The Facts About the Acoustical Performance of Metal
Building Insulation
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Metal Building insulation greatly reduces the level of both
exterior and interior noise by preventing transmission of exterior
sounds to the interior of the building and absorbing reverberating
sounds within the building. This fact sheet discusses the
fundamentals of acoustical performance and shows how to improve
sound control in typical wall and roof assemblies through the use
of fiber glass insulation.
Metal building insulation has been used for many years to
thermally insulate the walls and roofs of metal buildings. An
additional benefit is that it provides a better acoustical
environment both inside and outside the building. Metal building
insulation can absorb interior noise to provide a quieter work
environment. It can also decrease the amount of noise transmitted
into or out of a building.
Because of the porous nature of metal building insulation, it
is an excellent absorber of sound. It can reduce noise levels in a
building up to 5-6 dB. This same sound absorbing property is used
to reduce the amount of sound that is transmitted through a wall
or roof. Thus, it can reduce equipment noise transmitted to
neighbors. It can also reduce outside noise so that building
occupants are not disturbed by exterior noise sources such as
traffic.
Sound Absorption Coefficient
The sound absorption properties of a material are expressed in
terms of a sound absorption coefficient. This coefficient
typically ranges from 0.05 to 1.20. The higher the coefficient the
better the material absorbs sound.
Sound absorption coefficients are measured at several
frequencies since it varies with frequency. A material with an
absorption coefficient of 0.66 at a particular frequency, means
that 66% of the sound that strikes that material is absorbed or
conversely 34% of the sound is reflected back into the room.
Metal building insulation is an excellent sound absorber with
coefficients ranging from 0.20 to 1.20.
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Vapor Retarder Facing |
Noise Reduction Coefficients (NRC) |
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PSK
Light Duty |
.85 |
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PSK
Standard Duty |
.85 |
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PSK
Heavy Duty |
.75 |
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FSK
Heavy Duty |
.80 |
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PSF |
.90 |
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Vinyl |
.85 |
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NRC rating is for facing laminated to R10
and R19 fiber glass.
Tested in accordance with ASTM C423 on an “A” mounting.
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Noise Reduction Coefficient (NRC)
A single number rating has been established to
express the ability of a material to absorb sound at multiple
frequencies. This single number rating is called the noise
reduction coefficient (NRC). Again, the higher the NRC value, the
better a material absorbs sound. NRC values for faced metal
building insulation range from about 0.75 to 0.90.
Sound Transmission Loss
The ability of a wall or roof to reduce the amount of sound
transmitted through it is called sound transmission loss. Sound
transmission loss is expressed in decibels (dB) and it also varies
with frequency. Most materials and constructions reduce the
transmission of high frequency sounds more than low frequency
sounds.
When building a wall or roof it is imperative that there are no
air (sound) leaks in the construction. Sound leaks can drastically
reduce the effectiveness of a wall to reduce the transmission of
sound from one space to another. The construction should be as
tight as possible. Where gaps exist, they should be filled with a
flexible sealant such as a non-curing Butyl, siliconized acrylic
latex or an acrylic latex.
Sound Transmission Class (STC)
A single number rating system used to express the sound
transmission loss properties of a wall or roof is the sound
transmission class (STC). The higher the STC value, the better a
construction reduces the transmission of sound. In a typical metal
building construction the values for STC range from a low of about
20 to a high of 55. The STC rating has been in existence for many
years and is based on speech sounds.
Outdoor-Indoor Transmission Class (OITC)
Recently a new single number rating has been introduced. It is
called the outdoor-indoor transmission class (OITC). It is used to
specify the sound transmission loss properties of exterior
building elements such as walls and windows. The OITC uses outside
noise sources such as traffic, aircraft and trains to calculate a
single number rating. The OITC is the preferred rating for
exterior walls and roofs of metal buildings.
Conclusion
Noise is becoming an indoor environmental pollution issue as it
can effect the health and performance of the building occupants.
Construction techniques to reduce sound are becoming increasingly
important and many builders and architects are looking for
cost-effective ways to further reduce sound transmission in metal
buildings.
Adding faced metal building insulation alone to the metal
building construction can reduce noise levels in a metal building
by 5-6 dB. However, construction techniques do impact the way
sound travels. To maximize a metal building's acoustical
performance, the wall and/or roof panels should include at least
one layer of faced metal building insulation, and one layer of
unfaced metal building insulation. Additionally, the construction
should be tight, with attention to detail such as filling gaps
with flexible sealants to assure that sound does not transit via
air leaks from one space to another.
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Walls |
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STC 21 / OITC 17 |
STC 28 / OITC 20 |
STC 29 / OITC 20 |
STC 50 / OITC 35 |
STC 54 / OITC 39 |
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No Insulation |
R-10 Faced 202-96 Insulation Over the
Grits |
R-13 Faced 202-96 Insulation Over the
Grits |
R-13 Faced 202-96 Insulation Over the
Grits 3 5/8" Steel Studs on 24" Centers with 1/2" Gyp.
