustical test report and to specify and insure the channel is installed in exactly the same manner in which it was installed in the acoustical test lab. If the resilient channel has not been tested by an independent test lab and is simply another look alike channel, do not use it, select another with a known performance rating. Above all, be aware that not all resilient channels perform the same.
Do not skimp on floor ceiling construction, as it may be costly to improve the sound isolation performance after the fact. It is highly cost effective to insulate the space between the floor joists and applying 2 layers of gypsum board to the underside of the resilient channel as apposed to a single layer.
How Sound Transmits
Contrary to popular perception that sound simply passes through a material, such is not the case. Sound waves are form of energy that energizes any material that the sound waves come in contact with. Thus sound energy that impacts on a wall for floor/ceiling assembly will cause the material to vibrate like a radio speaker; the energized material then becomes the transmitter of the sound energy.
With the introduction of thinner lightweight building materials the key to effective noise control is to use materials with different acoustical characteristics that unbalance the composite material assembly in a manner that will dissipate and diffuse the sound energy. Insulation in the cavity converts some of the energy in to heat while a resilient channel will help minimize the direct connection of the gypsum board from one side of the assembly to the other. Each material and relationship to one another produces small increases in sound isolation that reduces the transmission of sound through the whole system.
A 2″×4″ wooden stud wall system with 5/8″ gypsum board on either side will produce an STC rating of 35. By adding insulation into the wall cavity will increase the STC rating by another 5 points to 40. Adding a resilient channel on one side adds another 5 points for an STC rating of 45. Adding another layer of 5/8″ gypsum board on either side still only adds another 5-8 points to achieve a 50-53 STC. Each wall assembly should be looked at very carefully in order to determine the manner in which the materials were used and installed. Such variables as the stud spacing, the thickness and density of the insulation, the spacing of the resilient channels, whether the gypsum board is installed with the long dimension vertically or horizontally; all these variables and more will have an impact on the final sound performance of the installed assembly.
I Have a Noise Problem, What Can I Do?
If there is any consolation, perhaps the most frequently encountered problem may be the easiest to fix, furthermore it can also be one of the easiest problems to detect. As previously indicated, the lack of effective caulking at the floor line behind the baseboard is one of the most common causes of sound transmission from one space to another. It can be detected quite easily just by listening. It may necessitate having to get on your knees and placing your ear close to the baseboard. If the sounds you hear from the adjacent space are more distinguishable than from other parts of the wall surface, you may have found the problem yourself at no cost. The solution is then to remove the baseboard and caulk any voids between the gypsum board and the floor. You would be surprised how often this turns out to be the problem.
If the problem is not an air/sound leak then the problem becomes a little more complicated. Simply adding another layer of gypsum board may not necessarily be an effective solution as an additional layer of gypsum board may only improve the performance by 2-3 points, which is barely detectable by the human ear. Adding a resilient channel to the existing wall or ceiling and an additional layer of gypsum board will not work, as the resilient channel requires a larger airspace behind it to register any significant improvement. Also adding a layer of lead or loaded barrier will only produce a minimal improvement that is not a cost-effective solution.
Unfortunately, a more effective solution will be to remove one layer of gypsum board to ascertain if the wall has been insulated, if it contains a properly installed resilient channel. At the same time you need to look to see if there are any holes in the bottom plate of the wall where electrical or plumbing services have been installed and ensure that they have been adequately sealed with caulking compound.
Before you commence this type of remediation it might be advisable to employ the services of an acoustical engineer who can take sound measurements with specialized sound equipment, which by probing can detect weak links or pathways in the wall or ceiling assembly.
In recent years recycling old industrial buildings has become a very popular means of providing high-rise loft type dwellings. Frequently the existing finishes of existing concrete, brick or wood are left as the interior finish, supposedly to provide the “loft” type of décor. Such designs require even more design attention if sound privacy is to be achieved. Potential noise problems can be quite challenging so the buyer should insist that actual on-site testing will validate the sound design performance criteria.
Finally, if you do have a sound problem in your dwelling unit and are seeking help to resolve the problem be sure to describe the problem as more than “I can hear my neighbors” Try to provide as much information as you possibly can. Describe the nature of the sounds, when and where you can hear it. Is it impact noise or airborne noise or a combination of both? When was the unit built and if possible what the nature of the construction is. If the unit is of recent construction vintage you may need to procure a set of architectural drawings. The more information you can provide the closer you will come to determining the nature of the problem and finding a solution.
Beyond the lack of caulking compound to seal obvious leaks, do not be deluded into thinking there are any easy fixes for noise problems and anyone who tells you otherwise should be able to provide conclusive data that their simple solutions will work satisfactorily.
Due to the complexity of acoustical and noise problems in residential buildings along with an overwhelming variety of material designs and combinations, it is impossible to cover all problems in a short article such as this. A more authoritative reference resource can be found in “Noise Control Manual for Residential Buildings” by David Harris, published by McGraw Hill.