December 2-December 15, 2015 —
COLORADO REAL ESTATE JOURNAL
— Page 29
I
n times past, builders
used newspapers to insu-
late walls in homes and to
stuff into drafty gaps. If you’ve
ever remodeled one of the old
Victorian homes you would
have found these aged and yel-
lowed newspapers stuffed in
every nook and cranny of the
exterior walls. Upon examina-
tion, you would have discov-
ered that these newspapers
were full of advertisements
touting miracle elixirs that
would cure all that ails you.
Even in those times, crafty
advertisers realized that the
readers are, in general, a gull-
ible bunch. They would believe
most anything if it was in print
and happened to deal with
something they knew little
about.
Today, we are barraged by
new miracle products that
claim to do the unimaginable.
Some of these products are
viable, but it takes a prudent
shopper to sift through and
find products that actually per-
form to the level claimed in the
marketing or sales literature.
Acoustical
consultants
encounter new products every
day that claim hard-to-believe
acoustical performances. One
of the most common products
in this category are those used
to mitigate impact sound, such
as footfall noise, a common
complaint in multifamily hous-
ing. Next to moisture issues,
sound isolation control is the
most litigious problem in mul-
tifamily housing.
There are two basic measures
used in the industry to rate
the acoustical performance of
a floor-ceiling assembly: Sound
Transmission Class and the
Impact Insulation Class. The
STC is a measure of the per-
formance of the floor-ceiling
assembly to isolate airborne
sounds, such as voices, televi-
sions, stereos, barking dogs,
etc. The IIC is a measure of
the floor-ceiling assembly to
isolate impact noise (footfall)
and other impact noises, such
as furniture being dragged
across the floor. We have found
that achieving acceptable lim-
its of impact sound is usually
the most difficult, especially
in lighter-weight wood-frame
construction. The IIC rating
typically ranges between a low
of around 20 to a high of 80,
with 20 being very poor and 80
being excellent.
n
Suspicious advertising.
A simple search on the Inter-
net for impact sound insula-
tion underlayments lead to the
following product literature
verbiage. The product name
has been disguised for obvious
reasons. This product is 0.08
inches thick and is described
on the manufacturer’s website
as, “(This) underlayment is the
most technologically advanced
flooring underlayment avail-
able. (This underlayment) is
acoustically superior to all the
underlayments.” It goes on to
state for this particular prod-
uct, the Impact Insulation Class
equals 72.
With a limited knowledge of
IIC, except that some build-
ing codes call for a minimum
of 50, the temptation to hur-
riedly specify this product with
its remarkable impact-sound
i n s u l a t i n g
performance
(72) could
be
almost
irresistible.
But,
wait
a
minute.
Let’s exam-
ine this boast
of
impact
sound insu-
lation perfor-
mance before
we rush to
get it into the
floors of our
project. First
it needs to be understood that
it is not the underlayment that
has been found to have an IIC
rating. An impact-sound insu-
lation test is conducted on a
complete floor-ceiling assem-
bly. That is, the assembly being
rated consists of the surface or
finish we walk on, down to the
ceiling below.
One should ask what was
the floor finish tested. Was it
carpet and pad? Was it ceramic
tile or marble? Was it an engi-
neered wood floor or tongue
and groove?
Next we should ask what
was the structural floor. Was
it 8-inch-thick concrete? Was
it formed-in-place or preten-
sioned or post-tensioned? Was
it lightweight concrete on ply-
wood or OSB subflooring on
wood joists? What was the joist
spacing?
We also need to know about
the ceiling. Was the assembly
tested with or without a ceil-
ing? Was it resiliently suspend-
ed or rigidly attached? Was
it acoustical tile, one layer of
gypsum board, two layers of
gypsum board, etc.? What was
the depth of the ceiling cavity?
Was there fiberglass or mineral
wool in the ceiling cavity?
All of this information would
be available in the laboratory
test report and, based on this
information, a designer could
determine if the floor-ceiling
system tested was appropri-
ate for his or her project with
respect to impact isolation.
It has been our experience
that, more often than not, when
a copy of the test report is
requested from the manufac-
turer of these unbelievably
high IIC performing underlay-
ments, they are not provided.
The manufacturer is unwilling
to release the very information
an architect, designer or con-
sultant needs to evaluate and
validate the acoustical claims of
the underlayment given in the
marketing and sales literature.
n
Beware.
Whenever the
designers (architects), develop-
ers or owners of multifamily
residences are concerned with
impact noise from the occu-
pants above, adequate acousti-
cal separation is paramount.
Many new homeowners have
certain expectations of how
much they expect to hear from
their neighbors located only
inches away. If you Google
“floor-sound-insulation,” you
will get a multitude of prod-
ucts whose advertised acousti-
cal performance appears too
good to be true, and there is a
good chance it is. The achieve-
ment of adequate sound insula-
tion (airborne or impact) in a
multifamily dwelling can be a
difficult feat and there are usu-
ally no easy solutions.
s
Construction, Design & Engineering
Michael B.
Barnhardt
Senior Acoustical
Consultant, D.L.
Adams Associates,
Denver