Board on Interior |
R-13 Faced 202-96 Insulation Over the
Grits
3 5/8" Steel Studs on 24" Centers with R-11 Batts and 1/2"
Gyp. Board on Interior |
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Roofs |
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STC 24 / OITC 18 |
STC 29 / OITC 20 |
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No Insulation |
R-10 Faced 202-96 Insulation Over the Purlins |
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STC 32 / OITC 22 |
STC 36 / OITC 24 |
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R-19 Faced Insulation Over the Purlins |
202-96 Insulation Over and Between the Purlins to Fill the
Cavity (R-25 Combined) |
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Assemblies tested in accordance with
ASTM E 90.
STC rating determined in accordance with ASTM E 413.
OITC ratings determined in accordance with ASTM E 1332.
Roof Construction is 24 ga. standing seam roof with 8” Z
purlins on 5’ centers.
Wall Construction is 26 ga. wall panels screwed to 8” Z
purlins on 7’ centers. |
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Metal Building Acoustical Performance |
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Sound Transmission Loss |
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Roofs |
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Transmission Loss -dB at Octave Band Frequencies |
STC
Rating |
OITC
Rating |
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Construction Type |
125 |
250 |
500 |
1000 |
2000 |
4000 |
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No Insulation |
12 |
13 |
19 |
24 |
30 |
32 |
24 |
18 |
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R-10 Faced 202-96 (Rev. 2000) insulation
over the purlins |
12 |
16 |
26 |
37 |
45 |
49 |
29 |
20 |
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R-19 Faced 202-96 (Rev. 2000) insulation
over the purlins |
13 |
20 |
30 |
41 |
49 |
51 |
32 |
22 |
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202-96 (Rev. 2000) insulation over the
purlin and between
the purlin to fill the cavity (R25 combined) |
14 |
24 |
34 |
44 |
53 |
56 |
36 |
24 |
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Walls |
No Insulation |
12 |
14 |
19 |
19 |
20 |
27 |
21 |
17 |
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R10 faced 202-96 (Rev. 2000) insulation
over the girts |
13 |
16 |
25 |
32 |
37 |
46 |
28 |
20 |
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R13 faced 202-96 (Rev. 2000) insulation
over the girts |
13 |
17 |
26 |
33 |
36 |
47 |
29 |
20 |
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R13 faced 202-96 (Rev. 2000) insulation
over the girts,
3 5/8” steel studs on 24” centers with 1/2” gyp. board on
interior |
26 |
40 |
51 |
60 |
64 |
65 |
50 |
35 |
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R13 faced 202-96 (Rev. 2000) insulation
over the girts,
3 5/8” steel studs on 24” centers with R-11 Batts and
1/2” gyp. board on interior |
31 |
43 |
55 |
68 |
73 |
75 |
54 |
39 |
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Sound Transmission Class (STC) in
accordance with ASTM E 90.
Roof construction is 24 ga standing seam roof with 8” Z
purlins on 5’ centers.
Wall construction is 26 ga wall panels screwed to 8” Z girts
placed on 7’ centers.
Interior metal furring wall studs were 3 5/8” by 25 ga on 24”
centers. |
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Sound Absorption |
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Absorption Coefficients @ Octave Band Frequencies |
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R19 Insulation Laminated with Vapor
Retarder Facing |
125 |
250 |
500 |
1000 |
2000 |
4000 |
NRC |
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PSK Light Duty Facing |
1.06 |
1.2 |
0.93 |
0.8 |
0.51 |
0.3 |
0.85 |
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PSK Standard Duty Facing |
1.04 |
1.23 |
0.91 |
0.78 |
0.49 |
0.28 |
0.85 |
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PSK Heavy Duty Facing |
1.07 |
1.17 |
0.83 |
0.63 |
0.35 |
0.2 |
0.75 |
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FSK Heavy Duty Facing |
1.06 |
1.17 |
0.89 |
0.72 |
0.43 |
0.24 |
0.80 |
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PSK Facing |
1.06 |
1.22 |
0.93 |
0.83 |
0.57 |
0.34 |
0.90 |
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Vinyl Facing |
0.95 |
1.2 |
0.94 |
0.73 |
0.52 |
0.37 |
0.85 |
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Unfaced |
0.89 |
1.22 |
1.02 |
0.98 |
1.01 |
1.00 |
1.05 |
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Sound Absorption Coefficient in
accordance with ASTM C 423 using an “A” mounting. |
About NAIMA
NAIMA is the association for North American
manufacturers of fiber glass, rock wool, and slag wool insulation
products. Its role is to promote energy efficiency and
environmental preservation through the use of fiber glass, rock
wool, and slag wool insulation, and to encourage the safe
production and use of these materials.
For more information, contact:
NAIMA
44 Canal Center Plaza, Suite 310
Alexandria, VA 22314
Phone: (703) 684-0084
Fax: (703) 684-0427
E-mail:
click here for online contact form
web site:
http://www.naima.org
NAIMA Metal Building Committee Members
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