Originally appeared in the AIA Design for Aging Newsletter in August 2014.
Moving is always stressful. You have to find enough boxes to hold all your stuff. You have to have utilities shut off in one place and turned on in another, hopefully at the appropriate times. You need a van and a lot of friends who will move you for pizza and beer or soda.
Moving into a retirement community is stressful too, although hopefully you can afford professional movers at this point in your life. However there are a lot of adjustments to be made. For one, most of the residents moving in will be leaving a single family home and are accustomed to the buffer they have between their house and any neighbors. This is not the case in most residential accommodations in a CCRC. In most instances, at best, you will have one neighbor directly on the other side of the wall from you. In many cases, you will have neighbors to both sides, plus above and below.
Sales people will likely not understand and thus not explain to residents the reality about what they may expect to hear from their neighbors. And this is a disservice to the residents and to the administrators who will hear the complaints. But expectations need to be managed in order to not to disappoint new move-ins. The walls, ceilings and floors between units will in most cases never be “sound proofed”, but we as designers will do what is possible to manage and dissipate sound to acceptable levels.
I grew up in a semi-detached home until I was 15 and then lived in a townhouse with my family or the college dorms until I was 27, when I bought a single family home with my wife. You could say I was used to having neighbors. For almost 30 years I expected to hear my neighbors come in the door, hear their garbage disposal and generally, hear a bit of their everyday life. But as long as the neighbors kept their AC/DC album to a normal level, this was ok because this is what I had come to expect. However, this is not what many incoming residents to retirement living may expect. They may expect the same quite environment they have now in a single family home. They have no children. They may even live completely alone. The only sound they may hear is made directly by themselves personally.
None of the close quarter living units I experienced growing up were even close to complying with ‘modern’ sound requirements. Current building codes address both air-borne sound and structure-borne sound. Simply stated air-borne sound is hearing your neighbor’s voice or TV. Structure-borne noise is hearing your neighbor’s footfalls above you or their garage door open. So as a minimum the wall, floor and ceiling assemblies between dwelling units must meet and sound transmission class of 50. This far exceeds standard wall construction found in older building stock or in a single family home. A wood stud wall with a layer of wall board on either side has an STC of about 34. To get to about 50-54 STC (as measured in a laboratory) a wood stud wall must have 2 layers of wall board on one side of the studs, the stud cavity is filled with fiberglass insulation, with another layer fastened resilient metal clips which offset the board from the stud by ½ inch. These clips allow one side of the wall to vibrate independently from the other side and as such the noise does not translate from one side of the clip to the other at 100%. The fiberglass insulation works as an attenuator, reducing the strength of the signal, so to speak. This wall is also in effect 50% more dense than the standard wall. The building codes also require that all openings, cracks and seems must be sealed with acoustical caulk and that penetrations, such as electrical outlets, must be staggered between studs, so that there aren’t one in each side within the same cavity opening.
Also, from the laboratory to the field conditions of the actual building, the STC is expected to be reduced by 5 levels. This is most likely due to imperfect conditions and inherent weak points in corners and along edges, as well as penetrations needed. So while we design to meet an STC of 50 in our drawings and the code plan reviewers see this, it is expected that a field test on the same assembly would provide a result of 45 and this still meets code. Sound will penetrate a system at the weakest point, so anywhere the defenses are down such as at a door or an electrical box, that is where the sound will transmit. Unfortunately, if the rest of the room is treated well acoustically, it doesn’t really offset a break in the assembly, like a hole or seam that is unsealed. It only takes a small hole in a rubber raft to sink it.
