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.
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| When Aerosmith is your neighbor...you're going to hear something. |
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.
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| 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.
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| 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.
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| Example of an STC 37 Floor - Photo Credit: National Gypsum |
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| 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.
