Sound Isolation and Noise Control
Tips on controlling sounds and noise in
Whether you're in an
office building or a hospital room, a classroom or your home,
acoustics play a major role in how a building or space functions.
When designing rooms or buildings, it's important to take into
consideration how sound waves act in a space. Depending on the type
of surface it strikes, sound waves are absorbed, reflected or
transmitted. Sound waves reflect off of hard surfaces, such as
walls, roofs and floors, which can cause an interior that echoes.
To create a space that doesn't echo, you want to absorb the sound
waves that bounce around a room, using materials that are light and
fluffy. To block sound from travelling to other rooms, a heavier,
dense material is required. Often, this means adding additional
layers of drywall to make the walls or ceilings thicker.
Benjamin Markham, LEED AP, director, architectural
acoustics at Cambridge, Mass.-based Acentech, an
acoustical consulting firm, says the nature of the required
communication within a space is what dictates the requirements for
noise control and sound isolation. "The starting point is what kind
of goals are there in terms of communication, on the one hand, and
privacy or confidentiality, on the other hand," he explains. "Once
we have an understanding of the building program, we set goals for
noise control and sound isolation."
For metal buildings, Markham says there are specific
constructions that help achieve those goals, starting with the
walls and floor/ceiling assemblies. And within those assemblies,
there are three tools designers can use to isolate sound from one
space to another: mass, separation and insulation.
Mass and Separation
Metal buildings, which are lighter in weight than a
concrete building, for example, have to use different strategies to
control sound than mass alone. "Unlike a really heavy mass
building, you don't have the benefit of having an exterior which is
not going to be as willing to conduct sound as a metal building
is," explains Lucas Hamilton, manager of building science
applications at CertainTeed, Malvern, Pa. One way to help with
sound and noise in a metal building, he says, is by putting
insulation between the surface of the building and the occupied
"In a metal building, we can design buildings that
are more structurally efficient: the walls don't weight as much,
and we get the sound isolation benefit from the fact that we have
two masses rather than one," Markham explains. "You build a stud
and there's drywall on either side of that stud.
There's a mass, and then there's a separation--an
insulated separation ideally-and then another mass on the other
side. And that separation is what allows us to design constructions
that block just as much sound as other constructions that are much,
much heavier. And we're able to do it at a lighter weight."
The same is true in floors and ceilings. "If you have
a concrete slab, the sound isolation that you get is from the mass
of that concrete slab," Markham explains. "With a steel building,
most of the time, there is a ceiling. So when you have a steel
building, you have a lighter weight building; it doesn't weigh as
much as that cast-in-place concrete slab. But, with one mass at the
floor and a second mass at the ceiling, we can, with a lighter
structure, block just as much sound."
In most projects, the type of structure and how much
it weighs is determined before noise control and sound isolation
are considered. "The mass of those assemblies, in terms of
the basic structure, is usually set and established by other
priorities," Markham says. "And that's OK, because we have other
tools that we can use by taking advantage of the separation
If a floor assembly, such as lightweight concrete on
a metal deck, is a given in the structure, Markham says that still
leaves the ceiling as an option. Things to look at include how
heavy the ceiling is, how it is suspended from the deck, and how
deep the ceiling plenum is. "Those tools have an enormous impact on
how much sound is isolated by the floor/ceiling assembly," he
Markham explains that the first thing you want to set
is how heavy the ceiling needs to be. How many layers of drywall
does it have on it? Is it suspended concrete panels or a
lightweight acoustical ceiling tile?
Second, how is the ceiling suspended? If it's furred
down with something rigid, such as a ceiling furred down with
studs, it doesn't offer much true separation since there is a rigid
connection that ties one mass to the next. Instead, if the ceiling
is suspended with a wire hanger, it provides better separation.
Better yet, Markham says the ceiling can be isolated with a
resilient isolator that works a bit like a shock absorber, such as
a resilient hanger.
Third, how deep is the ceiling? "The more space there
is between those two masses-between the deck and the ceiling-the
better the sound isolation is likely to be," Markham explains.
"Especially in low frequencies. That depth needs to be coordinated
with the rest of the design--HVAC, plumbing, and all sorts of
things. But the depth is an important factor in how much sound gets
isolated as well."
And, once the depth of the ceiling is set, insulation
should be added between the deck and the ceiling. For wall
assemblies, Markham says having a stud wall with drywall on either
side of it provides some separation. The first upgrade is to add
insulation to the cavity, which provides additional benefits. To
improve the separation further, he suggests adding mass (e.g., two
layers of drywall on each side instead of one). For the best
acoustical improvement, introduce separation by creating either a
double-stud or staggered-stud wall. Another option for providing
separation is a resilient channel or clip, similar to ceiling
Once the ceiling and wall assemblies are in place,
Markham says it's important to maintain their integrity. For walls,
that means not having outlets back to back. For ceilings, it's not
putting in a bunch of recessed lights and HVAC connections that
poke a lot of holes in it. "Coordinating ceilings in a way that is
in balance with your acoustical goals with the other building
systems, building needs--lighting, HVAC, sprinklers, and so
forth--is quite an important step, to make sure you are getting the
most sound isolation benefit out of the ceiling that you've
Insulation and Energy
In general, energy-efficient metal buildings tend to
be very quiet metal buildings, since sound and heat flow are
closely tied together in regards to what types of materials they
are conducted by. "Thermal insulation plays this dual role of
reducing the acoustic energy as well as the thermal energy flow,"
Hamilton says. "Because it's playing both of these roles
simultaneously, that's why you get this quiet and comfortable
"Insulation is useful because it absorbs sound
between those two masses," Markham says. "It can also provide some
structural damping of the skins, such as drywall. But what it's
mostly useful for is absorbing the sound that's inside that cavity,
and that boosts the sound isolation performance of the overall
There are many types of insulation available--mineral
wool, fiberglass, cellulose, open-cell foam, Icynene, etc.--and
there are minor differences between them and how they absorb sound.
Note that closed-cell foam is not acoustically absorptive.
For thermal control, Hamilton says you also want an
insulation that is appropriate for sound absorption. "The ones that
absorb sound best are soft and fluffy, rather than rigid board
insulations, which may be good thermal insulations but are not good
at controlling sound," he explains. "You want something that
absorbs sounds, similar to if you were to stick your head under a
pillow. That's why fluffy insulations work better than rigid
"What's key is that the building insulation itself
have a high noise reduction coefficient (NRC)," adds Hamilton. "You
want this material to be one that absorbs sound as opposed to
conduct sound." NRC expresses the ability of materials to absorb
sound at multiple frequencies, with the higher the number, the
better the performance.
Once the floor, ceiling and wall assemblies are set
up for sound absorption and blocking, it's important to avoid
penetrations and use acoustical sealants to get the most benefit.
"Providing acoustical sealants at the penetrations and at the
perimeter of these assemblies, is a way of preventing leaks and
gaps that would undermine the performance of the assembly," Markham
Different kinds of structures provide different
degrees of damping on the skins that are applied to them. Markham
says this is true of drywall and windows, and as such drywall that
is not well damped will not provide as much sound isolation benefit
at certain frequencies. "There are products out there that
introduce damping to the mass layers," he explains. "There are
windows that have internal lamination, for example, and that
internal lamination introduces damping to that glass, and that
means that at the frequencies where this particular issue is
relevant, the introduction of that damping improves the sound
Markham goes on to say that there is drywall with a
viscoelastic damping layer inside, which provides more damping than
traditional drywall. This provides better performance at the
frequencies that are most effected by damping.