So in a sense, a standard party wall is about 15 to 20 STC points higher than it would have been prior to the regulations in the building codes. That seems pretty good, but is it? Consider these facts. A rule of thumb is for every 10 STC you add to an assembly, the sound coming to the other side is roughly half as loud. In diminishing returns, 5 STC is clearly noticeable, 3 STC is just barely perceptible, and 1 STC is almost imperceptible. Mass is important to acoustical performance. If you double the thickness of a membrane, such as 2 layers of wall board in lieu of one, the STC rating will increase by about 5, which is clearly noticeable. Installing insulation is a wall also adds about 5 to the STC.
|Example of an STC 30 wall - Photo Credit: Gypsum Association|
Walls assemblies with STC values far exceeding the code are often called a “luxury” and as such they come with a price. A wall with an STC of 60 will pretty much eliminate the perception of loud speech from one side of the wall to another. A double wall certainly improves STC ratings. But they take up a lot of square footage (which often can’t be factored into rentable space) and they are more costly to build. Also masonry walls are very dense and as such very good insulators of sound, but again come at a cost. A 10 inch hollow block wall by itself attains nearly a 50 STC.
|Example of a 55-59 STC Wall - Photo Credit: Gypsum Association|
Floors will be very similar to walls, except a typical assembly “sandwich” would be made up of wood joists and fiberglass insulation topped with plywood subfloor and gypsum poured topping. The bottom would have several layers of wall board attached to the same kind of metal clips on the underside of the joists. Additionally, a floor needs to perform in terms of impact noise, i.e. footfalls, which is a structure-borne noise. Typically this is addressed additionally with an acoustical mat placed between the gypsum topping and the plywood in the assembly. These mats provide additional mass as well as resilience to the floor make up. The mats can also be placed right below flooring as well.
|Example of an STC 37 Floor - Photo Credit: National Gypsum|
|Example of an STC 60 Floor - Photo Credit: National Gypsum|
STC ratings are a fairly sensible predictor of how a wall will perform. However, SCT uses a range of 125 to 4000 Hertz, which are the range of frequencies associated with human speech. This range does not really consider very high or very low frequencies, such as those produced by machines, air handlers or electrical transformers. It isn’t perfect but the STC rating system is the standard by which designers live by.
I am using examples above in terms of wood construction because that is fairly standard in low to mid-rise residential construction. But actually metal studs preform a bit better than wood studs. This is due to their flexibility characteristics as they a can soften or decouple some of the noise vibrations from one side of the wall to another. In terms of the big three in acoustical dissipation, there is Mass, Airspace between and Resiliency (or materials that flex and decouple). Any time you can add two or more of these properties to an assembly, improvements will be realized.
During the pricing exercises on building or renovation project, we as designers are often asked to make concessions to reduce costs. Many of these decisions, which the Owner must be a part of, may affect acoustical comfort. These items include replacing cast iron waste pipes for PVC pipes, reducing or changing types of insulation on pipes, providing alternate wall assemblies (here we can point to code now to limit this reductions), alternate finishes which may be less absorptive of sound, alternate HVAC and mechanical items that may perform worse acoustically or alternative door hardware. All of these issues can degrade the acoustical comfort in a building versus the initial design, so be careful.
How does this all translate to the expectations of future residents? When discussing their future neighbors, the sales team must not convince the clients they won't hear anything their neighbor does. It is expected in new construction that dwelling units will not be sound proofed, but that sound will be reduced to an accepted standard. They are likely moving into new type of housing product whether it be apartment or semi-detached home, so it must be explained that there is an inherent difference between living on your own plot versus living in a community. The sales team should learn, with the help of their design professionals, how a standard house wall performs next to the proposed party walls in the housing product. How do they relate in terms of STC to each other and to the minimums mandated by code? If the product is new, a pricing alternate could be explored for “luxury” STC 60 walls. It could be an option to residents to buy up to this option. But this is a very difficult feature to add later.
I’ve always found it interesting that in aging, it is often said the hearing goes first, yet in many cases the resident population we serve seem to be ultra-sensitive to sounds in their new homes. I believe much of this is the result of expectations. People coming to live in an apartment after having lived on their own plot for 30 or 40 years tend not to expect to hear their neighbors at all. They don’t have common walls or hallways. They don’t have elevators nearby. They may be on the same routine as their spouse and don’t worry about someone being a night owl while the other is an early bird. Let’s face it, if they’ve lived with another person for 40 year, they probably have adjusted to their routine. A new neighbor is a completely different story. They are probably used to the noises of their old HVAC system, but their new one may make different sounds. Not more noise, just different.